ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES

INSTITUTE OF TECHNOLOGY DEPARTMENT OF CHEMICAL ENGINEERING

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LLEEAATTHHEERR

By

BINYAM TESHOME

A Thesis submitted to the school of Graduate Studies of Addis Ababa University in partial fulfillment of the Requirements for the Degree of

Master of Science in Chemical Engineering (Food Engineering)

Advisor: Mr. Adamu Zegeye

May, 2010

Addis Ababa

Ethiopia

i

ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE STUDIES

INSTITUTE OF TECHNOLOGY DEPARTMENT OF CHEMICAL ENGINEERING

EEFFFFEECCTT OOFF PPRROOCCEESSSSIINNGG OONN SSOOMMEE QQUUAALLIITTYY AATTTTRRIIBBUUTTEESS OOFF MMAANNGGOO ((MMaannggiiffeerraa iinnddiiccaa)) FFRRUUIITT

LLEEAATTHHEERR

By

Binyam Teshome

Approved by the Examining Board: _____________________ ___________________

Chairman, Departments Graduate Committee

Mr. Adamu Zegeye ___________________

Advisor

Dr. Cherinet Abuye ___________________

External Examiner

Dr. Eng. Shimelis Admassu ___________________ Internal Examiner

ii

Acknowledgment

I would like to forward my deepest gratitude to my advisor Mr. Adamu Zegeye for his keen interest

in my thesis work, follow up of my progress, encouragement and support.

I acknowledge Addis Ababa Institute of Technology for the financial support. I am also grateful to

the academic staff of the Department of Chemical Engineering for imparting tremendous

knowledge to me. I appreciate Dr. Eng. Shimelis Admassu for his constant supervision and

recommendation during my project work. Thanks to the Ethiopian Health and Nutrition Research

Institute (EHNRI) for letting me use their food analysis laboratory and facilitating my research,

especially Dr. Cherinet, Ato Adamu and Israel. Ethiopian Et-Fruit Company is also appreciated for

providing the mango varieties used in this research. I thank all the technical staff of my

Departments laboratory, particularly, Ato Hintsasilase Seifu and also Yeshihareg Nesibu for

providing me all the necessary support during the research.

Equally and importantly, I would like to acknowledge all family members particularly Girum

Teshome and my dearest wife Hayley Teshome, who contributed towards my success with their

financial support and encouragement in the course of this research, and also honor my friends who

shared my idea when I was in need.

iii

Table of Contents

CHAPTER Title Page

Title Page i

Acknowledgment ii

Table of Contents iii

List of Tables vi

List of Figures viii

List of Abbreviations ix

Abstract x

1 INTRODUCTION 1

1.1. Background 1

1.2. Statement of the problem 3

1.3. Objectives 4

1.4. Structure of the thesis 5

2 LITERATURE REVIEW 6

2.1. Production and marketing of Mango fruits in Ethiopia

2.1.1 Exporting Mango fruits

6

7

2.1.2 Mango value chain analysis in Ethiopia 8

2.1.3 Asossa market 9

2.1.4 Addis Ababa market 9

2.2 Processing of Mango fruits in Ethiopia 12

2.3 Selected Mango varieties for processing 13

2.4 Medicinal uses and by-products of Mango 14

2.5 Mango processing technologies 14

2.5.1 Ripe Mango processing 16

2.6 Fruit leather processing 17

2.6.1 Preparation of fruits 17

2.6.2 Heating, drying and packaging 18

2.7 Mango fruit leather recipes and processing procedures 19

iv

2.7.1 Adding sweeteners and flavoring to fruit leather

2.8 Quality control

2.9 Effect of processing on food quality attributes

2.9.1 Physicochemical properties

2.9.2 Changes on Vitamins

2.9.3 Flavor and pigment components

2.9.4 Sensory attributes

2.9.5 Influence of drying process

2.10 Food safety

20

20

22

23

24

26

29

30

31

3 MATERIALS AND METHODS

32

3.1 Raw material source and equipment 32

3.2 Approach for selection and preparation of Mango fruits 32

3.3 Development of Mango fruit leather 33

3.3.1 Raw material preparation and formulation of the puree mix 33

3.3.2 Heating and drying the puree mix 34

3.4 Methods for studying the effect of processing 37

3.4.1 Effect of processing on drying time 37

3.5 Quality parameters for studying the effect of processing 38

3.5.1 Proximate analysis methods for the puree and leather 38

3.5.2 Physicochemical analysis 41

3.5.3 Texture analysis of the Mango leather 42

3.5.4 Microbiological analysis 43

3.5.5 Sensory evaluation 44

3.6 Experimental design and data analysis 44

4 RESULTS AND DISCUSSION 45

4.1 Physicochemical properties of Mango puree 45

4.2 Proximate analysis results of the Mango puree and puree mix 46

4.2.1 Keitt Mango variety 47

4.2.2 Tommy Atkins Mango variety 47

v

4.3 Effect of heating temperature on viscosity of Mango puree mix 48

4.3.1 Keitt Mango variety 49

4.3.2 Tommy Atkins Mango variety 50

4.4 pH of the puree mix 51

4.5 Effect of drying on the proximate and Vitamin C content of fruit

leather

51

4.6 Effect of temperature and puree load on drying time 52

4.6.1 Drying characteristics of Mango puree mix 52

4.6.2 Analysis of moisture loss during drying process 53

4.7 Texture analysis of the Mango leather 54

4.8 Proximate analysis of Mango fruit leather 55

4.8.1 Moisture content 56

4.8.2 Protein content 57

4.8.3 Fat content 57

4.8.4 Crude fiber content 58

4.8.5 Ash content 58

4.8.6 Carbohydrate content 59

4.8.7 Effect of processing on Vitamin C content of Mango leather 59

4.9 Microbiological analysis of Mango fruit leather 60

4.10 Sensory analysis of Mango fruit leather 61

4.10.1 Effect of drying temperature, puree load and fruit varieties

on the sensory qualities

61

5 SUGGESTED TYECHNOLOGY FOR MANGO LEATHER

PROCESSING

66

5.1 Process description 66

6 CONCLUSIONS AND RECOMMENDATION 94

6.1 Conclusion 94

6.2 Recommendation 96

REFERENCES 97

ANNEXES 102

vi

List of Tables

Chapter Table Title Page

2 2.1 Estimate of area, production and yield of Mango fruits 6

4 4.1 Physico-chemical properties of fruit pulp for the mango varieties 45

4.2 Proximate analysis result for Keitt and Tommy Atkins varieties of

Mango puree and puree mix 46

4.3 Results of viscosities for Keitt and Tommy Atkins variety mango

puree mixes measured at different heating temperature 48

4.4 Proximate analysis result for Mango fruit leathers 51

4.5 Designed sample codes for both varieties of mangos with drying

temperature and puree load 52

4.6 Effect of drying air temperature and puree load on drying time of

Keitt Mango fruit leather 53

4.7 Weights and moisture loss of Keitt variety mango leather 53

4.8 Results of compression test using Texture Analyzer to different

number of Mango leather sheets (layers) 54

4.9 Effect of temperature on proximate composition of mango leather 55

4.10 Effect of puree load on proximate composition of mango leather 55

4.11 Effect of fruit variety on proximate composition of mango leather 56

4.12 Effect of drying temperature, puree load and fruit variety on

vitamin C content 59

4.13 Result of microbiological analysis of mango fruit leather 60

4.14 Effect of drying temperature on sensory qualities 61

4.15 Effect of puree load on sensory qualities 61

4.16 Effect of fruit variety on sensory qualities 62

4.17 Proximate and physicochemical composition of Mango and puree 68

4.18 Specific heat relationships for food product components 73

4.19 Recipes, calculations and amount of ingredients for making

Mango leather 85

4.20 Typical losses during processing of fruits and vegetables 86

vii

4.21 Machinery and equipment required for mango leather production 88

4.22 Manpower requirement for Mango leather production 89

4.23 Raw material costs for Mango leather production 89

4.24 Cost of utilities for Mango leather production 90

4.25 Fixed capital cost estimation for Mango leather production 91

4.26 Estimation of total product cost for Mango leather 92

viii

List of Figures

Chapter Figure Title Page

1 1.1 Structure of the thesis 5

2 2.1 Wholesale Mango market in Addis Ababa Market share by region 10

3 3.1 Process flowchart for Mango leather processing 36

4 4.1 Viscosity verses temperature of Keitt variety puree mix 49

4.2 Viscosity verses temperature of Tommy Atkins variety puree mix 50

4.3 Qualitative flow diagram for Mango leather processing 67

4.4 Quantitative flow diagram for mango leather processing 78

4.5 Quantitative flow diagram for daily production of mango leather 80

4.6 Equipment layout for mango leather processing 81

ix

List of Abbreviations

AAU Addis Ababa University

AMARI Awash Melkasa Agricultural Research Institute

AOAC Association of Official Analytical Chemists

BAM Bacteriological Analytical Manual

CIA Central Intelligence Agency

CSA Central Statistical Authority

EHNRI Ethiopian Health and Nutrition Research Institute

ETB Ethiopian Birr

Et-Fruit A state owned Ethiopian Fruit Marketing Agency

FAO Food and Agriculture Organization

FDA Food and Drugs Administration

GTZ Gesellschaft fr Technische Zusammenarbeit

LSD List Significance Difference

MC Moisture Content

ppm parts per million

RH Relative Humidity

SPSS Statistical Package for Social Scientists

TCA Trichloro Acetic Acid

TSS Total Soluble Solid

UAE United Arab Emirates

USD United States Dollar

USDA United States Drug Administration

x

Abstract

The seasonal production of mango fruit in Ethiopia has to be considered as an opportunity for the

utilization of the fruit. The objective of this research was to study the influence of processing on

some quality attributes of mango fruit leather developed from two fruit varieties namely, Keitt

(local mango) and Tommy Atkins (export standard mango). First, 3.2 kg of mango fruit from both

varieties were allocated for the process to be peeled, cut, sliced into pieces and stones removed.

Mango puree was made using a food processor to obtain 1.65 kg puree. It was put in a beaker and

covered with aluminum foil and then inserted into a water bath fitted with thermostat to control the

temperature. Additional ingredients of Honey, Ginger and Lemon Juice were added and mixed. In

order to cook and shorten the drying time, the mixture was heated at three different temperatures,

600C, 700C and 800C whilst being continuously stirred. The puree mixture was poured onto the

trays to an approximate thickness of 0.64 cm. The trays containing the puree were placed in a

drying oven. Oven drying was conducted for 8 h and finally 0.52 kg of mango leather was obtained.

Drying experiment was also undertaken using convective hot air dryer to minimize the drying time

of the fruit leather using a similar procedure. A minimum drying time of 4 h was achieved in a

convective hot air dryer for Keitt mango fruit leather at 800C with 0.4 g/cm2 puree load. The major

factors considered to have an effect on the leather quality were drying temperatures of 600C, 700C

and 800C, puree load of 0.4 g/cm2 and 0.6 g/cm2 and fruit variety. The developed leather underwent

physico-chemical, textural, microbiological and sensory analysis. The data obtained was analyzed

using SPSS version 17 statistical software. The result indicated that 70.3 % of moisture loss

resulted in the drying process. The viscosity of the mango puree was found to be dependent on

heating temperature. As the temperature increased, the viscosity of the puree first decreased and

then increased within the range of temperature 25.1 to 70.0 0C. The texture analysis result of the

final mango leather showed that 4 sheets and 5 sheets of leather with 5mm and 6mm thickness,

respectively, were found to be suitable for a single bite. The results of the proximate analysis for

both varieties of mango fruit leather indicated that the processing affected the nutritional

composition of the fruit leather. The vitamin C content was also found to be dependent on all

drying temperature, puree load and fruit variety. The vitamin C content of the Keitt mango leather

(26.93%) is greater than that of Tommy Atkins mango leather (22.71%). When compared to the

fresh puree mix, the Keitt mango leather is decreased by 39.66% and that of the Tommy Atkins

mango leather is decreased by 57.82%. The result of microbiological analysis for yeast, coliform,

xi

fecal coliform, E.coli, and Shigella species was found to be safe (

1

CHAPTER 1

INTRODUCTION

1.1 Background

Mango (Mangifera indica L) is a highly seasonal tropical fruit, very popular among millions of

people in the tropics. It also occupies a prominent place among the best fruits of the world.

However, it is in constant demand, there is a pre-harvest scarcity and at times a post-harvest glut

for this fruit. To increase the availability of this fruit throughout the year, the surplus production

must be processed into a variety of value-added products (Saxena and Arora, 1997; Srinivasan et

al., 2000; Singh et al., 2005). Dried mango products could successfully serve this purpose.

Mangos can be processed into a number of unique products such as dried mango pieces, chutney

and mango leathers (Azeredo, et al., 2006). Processing of mangos enables exporters to serve their

markets even during off season periods for fresh fruits. Mangos are a highly nutritious fruits

containing carbohydrates, proteins, fats, minerals, and vitamins, in particular vitamin A (beta

carotene), vitamin B1, vitamin B2, and vitamin C (ascorbic acid). As the fruit ripens, concentrations

of vitamin C decrease and glucose, fructose, and sucrose concentrations increase (Bally, 2006).

Drying of agricultural products is the oldest and widely used preservation method. It involves

reduction as much water as possible from foods to arrest enzyme and microbial activities hence

stopping deterioration. Moisture left in the dried foods varies between 2-30% depending on the

type of food. In tropical countries, solar dryers can be used to dry fresh produce when average

relative humidity is below 50% during drying period. Drying lowers weights and volume of the

product hence lowers costs in transportation and storage. However, drying allows some lowering in

nutritional value of the product e.g. loss of vitamin C, and changes of color and appearance that

might not be desirable (GTZ, 2009).

Fruit leathers are dried sheets of fruit pulp which have a soft, rubbery texture and a sweet taste.

They can be made from most fruits, although mango, apricot, banana and tamarind leathers are

amongst the most popular. Leathers can also be made from a mixture of fruits. Fruit leathers are

made by drying a very thin layer of fruit puree and other ingredients to produce a leathery sheet of

dried fruit with a texture similar to soft leather (Andress & Harrison, 1999). They may be eaten as

snack foods as a healthy alternative to boiled sweets and also used as ingredients in the

2

manufacture of cookies, cakes and ice cream. Fruit leathers are often targeted at the health food

market, using marketing images such as pure, sun dried, and rich in vitamins.

Mango leather is a traditional product prepared from sound ripe mango. Traditionally, sun drying is

the process employed for preparing mango leather from ripe fruit pulp. However the sun-dried

product is discolored and the process is unhygienic and lengthy. Cabinet drying has been carried

out for making mango leather (Heikal et al., 1972; Mir and Nath, 1995) resulting into a product

with improved color and flavor.

The preservation of fruit leathers depends on their low moisture content (15-25%), the natural

acidity of the fruit and the high sugar content. When properly dried and packaged, fruit leathers

have a shelf life of up to 9 months (FPT, 2009). Although fruit leather is a relatively well

established product overseas, few studies have been published about this kind of product. Most of

the studies utilize not only fruit purees in the fruit leather, but also other ingredients (especially

sugars) and additives. For instance, Chan and Cavaletto (1978) prepared papaya leathers with

sucrose and SO2. They observed that SO2 reduced changes in the colour of papaya leathers during

both processing and storage. Che Man, et al., (1992) prepared sapota leathers from sapota puree,

sucrose, rice flour, sorbic acid, and sodium metabisulphite; the leathers were shelf-stable for 3

months. Jackfruit leathers with added sucrose and sorbic acid were produced by Che Man and

Taufik (1995); the product remained stable for 2 months. Irwandi, et al., (1998) produced 12-week

stable durian leathers from a formulation including sucrose and sorbic acid. Vijayanand, et al.,

(2000) produced 3-month shelf-stable guava leathers with sucrose and metabisulphite. Mango

leather products have very low protein content (12%). Therefore several studies have increased

protein content in the mango leather by adding shrimp flour and rice flour, whey protein isolate and

soy protein isolate (Exama & Lacroix, 1989; Payumo, et al., 1981; Chauhan, et al., 1998). All the

above-mentioned studies reported good consumer acceptance of the fruit leather product.

3

1.2 Statement of the problem

Mango puree and leather products are largely unknown in Ethiopia, but may have good potential

for a number of reasons. According to Kadir (2009) the current postharvest loss of mango fruits in

Ethiopia is more than 26.3%. However, there is a growing international demand for dried mango

fruits and mango fruit leathers. Consequently the abundant supply of mango fruit in Ethiopia could

be utilized to create new products (including organic fruit leathers) for this overseas market.

The expansion of the bakery industry has created a demand for new ingredients, for cake

production, which are imported and are relatively expensive. Mango fruit leather, produced locally,

could be utilized as a cheaper alternative ingredient. There is also a growing consciousness over the

negative effects of sugar confectionery on dental health and at present there are few alternatives for

concerned parents to give to their children. Therefore, fruit leather products would be a more

acceptable healthy alternative. The current drying method used widely for making fruit leathers is

use of electrical oven and convective hot air drying. The drawback of hot air drying method is a

long drying time and the controlling of drying conditions (including increasing drying temperature,

decreasing initial moisture content of the puree and so on) will result in the quality of the mango

fruit leather. The technology of electrical oven drying method had long been employed to extend

the shelf life of foods. However, there is an urgent need to conduct basic studies to investigate the

effects of processing on the total drying time and some qualities of the mango fruit leather to

optimize the process and set up the processing industry.

The quality of mango fruit leather and the total drying time is directly affected by the drying

method, type of dryer, oven design and operating parameters. These parameters must be well

established and controlled for each type of fruit leathers. In the production of mango fruit leathers,

the puree making process and mixing with other ingredients, the drying temperature, and the puree

load on each tray during drying, the total drying time, packaging of the product and appropriate

storage conditions should be well established for high quality product. In this study, the effects of

processing on some qualities of mango fruit leathers and the total drying time taken are

investigated.

4

1.3 Objectives

The general objective of the thesis work is to study the influence of processing on some quality

attributes of mango fruit leathers.

The specific objectives of the thesis are to:

Produce fruit leather from locally grown mangos

Conduct physico-chemical analysis of both raw and processed product

Study the effect of processing on the qualities of the fruit leather

Suggest a manufacturing process for mango leather production

Significance:

The study is believed to be significant in that it will:

Reduce postharvest loss of mango fruit in Ethiopia

Produce the best quality mango leather products

Reassure the consumer that the mango leather product is safe for consumption

Optimize the processes for production of good quality mango leather products

Scope:

The study generally covers:

The processing method for production of mango fruit leather

Development of mango leather

Laboratory analysis majorly on: Physico-Chemical Analysis, Proximate Analysis (Nutritional Composition Analysis), Microbiological Analysis

Sensory Evaluation

Suggestion of technology and economic analysis

5

1.4 Structure of the thesis

Fig. 1.1 Structure of the thesis

6

CHAPTER 2

LITERATURE REVIEW

2.1 Production and marketing of Mango fruits in Ethiopia

The Ethiopian government has a plan to expand mango production by distributing high yielding

varieties for small scale farmers, especially in the Southern and Oromia region, by grafting mangos

of known and high yielding varieties. In July 2006, it was announced that the Oromia Government

distributed 14,000 improved seeds of mango. The production of mango fruits for the past six years

in Ethiopia was considered for the study which was found from CSA (2009), and is summarized

and presented below in Table 2.1. With an increase in Ethiopian mango crop production and

considering the current postharvest loss of mango fruits is at 26.3%, there is not only a need but

also a potential for the fruit to be processed into various product types, consequently increasing the

market potential of the mango fruit (Kader and Truneh, 2009). Industrial processing opportunities,

to increase the market value of the initial fruit, may lead to the potential development of the

following products:- Food (mango juice and fizzy drinks, canned fruits and pulp, fruit leather, dried

pieces, jam and chutney), domestic (mango detergent and cleaning agents), beauty (as an applied

product in skin creams products).

Table 2.1 Estimate of area, production and yield of Mango fruits, Meher season

Year Number of

holders

Area in

hectare

Production in

quintal

Yield

(qt/ha)

2003/04 (1996) E.C 350,067 4,964.00 292,283.00 58.88

2004/05 (1997) E.C 414,574 5,814.00 301,715.00 51.89

2005/06 (1998) E.C 463,868 5,400.31 547,291.24 104.06

2006/07 (1999) E.C 558,976 6,796.10 626,111.83 94.08

2007/08 (2000) E.C 695,030 6,730.83 484,360.97 71.96

2008/09 (2001) E.C 716,447 6,051.00 441,582.00 72.97

7

2.1.1 Exporting Mango fruits

At present, very little mango is exported from Ethiopia with only 4 tonnes exported in 2006 at a

value of less than US$1000 according to FAO. This represents a significant decline since 2002

when 811 tonnes were exported at a value of US$675,000 (US$832 per tonne). This appears to

have been a particularly high value year however, as the longer term average price for mango

exports has been approximately US$323 per tonne. Anecdotal information from key informants

suggested that one of the main reasons for the drop in mango exports has been the variable quality

of Ethiopian mango exports on arrival in overseas countries. It was reported that Et-Fruit (the state

owned Ethiopian Fruit marketing agency) had been exporting mangoes to countries such as

Djibouti, Saudi Arabia and UAE but had lost some of those contracts due to the poor quality of the

shipments on arrival. This situation highlights the key challenges faced in trying to develop the

export market for Ethiopian mangoes: Under-developed packaging and cold chain for exporting,

High cost of freight to overseas countries, Competing product from Egypt and South Africa and

Minimal production of commercial varieties

In order to begin considering export markets as a viable opportunity, it is essential to consider the

nature of demand in export markets. It is very clear that overseas markets are increasingly

demanding higher quality, commercial varieties of mangoes, and are also becoming more

sophisticated in their preferences for products that are organic. In Asossa then, the first step to even

consider export markets would be to begin growing more commercial varieties such as Kent, Keitt

and Tommy Atkins. Even if the export market was not a viable option in the short term, these

commercial varieties would present a better alternative to the domestic market with less fiber and

higher levels of sweetness than existing hybrid varieties (FAO, 2009).

In Ethiopia, the domestic market, consumption is largely in its fresh form due to the fact that the

cost increment for processing and packaging would make it beyond the purchasing power of the

vast majority of the Ethiopian consumer group (low-income). However, since 1997 the demand for

canned fruits in Ethiopia has increased by 7% suggesting there is a sufficient domestic market for

canned mangoes to be produced. The mango export markets are where the greatest growth

potentials exist for mango producers. The global mango markets are supplied by countries that are

strategically positioned to be preferred suppliers. For example, West Africa is a key supplier to

Europe due to its proximity to Europe and direct sea-links (Truneh, 2009).

8

2.1.2 Mango value chain analysis in Ethiopia

Ethiopia is a country that is often associated with famine and food shortage. Whilst this perception

is the reality for much of the country at certain times, there are also regions within Ethiopia that are

well suited to producing a surplus for particular agricultural commodities. One such location is the

Asossa Homosha region in western Ethiopia, which is particularly suitable to the production of

mangoes. In a 2006 study, it was estimated that as much as 28% of the mangoes sold in the capital

Addis Ababa, were grown in the Asossa region (WAFC, 2006).

Though the immediate market is small, there is a short and established value chain to Addis Ababa

via a 700 km trip. Typically, Asossa exports between 150-300 (10-ton) truckloads of fruit per

season to various regions, principally Addis Ababa. In spite of the high cost of imported fruit,

nationally the volume has risen by 100% in the last seven years, while that of imported juices has

more than doubled in the last four years, evidence of an up-scaling market. The farm-gate price of

mangoes in Asossa ranges from 0.25 to 1.15 Birr/kg while the retail price is approximately 5 Birr

per kg in Addis, compared to 10 Birr per kg of other imported whole fruits. Farmers typically

achieve approximately 5 to 8% of the final retail price (at lower levels) giving them about

1,400Birr in annual income, while wholesalers get about 30% of it but meet the high transport

costs. Analysis reveals a reasonably resilient subsector with a favored market position of the

Assosa mango regional brand. Also, the region appears to have a comparative advantage with

ideal growing conditions for mangoes and high yielding trees. At the production level however, the

value chain is quite rudimentary with mainly subsistence level cultivation, harvesting and post-

handling techniques that limit the quality of the fruit. Upstream there are also issues with most

grading and packaging being undertaken following a long road journey to the capital, undermining

not only the quality of fruit but also the potential value generated at the farmer level. At the

wholesale level in Addis Ababa, market traders dominate the landscape and operate in ways that

make it difficult for new entrants to enter the market. Addis wholesalers have strong relationships

with the traders based in Asossa and these two levels of the value chain account for most of the

final retail price. Given the roles they play, it appears that there is not a proportionate addition of

value in the chain, and that is where opportunities lie for improving farmer level value capture in

the chain (James et al., 2009).

9

2.1.3 Asossa market

Within the market in Asossa, there are three main channels for selling mangoes: Farm gate that

mainly sell to traders (who sell on to Addis), consumers and small retailers; Asossa Town Market

that mainly sell to local consumers and Small Retailers that mainly sell to local consumers. The

market is dominated by the open town market where many farmers bring their produce for sale.

During peak mango season, this market is saturated with mangoes to the point that prices fall

dramatically and many farmers do not even bother to carry their produce home at the end of the

day. As well as the open Asossa market, there are a number of kiosk-style small retailers in Asossa

which suffer from similar problems at peak supply times. A significant point to note is that much of

the mango being supplied at the regional market is not the top grade being produced, but is actually

the remaining produce from what has been already sold to traders at farm gate. In this way, traders

are siphoning the best quality mangoes to sell in the Addis market, but also provide very little

choice to disorganized farmers about where to sell. This study found that farmers on average sell

between 0.4 and 1.15 birr depending on quality, and also customer. The lower price tended to be

achieved in the Asossa market, with the higher price being received at farm gate from traders

purchasing only the higher quality mangoes (Aithal and Wangila, 2006).

2.1.4 Addis Ababa market

The market is dominated by two large wholesale markets, being the Mercato and the Piazza. These

markets are the main destination for agricultural produce arriving from around the country. These

markets serve not only consumers, but are also where supermarkets, large retailers, hotels and

thousands of small kiosk-like retailers source their mangoes. Actual data on the volume of mangoes

sold in these markets is very unreliable, however a number of interview sources have identified that

in the past five years there has been significant growth in market size and increasing consumer

demand. This is largely to do with a steadily increasing population (3.2% p.a.), more sophisticated

consumer preferences for exotic and tropical fruits, and growing incomes amongst emerging

middle and upper class consumers. The average price on the wholesale markets in Addis Ababa

was approximately 3.5 birr per kg, or 3,500 birr per tonne, whereas the final retail price in Addis

could reach as high as 5 birr per kg (5,000 birr per tonne). By analyzing the price differentials

throughout the value chain, it is clear to see that farmers only capture a small portion (8%) of the

final retail price. There is no reliable data on the number of small retailers in Addis, but it is

estimated there are thousands of street level small retailers/kiosks - some of them dealing

10

exclusively in fruit, whilst others sell a range of consumable goods. These are a major channel for

selling mangoes on to final consumers and are particularly convenient as a street level channel in

places of high traffic, with high turnover of goods (CIA, 2008).

Fig. 2.1 Wholesale Mango market in Addis Ababa Market share by region

Source: (Aithal and Wangila, 2006)

The Mercato and Piazza markets are largely controlled by approximately ten major wholesalers,

who deal in fruits and vegetables from all over the country. Industry sources mentioned that the

Addis wholesalers are organised under groups that have strong ethnic ties and tend to operate in

ways that have been described as cartels. Similar to the upstream nature of the value chain, the

wholesalers in Addis operate in a heavily crowded, poorly structured, and underdeveloped market

infrastructure. There is no known refrigerated storage facilities in the market as the cost of this

investment has always been seen as too high. The typical wholesale price in Addis is approximately

3,500 birr per tonne and means that Addis wholesalers achieve between 20-40% of the final retail

price. This is a considerable portion of the final price and reflects the risk that Addis wholesalers

take in ordering mangoes from Asossa. Other value add activities that wholesalers undertake is re-

packaging and grading the fruit on arrival in Addis, as produce most often arrives in bulk having

11

not yet undergone any systematic grading or packaging. These are functions that are possible at the

farm level and may be areas where farmers can extract a greater price and generate more value in

the chain (Aithal and Wangila, 2006).

According to a recent update from the mango value chain analysis by James et al., (2009), it has

been indicated that within the first six months of the project implementation, the following have

been achieved:

19 farmers cooperatives have been set up and linked to an umbrella cooperative union. Out

of these, 100 Cooperative members have been trained on Mango Processing especially in

producing jam, juice, compote, vinegar, wine etc. This processing is under taken on site in

Asossa.

Farm gate Price of Mango increased from 25 Birr/100kg to 175 and the farmers have started

using weighing scales to measure quantities rather than counting pieces or heaps.

Between March and June 2009, 357 tonnes of mangoes were sold at the price of 569,084

Birr (roughly USD 46,000) to the most reputable fruit dealer- Et-Fruit for the first time.

With World Vision supervision, the income was equitably shared among the farmers.

4,000 bottles of various processed mango products like jam, juice, wine and compote have

been packed and sold to a number of super markets in Addis Ababa.

The farmers have entered into partnership with the Ecological Products of Ethiopia,

(Ecopia) to process and market mango products.

12

2.2 Processing of Mango fruits in Ethiopia

The mango processing industry in Ethiopia is in its infant stage. However, mango is grown in many

parts, especially in the Rift Valley, western and south-western parts of the country. The national

research system has developed a number of varieties but they are not widely spread. Experiences

from other countries in growing this crop will therefore contribute to the success and distribution of

this fruit. The mango industry in Kenya has expanded considerably over recent years, not only in

size but also in the geographical location of commercial and homestead plantings. No longer is

commercial mango cultivation restricted to the Coast Province, as significant plantings of improved

cultivars now also exist in the Eastern and Central provinces, among other regions (EAP, 2009).

The fruit processing industry in Ethiopia is very weak, considering the substantial amount of fruit

that is grown in the country. No doubt, one of the reasons for this is the highly developed

processing industries in other countries which are able to export into countries like Ethiopia and

sell the final product at low cost. Indeed, there were a number of imported, long-life mango juice

brands available throughout Ethiopia and is certain to act as a competitive entry barrier for

domestically produced juice. Investigations of local processors found only one significant player,

who actually imported frozen mango flesh from India for processing juice in Ethiopia. The main

considerations for purchasing Indian imports were the variety, quality, consistency, and price of the

imports. When asked about replacing imports with Ethiopian produced mango, the informant

indicated that would be his preference, however so far, Ethiopian fruit was not able to compare on

the key criteria identified, particularly on price. The informant did however predict that juice

processing would begin to emerge as a more viable sector, as mango juice is clearly the most

favored juice product by consumers. He indicated that demand for the juice as a category was

seeing strong growth, with mango leading this growth. The other key challenges for developing a

fruit processing sector in Ethiopia include: lack of technical knowledge in processing, low level of

technical support for maintenance, low capital base from which to invest, and many low priced

mango juice imports (James et al., 2009).

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2.3 Selected Mango varieties for processing

Tommy Atkins Mango variety

It is one of the most popular mangos in the world and cultivated in Florida early 1920's. The

Mango cultivar was developed and grown for commercial export. The fruit is a regular oval,

medium to large sized, 12 to 24 ounces, yellowish-orange with deep red to purple blush, thicker

skinned, juicy but firm with medium fiber.

Pic. 2.1 Tommy Atkins (LFI, 2003)

Keitt Mango variety

Indian strain thought to have originated, like the Haden, from a seedling of Mulgoba 1945,

Homestead, Florida. The fruit is a large (20-26 oz.) ovate tapering with slight nose-like

protuberance above its tip. Green to orange-yellow as it ripens; firm flesh with a piney sweetness

and minimal fiber surrounding the seed area. It is a late fruiting mango, often available into fall.

Pic. 2.2 Keitt (LFI, 2003)

Kent Mango variety

Kent mango was first cultivated in Florida in 1944. It is a direct descendant of the Brooks cultivar,

derived from the Sandersha seedling. The fruit is a regular oval shape, large 20 - 26 ounces, with

plump cheeks, greenish-yellow color with red shoulder. Very rich and sweet with fiber-free flesh

(slices clean to the pit - like butter when ripe!) It is a softer mango that really should not be put to

the squeeze test.

14

Pic. 2.3 Kent (LFI, 2003)

2.4 Medicinal uses and by-products of Mango

Mangos are an excellent source of Vitamins A and C, as well as Potassium, Beta-carotene,

enzymes and anti-oxidants. Mangoes are high in fibre, but low in calories (approximately 110 per

average sized mango) fat (only 1 g) and sodium. Mangoes are a good staple for your daily diet. It

has a reputation (not necessarily scientifically proven) as an alternative or complementary medicine

for a wide range of illnesses including beriberi, bronchial diseases, anxiety, insomnia, fatigue,

depression, digestive problems heartburn, constipation, kidney stones.

Mango kernel contains high amounts of fat and starch. The oil extracted from kernel is of good

quality and could be used in cosmetic and soap industries. The kernel flour (starch) after mixing

with wheat or maize flour is used in chapattis in India. About ten percent alcohol could be obtained

from mango kernel by co-culture fermentation (Truneh, 2009).

2.5 Mango processing technologies

The processing of fruits has two objectives. Firstly, to preserve by slowing down the natural

processes of decay caused by microorganisms, enzymes in the food, or other factors such as heat,

moisture and sunlight. The second objective is to convert them into different foods which are

attractive and in demand by consumers Food Processors should utilize their skills to develop

recipes and create attractive products that consumers want to eat. Thereby successful Food

Processors increase product sales and generate profits. Food Processors must select their products

with caution. It is not enough to assume that processing can be a successful business simply

because there a large quantities of cheap fruit available in the marketplace. There must be a good

demand for the end product and this must be clearly identified before designing and investing in the

business. The best types of products for small-scale production are those that have a high added-

value as well as a good demand. A high added value means that cheap raw materials can be

processed into relatively expensive products. It also means that this can be done at a small scale of

processing, using equipment that is affordable (Fellows and Quaouich, 2004).

15

Fruits like mangos, pawpaw, guavas and bananas, can easily be dried. However, they should be

harvested at the right stage and ripeness. Hard ripe stage in mangoes, pawpaw and bananas gives

best results. Avoid overripe, under mature fruits in order to obtain good products. To prepare the

fruits for drying, wash them thoroughly with clean water. Scrubbing with a brush might be

necessary like in case of mango fruit with a lot of latex cover. The fruits are peeled if necessary and

cut into smaller uniform pieces to ensure faster drying. Stainless steel knives are recommended for

peeling and cutting of the slices or pieces. To avoid discoloration and excessive vitamin losses,

treatment with anti-oxidants like citrus (lemon) juice is done. Fruits like pineapples may require

pre-cooking to soften fibrous tissue hence hasten drying. Drying is done on trays, which should be

made of wood, fabric, plastic or sisal material. This is because metal materials may affect the

drying product negatively e.g. copper destroys vitamin C, iron rusts, aluminum discolors fruits and

corrodes. Most fruits have natural acids and sugars which are preservatives therefore moisture

contents of about 20% i.e. leathery and springy dry (not brittle) is good for storage. This is however

dependent on the fruit or vegetable. After the correct stage of dryness is achieved the product

should be removed from the dryer parked, and stored in a dry, dark store to avoid loss of vitamin A

(GTZ, 2009).

Mangos are processed at two stages of maturity. Green fruit is used to make chutney, pickles,

curries and dehydrated products. The green fruit should be freshly picked from the tree. Fruit that is

bruised, damaged, or that has prematurely fallen to the ground should not be used. Ripe mangoes

are processed as canned and frozen slices, puree, juices, nectar and various dried products. Mango

processing within the home and cottage industries converts the fruit into many other products.

Mango processing presents many problems as far as industrialization and market expansion is

concerned. The trees are alternate bearing and the fruit has a short storage life; these factors make it

difficult to process the crop in a continuous and regular way. The large number of varieties with

their various attributes and deficiencies affects the quality and uniformity of processed products.

Additionally, the lack of simple, reliable methods for determining the stage of maturity of varieties

for processing also affects the quality of the finished products. Many of the processed products

require peeled or peeled and sliced fruit. Within Ethiopia the lack of mechanized equipment for the

peeling of ripe mangoes is a serious bottleneck for increasing the production of these products. A

significant problem in developing mechanized equipment is the large number of varieties available

and their different sizes and shapes. The cost of processed mango products is also too expensive for

the general population in the areas where most mangoes are grown. However, there is a

16

considerable export potential to developed countries but in these countries the processed mango

products must compete with established processed fruits of high quality and relatively low cost

(Dauthy, 1995).

2.5.1 Ripe Mango processing

Mango Puree

Mangoes are processed into puree for re-manufacturing into products such as nectar, juice, squash,

jam, jelly, dehydrated products such as fruit leathers. The puree can be preserved by chemical

means, or frozen, or canned and stored in barrels. This allows a supply of raw materials during the

remainder of the year when fresh mangoes are not available. It also provides a more economical

means of storage compared with the cost of storing the finished products, except for those which

are dehydrated, and provides for more orderly processing during peak availability of fresh

mangoes. Mangoes can be processed into puree from whole or peeled fruit. Because of the time and

cost of peeling, this step is best avoided but with some varieties it may be necessary to avoid off-

flavors which may be present in the skin. The most common way of removing the skin is hand-

peeling with knives but this is time-consuming and expensive. Steam and lye peeling have been

accomplished for some varieties. Several methods have been devised to remove the pulp from the

fresh ripe mangoes without hand-peeling. A simplified method is as follows: the whole mangoes

were exposed to atmospheric steam for 2 to 2 and 1/2 min in a loosely covered chamber, and then

transferred to a stainless steel tank. The steam-softened skins allowed the fruit to be pulped by a

power stirrer fitted with a saw-toothed propeller blade mounted 12.7 to 15.2 cm below a regular

propeller blade. The pulp is removed from the seeds by a continuous centrifuge designed for use in

passion fruit extraction. The pulp material is then passed through a paddle pulper fitted with a

0.084 cm screen to remove fiber and small pieces of pulp.

Mango puree can be frozen, canned or stored in barrels for later processing. In all these cases,

heating is necessary to preserve the quality of the mango puree. In one process, puree is pumped

through a plate heat exchanger and heated to 90C for 1 min and cooled to 35 C before being

filled into 30 lb tins with polyethylene liners and frozen at -23.50 C. In another process, pulp is

acidified to pH 3.5, pasteurized at 90C, and hot-filled into 6 kg high-density bulk polyethylene

containers that have been previously sterilized with boiling water. The containers are then sealed

and cooled in water. This makes it possible to avoid the high cost of cans. Wooden barrels may be

used to store mango pulp in the manufacture of jams and squashes. The pulp is acidified with 0.5 to

17

1.0% citric acid, heated to boiling, cooled, and SO2 is added at a level of 1000 to 1500 ppm in the

pulp. The pulp is then filled into barrels for future use.

Dried/dehydrated Mango

Ripe mangoes are dried in the form of pieces, powders and flakes. Drying procedures such as sun-

drying, tunnel dehydration, vacuum-drying, osmotic dehydration may be used. Packaged and stored

properly, dried mango products are stable and nutritious. One described process involves as pre-

treatment dipping mango slices for 18 hr (ratio 1:1) in a solution containing 40 Brix sugar, 3000

ppm SO2, 0.2% ascorbic acid and 1% citric acid; this method is described as producing the best

dehydrated product. Drying is described using an electric cabinet through flow dryer operated at

60 C. The product showed no browning after 1 year of storage (Dauthy, 1995). Mango fruits can

also be dried in the form of leathers or bars.

2.6 Fruit leather processing

Fruit leathers are dried sheets of fruit pulp which have a soft, rubbery texture and a sweet taste.

They can be made from most fruits, although mango, apricot, banana and tamarind leathers are

amongst the most popular. Leathers can also be made from a mixture of fruits. Fruit leathers are

eaten as snack foods instead of boiled sweets. They are also used as ingredients in the manufacture

of cookies, cakes and ice cream. The preservation of fruit leathers depends on their low moisture

content (15-25%), the natural acidity of the fruit and the high sugar content. When properly dried

and packaged, fruit leathers have a shelf life of up to 9 months (FPT, 2009).

2.6.1 Preparation of fruits

Fruit should be washed in clean water, peeled and the stones removed. Washing water can be

chlorinated by adding 1 teaspoon of bleach to 4.5 liters of water. All fruit should be ripe and free

from bruising. Any rotten or bruised fruit should be thrown away as this will spoil the color and

flavor of the leather. The puree must be heated to a higher temperature for a longer time to destroy

the enzyme (it must be boiled for 20 minutes). Only stainless steel knives should be used to chop

the fruit. Other metals will discolor the fruit flesh. At the simplest level, fruit is made into a puree

by hand using a food mill. If electricity is available, a liquidizer or blender can be used to increase

the production output. The liquidized fruit is strained or sieved to remove the fibers, seeds, etc to

make a smooth puree. Fruit puree can be semi-processed and stored in sealed drums for further

processing later in the season. Sulphur dioxide (SO2) (600ppm) is added to the drums to prevent the

18

growth of micro-organisms. The semi-processed fruit can be stored for several months. Chemical

preservatives may be added to the fruit puree to maintain a bright color in the leather. Preservatives

are also added if the puree is to be stored before processing. A variety of ingredients can be added

to the fruit puree - sugar to increase the sweetness, citric acid to increase the acidity and chopped

nuts, coconut or spices to vary the taste and flavor.

2.6.2 Heating, drying and packaging

The puree must be heated to 900 C to inactivate the enzymes and reduce the level of

microbiological contamination. A double pan boiler is recommended for heating to avoid burning

the puree. The fruit puree is poured in a thin layer (3-6mm thick) on plastic trays or wooden trays

lined with greaseproof paper. The puree can be poured into a square which is later cut into small

pieces, or into small circles which are rolled up when dry. The leathers should not be dried in direct

sunlight as this will cause the color to fade and reduce the levels of vitamins A and C. Indirect solar

dryers or mechanical dryers should be used. The leather should be dried overnight in a solar dryer

or for about 5 hours in a mechanical dryer. After this time it is turned over and dried on the other

side. The leather is dried until it has a final moisture content of 15-25%. After drying, the leather

pieces should be dusted lightly with starch to prevent them sticking together. All equipment must

be thoroughly cleaned each day to prevent contamination by insects and micro-organisms.

In developing countries fruit leather is usually packaged cheaply with easily sourced materials. The

fruit leather is sold as a roll that is interleaved with greaseproof paper to prevent it from sticking

together. Strips of the leather are weighed, laid on a piece of greaseproof paper and rolled with the

paper. The rolls or discs of leather are packed in polythene or polypropylene heat-sealed bags. The

bags should be placed in boxes to protect them from the light. Fruit leather products in Europe are

packaged as a bar or as mini sweets, within a sealed plastic/foil case. The fruit leather bars within

their plastic/foil case may be packaged and sold as a multipack within a cardboard box made from

recycled paper products. The attractive, modern design of the packaging is specifically aimed at the

health conscious, luxury product niche within the consumer market (FPT, 2009).

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2.7 Mango fruit leather recipes and processing procedures

The following basic recipes are only guidelines since they depend on the composition of fruit

(which varies between different types) and the different consumer tastes for sweetness. The recipes

needed for mango leather preparation are: fully ripe mango, Sugar (10-15% the pulp weight

according to the variety used and consumer taste), lemon juice or citric acid 2 spoons per kg pulp),

Sodium of potassium metabisulphite (2g per kg pulp), and Glycerin for foods.

The general procedure for making mango fruit leather is as follows:

1. Wash the mangoes in clean water. Drain, Sort and remove any unripe or over-ripe fruit.

2. Peel the fruit with a stainless steel knife and cut the flesh into small pieces.

3. Extract the pulp using a pulper.

4. Weigh the pulp and mix with the sugar, lemon juice and metabisulphite in the ratios

above.

5. Heat at 70-80 0C.

6. Remove the foam from the top of the mixture. Grease the surface of trays with glycerin

to prevent the leather from sticking.

7. Pour the hot puree onto the trays at a ratio of 15kg per square meter of tray area.

8. Place the trays in a dryer. Leave to dry until a final moisture content of 15%. The

product will have a soft, leather-like consistency.

9. Place three sheets of leather on top of each other and cut into small 4x4cm squares.

Wrap each square in cellophane. It may be necessary to dust the squares with corn flour

to prevent excess stickiness.

10. Pack in plastic bags, label and store in a cool dry place (FPT, 2009).

Mango fruit leather can also be made using electric dehydrator or drying oven. Andress (2004)

formulated mango fruit leather with different recipes and methods as described below.

Recipes: include; 4 cups mango puree (from about 4 large, unripe mangoes), 1 cup clover

honey, teaspoon ground cinnamon, teaspoon ground nutmeg, and teaspoon ground cloves.

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Yield: about 2 dryer trays (14 inches in diameter); 8 fruit rolls.

2.7.1 Adding sweeteners and flavoring to fruit leather

Once you have the basics of making fruit leathers it is fun to try some new flavoring, toppings, or

fillings. Below are some new ideas.

Sweetening - If the puree needs some sweetening, add up to cup sugar for each 2 cups of fruit.

Sugar substitutes may be used. Aspartame sweeteners however may lose sweetness during drying.

Spices Add spices to the puree. Add until the taste is acceptable. Begin by adding 1/8-teaspoon

for each 2 cups of puree. Try: cinnamon, cloves, ginger, mint, nutmeg, allspice.

Flavorings Add flavorings to the puree using only 1/8-teaspoon person 2 cups of puree to start.

Try almond extract, lemon peel, orange extract, vanilla or peppermint.

Toppings After spreading the puree on the drying sheet and before drying, sprinkle a topping

over the puree. Try not to cover entire puree, but just lightly sprinkle the topping. Try coconut,

dried fruits, granola, and sunflower seeds.

Fillings After the fruit leather is dried and cool, spread a thin layer of these fillings. Then roll, cut

and serve. If not served immediately, store in the refrigerator or wait to spread filling until just

before serving. Try melted chocolate, softened cream cheese, peanut butter, marshmallow cream,

jam or jelly. Here is an idea for adding dairy foods and calcium to your diet in a fun tasty way.

Yogurt Drops - 18-ounce vanilla yogurt, 13-oz package of sugar free gelatin powder (any flavor)

and mix the gelatin powder with the yogurt. Using a spoon drop the mixture onto a fruit leather

drying tray. They can be done in small rounds or as leather. Dry until sticky and store in the

refrigerator or freezer. This makes great healthy snack and provides another way to get dairy

products and calcium in the diet (Brown, 2009).

2.8 Quality control

Quality control begins with the acquisition of high-quality fruit concentrate. Many purees are

supplied by well-known fruit processors. Other quality control methods include careful calibration

of all additives, particularly of those additives that affect hardening/malleability (malto-dextrin in

particular). Also, cooking and drying temperatures are monitored closely to ensure moisture

content. Scales are carefully calibrated so that each roll contains just the right amount of extruded

21

product; similarly, the packaging machine is checked and re-checked so that each cardboard

package includes the correct number of fruit leathers. Sample testing is performed periodically as

well (Nancy, 2009).

One of the most important concerns of the food manufacturer is to produce a final product that

consistently has the same overall properties, i.e. appearance, texture, flavor and shelf life. When we

purchase a particular food product we expect its properties to be the same (or very similar) to

previous times, and not to vary from purchase-to-purchase. Ideally, a food manufacture wants to

take the raw ingredients, process them in a certain way and produce a product with specific

desirable properties. Unfortunately, the properties of the raw ingredients and the processing

conditions vary from time to time which causes the properties of the final product to vary, often in

an unpredictable way. How can food manufacturers control these variations? Firstly, they can

understand the role that different food ingredients and processing operations play in determining

the final properties of foods, so that they can rationally control the manufacturing process to

produce a final product with consistent properties. This type of information can be established

through research and development work (see later). Secondly, they can monitor the properties of

foods during production to ensure that they are meeting the specified requirements, and if a

problem is detected during the production process, appropriate actions can be taken to maintain

final product quality (McClements, 1999).

Quality control points:

Use only ripe fruits without bruising or damage. Over-ripe ones can easily become

damaged and bruised. Under-ripe fruits will not have the full flavor.

Use a double boiling pan to avoid burning which can occur if direct heating is used.

Weigh all ingredients to the correct formulation.

Do not dry the leather in direct sunlight as there will be loss of color and vitamins A and

C.

Dust the leather lightly with starch before packing to reduce their stickiness.

Seal the leather packed in the form of a roll interleaved with greaseproof paper to avoid it

sticking together.

22

Check the correct fill-weight before sealing the bags.

If available, use 400 gauge polypropylene bags as they provide greater protection against

moisture (Nancy, 2009).

Manufacturers measure the properties of incoming raw materials to ensure that they meet certain

minimum standards of quality that have previously been defined by the manufacturer. If these

standards are not met the manufacturer rejects the material. Even when a batch of raw materials has

been accepted, variations in its properties might lead to changes in the properties of the final

product. By analyzing the raw materials it is often possible to predict their subsequent behavior

during processing so that the processing conditions can be altered to produce a final product with

the desired properties. Monitoring of food properties during processing is advantageous for food

manufacturers to be able to measure the properties of foods during processing. Thus, if any

problem develops, then it can be quickly detected, and the process adjusted to compensate for it.

This helps to improve the overall quality of a food and to reduce the amount of material and time

wasted. Traditionally, samples are removed from the process and tested in a quality assurance

laboratory. This procedure is often fairly time-consuming and means that some of the product is

usually wasted before a particular problem becomes apparent. For this reason, there is an increasing

tendency in the food industry to use analytical techniques which are capable of rapidly measuring

the properties of foods on-line, without having to remove a sample from the process. These

techniques allow problems to be determined much more quickly and therefore lead to improved

product quality and less waste. The ideal criteria for an on-line technique is that it be capable of

rapid and precise measurements, it is non-intrusive, it is nondestructive and that it can be

automated. Once the product has been made it is important to analyze its properties to ensure that it

meets the appropriate legal and labeling requirements, that it is safe, and that it is of high quality. It

is also important to ensure that it retains its desirable properties up to the time when it is consumed

(McClements, 1999).

2.9 Effect of processing on food quality attributes

Foods undergo changes as a result of processing; such changes may be physical, chemical,

enzymatic, or microbiological (Singh & Heldman, 2001). Food processing is any and all processes

to which food is subjected after harvesting for the purposes of improving its appearance, texture,

palatability, nutritive value, keeping properties and ease of preparation, and for eliminating

microorganisms, toxins and other undesirable constituents (David & Arnold,1999).

23

The composition of a food largely determines its safety, nutrition, physicochemical properties,

quality attributes and sensory characteristics. Most foods are compositionally complex materials

made up of a wide variety of different chemical constituents. Their composition can be specified in

a number of different ways depending on the property that is of interest to the analyst and the type

of analytical procedure used: specific atoms (e.g., Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur,

Sodium, etc.); specific molecules (e.g., water, sucrose, tristearin, b-lactoglobulin), types of

molecules (e.g., fats, proteins, carbohydrates, fiber, minerals), or specific substances (e.g., peas,

flour, milk, peanuts, butter). Government regulations state that the concentration of certain food

components must be stipulated on the nutritional label of most food products, and are usually

reported as specific molecules (e.g., vitamin A) or types of molecules (e.g., proteins) (McClements,

1999).

Many unit operations, especially those that do not involve heat, have little or no effect on the

nutritional quality of foods. Examples include mixing, cleaning, sorting, freeze drying and

pasteurization. Unit operations that intentionally separate the components of foods alter the

nutritional quality of each fraction compared with the raw material. Unintentional separation of

water-soluble nutrients (minerals, water-soluble vitamins and sugars) also occurs in some unit

operations (for example blanching, and in drip losses from roast or frozen foods.

Processing using heat is a major cause of changes to nutritional properties of foods. For example

gelatinization of starches and coagulation of proteins improve their digestibility, and anti-

nutritional compounds (for example a trypsin inhibitor in legumes) are destroyed. However, heat

also destroys some types of heat-labile vitamin, reduces the biological value of proteins (owing to

destruction of amino acids or Maillard browning reactions) and promotes lipid oxidation. Therefore

a continuing aim of food manufacturers should be to find improvements in processing technology

which retain or create desirable sensory qualities and nutritional properties or reduce the damage to

food caused by processing (Fellows, 2000).

2.9.1 Physicochemical properties

The physiochemical properties of foods (rheological, optical, stability, flavor) ultimately

determine their perceived quality, sensory attributes and behavior during production, storage and

consumption. The optical properties of foods are determined by the way that they interact with

electromagnetic radiation in the visible region of the spectrum, e.g., absorption, scattering,

transmission and reflection of light. For example, full fat milk has a whiter appearance than skim

24

milk because a greater fraction of the light incident upon the surface of full fat milk is scattered due

to the presence of the fat droplets.

The rheological properties of foods are determined by the way that the shape of the food changes,

or the way that the food flows, in response to some applied force. For example, margarine should

be spread able when it comes out of a refrigerator, but it must not be so soft that it collapses under

its own weight when it is left on a table. The stability of a food is a measure of its ability to resist

changes in its properties over time. These changes may be chemical, physical or biological in

origin. Chemical stability refers to the change in the type of molecules present in a food with time

due to chemical or biochemical reactions, e.g., fat rancidity or non-enzymatic browning. Physical

stability refers to the change in the spatial distribution of the molecules present in a food with time

due to movement of molecules from one location to another, e.g., droplet creaming in milk.

Biological stability refers to the change in the number of microorganisms present in a food with

time, e.g., bacterial or fungal growth. Foods must therefore be carefully designed so that they have

the required physicochemical properties over the range of environmental conditions that they will

experience during processing, storage and consumption, e.g., variations in temperature or

mechanical stress. Consequently, analytical techniques are needed to test foods to ensure that they

have the appropriate physicochemical properties (McClements, 1999).

2.9.2 Changes on Vitamins

Vitamins are minor components of foods which play an essential role in human nutrition. They are

organic compounds that are necessary in small amounts for proper growth. In general human

beings and animals can not be in a healthy state without vitamins, carbohydrates, fats, proteins,

minerals and water. Very small quantities of vitamins are necessary for health, but a lack of them

may upset the normal metabolism, resulting in deficiency diseases. Many of the vitamins are

unstable under certain conditions of processing and storage and their levels in processed foods,

therefore, may be considerably reduced. Most of the vitamins are also heat sensitive. The

occurrence of the vitamins in the various food groups is related to their water or fat solubility.

Vitamins are classified into two main groups: water soluble vitamins and Fat soluble vitamins

(Deman, 1980).

25

2.9.2.1 Effects of preliminary treatments: trimming and washing on Vitamins

The peeling and trimming of fruits and vegetables can cause losses of vitamins to the extent that

they are concentrated in the discarded stem, skin, or peel fractions. Although this can be a source of

significant loss relative to the intact fruit or vegetable, in most cases this must be considered to be

an inevitable loss regardless of whether it occurs in industrial processing or home preparation.

Alkaline treatments to enhance peeling can cause increased losses of labile vitamins such as float,

ascorbic acid, and thiamin at the surface of the product. However, losses of this kind tend to be

small compared to the total vitamin content of the product. Any exposure of cut or otherwise

damaged tissues of plant or animal products to water or aqueous solutions causes the loss of water-

soluble vitamins by extraction (leaching). This can occur during washing, transportation via

flumes, and exposures to brines during cooking. The extent of such losses depends on factors that

influence the diffusion and solubility of the vitamin, including pH (can affect solubility and

dissociation of vitamins from binding sites within the tissue), ionic strength of the extract,

temperature, the volume ratio of food to aqueous solution, and the surface-to-volume ratio of the

food particles (Fennema, 1996).

2.9.2.2 Effects of blanching and thermal processing on Vitamins

Blanching, a mild heat treatment is an essential step in the processing of fruits and vegetables. The

primary purposes are to inactivate potentially deleterious enzymes, reduce microbial loads, and

decrease interstitial gasses prior to further processing. Inactivation of enzymes often has a

beneficial effect on the stability of many vitamins during subsequent food storage. Blanching can

be accomplished in hot water, flowing steam, hot air, or with microwaves. Losses of vitamins occur

primarily by oxidation and aqueous extraction (leaching), with heat being a factor of secondary

importance. Blanching in hot water can cause large losses of water-soluble vitamins by leaching. It

has been well documented that high-temperature, short-time treatments improve retention of labile

nutrients during blanching and other thermal processes. The elevated temperature of thermal

processing accelerates reactions that would otherwise occur more slowly at ambient temperature.

Thermally induced losses of vitamins depend on the chemical nature of the food, its chemical

environment (pH, relative humidity, transition metals, other reactive compounds, concentration of

dissolved oxygen, etc.), the stabilities of the individual forms of vitamins present, and the

opportunity for leaching. The nutritional significance of such losses depends on the degree of loss

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and the importance of the food as a source of the vitamin in typical diets (Da-Silva and Williams,

1991).

2.9.2.3 Effect of processing on Vitamin C

Vitamin C (L-ascorbic acid) is the least stable of all vitamins and will easily be destroyed during

processing and storage. The rate of destruction of vitamin C is increased by the action of metals,

especially copper and iron, and also by the action of enzymes. Exposure to oxygen and light and

prolonged heating in the presence of oxygen during processing will decrease the vitamin C content

of foods. Factors that affect vitamin C destruction during processing include heat treatment and

leaching. The severity of processing conditions can often be judged by the percentage of ascorbic

acid that has been lost. The extent of loss depends on the amount of water used. Vegetables during

blanching covered with water may lose 80% half covered 40% and quarter covered 40% of the

ascorbic acid. Particle size affects the loss, for example in blanching of small pieces of carrots,

losses may range from 32-50% and losses from large pieces only 22-33%. Blanching of cabbage

may result in 20% loss of ascorbic acid and subsequent dehydration may increase this to a total of

50%. In the processing of milk losses may occur at various stages. From an initial level of about

22mg/l in raw milk the content in the product reaching the consumer may be well below 10mg per

liter. Ascorbic acid is oxidized in the presence of air under neutral and alkaline conditions. At acid

pH the vitamin is more stable for example in citrus juice. Since oxygen is required for the

breakdown, removal of oxygen should have a stabilizing effect. For the production of fruit drinks

it is recommended to de-aerate the water to minimize the vitamin C loss. The type of container may

also affect the extent of ascorbic acid destruction. Use of tin cans for fruit juices result in rapid

depletion of oxygen by the electrochemical process of corrosion. In bottles all of the residual

oxygen is available for ascorbic acid oxidation. To account for processing and storage losses it is

common to allow for a loss of 7-14mg of ascorbic acid per 100ml of fruit juice (Fennema, 1996).

2.9.3 Flavor and pigment components

The flavor of a food is determined by the way that certain molecules in the food interact with

receptors in the mouth (taste) and nose (smell) of human beings. The perceived flavor of a food

product depends on the type and concentration of flavor constituents within it, the nature of the

food matrix, as well as how quickly the flavor molecules can move from the food to the sensors in

the mouth and nose. Analytically, the flavor of a food is often characterized by measuring the

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concentration, type and release of flavor molecules within a food or in the headspace above the

food (McClements, 1999).

Fresh foods contain complex mixtures of volatile compounds, which give characteristic flavors and

aromas, some of which are detectable at extremely low concentrations (Fellows, 2000). These

compounds may be lost during processing, which reduces the intensity of flavor or reveals other

flavor/aroma compounds. Volatile aroma compounds are also produced by the action of heat,

ionizing radiation, and oxidation or enzyme activity on proteins, fats and carbohydrates. Examples

include the Maillard reaction between amino acids and reducing sugars or carbonyl groups and the

products of lipid degradation or hydrolysis of lipids to fatty acids and subsequent conversion to

aldehydes, esters and alcohols. The perceived aroma of foods arises from complex combinations of

many hundreds of compounds, some of which act synergistically (Maruniak and MacKay-Sim,

1984). In addition, the perceived flavor of foods is influenced by the rate at which flavor

compounds are released during chewing, and hence is closely associated with the texture of foods

and the rate of breakdown of food structure during mastication (Clark, 1990).

The colors of foods are the result of the presence of natural pigments or of added dyes. Pigments

are a group of natural colorants found in animal and vegetable products (Deman, 1980). These

pigments are organic in their nature and generally considered to embrace the pigments already

formed in the foods as well as those which can be formed on heating, storage or processing. Many

naturally occurring pigments are destroyed by heat processing, chemically altered by changes in pH

or oxidized during storage. As a result the processed food may lose its characteristic color and

hence its value. Maillard browning is an important cause of both desirable changes in food color

(for example in baking or frying and in the development of off-colors (for example during canning

and drying. Major food processing activities such as ambient temperature processing, processing by

the application of heat and processing by the removal of heat will affect the flavor, aroma and

pigment of food stuffs (Fellows, 2000).

2.9.3.1 Heat induced processing effects on flavor and color

Most foods have no significant changes to flavor or aroma when correctly blanched, but under-

blanching can lead to the development of off-flavors during storage of dried or frozen foods. In

fruit juices the main cause of color deterioration is enzymatic browning by polyphenoloxidase. This

is promoted by the presence of oxygen, and fruit juices are therefore routinely de-aerated prior to

pasteurization. In fruits and vegetables, chlorophyll is converted to pheophytin, carotenoids are

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isomerized from 5, 6-epoxides to less intensely colored 5, 8-epoxides, and anthocyanins are

degraded to brown pigments. Changes are due to complex reactions which involve the degradation,

recombination and volatilization of aldehydes, ketones, sugars, lactones, amino acids and organic

acids. In aseptically sterilized foods the changes are again less severe, and the natural flavors of

milk, fruit juices and vegetables are better retained. Aroma compounds that are more volatile than

water can be lost during evaporation. This reduces the sensory characteristics of most concentrates;

in fruit juices this results in loss of flavor, although in some foods the loss of unpleasant volatiles

improves the product quality, for example in cocoa (Anon, 1981).

Heat not only vaporizes water during drying but also causes loss of volatile components from the

food and as a result most dried foods have less flavour than the original material. The extent of

volatile loss depends on the temperature and moisture content of the food and on the vapor pressure

of the volatiles and their solubility in water vapor. Volatiles which have a high relative volatility

and diffusivity are lost at an early stage in drying. Foods that have a high economic value due to

their characteristic flavors (for example herbs and spices) are dried at low temperatures (Mazza and

LeMaguer, 1980).

The open porous structure of dried food allows access of oxygen, which is a second important

cause of aroma loss due to oxidation of volatile components and lipids during storage. Most fruits

and vegetables contain only small quantities of lipid, but oxidation of unsaturated fatty acids to

produce hydro peroxides, which react further by polymerization, dehydration or oxidation to

produce aldehydes, ketones and acids, causes rancid and objectionable odours. Some foods (for

example carrot) may develop an odour of violets produced by the oxidation of carotenes to -

ionone (Rolls and Porter, 1973). Evaporation darkens the color of foods, partly because of the

increase in concentration of solids, but also because the reduction in water activity promotes

chemical changes, (for example Maillard browning). As these changes are time and temperature

dependent, short residence times and low boiling temperatures produce concentrates which have a

good retention of sensory and nutritional qualities (Anon, 1981). Blanching brightens the color of

some foods by removing air and dust on the surface and thus altering the wavelength of reflected

light. The time and temperature of blanching also influence the change in food pigments according

to their D value (Fellows, 2000).

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2.9.4 Sensory attributes

The quality and desirability of a food product is determined by its interaction with the sensory

organs of human beings, e.g., vision, taste, smell, feel and hearing. For this reason the sensory

properties of new or improved foods are usually tested by human beings to ensure that they have

acceptable and desirable properties before they are launched onto the market. Even so, individuals'

perceptions of sensory attributes are often fairly subjective, being influenced by such factors as

current trends, nutritional education, climate, age, health, and social, cultural and religious patterns.

To minimize the effects of such factors a number of procedures have been developed to obtain

statistically relevant information. For example, foods are often tested on statistically large groups

of untrained consumers to determine their reaction to a new or improved product before full-scale

marketing or further development. Alternatively, selected individuals may be trained so that they

can reliably detect small differences in specific qualities of particular food products, e.g., the mint

flavor of a chewing gum Although sensory analysis is often the ultimate test for the acceptance or

rejection of a particular food product, there are a number of disadvantages: it is time consuming

and expensive to carry out, tests are not objective, it cannot be used on materials that contain

poisons or toxins, and it cannot be used to provide information about the safety, composition or

nutritional value of a food. For these reasons objective analytical tests, which can be performed in

laboratory using standardized equipment and procedures, are often preferred for testing food

product properties that are related to specific sensory attributes. For this reason, many attempts

have been made to correlate sensory attributes (such as chewiness, tenderness, or stickiness) to

quantities that can be measured using objective analytical techniques, with varying degrees of

success (McClements, 1999).

Many types of food processing techniques have been employed throughout human history, mainly

to ensure microbiological and chemical safety of foods and to improve palatability. Growing

consumer demand for healthy, nutritious and convenient food is a key driver for improvements and

new developments in food processing. New processes or newly recognized compounds, often

identified due to improved analytical capabilities, require careful evaluation of potential human

health impact. The most important quality attributes of a food to the consumer, are its sensory

characteristics (texture, flavor, aroma, shape and color). These determine an individuals preference

for specific products, and small differences between brands of similar products can have a

substantial influence on acceptability. So during processing great care must be taken to retain or

enhance these properties (Fellows, 2000).

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2.9.5 Influence of drying process

Drying of agricultural products is the oldest and widely used preservation method. It involves

reduction as much water as possible from foods to arrest enzyme and microbial activities hence

stopping deterioration. Moisture left in the dried foods varies between 2-30% depending on the

type of food. In tropical countries, solar dryers can be used to dry fresh produce when average

relative humidity is below 50% during drying period. Drying lowers weights and volume of the

product hence lowers costs in transportation and storage. However, drying allows some lowering in

nutritional value of the product e.g. loss of vitamin C, and changes of color and appearance that

might not be desirable (GTZ, 2009).

Fruits like mangoes, pawpaw, guavas and bananas, can easily be dried. However, they should be

harvested at the right stage and ripeness. Hard ripe stage in mangoes, pawpaw and bananas gives

best results. Avoid overripe, under mature fruits in order to obtain good products. To prepare the

fruits for drying, wash them thoroughly with clean water. Scrubbing with a brush might be

necessary like in case of mango fruit with a lot of latex cover. The fruits are peeled if necessary and

cut into smaller uniform pieces to ensure faster drying. Stainless steel knives are recommended for

peeling and cutting of the slices or pieces. Drum-drying of mango puree is described as an efficient,

economical process for producing dried mango powder and flakes. Its major drawback is that the

severity of heat preprocessing can produce undesirable cooked flavors and aromas in the dried

product. The drum-dried products are also extremely hydroscopic and the use of in-package

desiccant is recommended during storage (Dauthy, 1995).

To avoid discoloration and excessive vitamin losses, treatment with anti-oxidants like citrus

(lemon) juice is done. Fruits like pineapples may require pre-cooking to soften fibrous tissue hence

hasten drying. Drying is done on trays, which should be made of wood, fabric, plastic or sisal

material. This is because metal materials may affect the drying product negatively e.g. copper

destroys vitamin C, iron rusts, aluminum discolors fruits and corrodes. Most fruits have natural

acids and sugars which are preservatives therefore moisture contents of about 20% i.e. leathery and

springy dry (not brittle) is good for storage. This is however dependent