dissertation on-utilization of unmarketable potatoes for preparation of instant potato soup powder

8/2/2019 Dissertation on-Utilization of Unmarketable Potatoes for Preparation of Instant Potato Soup Powder

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UTILIZATION OF UNMARKETABLE POTATOES FOR

PREPARATION OF INSTANT POTATO SOUP POWDER

by

Sajan Palanchoke

Food Technology Instruction Committee

Institute of Science and Technology

Tribhuvan University, Nepal

2008


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Utilization of Unmarketable Potatoes for Preparation of Instant

Potato Soup Powder

A dissertation submitted to theFood Technology Instruction Committee

in Tribhuvan University in partial fulfillment of the requirements

for the degree of B. Tech. in Food Technology

by

Sajan Palanchoke



Tribhuvan University

Dharan, Hattisar, Nepal

December 2008


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iii

Tribhuvan University



Central Campus of Technology, Dharan

Approval Letter

This dissertation entitled Utilization of Unmarketable Potatoes for Preparation of

Instant Potato Soup Powderpresented by Sajan Palanchoke has been accepted as the

partial fulfillment of the requirements for the B. Tech. in Food Technology.

Dissertation Committee

1. Chairperson

(Mrs. Geeta Bhattarai, Lecturer)

2. External examiner

(Mr. Bhisma Nanda Baidhya, Prof.)

3. Supervisor

(Mr. Shyam Kumar Mishra, Lecturer)

Date: December, 2008


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iv

Acknowledgements

It is my great privilege to work for the present investigation under the expert guidance and

kind supervision of lecturer Shyam Kumar Mishra, Central Campus of Technology,

Dharan. I express my deep sense of gratitude to him for his soulful advice, painstaking

efforts, fruitful discussion and constant encouragement during the course of work and also

highly indebted and grateful for his personal efforts and sacrifice of his most precious and

valuable time to have made it possible to bring the experiment to completion.

To me it is a matter of great satisfaction and pleasure to express my humble gratitude to

Associate ProfessorDr. Ganga Kharel, Asst. Dean, Central Campus of Technology. I also

gratefully express my sincere gratitude to Mrs. Geeta Bhattarai, Chairperson, FoodTechnology Instruction Committee, Mr. Pushpa Prasad Acharya, Chairman, Department of

Quality Control Surendra Bahadur Katawal Associate Professor, Lecturer Pashupati

Mishra, Assistant Campus Chief and Lecturer, Basanta Kumar Rai (Central Campus of

Technology, Dharan) for their support to work.

I am very much conscious to express my department and thanks to all the teachers and staff

members Hari Khanal, Sujan Dhakal and all my friends especially Rajkumari Shah, Bimala

Pokhrel, Roshna Ojha, Sussanna K.C., Amit Bhusan Suman, Santosh Dahal and kindly

juniors Rewati Raman Bhattarai, Sudip Thaguna, Nawaraj Gautam, Roshan Shrestha and

Mahalaxmi Pradhananga for their helping hands.

Finally, I am highly indebted to my parents and all family members for their constant

support, encouragement and frequent inspirations in this endeavor, by which I am able to

stand at this point of life.

Sajan Palanchoke


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v

Abstract

Potato flour is a highly versatile raw material that can be used in several processed foodproducts. Unmarketable potatoes were turned into flour and used to prepare instant potato

soup powder. The samples of potatoes were studied for peeling losses from different

peeling methods viz; hand peeling, abrasive peeling and mashing peeling, chemical

characteristics between potatoes and its flour and functional properties of the flour.

The abrasive peeling method was more economical for producing potato flour due to its

higher yield compared to other two peeling methods.

The chemical composition of the potato (dry basis) and the flour varied significantly.

Slight variations in functional properties between the different sizes of flour particle were

observed.

The recipies for the standardization of instant potato soup powder (IPSP) were worked out

by mixing potato flour made from unmarketable potatoes with ingredients like salt, citric

acid and msg in different proportions. The best IPSP recipe was selected on the basis of

higher sensory score for prepared soups on 9-point Hedonic scale. The results indicated the

recipie containing 3.33 parts of flour (m/v), 1.33 parts of salt (m/v), 0.04 parts of citric

acid (m/v), 0.13 parts of msg (m/v) and 100 parts of water (v/v) was rated superior from

different optimizing steps. The potato flour particle size of 150m was found to be

superior among the other two particle sizes. The cost of production per 100g of IPSP was

Rs 30.3. It is estimated to serve 3 liters of soup from 100g of instant potato soup powder.


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Contents

Approval letter ....iii

Acknowledgements ... iv

Abstract ... v

List of Tables and Figures ix

1 Introduction ...........................................................................................................................1

1.1 General Introduction ......................................................................................................... 1

1.2 Statement of the Problem ................................................................................................. 2

1.3 Objective of the study ....................................................................................................... 3

1.3.1 General objective ..................................................................................................... 3

1.3.2 Specific objectives .................................................................................................. 3

1.4 Significance of the study .................................................................................................. 4

1.5 Limitations of the study .................................................................................................... 4

2 Literature review ................................................................................................................... 5

2.1 Historical background....................................................................................................... 5

2.2 Structure of Potato Tuber ................................................................................................. 6

2.3 Chemical Composition of Potato ...................................................................................... 82.4 Nutritive Value of Potatoes and Potato Flour ................................................................... 9

2.5 Potatoes in Nepal ............................................................................................................ 11

2.5.1 Geography and Production zones .......................................................................... 12

2.5.1.1 Physical Geography ................................................................................................. 12

2.5.1.2 Climate ........................................................................................................................ 13

2.5.1.3 Regional Distribution of Potato Production ..................................................... 13

2.5.2 Production Systems and Constriants .................................................................... 14

2.5.2.1 Land Use and Land Tenure ................................................................................... 14

2.5.2.2 Cropping Calendar ................................................................................................... 15

2.5.2.3 Cropping Patterns and Fertility ............................................................................ 152.5.2.4 Occurrence and Control of Potato Diseases and Pests .................................. 17

2.5.3 Varieties and Seed Systems .................................................................................. 18

2.5.3.1 Varieties ...................................................................................................................... 18

2.5.3.2 The "Informal" Seed System................................................................................. 19

2.5.3.3 The "Formal" Seed System.................................................................................... 20

2.5.4 Consumption, Storage and Marketing .................................................................. 21

2.5.4.1 Consumption.............................................................................................................. 21

2.5.4.2 Storage ......................................................................................................................... 21

2.6 Grading and Marketing of Potatoes ................................................................................ 22

2.6.1 Size Grading of Potatoes ....................................................................................... 22

2.6.2 Economics of Grading ........................................................................................... 23

2.6.3 Potatoes preferences of Consumers ....................................................................... 23


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2.7 Utilization of Potatoes .................................................................................................... 24

2.7.1 Food uses: fresh, "frozen", dehydrated .................................................................. 24

2.7.2 Non-food uses: Glue, animal feed and fuel-grade ethanol .................................... 26

2.7.3 Seed potatoes: renewing the cycle ......................................................................... 26

2.7.4 Potato flour ............................................................................................................ 262.7.4.1 Methods of Manufacture ......................................................................................... 27

2.7.4.2 Uses of Potato flour .................................................................................................. 29

3 Materials and methods ........................................................................................................ 30

3.1 Raw materials ................................................................................................................. 30

3.1.1 Collection of raw materials.................................................................................... 30

3.2 Preparation of Potato Powder ......................................................................................... 30

3.2.1 Cleaning ................................................................................................................. 32

3.2.3 Peeling and slicing ................................................................................................. 32

3.2.4 Blanching and pretreatment of the potato slices .................................................... 323.2.5 Dehydration ........................................................................................................... 32

3.2.6 Size Reduction and Sieving ................................................................................... 32

3.2.7 Preparation of Instant Potato Soup Powder (IPSP) ............................................... 32

3.3 Analytical method .......................................................................................................... 33

3.3.1 Physical Parameter ................................................................................................ 33

3.3.1.1 Dimensions, sp. gr., shape of the tubers, peeling loss and flour yield ....... 33

3.3.1.2 Determination TSS (Total Soluble Solid) .......................................................... 33

3.3.1.3 Determination of Gelatinization temperature of potato flour ....................... 34

3.3.1.4 Determination of water absorption capacity of flours of different size ..... 34

3.3.1.5 Determination of Bulk density of flours of different size..............................

34

3.3.2 Chemical parameters ........................................................................................... 34

3.3.2.1 Determination of moisture content, protein content, crude fiber Reducing

sugar, sugar,sugar,Total sugar, Starch, vitamin C and Ash content ................................... 34

3.4 Optimization of ingredients in Instant Potato Soup Preparations ................................... 35

3.4.1Optimization of water ............................................................................................ 35

3.4.2 Optimization of salt ............................................................................................... 36

3.4.3 Optimization of citric acid ..................................................................................... 36

3.4.4 Optimization of monosodium glutamate (msg) ..................................................... 36

3.4.5 Optimization of potato flour particle size... 36

3.5 Sensory evaluations ........................................................................................................ 363.5.1 Sensory evaluation of Peeled Potatoes by different methods ................................ 36

3.5.2 Sensory evaluation of the instant potato soup preparations .................................. 36

3.6 Statistical Analysis ......................................................................................................... 37

3.7 Cost Calculation ............................................................................................................. 37

4 Results and Discussion ........................................................................................................ 38

4.1 Physical Characteristics of Unmarketable potato (Solanum tuberosum) ........................ 38

4.2 Chemical composition of Potato and Potato flour ........................................................... 40

4.3 Effect of Flour Particle size on Bulk Density and Water Absorption ............................. 41

4.4 Sensory Evaluation ......................................................................................................... 43


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4.4.1 Sensory Evaluation of Peeled Potatoes, peeled by different methods ................... 43

4.4.2 Optimization of Water Amount in Potato Soup .................................................... 43

4.4.3 Optimization of Salt Amount in Potato Soup ........................................................ 45

4.4.4 Optmization of Citric Acid Amount in Potato Soup ............................................. 46

4.4.5 Optimization of MSG Amount in Potato Soup ...................................................... 47

4.4.6 Optimization of Potato Flour Particle Size in Potato Soup .................................... 48

5 Conclusions and Recommendations .................................................................................. 51

5.1 Conclusions ..................................................................................................................... 51

5.2 Recommendations ........................................................................................................... 51

6 Summary .............................................................................................................................. 53

References ............................................................................................................................ 56

APPENDICES ...................................................................................................................... 61

Appendix A ........................................................................................................................... 61

Appendix B ............................................................................................................................ 62

Appendix C ............................................................................................................................ 63

Appendix D ........................................................................................................................... 65

Appendix E ............................................................................................................................ 67

Appendix F ............................................................................................................................ 69

Appendix G ........................................................................................................................... 71

Appendix H ........................................................................................................................... 73

Appendix I ............................................................................................................................. 75

Appendix J ............................................................................................................................. 81

Appendix K ........................................................................................................................... 82

Appendix L ............................................................................................................................ 86

Appendix M ........................................................................................................................... 87

Appendix N ........................................................................................................................... 89


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List of Tables and Figures

Tables

Table 2.1 Proximate analysis of white potatoes .................................................................... 8

Table 2.2 Inorganic Constituents of Potatoes ..................................................................... 10

Table 2.3 Cropping Calender in Nepal ................................................................................ 15

Table 2.4 Utilization of U.S. Potato Crops ......................................................................... 25

Table 4.1 Physical Characteristics of Unmarketable potato ............................................... 38

Table 4.2 Physical Characteristics of Unmarketable potato. ............................................... 39

Table 4.3 Chemical composition* of Potato and Potato flour ............................................ 41

Table 4.4 Summary of LSD (5%) test for difference between formulation (panelist =5)* . 43






Table B.1: The Average Chemical Composition of Flours Produced From Potatoes Grown

In Various Areas of USA ..................................................................................................... 62

Table D.1 Two way ANOVA (no blocking) for color in the optimization of water amount

in potato soup ....................................................................................................................... 65

Table D.2 Two way ANOVA (no blocking) for consistency in the optimization of water

amount in potato soup .......................................................................................................... 65

Table D.3 Two way ANOVA (no blocking) for flavor in the optimization of water amount

in potato soup. ....................................................................................................................... 65

Table D.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of

water amount in potato soup ................................................................................................. 66

Table D.5 Two way ANOVA (no blocking) for taste in the optimization of water amount in

potato soup ............................................................................................................................ 66

Table E.1 Two way ANOVA (no blocking) for color in the optimization of salt amount inpotato soup ............................................................................................................................ 67

Table E.2 Two way ANOVA (no blocking) for consistency in the optimization of salt

amount in potato soup ........................................................................................................ 67

Table E.3 Two way ANOVA (no blocking) for flavor in the optimization of salt amount in

potato soup ............................................................................................................................ 67

Table E.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of

salt amount in potato soup ..................................................................................................... 68

Table E.5 Two way ANOVA (no blocking) for taste in the optimization of salt amount in

potato soup ............................................................................................................................ 68


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Table F.1 Two way ANOVA (no blocking) for color in the optimization of citric acid

amount in potato soup ........................................................................................................ 69

Table F.2 Two way ANOVA (no blocking) for consistency in the optimization of citric

acid amount in potato soup ................................................................................................... 69

Table F.3 Two way ANOVA (no blocking) for flavor in the optimization of citric acid

amount in potato soup ......................................................................................................... 70

Table F.4 Two way ANOVA (no blocking) for overall accepatance in the optimization of

citric acid amount in potato soup .......................................................................................... 70

Table F.5 Two way ANOVA (no blocking) for taste in the optimization of citric acid

amount in potato soup ........................................................................................................... 70

Table G.1 Two way ANOVA (no blocking) for color in the optimization of msg amount in

potato soup ............................................................................................................................ 71

Table G.2 Two way ANOVA (no blocking) for consistency in the optimization of msgamount in potato soup .......................................................................................................... 71

Table G.3 Two way ANOVA (no blocking) for flavor in the optimization of msg amount in

potato soup ............................................................................................................................ 71

Table G.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of

msg amount in potato soup .................................................................................................... 72

Table G.5 Two way ANOVA (no blocking) for taste in the optimization of msg amount in

potato soup ............................................................................................................................ 72

Table H.1 Two way ANOVA (no blocking) for color in the optimization of potato flour

particle size in potato soup .................................................................................................... 73Table H.2 Two way ANOVA (no blocking) for consistency in the optimization of potato

flour particle size in potato soup ........................................................................................... 73

Table H.3 Two way ANOVA (no blocking) for flavor in the optimization of potato flour

particle size in potato soup .................................................................................................... 73

Table H.4 Two way ANOVA (no blocking) for overall acceptance in the optimization of

potato flour particle size in potato soup ................................................................................ 74

Table H.5 Two way ANOVA (no blocking) for taste in the optimization of potato flour

particle size in potato soup .................................................................................................... 74

Table I.1 Scores of sensory attributes in the optimization of water amount in potato soup 75

Table I.2 Scores of sensory attributes in the optimization of salt amount in potato soup ... 76

Table I.3 Scores of sensory attributes in the optimization of citric acid amount in potato

soup ....................................................................................................................................... 77

Table I.4 Scores of sensory attributes in the optimization of msg amount in potato soup .. 78

Table I.5 Scores of sensory attributes in the optimization of potato flour particle size in

potato soup ............................................................................................................................ 79

Table I.6 Scores of sensory attributes in the sensory evaluation of the peeled potatoes. ..... 80

Table J.1 Two way ANOVA (no blocking) for of the grade points for the peeled potatoesappearance ............................................................................................................................ 81


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Table K.1 t-test (Two-Sample Assuming Equal Variances) for the ash content of potato

and potato flour. ..................................................................................................................... 82

Table K.2 t-test (Two-Sample Assuming Equal Variances) for the crude fibre of potato and

potato flour ........................................................................................................................... 82

Table K.3 t-test (Two-Sample Assuming Equal Variances)for the starch content of potato

and potato flour ...................................................................................................................... 83

Table K.4 t-test (Two-Sample Assuming Equal Variances) for the reducing sugar content

of potato and potato flour ..................................................................................................... 83

Table K.5 t-test (Two-Sample Assuming Equal Variances)for total sugar of potato and

potato flour ........................................................................................................................... 84

Table K.6 t-test (Two-Sample Assuming Equal Variances) for vitamin C of potato and

potato flour ........................................................................................................................... 84

Table K.7 t-test (Two-Sample Assuming Equal Variances) for protein content of potato andpotato flour ........................................................................................................................... 85

Table K.8 One way Anova (no blocking) for peeling losses between hand peeling, the

abrasive peeling and mashing peeling .................................................................................. 85

Table L.1 Cost calculation of potato flour ............................................................................ 86

Table L.2 Cost calculation of instant potato soup powder (IPSP) ....................................... 86

Table M.1 Recipe for the formulations for optimization of water ..................................... 87

Table M.3 Recipe for the formulations for optimization of citric acid .............................. 87

Table M.4 Recipe for the formulations for optimization of msg ........................................ 88Table M.5 Recipe for the formulations for optimization of flour particle size. ................ 88

Table N.1: Functional properties of Potato flour .................................................................. 89

Figures

Fig 2.1 Structure of Potato Tuber ........................................................................................... 7

Fig 3.1 Methodology for the preparation of instant potato soup powder ............................ 31

Fig 3.2 Preparation of Soup from instant potato soup powder ............................................. 33

Fig 4.1 Effect of potato flour particle size on bulk density ................................................. 42

Fig 4.2 Effect of potato flour particle size on water absorption ........................................... 42

Fig C.1 A grading scale for peeled potatoes description of the quality grades for peeled

Potatoes potatoes ................................................................................................................... 64


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Part I

Introduction

1.1 General introductionPotato is the term which applies either to the starchy tuberous crop from the perennial plant

Solanum tuberosum of the Solanaceae, or nightshade, family, or to the plant itself. Potato is

the world's most widely grown tuber crop, and the fourth largest food crop in terms of

fresh produce after rice, wheat, and maize ('corn') (Anon. 1, 2008).

Potato is a versatile, carbohydrate-rich food highly popular worldwide and prepared and

served in a variety of ways. Freshly harvested, it contains about 80 percent water and 20

percent dry matter. About 60 to 80 percent of the dry matter is starch. On a dry weight

basis, the protein content of potato is similar to that of cereals and is very high in

comparison with other roots and tubers. In addition, the potato is low in fat. Potatoes are

rich in several micronutrients, especially vitamin C - eaten with its skin; a single medium

sized potato of 150 g provides nearly half the daily adult requirement (100 mg). The potato

is a moderate source of iron, and its high vitamin C content promotes iron absorption. It is

a good source of vitamins B1, B3 and B6 and minerals such as potassium, phosphorus andmagnesium, and contains folate, pantothenic acid and riboflavin. Potatoes also contain

dietary antioxidants, which may play a part in preventing diseases related to ageing, and

dietary fiber, which benefits health. (Prokop, 2008).

Potatoes produce more nutrition, energy and edible biomass per unit area and time than

any other major crop (Anderson, 2008).Potatoes contain lower levels of phytic acid than

other plant foods and reasonable amounts of all the essential amino acids except

methionine and cystine. (Kulkarni et al., 2008).The nutritional value per 100g potato is 80

Kcal (320 kJ).(Anon. 1, 2008).

World potato production reached a record 320 million tonnes in 2007.Consumption has

increased: from an average of 9 kg/person in 1961-63 to over 14 kg/person nowadays.

Long taken for granted in developed countries, the potato has the potential to relieve the

pressure of increasing cereal prices on the poorest people and contribute significantly to

food security. World potato production and consumption are currently expanding more

slowly than global population. (Prakash, 2008).


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The United Nations is appealing for continued global attention on the role the potato can

play in providing food security and eradicating poverty in helping to achieve the

Millennium Development Goals. It said the potato is a staple, nutritious food that can

provide poor people with an inexpensive food that can stop hunger and keep people

healthy (Schlein, 2008).

Hundreds of millions of people in the developing countries are facing crisis as the cost of

their staple foods continues to rise. Rice prices have almost doubled during 2008 and wheat

prices are climbing rapidly. But the price of the potato, the worlds third most important

food crop, has remained stable ( Prokop, 2008).

In Nepal potato is grown over an area of1,53,534 ha with an annual average production

of1,943,246 t with an average yield of 12.6 t/ha (FAOSTAT, 2008). By estimated 2003

data, Nepal's population of slightly more than 25 million people consumed 1,650,000

metric tons of potatoes, or about 65 kilograms (kg) annual per capita consumption (Brown

and Scheidegger, 1995).

Different sized potatoes are produced at farm level. Consumer preferences of the

potatoes are high for large and medium sized potatoes. At farm level it is not preventable to

produce grade A and B potatoes without the production of grade D potatoes

(unmarketable) (Devraj et al., 2007). In potato production small tubers are considered as

losses because of low marketability characteristics (Haravani and Ahmadabad, 2008).

Unmarketable potatoes (


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Furthermore small tubers show a greater weight loss during storage relative to that of the

larger tubers in same storage environment (Wiersema et al., 1987).This prompts for the

immediate processing of such potatoes after harvesting.

Slow increase in world food production and declining rates of yield growth in main food

crops threaten world food security. Land and water constraints, underinvestment in rural

infrastructure and agricultural innovation lack of access to agricultural inputs, and weather

disruptions are impairing productivity growth and the needed production responses. These

factors, combined with sharp increases in food prices in recent years, have added to

concerns about the food and nutrition situation of people around the world, especially the

poor in developing countries. (Braun et al., 2008).As cereal prices rise, potatoes have the

potential to be the affordable food for the developing countries. So optimum utilization of

the produced potatoes is necessary.

International trade in potatoes and potato products still remains thin relative to

production, as only around 6 percent of output is traded. (Prakash, 2008). Processing of

potato can increase the trade of potato products.

In many developing countries, and especially in urban areas, rising levels of income are

driving a "nutrition transition" toward more energy-dense foods and prepared food

products. As part of that transition, demand for potato is increasing. (Dr Anderson, 2008).

In Nepal, by most accounts, potato seed generally consists of either smaller tubers culled

from a previous harvest (especially at higher altitudes), or smaller potatoes purchased from

ware markets (more common at lower altitudes) (Anon. 4, 2000).No attention has been

paid to prepare the value added products and emphasize the food use of the unmarketable

potatoes.

1.3 Objective of the study

1.3.1 General objective

The main objective of this research work is to prepare a value added product from

unmarketable potatoes.

1.3.2 Specific objectives1. To study peeling loss of the unmarketable potatoes from different peeling methods.

2. To study the total cost for formulation of new product and determine how economic

is it.


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3. To prepare potato powder and formulate a product; Instant Potato Soup Powder.

1.4Significance of the studyThe processing of unmarketable potatoes prevents colossal loses, adds value to the produce

and gives better returns to the growers.

In the present context of food insecurity and malnutrition, the utilization of the waste

going and sound unmarketable potatoes by some value addition can contribute to meet the

complex challenge of reducing poverty and ending hunger and malnutrition in a

sustainable manner.

This technological approach can be easily and economically applied in small scale,

creating additional employment opportunities.

Also this work introduces a new value added commodity prepared from potatoes.

1.5Limitations of the studyDespite the importance of the study, several inevitable circumstances limit the scope of the

work. The limitations are:

a. The study is limited to only a single potato variety, due to time constrains.

b. The sampling was done at the local region of Dharan, so it may not represent

the whole population in general.

c. The study is only to prepare a product; the potatoes can also be processed into

other varieties of products which couldnt be done due to lack of time and

adequate knowledge.


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Part II

Literature review

2.1 Historical background

The origin of the potato was the South American continent. Various species of wild tuber-

bearing Solanums are found in Central America, Mexico, and as far north as Colorado. But

before the coming of Columbus the potato was not cultivated outside of South America.

Possibly 2000 years before the Spanish conquest the native South Americans brought

potatoes under cultivation. In 1537, the Spaniards first came in contact with the potato in

one of the valleys of the Andes. (Smith, 1976).

The diffusion of the potato from the Andes to the rest of the globe reads like an

adventure story, but it began with a tragedy. The Spanish conquest of Peru between 1532

and 1572 destroyed the Inca civilization and caused the deaths - from war, disease and

despair - of at least half the population. The conquistadores came in search of gold, but the

real treasure they took back to Europe was Solanum tuberosum. The first evidence of

potato growing in Europe dates from 1565, on Spain's Canary Islands. By 1573, potato was

cultivated on the Spanish mainland. Soon, tubers were being sent around Europe as exotic

gifts - from the Spanish court to the Pope in Rome, from Rome to the papal ambassador in

Mons, and from there to a botanist in Vienna. Potatoes were grown in London in 1597 and

reached France and the Netherlands soon after. But once the plant had been added to

botanical gardens and herbalists' encyclopedias, interest waned. European aristocracy

admired its flowers, but the tubers were considered fit only for pigs and the destitute.

Superstitious peasants believed the potato was poisonous. At the same time, however,Europe's "Age of Discovery" had begun, and among the first to appreciate potatoes as food

were sailors who took tubers to consume on ocean voyages. That is how the potato reached

India, China and Japan early in the 17th century. The potato also received an unusually

warm welcome in Ireland, where it proved suited to the cool air and moist soils. Irish

immigrants took the tuber - and the name, "Irish potato" - to North America in the early

1700s. (FAO, 2008).

The potato (Solanum tuberosum L.) was introduced to coastal southern Asia in the late

sixteenth or early seventeenth century by European (initially Portuguese) mariners, but the


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historical record for roughly the following two centuries is complicated by the word itself

(Purseglove, 1968).

The first unambiguous evidence of potato cultivation in Nepal dates to 1793, in records

by a British Colonel Kirkpatrick (Akius et. al. 1990, cited in Khatri and Rai 2000, p. 61).

The potato remained a relatively minor and unrecognized crop in Nepal for over 150 years,

until the first official attempt to improve potato production in Nepal occurred in 1962

under a program sponsored jointly by Nepal and India. In 1972 the National Potato

Development Programme was founded by the Government of Nepal, focusing on the

production of higher quality potato seed tubers. Over the past few decades, potato has

become the fastest growing staple crop in Nepal. (Chapagain, 2001).

2.2 Structure of potato tuber

As the potato plant grows, its compound leaves manufacture starch that is transferred to the

ends of its underground stems (or stolons). The stems thicken to form a few or as many as

20 tubers close to the soil surface. The number of tubers that actually reach maturity

depends on available moisture and soil nutrients. Tubers may vary in shape and size, and

normally weigh up to 300 g (10.5 oz) each. At the end of the growing season, the plant's

leaves and stems die down to the soil level and its new tubers detach from their stolons.The tubers then serve as a nutrient store that allows the plant to survive the cold and later

regrow and reproduce. Each tuber has from two to as many as 10 buds (or "eyes"),

arranged in a spiral pattern around its surface. The buds generate shoots that grow into new

plants when conditions are again favorable. (FAO, 2008)

Morphologically the tuber is a fleshy stem bearing buds or eyes in the axils of scale-like

leaves which soon shed, leaving a ridge or leaf scar subtending the bud. (Clark, 1921).

The anatomy of the potato plant, including the tuber, has been described in detail by

Artschwager (1918 and 1924) and others. The tuber itself is essentially an abruptly

thickened underground stem closely resembling the aerial stem of the plant (Talburt et al,

1975).

Externally the tuber clearly shows its relation to the aerial stem. Each eye is a

rudimentary scale leaf or leaf scar with its auxiliary buds. As on the stem, these are

arranged in a right-handed or left-handed spiral around the tuber, 13 eyes to 5 turns of the

helix (5/13 phyllotaxy). Each eye contains at least three buds together with protecting

scales. (Schwimmer et al, 1957).


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The principal areas in the mature tuber from the exterior inward are the periderm, cortex,

vascular cylinder, perimedullary zone and central pith. The periderm is 6 to 10 cell layers

thick acting as a protective area over the surface of the tuber. Small lenticel-like structures

occur over the surface of the tuber. Small lenticel-like structures occur over the surface of

the tuber. These develop in the tissue under the stomates and are initiated in the young

tuber when it still has an epidermis. Periderm thickness varies considerably between

different varieties. Cultural conditions also, however, influence thickness of periderm

rendering this characteristic too variable to use for variety identification (Fig 2.2).The

cortex is a narrow band of storage tissue next to the periderm. The outer layers of cells

contain protein crystals, tannins, pigments in colored varieties, and some starch. The

vascular cylinder and the perimedullary zones are narrow. These zones contain secondary

xylem and phloem. The principal region of storage parenchyma is immediately inside the

vascular ring (Talburt et al, 1975). Tuber growth is largely due to enlargement of the

perimedullary zone and is of procambial origin (Reeve et al, 1973).

The pith consists of a small central core with arms of medullary parenchyma radiating

from it. The cells are low in starch, high in water, and are more translucent than other

tissues (Talburt et al, 1975).

Fig. 2.1 Structure of potato tuber


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2.3 Chemical composition of potato

Starch, comprising some 65 to 80 percent of the dry weight of the potato tuber, is

calorically the most important nutritional component. The two main or perhaps sole

components of the starch, amylose and amylopectin, are present in a ratio of 1:3

(McCready and Hassid, 1947). Of the minor constituents of the starch granule only

phospho9rus has been shown to be chemically combined with the starch (Posternak,

1951).The sugar content of potatoes may vary from only trace amounts to as much as ten

percent of the dry weight of the tuber and thus 1/3 to of the non-starch solids (Barker,

1938).Sucrose, glucose, and fructose comprise the major sugar of the potato (Schwimmer

et al., 1954).Nonstarch polysaccharides largely comprise the cell wall and cementing

substances between the cells of the tuber. These largely are (1).Celluloseis present in the

cell wall and comprises 10-20% of the nonstarch polysaccharide of the potato (2) Crude

fiber consists largely of cell wall components including suberin and lignin. Approximately

one per cent of the dry weight of tubers is crude fiber although extremes of 0.2-3.5% have

been found. (3) Pectic substances are polymers of galac-turonic acid with the carboxyl

groups largely methylated. It ranges from 0.7 to 1.5% of the dry weight of the potato, the

skin being especially high in this substance (Potter and McComb, 1957). (4)Hemicelluloses

are mixed glycosidic chains containing combinations of glucuronic acid with xylose and of

galacturonic acid with arabinose. Approximately 1% of the total crude polysaccharide of

the potato is hemicellulose and occurs largely in the cell walls (Schwimmer and Burr,

1975). (5)Potatoes also contains ethanol-soluble oligosaccharides which consists of

glucose and fructose residues (Schwimmer and Weston, 1956).

Table 2.1 Proximate composition of white potatoes.

Average percent Range percent

Water 77.5 63.2-86.9

Total solids 22.5 13.1-36.8

Protein 2.0 0.7-4.6

Fat 0.1 0.02-0.96

Carbohydrate

Total 19.4 13.3-30.53

Crude fiber 0.6 0.17-3.48

Ash 1.0 0.44-1.9(Source: Kroner and Volksen, 1950)


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The total nitrogen content of potatoes ranges from one to two percent of the dry weight.

About 1/3 to of the total nitrogen is present as protein. The proteins of potato tubers are

comprised of about 60-70% globulins and 20-40% glutelins with no albumins or

prolamines present. Amino acid composition of these two fractions differs: glutelins

contain more cystine, aspartic acid, proline, and tryptophan than do the globulins. Free

ammo acids amounted to 4050% of nonprotein N (Tavrovyskaya, 1964).The bulk of non

protein fraction, comprising up to two-thirds of the total nitrogen, is present as free amino

acids as shown by work of Ashford and Levitt (1965).21 amino acids have been identified

as normal constituents of the alcohol soluble nitrogen of potato tuber tissue (Dent et al.,

1947).

The average fat content (ether-extractible matter of the potato is in the neighborhood of

0.01 percent on a fresh weight basis, with a range of about 0.02 to 0.2 percent (Schwimmer

and Burr, 1967) of which 40% linoleic, 30%linolenic, 5% oleic, and 25% saturated acids

are present (Highlands et al., 1954).

In addition to the amino and fatty acid the following organic acids have been found in

potaotes: citric, isocitric, ascorbic, lactic, malic, tartaric, succinic, oxalic, hydroxymalonic,

aconitic, phytic, alpha ketoglutaric, quinic, caffeic, and chlorogenic (Kroner and Volksen,

1950). The total acid content in the juice of potatoes is several times greater than the

content of acids capable of being initially titrated and is 0.84-1.15% calculated as citric

acid. One medium sized potato contains 20 mg. of vitamin C (Mc cay, 1956).The phenolic

compounds of poatatoes are associsated with the color of the raw poataotes. Tyrosine, the

major monohydric phenol of potatoes, is present in the inner portion of the tuber and

constitutes 0.1 to 0.3 % of the dry weight of the potato. The inorganic constituents or

mineral content of potatoes are tabulated in table 2.2.

2.4 Nutritive value of potatoes and potato flour

Nature has designed only a few foods that are capable of nourishing the great population of

the world. Of these, the white potato is one. Beneath its skin are liberal stores, not only of

energy, but of nitrogen and a high quality protein that will support growth and health.

Valuable minerals are there such as iron and magnesium and essential vitamins such as

vitamin C and several of the B vitamins. These are ample reasons why nutritional

deficiencies are little known in the countries whose populations depend on potatoes as their

basic food. The composition of potatoes varies as to varieties, storage, season, soils, and


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fertilization. However, average values to remember for the chief components of potatoes

are: protein and protein-like substances, two percent; carbohydrates about 18 percent; fat,

one-tenth of one percent; and water almost 80 percent. In addition of course are the

vitamins and minerals in potatoes, expressed in milligrams.The high water content of

potatoes should be noted, because when potatoes are compared in values to a food such as

rice which is nearly dry, the impression given is unfair. For instance, potatoes with two

percent protein would appear inferior to rice with sevent percent protein. For a truer

comparison, one should multiply the values of potatoes by five. This gives a value of ten

percent for the protein. If the quality of the protein is equally good, this explains why

millions of men can live on a diet comprised mostly of rice and others can thrive equally

well or even better upon a diet rich in potatoes. This matter of expressing chemical values

on a moist or dry basis is well known to food chemists, but it is poorly understood by

those who are not accustomed to thinking in these terms.(McCay, 1956).

Table 2.2 Inorganic constituents of potatoes.

Dry Basis (mg per 100 gm.)

Dry Basis (ppm.)

P 43.0-605 Br 4.8-8.5

Ca 10-120 B 4.5 -8.6Mg 46-216 I 0.5 -3.87

Na 0-332 Li TraceK 1394-2825 As 0.35

Fe 3-18.5 Co 0.065

S 43-423 Ni 0.26Cl 45-805 Mo 0.26

Zn 1.7-2.2

Cu 0.6-2.8

Si 5.1 -17.3

Mn 0.18-8.5

Al 0.2-35.4

(Source: Lampitt and Goldenberg, 1940)

Although potato flour is used in the baking industry, it has not been used much in home

cookery and is not widely available in retail stores. Hence, it is a product somewhat

foreign to the housewife, but one that could be used. Potato flour has found some use in

preparing special foods in mental hospitals for groups such as the spastic feeble-minded.It

is very useful in making mixtures of high nutritive value. In these cases it is easily prepared


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as a gruel with hot water on milk. Such gruels have special merit because they are slightly

sticky and hence not easily rejected by those who must be fed regularly. (McCay, 1956).

2.5 Potatoes in Nepal

Agriculture remains the mainstay of the national economy of Nepal, accounting for

approximately 40 percent of the Gross Domestic Product (GDP) and 81 percent of

employment (Chapagain, 2001). Most agricultural production is still characterized by

relatively low mechanical and chemical inputs. Since the 1960s, productivity of major

crops such as wheat, paddy rice, and sugarcane has grown in absolute terms, but relatively

less than Nepal's neighboring South Asian countries which raised productivity at a faster

rate with more rapid and intensive adoption of green revolution technologies (Chapagain,

2001). Agricultural production in Nepal has been enhanced by an expansion of land

accessible to irrigation, from approximately 6,200 hectares in 1956 to nearly 583,000

hectares by 1990 (Anon. 2, 2008).

In the 1970s, a national potato development programme, focused on improving the

quality of seed potato, stimulated a rapid expansion of both cultivated area and production,

which increased from 300 000 tonnes in 1975 to a record 1.97 million tonnes in 2006. The

potato is now Nepal's second staple food crop, after rice, and per capita consumption hasalmost doubled since 1990 to 51 kg a year. Potatoes are widely grown in Nepal, at below

100 m altitude in the south to as high as 4 000 m in the northern mountains. The tuber is

particularly favored by farmers in high hills areas (roughly 1 800 to 3 000 m): it is more

productive than rice and maize and the cool climate is well suited to production of seed

tubers for sale at lower altitudes. (FAO, 2008).

Current and potential gains in agricultural productivity should, however, be considered in

light of population growth, increasing at an annual rate of 2.3 percent as of 2003, and the

diminishing quality of agricultural land. Population density is particularly high in the

valleys and lowlands where the vast majority of the population of Nepal is concentrated.

Potato, as a crop capable of high productivity relative to land and time, is likely to remain

important to Nepal's food security and agricultural economy (Chapagain, 2001).


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2.5.1 Geography and production zones

2.5.1.1 Physical geography

Nepal is a landlocked country of approximately 147,000 square kilometers located between

China and India, "a yam caught between two rocks" (Anon. 2, 2008). However, for a small

country, Nepal is a land of great physical diversity, from tropical plains in the south of less

than 100 meters above sea level (masl) to hills and mountain ranges, reaching the world's

highest peak, Sagarmatha (Mount Everest) at over 8,800 masl. The increasing elevation isnot always uniform, but rather is characterized by a maze of mountains, hills, and lower

altitude valleys, resulting in a wide diversity of ecotypes and strong variations over short

horizontal distances. Differences in altitude, slope and aspect (the direction in which the

slope of the land faces) can result in a tremendous diversity of soils, drainage, solar

exposure, diurnal temperature regimes, and evapotranspiration conditions.

Nepal can be classified very generally into altitudinal zones which form roughly parallel

belts from east to west, occasionally bisected by the country's river systems. These zones

can be described as (Dhital 2000, pp. 7-10):

Terai (below 350 masl), the southern belt, forming the northern rim of the greater

alluvial Indo-Gangetic Plain stretching from the Punjab of Pakistan and India to the

delta of the Ganga (or Ganges) in Bangladesh, accounting for 17 percent of total

land area, but 42 percent of cultivated land, much of it devoted to rice and wheat;

Low Hills (350 - 1,000 masl), characterized by river valleys which support rice,

maize, and wheat, and in some areas double cropping of rice where irrigation isavailable;

Mid Hills (1,000 - 1,800 masl), with a warm climate that supports citrus, as well as

maize, rice, wheat, finger millet, soybean, and some potato;

High Hills (1,800 - 3,000 masl), where potato becomes the most important crop,

both for subsistence and commercial production, other crops including temperate

fruits, barley, and buckwheat;


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Mountains (above 3,000 masl), where permanent settlement is not common and

agriculture is possible only in valleys along southeastern slopes, and people are

otherwise dependent on livestock production and tourism.

2.5.1.2 Climate

Although Nepal's latitudinal range is narrowly restricted from approximately 27 to 30 N,

climatic variations, determined primarily by altitude, range from tropical and subtropical to

cool temperate to permanent arctic cold. The complexity of factors which determine

Nepal's climate can make it highly variable not only over space, but also over time. Local

climatic variation is one of the most serious risk factors facing farmers in Nepal; hazards

can include drought, extreme rain, and even hail (Dhital 2000, pp 8-10).

Precipitation is determined by several factors, especially altitude, longitude, and local

aspect. Up to approximately 3,000 masl, annual precipitation generally increases with

greater altitude, but thereafter decreases. Longitude is a factor since the summer monsoon,

generated by moist tropical air over the Bay of Bengal, decreases from east to west. At

lower altitudes, eastern Nepal receives approximately 2,500 millimeters (mm) of rain

annually, the Kathmandu area about 1,420 mm, and western Nepal about 1,000 mm. The

monsoon, generally from June through September, is the most important source ofprecipitation to farmers, providing more than 70 percent of the annual precipitation

received by the plains and lower altitude Himalayas. However, within this general pattern,

local conditions can vary over short distances. Aspect is locally significant since slopes

facing predominately east or south receive more precipitation, while slopes facing north

toward Tibet are especially arid. Winter snowfalls in the Himalayas are also an important

source of water for spring and summer crops, especially as more land has been made

accessible to irrigation (Anon. 2, 2008).

2.5.1.3 Regional distribution of potato production

Potatoes are widely grown throughout Nepal, from the southern terai at altitudes below

100 masl, to the northern mountains as high as 4,000 masl. The potato crop becomes

relatively more important in the high hills areas (from roughly 1,800 to 3,000 masl), as it

becomes more productive relative to staples such as rice, maize and finger millet. This

altitude range is also well suited to the production of potatoes to be used as seed tubers in

lower altitude areas, since viral degeneration generally occurs more slowly at higher


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altitudes and storage is much less of a challenge. The harvest in the high hills area, from

July to September, also complements the cropping calendar of the terai and low hills,

where planting takes place from September through December (Dhital 2000, p. 12).

2.5.2 Production systems and constriants

2.5.2.1 Land use and land tenure

As of 1998-99, land use distribution in Nepal was estimated by percentage as: Agriculture

27; Forest 38; Pasture 12; Other 23 (e.g. scrubland, permanent snow, and rock) (Khatri and

Rai 2000, p. 5). Forests in Nepal are being lost very rapidly, by roughly half from 1950 to

1980 (Anon. 2, 2008). Maintaining a forest cover of approximately 38 percent has become

a policy goal, but a difficult challenge as much of the remaining forest cover is in the terai,

the destination over the past several decades of settlers from higher latitudes (Chapagain,

2001). Nepal's future agricultural sustainability will have to rely on the productivity of

existing agricultural land, not new land developments.Nepal is still contending with a long

history of feudalism, whereby landlords held most of the kingdom's agricultural land.

Beginning in the 1950s, several legal remedies have been initiated by the state to limit land

ownership and regulate rent paid by tenants, but with limited results. In some cases, legal

reforms were expected well in advance of their passage, allowing landlords to redistribute

surplus land (on paper) among relatives or to otherwise conceal ownership. The amount of

land clearly redistributed under legal remedies has been estimated at less than two percent

of all agricultural holdings (Chapagain, 2001).

Due partly to the continued concentration of landholding, as well as the effects of a

rapidly growing population on land division via inheritance, most agricultural land

holdings are very small-scale and fragmented. A farm usually consists of several small

nonadjacent parcels. According to the 1991 National Sample Census of Agriculture (cited

by Chapagain, 2001), the average number of parcels per farm was nearly four, while the

number of parcels per hectare was just above four. These figures are regionally variable,

but that average is characteristic of the hills region where the potato crop is most

important. Land fragmentation partly reflects a strategy to minimize risk by exploiting a

wider range of ecologies, but can also be considered a structural challenge to agricultural

modernization, as small and fragmented holdings can inhibit the adoption of new

technologies, such as irrigation structures, to enhance production (Chapagain, 2001).


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2.5.2.2 Cropping calendar

The great agro-ecological diversity of Nepal allows for potato cultivation to occur

somewhere at any time of year. Potato is a winter crop in the terai and low hills, a spring

and autumn crop in the mid hills, and a summer crop in the high hills and mountains. The

duration of a crop is variable by variety, but is longer at higher altitudes. The generalized

cropping calendar is summarized in Table 2.3 (Dhital 2000, p. 13).

2.5.2.3 Cropping patterns and fertility management

Agriculture in Nepal remains predominately subsistence-based with minimal use of

external inputs, depending on a close interrelationship among crops, forestry and

livestock. Crops supply feed to livestock, while crop production depends on animal draft

power and manure as fertilizer (Dhital 2000, p. 10). Forest management has long been an

essential component of land management, given the extremely high potential for erosion

facing most land in Nepal.

Table 2.3 Cropping calender in Nepal

Zone Altitude (masl) Planting Months Harvesting Months

Terai Up to 350 October - November January - February

Low Hills 350 - 1,000 September - December December - March

Mid Hills 1,000 - 1,800 January - February April - June

August - September November - December

High Hills 1,800 - 2,200 February - March July - August

2,200 - 3,000 March - April July - September

Mountains 3,000 - 4,000 Late April - Early May September - October

(Source: Dhital, 2000)


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Given the extreme features of the physical geography above the terai and low hills,

effectively isolating small communities, many farmers have had minimal access to either

markets or wider social networks. That isolation, combined with the capricious climate

across much of Nepal, has favored agricultural strategies driven more by risk aversion than

profit seeking, although this situation is changing in some places with greater road access.

Intercropping, as opposed to crop specialization, remains a common practice, especially at

higher altitudes.The Nepal Agricultural Research Council (NARC) has reported that

studies conducted to assess the effects of intercropping various legume crops on the

production of rice and potato did not provide evidence of enhanced yields of potatoes,

though the grain and straw production of rice were both positively influenced by previous

legume crops, and potatoes contributed a high share of food energy relative to time and

land area. Two cropping patterns which provided high grain and straw yields of rice were:

faba bean-potato-rice, and sweet lupine-potato-rice (Anon. 3, 2008).

The Potato Development Section (PDS) of the Department of Agriculture has

recommended soil amendments of either farmyard manure at the rate of 20 tons per hectare

(T/HA) or commercial fertilizer at the approximate rate (by T/HA) of: Nitrogen 100;

Phosphorous 100; and Potassium 60 (PDS, 2002, pp. 11-37). In practice, application

depends on the availability of commercial fertilizer and/or animal resources and labor to

apply manure. Since seed tubers are a major factor of production costs, farmers have to

weigh the relative benefits of larger tubers, which produce faster initial growth and higher

potential yields, but at higher cost. By most accounts, potato seed generally consists of

either smaller tubers culled from a previous harvest (especially at higher altitudes), or

smaller potatoes purchased from ware markets (more common at lower altitudes). General

recommendations of potato crop spacing by the Department of Agriculture are to plant 25-

50 gram tubers 60-75 centimeters (cm) row to row and 20-30 cm plant to plant, for anoverall seed rate of one to two tons per hectare. A crop stand of 30 main stems per square

meter is considered optimal (ibid.).The recommended practice for harvesting is to cut

haulms approximately ten days prior to harvest in order to promote maturation of the

potato skin and therefore minimize bruising and damage during harvest. It is not reported

to what extent this practice is followed. Potato harvesting in Nepal is predominately

manual, as mechanization is rarely feasible in the steep and isolated areas where much of

the crop is grown. (Anon. 4, 2008)


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2.5.2.4 Occurrence and control of potato diseases and pests

This list is not complete, but includes several diseases and pests known to be serious

constraints to potato cultivation in Nepal.

Late Blight (LB), possibly the greatest biological constraint to potato cultivation

worldwide, is caused by a fungus-like oomycete, Phytophthora infestans, which is a

specialized pathogen of potato and, to a lesser extent, tomato (another member of the plant

family Solanaceae).

Late blight was first reported in Nepal between 1883 and 1897 and has been appearing as

an epidemic since the mid 1990s (Ghimire et. al. 2003, p. 236). According to Dhital and

Ghimire (1996, cited in Ghimire et. al. 2003), a nation-wide crop failure due to LB

occurred in 1996, although production data reported by FAO for that year do not reflect a

drop in either yields or production. Regional outbreaks are common, and cultivars once

considered LB resistant are apparently becoming less so.

Isolates of P. infestans collected during the 1999 and 2000 cropping seasons and

characterized for nuclear and mitochondrial DNA polymorphisms provided evidence of the

introductions of relatively new populations including both A1 and A2 mating types,

possibly with implications regarding resistance to metalaxyl, a systemic fungicide widely

used in LB control, though probably not widely used in the lower input cultivation of

Nepal (Ghimire et. al. 2003).

Several varieties selected by CIP for resistance to LB have been evaluated in Nepal,

including CIP clones 387146.48, 387199.33, 388764.6, 387224.11 and 388764.26 (Khatri

and Rai 2000, p. 63).

Black Scurfis a fungus,Rhizoctonia solani, that attacks tubers, underground stems, and

stolons of potato plants, especially in cool, damp soils. Although generally described as

more of a cosmetic problem due to black irregular encrustations of fungal sclerotia, it has

been described as a major concern, spreading from the plains into the hills of Nepal. Seed

treatment of two percent acetic acid and 0.2 percent zinc sulfate or three percent boric acid

alone has been reported as an effective control (Khatri and Rai 2000, p. 63), although these

materials are probably not readily available to most farmers.

Bacterial Wilt ( Ralstonia solanacearum) is the most destructive bacterial disease of

potato and several other plants of economic importance. The bacterium identified in Nepal

has been identified as Race 3, biovar 2. Yield losses have been reported as annually andspatially variable, but potentially capable of nearly complete crop loss.


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Due to its wide host range and a lack of resistant varieties, the disease is difficult to

control, except via long-term rotation with non-host crops, use of disease-free planting

material, and hygienic practices in general (Khatri and Rai 2000, p. 63). There is some

evidence that non-solanaceous summer weeds might play a greater role as disease vectors

than was previously assumed (Pradhanang et. al. 2000). Control efforts are challenging,

but feasible with widespread community involvement.

Vulnerability appears to correlate with soil amendments. Various treatments of urea,

lime and stable bleaching powder (or SBP,) have been shown to correlate with varying

degrees of infection of the highly susceptible variety "Kufri Jyoti" in a field naturally

infested with R. solanacearum for over 15 years. A treatment of urea (428 kg/ha) and

lime (5 t/ha) followed by SBP (25 kg/ha) seemed to provide a suppressant effect, though

the use of SBP alone at the rate of 25 - 37 kg/ha might be more economically efficient

(Anon.5, 1998).

Viral Diseases. The common practice of keeping smaller potatoes (or larger potatoes cut

into smaller pieces) from a general harvest for seed, with little regard for disease, favors

the transmission of viral infection. Potato Virus X (PVX) has been reported as more

serious in the hills, while PVY is prevalent in the lower altitude plains. PVM and PVS are

found in both areas. Degeneration studies have indicated that yield can be decreased by

3.6 percent for each 10 percent increase in viral infection (Khatri and Rai 2000, p. 63).

2.5.3 Varieties and seed systems

2.5.3.1 Varieties

Since the potato is of relatively recent origin to Asia, far fewer varieties are cultivated than

in the potato's Andean homeland range. Brown and Scheidegger, writing in 1995, reported

that only eight varieties were in local cultivation in Nepal, of which four were included in

seed multiplication programs (Brown and Scheidegger 1995, p. 19). Nepal has very likely

received, formally or through less formal diffusion, several varieties developed by the

Central Potato Research Institute (CPRI) of India, including Kufri Jyoti, introduced to

Nepal in the mid 1960s and currently considered the oldest and most widely grown of

"improved varieties" (Dhital 2000, p. 47). Varieties that have been present for several

generations are likely to bear several local names. Sikha Local and Gumda Local are

popular varieties in the mid to high hills, both grown under various local names. Severalother varieties persist from their introduction via the British colonial presence in India


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several generations ago, e.g. Darjeeling Red Round and Magnum Bonum. Cultivar CIP-

379693.110 has more recently been introduced under the name P-110, recommended for

cool tropical to warm tropical regions. NPI/T-0012 was introduced via Mexico as a testing

material in the late 1960s and has since been maintained by farmers in the high hills of the

western region. All of these cultivars belong to Solanum tuberosum spp. tuberosum,

except NPI/T-0012, which may belong to the subspecies andigena (Dhital 2000, p. 47).

This brief listing is by no means complete. A section of the 1996-97 annual report

posted by the Nepal Agricultural Research Council (NARC) pertaining to varietal

improvement efforts noted that sixteen local cultivars collected from different areas of

Nepal were being used in trials, in addition to recently introduced varieties. Nonetheless,

the introduction of new varieties is a recent effort in Nepal (Anon. 3, 2008).

2.5.3.2 The "Informal" seed system

A "seed system" is broadly defined as "an interrelated set of components including

breeding, management, replacement and distribution of seed." (Thiele, 1998, p. 84). Most

tuber seed used in Nepal has been produced and distributed by farmers themselves (the

informal system). The replacement interval can depend on several factors, such as a

gradual decline in yields due to viral degeneration or a natural calamity such as hail,drought, or severe late blight (Rhoades 1985, cited in Dhital 2000, p.14).

In the terai zones, farmers often depend for seed on the ware potato market in India, much

of it based on potatoes kept in cold storage. In the mid-hills, farmers sometimes acquire

new seed from the mountains, taking advantage of slower viral degeneration at higher

altitudes. But even in the mid-hills, seed from the lower altitude terai probably accounts

for a greater volume than seed from higher altitude sites (Brown and Scheidegger 1995, p.

9).

Potato farmers at higher altitudes have traditionally been almost entirely self-sufficient in

seed, depending either on a portion of their own harvests retained for seed, or very local

exchanges. Varietal population structures at remote higher altitude locations have

generally reflected minimal input from the formal system. Tubers retained for seed are

usually small, typically ten to fifty grams (Dhital 2000, p. 14).


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2.5.3.3 The "Formal" seed system

The formal system refers to seed tubers produced and distributed by state-sponsored

institutions (possibly with some involvement of the private sector and/or non-government

organizations). Seed from the formal sector has generally been subject to inspections and

controls intended to assure that the seed is of the variety claimed, with low incidence of

disease or pest infestation, of appropriate physiological age and otherwise viable. "Pre-

basic" and "basic" seed are multiplied into "certified seed," generally in the form of smaller

seed tubers (tuberlets) available for distribution to farmers, although the precise definitions

of these terms are locally variable.

The higher altitude regions of Nepal, among the most isolated places in the world where

access by road is extremely limited, pose an especially difficult challenge to any attempt by

a formal system to make improved potato seed tubers more accessible to farmers. This

limitation, combined with the advantages offered by higher altitudes being less subject to

viral diseases, favors the placement of the last stages of seed multiplication by the formal

system as close as possible to the ultimate users. Such locations, however, pose a

challenge to regular supervision by a technical staff, leaving farmers with more

responsibility for the management of any certified seed made available to them by the

formal system.

This effort, under the direction of NARC with assistance from the Swiss Development

Corporation (SDC) and the International Potato Center (CIP), has depended on groups of

farmers who receive training, but little subsequent supervision or direct incentives. Since

many of these groups are located in mountainous regions, the "head points" in the

traditional seed system, the goal is to inject the entire system with higher quality seed,

including some of promising new varieties, and thereby to enhance yields widely

throughout Nepal. Potato production by farmers involved in this effort seems to have

improved significantly (Brown and Scheidegger, 1995 p. 17).

A program is operated by NARC to provide certified seed.

A history of recent efforts to distribute improved quality seed, with the current

focus on Seed Producer Groups (SPGs), is well described in the CIP Program.


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2.5.4 Consumption, storage and marketing

2.5.4.1 Consumption

By estimated 2003 data, Nepal's population of slightly more than 25 million people

consumed 1,650,000 metric tons of potatoes, or about 65 kilograms (kg) annual per capita

consumption. This is very high by world standards, about the same as Peru, within the

potato's center of origin, and over twice the average consumption rate of India. Higher

production in the high hills zone is reflected in higher consumption. Brown and

Scheidegger (1995, p. 39) estimated that in 1991-92, per capita consumption was

approximately 24 kg in the terai, and over twice that, 51 kg, in the hills and mountains.

Production and consumption have considerably increased in both areas since then.

The potato has been creatively adapted to Nepali cuisine, as for example potato curry

(Brown and Scheidegger, 1995).

2.5.4.2 Storage

In keeping with the great diversity of agro-ecologies and agricultural practices in Nepal,

there are several methods used to store potatoes. Generally, however, there is not much

initial distinction between seed and ware potatoes; all are stored the same way.

In the terai, at altitudes up to 350 masl where high temperatures do not allow for longer-

term storage (more than perhaps two months), potatoes are usually sold soon after harvest.

The cold storage industry, which has become very important to potato marketing in India,

has yet to develop in Nepal. More recently introduced "improved varieties" are generally

more susceptible to high storage temperatures (Dhital 2000, p. 16).

In the low and mid hills (approximately 350 - 1,800 masl), farmers do not generally try tostore potatoes for seed, but rather rely on seed obtained from other areas. At higher

altitudes within this range, seed potato storage in partial diffused light is an old established

practice, as potatoes are often kept in different layers in bamboo baskets. Diffused light

promotes the growth of sprouts which are short and stout, ideal for viable seed tubers

(ibid.). Longer-term storage becomes much more feasible in the high hills, above 1,800

masl. Several methods are used, including storage in darkness in any available space in a

farmhouse, in clamps dug into the ground, or in some cases leaving potatoes unharvested

in the field for an extended period, although this last option is uncommon due to a high


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instance of rotting (ibid.).Although the viability of traditional methods generally increases

with altitude, storage losses in general appear to be increasing due to growing infestations

of several diseases and pests, e.g. late blight, bacterial wilt, soft rot (Erwinia spp.), dry rot

(Fusarium spp.), and potato tuber moth (Phthorimaea operculella) (ibid.). (Dhital, 2000).

2.6 Grading and marketing of potatoes

The purpose of grading is to aid in standardization of a product and to facilitate marketing

it. Sorting and packing potatoes to a set of recognized official standards enables producer

and buyer to communicate more intelligently concerning the value of the product. An

important aspect of grading is the use of a set of uniformly accepted standards. Grading is

of direct benefit to all parties concerned in the buying and selling transaction (Smith,

1976).

Profitable marketing of an agricultural commodity is an essential part of the total

production program for the producer. Marketing provides the necessary step from the farm

to the consumer. Without an efficient marketing procedure, even the finest quality crop can

be an unprofitable one (Smith, 1976).

Marketing in potato production begin with some vital decisions as choice of variety and

planting practices which will affect tuber size, shape and consumer acceptance.Market demand for potatoes is made up of such factors as variety, color, size and shape of

tuber, grade, uniformity, cooking quality, package size and type, cleanliness, and other

quality factors. It also involves the form in which the commodity is marketed, i.e., fresh vs.

one of the many processed forms of potato products (Schoenemann, 1976).

In Nepal Although many farmers who grow potatoes do so for cash income (especially at

lower altitudes in relatively accessible areas), there are not yet any organized marketing

services or cooperative organizations to facilitate regular marketing. Such organizations

could develop from the seed producer groups, farmers organized to multiply and distribute

high quality seed tubers, but so far this subject has not yet been reported (Dhital, 2000).

2.6.1 Size grading of potatoes

In addition to various physical grading of the product, modern grade standards for potatoes

also provide for marketing in various tuber size classes. Sizing of potatoes has become a

more widespread practice in recent years. The development of individual tuber sizing

machines has led to marketing of potatoes in special count packs. It is now possible for a


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buyer to purchase containers of potatoes with all tubers practically identical in weight and

to a large degree identical in shape. This is of special value to the hotel and restaurant

trade, where uniformity is required in preparing and serving baked potatoes. Housewives,

too, often prefer buying packages of potatoes in which tubers are sized to definite limits

(Eberhard and Eke, 1951).

In potato production small tubers (smaller than 35 mm) are considered as losses because

of low marketability characteristics (Haravani and Ahmadabad, 2008). At farm level it is

not preventable to produce grade A and B potatoes without the production of grade D

potatoes (unmarketable) (Devraj et al., 2007).

In USA, it has been found that, whole potatoes, usually smaller than 1.5 inches in diameter,

make up the greatest part of the potatoes that are canned. The potatoes used are not

specifically grown for canning but are primarily the small sizes of potatoes not suitable for

fresh market (Talburt, 1975).

Since seed tubers are a major factor of production costs, In Nepal, farmers have to weigh

the relative benefits of larger tubers, which produce faster initial growth and higher

potential yields, but at higher cost. By most accounts, potato seed generally consists of

either smaller tubers culled from a previous harvest (especially at higher altitudes), or

smaller potatoes purchased from ware markets (more common at lower altitudes) (Anon. 4,

2008).

2.6.2 Economics of grading

The economics of grading potatoes often poses certain problems for the producer. Sorting

out the top premium quality tubers leaves a residue of potatoes of rather low general grade

quality which often commands a relatively low price (Kross, 1952). The residue is usually

of adequate quality to allow for their use in various processed products (Smith,

1976).Unmarketable potatoes due to their small size (


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sized potato tubers indicate the desire for a medium-sized potato. The reasons most often

given are: (1) right size for judging portions; (2) easy to peel and handle; (3) easily adapted

to several cooking methods, and (4) less waste in peeling (Anon.6, 1948). For baking

purposes at home a 7-10 oz. p

dissertation on-utilization of unmarketable potatoes for preparation of instant potato soup powder

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