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Introduction 1 CHAPTER 1 INTRODUCTION India with its varied geographic and agro-climatic climatic conditions has a large range of varieties of fruits in its basket and account for around more than 10% of world’s fruit production (Indian Horticulture Database, 2011). Different types of tropical, subtropical and temperate fruits are produced in the country. Citrus, banana and mango are the important tropical fruits largely produced in India. Of these Banana (Musa sp.) is the fourth most important food crop in the world after rice, wheat and maize with a world production of around 102028.17 thousand MT in 2010 (FAO, 2012). India is the largest producer of banana in the world with an annual production of around 29780.00 thousand MT in 2010 in an area of 830.0 thousand ha (FAO, 2012). The major banana producing states in India are Tamil Nadu, Maharashtra, Gujarat, Andhra Pradesh and Karnataka. Data depicted in Table 1.1 revealed that in India the production of banana is rapidly increasing year by year, it has been increased from 18887.8 to 29780 thousand MT from 2005-06 to 2010-11. Table: 1.1 Area, Production and Productivity of Banana in India Year Area (000’ ha) Production (000’ MT) Productivity (MT/ha) 2005-06 569.5 18887.8 33.2 2006-07 604.0 20998 34.8 2007-08 658.0 23823 36.2 2008-09 709.0 26217 37.0 2009-10 770.3 26469 34.4 2010-11 830.0 29780 35.9 Source: Indian Horticulture Database (2011) Banana fruits are normally harvested at the mature green stage. A common indicator of harvest at this stage is the visual fullness of fruit fingers called 'finger angularity'. Some cultivars are harvested at the 'full three-quarters' to 'full' stage of maturity. This maturity index is normally coupled with other visual signs including

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  • Introduction

    1

    CHAPTER 1

    INTRODUCTION

    India with its varied geographic and agro-climatic climatic conditions has a

    large range of varieties of fruits in its basket and account for around more than 10%

    of world’s fruit production (Indian Horticulture Database, 2011). Different types of

    tropical, subtropical and temperate fruits are produced in the country. Citrus, banana

    and mango are the important tropical fruits largely produced in India. Of these

    Banana (Musa sp.) is the fourth most important food crop in the world after rice,

    wheat and maize with a world production of around 102028.17 thousand MT in 2010

    (FAO, 2012). India is the largest producer of banana in the world with an annual

    production of around 29780.00 thousand MT in 2010 in an area of 830.0 thousand ha

    (FAO, 2012).

    The major banana producing states in India are Tamil Nadu, Maharashtra,

    Gujarat, Andhra Pradesh and Karnataka. Data depicted in Table 1.1 revealed that in

    India the production of banana is rapidly increasing year by year, it has been

    increased from 18887.8 to 29780 thousand MT from 2005-06 to 2010-11.

    Table: 1.1 Area, Production and Productivity of Banana in India

    Year Area (000’ ha) Production (000’

    MT)

    Productivity

    (MT/ha)

    2005-06 569.5 18887.8 33.2

    2006-07 604.0 20998 34.8

    2007-08 658.0 23823 36.2

    2008-09 709.0 26217 37.0

    2009-10 770.3 26469 34.4

    2010-11 830.0 29780 35.9

    Source: Indian Horticulture Database (2011)

    Banana fruits are normally harvested at the mature green stage. A common

    indicator of harvest at this stage is the visual fullness of fruit fingers called 'finger

    angularity'. Some cultivars are harvested at the 'full three-quarters' to 'full' stage of

    maturity. This maturity index is normally coupled with other visual signs including

  • Introduction

    2

    drying up of leaves and dryness of stylar ends. Days after the emergence about 150-

    155 days of flowering of the inflorescence are also used as indicator of harvest.

    Bananas are harvested, transported and stored at the green stage (maturity stage 1)

    until they reach their destination where they will be treated with ethylene for ripening

    and then sold to retail markets. In banana ripening has been divided into seven stages.

    Commercial standard colour charts are available in which 7 stages of ripening were

    reproduced and translated to a numerical scale where Stage 1=all green, 2= green

    with trace of yellow, 3= more green than yellow, 4= more yellow than green, 5=

    yellow with trace of green, 6= full yellow, 7= full yellow with brown spots. In

    banana, post harvest compositional changes following are important since banana is a

    climacteric fruit. Ripening stages of fruit are associated with changes in texture, color

    and flavor leading to the best eating stage. Mostly, banana peel color changes from

    green to yellow while going through the 7 stages of ripening (Stover and Simmonds,

    1987). Texture softens at different rates for each ripening stage partly due to the

    hydrolysis of starch and pectin in banana pulp (Tucker, 1993). The most important

    changes which correspond to the best eating quality for ripening banana are the

    changes in flavor which result from several metabolic reactions. During ripening,

    initiated by ethylene, there is a degradation of pectin structure (Loesecke, 1950).

    However, it is believed that the major cause for softening in ripening banana is

    degradation of starch in the pulp (Tucker, 1993). Starch is hydrolyzed into sugars.

    Starch decreases from 20-23% of fresh pulp in green bananas to 1-2% in fully ripe

    bananas. These changes are concomitant with the increasing sugar content (from 1-

    2% rising to 20%) in the pulp during ripening (Palmer, 1971). Of the total sugars

    present in banana pulp, sucrose (13%), glucose (4%) and fructose (3%) are

    predominant and contribute heavily to the sweet taste of ripe bananas (Seymour,

    1993). Color changes during ripening mainly result from degradation of chlorophyll

    in the peel in the early stages of ripening and the biosynthesis of carotenoids in later

    stages (Seymour, 1993). Tannins are known to interact with salivary proteins and

    glycoproteins, causing fruit to taste astringent, hence the loss of astringency in banana

    pulp during ripening may result from increased polymerization of tannins (Palmer,

    1971). Lipids and total protein content represent only small amounts in banana pulp.

    They do not change substantially during ripening (Goldstein and Wick, 1969).

    Acidity of banana pulp increases during ripening (from pH 5.4 in preclimacteric to pH

  • Introduction

    3

    4.5 in postclimacteric pulp) (Palmer, 1971). There is a report that the astringent taste

    of unripe bananas is probably attributable partly to their oxalic acid content, which

    undergoes significant decarboxylation during ripening (Seymour, 1993).

    Banana when fully ripened is a soft and delicate fruit with a post-harvest shelf

    life of 5-7 days. This makes it prone to injury during transport. Further, release of

    ethylene during bulk storage makes the fruit to ripen faster and the fruits likely to rot

    before reaching its destination. Hence, it has always being considered a ‘problem

    fruit’ with respect to transportation. These reasons contribute to a local market glut,

    resultant price crash and subsequent disinterest among the farming community to

    cultivate it on a large scale. It is hence important to overcome this problem by

    generating an increased demand of this fruit crop. Exploring possibilities of

    converting banana into a cash crop by developing products of commercial interest is

    one way of solving this problem. In developed countries 40-50 % of the annual

    agricultural produce is converted into value added commodities. However, in India it

    is less than 2 % annually. Such a situation further necessitates the development of

    value added products.

    Fruit juices are the most common and demanding products made out of most

    of the fruits. The conversion of fruits into juices was originally developed for utilizing

    the surplus fresh fruits but now processing fruit juices is firmly established in its own

    right as a major industry. Increased awareness in health issue leads to increased in

    consumption of fruit juices. The modern trends in fruit juice technology showed

    increased use of different varieties and species of fruits to produce a wide of finished

    products like juices and their concentrates having good qualities. Varietal characters

    and degree of ripeness of the fruit are important factors affecting quality of juices

    produced. The suitability of a particular variety and degree of ripeness for juice

    extraction is dependent upon a balance of acids and sugars, aroma constituents and

    vitamin content particularly ascorbic acid content.

    Over the last two decades, great advances have been made in the technology

    of fruit juice processing. The advances have been largely towards the improvements

    in the existing conventional processing procedures and equipments as well as

    introducing new techniques to achieve maximum yield of the juice with good quality.

    Mechanical processing, diffusion extraction and enzymatic extraction are the distinct

    methods use for the extraction of fruit juices. Freshly pressed fruit juices contain

  • Introduction

    4

    variable amounts of fine cellular particles with colloidal material, pectic substances,

    gum, protein, tannin and other compounds (Feldmann, 1987). The size of particles

    ranges from 0.001 to 1000 µ. The large particles of about 100 to 500 µ may settle

    down rapidly, other coarse particles may be removed by centrifugation or filtration.

    The types of filters commonly include plate and frame filter press, sheet filter, precoal

    filter and rotary vacuum filter. In addition to the classical methods, ultrafiltration has

    found applications in fruit juices. Colloidal materials in the range of 0.001 to 0.1 µ are

    removed by enzyme treatment (Heatherbell, 1984).

    Due to several advantages of enzymatic extraction method, recently it is used

    widely. Wide varieties of enzymes are in use for different purposes in fruit juice

    industry. Among them pectinases are the most important in the extraction and

    clarification of fruit juices (Kilara, 1982). Pectic substances and pectolytic enzymes

    play a important role in fruit juice processing. The mechanism of enzymatic

    clarification process involves three stages viz. solubilization of insoluble pectins,

    decrease in the viscosity of soluble pectins and finally flocculation of the suspended

    particles (Yamasaki et al., 1964). Most of the commercial pectic enzyme

    preparations used in fruit juice extraction and clarification are of fungal origin

    because of having a low pH optimum and other characteristics suited for fruit juices

    (Rombouts and Pilnik, 1978). These enzyme preparations are marketed either as

    liquid (concentrate) or in powder form. The powders are generally diluted by adding

    dextrose, filter aid and gelatin which also act as clarifying agents. Pectic enzyme

    preparations mainly contain a mixture of pectolytic enzymes like pectin methyl

    esterase (PE) and polygalacturonase (PG). They also contain other non-pectic enzyme

    activities such as cellulose, hemicellulase, amylase, esterase, phenolase etc. (Kilara,

    1982). Commercial enzyme preparations exhibit different enzyme characteristics like

    response to temperature, pH, substrate requirements etc. Quantity and characteristics

    of native pectin have a significant influence on the effectiveness of commercial

    pectinases. Temperature has a significant effect on the activity of pectic enzymes.

    There is a close relationship between temperature and time during enzymatic

    treatment of fruit juices. As temperature increases, the rate of pectin degradation

    increases and the time of enzyme treatment decreases (Baumann, 1981).

    Because bananas have a high sugar and a recognizable, desirable flavour; high

    value juices from the excess bananas could become valuable product. Banana could

  • Introduction

    5

    then compete in the market either as banana juices or as mixture of other juices

    because of its widely appreciated flavour and high nutritive value. Banana juice can

    also be applied to wine production. Generally, fruit juices are extracted by simple

    crushing and or grinding of fruits. However, in case of banana this process results in a

    sticky, lumpy mass with no juice. Bananas are usually too pulpy and pectinaceous to

    yield juice by simple pressing or centrifugation (Adao and Gloria, 2005). Of the

    problems associated with banana pulp processing, a high viscosity and browning

    problem seems to be the most severe.

    The turbidity and viscosity of banana juice are caused mainly by the

    polysaccharides in the juice such as pectin and starch. Pectin makes the clarification

    process harder because of its fibre-like molecular structure. Starch is also a common

    problem for juice processors. Polymeric carbohydrates like starch may make filtration

    difficult and cause post-process cloudiness. Depectinization using pectinase enzyme

    could effectively clarify fruit juices. In the presence of starch, some problems like

    slow filtration, gelling after concentration and post concentration haze may occur.

    Application of enzymes such as pectinase and amylase improved the clarification

    process for banana fruit juices (Koffi et al., 1991; Yusof and Ibrahim, 1994; Lee et

    al., 2006). Pectinase hydrolyzes pectin and causes pectin–protein complexes to

    flocculate. The resulting juice has a much lower amount of pectin and a lower

    viscosity, so any subsequent clarification process is shortened. The enzymatic

    clarification is influenced by a number of variables including concentration of the

    enzyme, temperature and incubation time of the treatment (Baumann, 1981;

    Lanzarini and Pifferi, 1989).

    Banana pulp is highly susceptible to enzymatic browning during pulping.

    Enzymatic browning is the result essentially of the action of polyphenol oxidases

    (PPO) on endogenous polyphenolics resulting in O-quinones which consequently

    polymerize to colour pigments (Mathew and Parpia, 1971). Both the organoleptic

    and biochemical characteristics of fruits and vegetables are altered by pigment

    formation. The rate of enzymatic browning in fruit and vegetables is governed by the

    active polyphenol oxidase content of the tissues, the phenolic content of the tissue,

    pH, temperature and oxygen availability within the tissue. Browning reactions

    produce undesirable dark brown colour, unattractive appearance and also may reduce

    the nutritive value of the prepared juices (Eskin et al., 1971; Scott, 1975).

  • Introduction

    6

    Various techniques and mechanisms have been developed over the years for

    the control of these undesirable enzyme activities. These techniques attempt to

    eliminate one or more of the essential components (oxygen, enzyme, copper, or

    substrate) from the reaction. Several methods such as the addition of browning

    inhibitors and the exclusion of oxygen as well as thermal processing have been used

    to inhibit enzymatic browning. The use of browning inhibitors in food processing is

    restricted by considerations relevant to toxicity, wholesomeness, and effect on taste,

    flavour, texture and cost. Browning inhibitors may be classified in accordance with

    their primary mode of action. Sulfiting agents are widely browning inhibitors but they

    effects on health. Therefore, sulfites alternatives such as ascorbic acid based

    formulations, PPO inhibitors, complexing agents (e.g. EDTA, sodium acid

    pyrophosphate), sulfyhydryl-containing amino acids, organic halides, edible coatings

    are being heavily investigated as possible substitute.

    Despite various reports on enzymatic depectinization, no work on the

    optimization of pectinase and cellulase treatment with respect to ripening or maturity

    stages of banana fruit is reported. Most of the researchers used fully ripened stage i.e.

    stage 7 for enzymatic clarification study. During ripening as there is drastic changes

    occur in the composition of pulp viz. starch, sugar content; enzyme requirement for

    clarification will also be vary at different ripening stages. Hence, in the present

    investigation bananas of three advanced maturity stages viz. stage 5, 6 and 7 have

    been selected for enzymatic clarification study.

    Thus the present research work was undertaken with following objectives

    1) To study the advanced maturity stages of banana.

    2) To standardize the process parameters for clarification of banana pulp of

    advanced maturity stages

    3) To study the physico-chemical characteristics of clarified banana juices

    4) To evaluate the sensory qualities of clarified banana juices

    5) To study the inhibition of browning of clarified banana juice