chapter 1 introduction -...
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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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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
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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
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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
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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).
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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