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EFFECT OF ALGINATE-BASED EDIBLE COATING AND HONEY
TREATMENTS ON KEEPING QUALITY OF FRESH-CUT STAR FRUIT
(Averrhoa carambola L.)
NOOR HIDAYAH BINTI MOHD NAWI
Final Year Project Report Submitted in
Partial Fulfilment of the Requirements for the
Degree of Bachelor of Science (Hons.) Food Science and
Technology in the Faculty of Applied Sciences
Universiti Teknologi MARA
JANUARY 2012
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This Final Year Project Report entitled “Effect of Alginate-Based Edible
Coating and Honey Treatment on the Keeping Quality of Fresh-Cut Star
Fruit (Averrhoa Carambola L.)” was submitted by Noor Hidayah binti Mohd
Nawi, in partial fulfilment of the requirements for the Degree of Bachelor of
Science (Hons.) Food Science and Technology, in the Faculty of Applied Sciences
and was approved by
_________________________________
Madam. Fuziah Mohamed Othman
Supervisor
B. Sc. (Hons.) Food Science and Technology
Faculty of Applied Sciences
Universiti Teknologi MARA
40450 Shah Alam
Selangor
___________________________ ____________________________
Dr. Anida Yusoff Assoc. Prof. Dr. Noorlaila Ahmad
Project Coordinator Head of Programme
B. Sc. (Hons.) Food Science and B. Sc. (Hons.) Food Science and
Technology Technology
Faculty of Applied Sciences Faculty of Applied Sciences
Universiti Teknologi MARA Universiti Teknologi MARA
40450 Shah 40450 Shah Alam
Selangor Selangor
Date:_____________________
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ACKNOWLEDGEMENT
Assalamualaikum w.b.t
In the name of Allah The Most Gracious and The Most Merciful. Alhamdulillah all
praises to Allah for the strengths and His blessing I managed to finish the final
year project report and fulfilled the entire requirement in a given time. It is
undeniable that it quite difficult for me to start writing the proposal and project
report at the beginning but I managed to finish it up successfully. Upon completion
of this project, I would like to express my little appreciation to many parties that
directly or indirectly involved in making this into view.
Special appreciation goes to my beloved supervisor, Mrs. Fuziah Mohamed
Othman for her supervision, giving me guideline, assistance and constant support
in fulfilling this report writing. Her invaluable help of constructive comments,
suggestions and recommendations has given me strength to be more comparative
and creative in solving problems, thus mentally prepared to face more challenging
in the future. Not forgotten, my heartfelt thanks goes to Assoc. Prof. Dr. Noorlaila
Ahmad, the head of programme of Bachelor in Sc. (Hons.) Food Science and
Technology, for her kindness in making me deeply understands and evaluates a
better way to propose a project.
I would like to express a warm gratitude and appreciation to the Pasir Puteh
MARDI station and their staff, Mr. Mohd Azhar for his cooperation and
permission to supply the star fruit samples. Besides, my special thanks to all staffs
of Food Technology especially Mrs. Siti Marhani, Miss Hariyah Hashim, Mrs.
Norahiza, Miss Nurul Shuhada, Mr. Osman and Mr. Mohd Fadzli for their
technical supports and valuable advice.
My deepest gratitude goes to my beloved family for their endless love, prayers,
moral support and encouragement. Last but not least, sincere thanks to all my
friends for their kindness and support in completion this report. Thanks for the
friendship and memories. Besides, my gratitude also goes to those who indirectly
contributed in this report writing and in expressing their opinion and
recommendations with the greatest wishing thank you very much.
Noor Hidayah binti Mohd Nawi
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TABLE OF CONTENTS
Page
ACKNOWLEDGEMENT iii
TABLE OF CONTENTS iv
LIST OF TABLES vi
LIST OF FIGURES vii
LIST OF ABBREVIATIONS viii
ABSTRACT x
ABSTRAK xi
CHAPTER 1 INTRODUCTION
1.1 Background and problem statement 1
1.2 Significance of study 3
1.3 Objectives of study 4
CHAPTER 2 LITERATURE REVIEW
2.1 Background of star fruit 5
2.1.1 Varieties of star fruit 6
2.1.2 Nutritional value of star fruit 6
2.2 Harvesting 8
2.2.1 Selection and storage of star fruit 8
2.2.2 Postharvest of star fruit 9
2.2.3 Physiological and physical disorders 9
2.3 Maturity of star fruit 10
2.4 Grading standard 12
2.5 Techniques used to improve the shelf-life and fruits quality 14
2.5.1 Film wrappings 15
2.5.2 Modified atmosphere packaging (MAP) 15
2.5.3 Controlled atmosphere packaging (CAP) 16
2.6 Edible Coatings 17
2.7 Types of edible coatings and films 17
2.6.1 Polysaccharide – based coatings 18
2.6.2 Lipid – based coatings 19
2.6.3 Protein – based coatings 19
2.8 Advantages of edible coatings and films 20
2.9 Disadvantages of edible coatings and films 20
2.10 Honey 20
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2.11 Alginate 21
2.12 Calcium and ascorbate 22
CHAPTER 3 METHODOLOGY
3.1 Materials 23
3.1.1 Star fruits 23
3.1.2 Edible coating materials 23
3.1.3 Film-forming and dipping treatment solutions 24
3.2 Methods 25
3.2.1 Pre-treatment of samples 26
3.2.2 Application of coating 27
3.2.3 Visual appearance 27
3.2.4 Weight loss determination 27
3.2.5 Firmness evaluation 28
3.2.6 Surface colour development 28
3.2.7 pH measurement 28
3.2.8 Total soluble solid (TSS) determination 28
3.2.9 Oxygen and carbon dioxide concentration 29
3.2.10 Statistical analysis 29
CHAPTER 4 RESULTS AND DISCUSSION
4.1 Visual appearance 30
4.2 Effect on weight loss 32
4.3 Effect on firmness 34
4.4 Effect on colour 35
4.5 Effect on pH 38
4.6 Effect on total soluble solid 39
4.7 Oxygen and carbon dioxide concentration 40
CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 43
CITED REFERENCES 44
APPENDICES 51
CURRICULUM VITAE 87
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LIST OF TABLES
Table Caption Page
2.1 Nutritional information of star fruits 7
2.2 Grading standards of ordinary star fruits based
on quantitative and qualitative evaluation
13
3.1
Coatings and dipping sample formulations 25
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LIST OF FIGURES
Figure Caption Page
2.1 Star fruit Maturity Index 11
3.1 Overall experimental scheme of study 26
4.1 Visual appearance of fresh-cut star
fruits during storage at 5°C for 12 days
30
4.2.1 Percentage weight losses of fresh-cut
star fruits during storage at 5°C
33
4.3.1 Firmness of fresh-cut star fruits during
storage at 5°C
34
4.4.1 Lightness (L* values) of fresh-cut star
fruits during storage at 5°C
35
4.4.2 Greenness (a* values) of fresh-cut star
fruits during storage at 5°C
36
4.4.3 Yellowness (b* values) of fresh-cut
star fruits during storage at 5°C
36
4.5.1 pH measurement of fresh-cut star
fruits during storage at 5°C
38
4.6.1 Total soluble solid (TSS) of fresh-cut
star fruits during storage at 5°C
39
4.7.1 Oxygen concentration of fresh-cut star
fruits during storage at 5°C
40
4.7.2 Carbon Dioxide concentration of
fresh-cut star fruits during storage at
5°C
41
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LIST OF ABBREVIATIONS
% : Percent
°C : Degree Celsius
°F : Degree Fahrenheit
AA : Ascorbic Acid
ANOVA : Analysis of variance
Ca2+
: Calcium ion
CaCl2 : Calcium Chloride
CAP : Controlled Atmosphere Packaging
cm : Centimetre
DNMRT : Duncan‟s new multiple range test
F1, 2, 3, 4 : Formulation 1,2,3,4
CO2 : Carbon Dioxide
FAMA : Federal Agricultural Marketing Authority
FDA : Food and Drugs Administration
GRAS : Generally Recognised As Safe
g : Gram
kg : Kilogram
M : Molar
m : Meter
MAP : Modified Atmosphere Packaging
MARDI : Malaysian Agricultural Research and Development
Institute
mg : Milligram
mL : Millilitre
mm : Millimetre
N : Newton
NaOH : Sodium Hydroxide
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O2 : Oxygen
PPO : Polyphenol Oxidase
PMA‟s : Pre-Market Approval
PVC : Polyvinyl chloride
TSS : Total Soluble Solid
w/v : Weight by Volume
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ABSTRACT
EFFECT OF ALGINATE-BASED EDIBLE COATING AND HONEY
TREATMENTS ON KEEPING QUALITY OF FRESH-CUT STAR FRUIT
(Averrhoa carambola L.)
The effect of alginate-based edible coating with honey treatments on keeping
quality of fresh-cut star fruit (averrhoa carambola L.) was investigated. Fresh cut
star fruits with maturity index 3 were coated with alginate film forming solution
prepared from 2% w/v powdered alginate, 1% w/v glycerol with 0.13% w/v
sunflower oil and water. After the excess of coating drip off for a minute,
subsequently immersed with one of four different dipping solution formulations:
2% calcium chloride (CaCl2) with 2% ascorbic acid (AA) (F1), 2% calcium
chloride (CaCl2), 2% ascorbic acid (AA) with 5% honey (F2), 2% calcium chloride
(CaCl2), 2% ascorbic acid (AA) with 10% honey (F3) and 2% calcium chloride
(CaCl2), 2% ascorbic acid (AA) with 15% honey (F4). The effectiveness of these
treatments were assessed by evaluating their impact on the visual appearance,
weight loss, firmness, oxygen and carbon dioxide concentration, total soluble
solid, pH, and colour measurement. Overall, it was found that alginate-based
coating with honey treatment prolonged the shelf life and keeping quality of fresh
cut star fruit up to 12 days of storage at 5°C. It was demonstrated that the
application of all treatments were able to slow down ripening process and
maintaining the keeping quality of fresh cut star fruit in term of texture (firmness),
giving better appearance and aroma, reducing percentage weight loss and acting as
good gas and moisture barrier depending on the formulation. It also lowering the
changes in pH and maintaining desirable pH of fresh cut star fruit. Moreover, it
was able to retard and slow down the enzymatic browning on fresh cut star fruit.
Coating and dipping treatment with F4, containing 15% honey solution, was the
most suitable and effective coating for fresh cut star fruit except for visual colour.
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ABSTRAK
KESAN KAEDAH SALUTAN BERASASKAN ALGINAT DAN KAEDAH
CELUPAN MADU PADA KUALITI PENYIMPANAN POTONGAN
BELIMBING SEGAR (Averrhoa carambola L.)
Kesan kaedah salutan berasaskan alginat dan kaedah celupan madu pada kualiti
penyimpanan potongan belimbing segar telah di kaji. Potongan belimbing segar dengan
indeks kematangan 3 telah disalut dengan larutan lapisan berasaskan alginat yang terdiri
daripada 2% berat/isipadu serbuk alginat, 1% berat/isipadu gliserol dengan 0.13%
berat/isipadu minyak bunga matahari dan air. Selepas lapisan salutan di biar menitis satu
minit, kemudian ia di celup dalam salah satu daripada empat rumusan celupan berbeza:
2% kalsium klorida dengan 2% askorbik asid (F1), 2% kalsium klorida, 2% askorbik asid
dengan 5% madu (F2), 2% kalsium klorida, 2% askorbik asid dengan 10% madu (F3), 2%
kalsium klorida, 2% askorbik asid dengan 15% madu (F4). Keberkesanan rawatan ini telah
di nilai berdasarkan kesan penerimaan keseluruhan, penurunan berat asal belimbing,
kekerasan, kepekatan oksigen dan karbon dioksida, jumlah gula larut, keasidan dan
perubahan warna. Secara keseluruhan didapati bahawa kaedah salutan berasaskan alginat
dan rawatan dengan madu dapat memanjangkan tempoh penyimpanan dan kualiti
potongan segar belimbing sehingga 12 hari pada suhu 5°C. Ia menunjukkan kaedah
rawatan dengan semua rumusan mampu memperlahankan proses masak, dan mengekalkan
kualiti potongan segar belimbing dari segi kekerasan, memberi rupa dan aroma yang lebih
baik, mengurangkan peratusan pengurangan berat dan bertindak dalam mengurangkan
kadar respirasi dan kehilangan kelembapan yang bergantung kepada rumusan berbeza. Ia
juga bertindak dalam mengurangkan perubahan keasidan dan mengekalkan kadar keasidan
pada paras rendah potongan buah belimbing. Selain itu, ia boleh menghalang dan
memperlahankan perubahan warna disebabkan oleh enzim. Di dapati, rumusan salutan dan
celupan dengan 15% madu (F4) adalah yang paling sesuai dan berkesan sebagai penyalut
potongan buah belimbing segar untuk semua parameter kecuali bagi parameter warna
fizikal.
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CHAPTER 1
INTRODUCTION
1.1 Background and problem statement
Nowadays, people are particularly very conscious of their health. They are
concerned of the types of foods that they consumed everyday whether it is healthy
or not. Several epidemiological studies have been done and the results have
indicated that a high intake of plant products is associated with a reduced risk of a
number of chronic diseases such as atherosclerosis and cancer (Gungaard et al.,
2003; Hashimoto et al., 2002).
The fresh-cut fruits industries has potential to grow due to their characteristics of
freshness, low caloric contents, commodity to be used and an active promotion of
fruits and vegetables as basic components of a healthy diet (Rosa et al., 2008).
However, because of health benefits claiming by taking the natural products, it has
been responsible for the current increasing of product and consumption of fresh-
cut fruits.
Eating quality of fresh-cut fruit products is not only influenced by the stage of
ripeness at cutting (Gorny et al., 1998) but also is highly dependent on the post
harvest history of fruit before processing. The quality of fresh-cut fruits is usually
judge based on their appearance and freshness. However, a mechanical operation
during processing damage the fruit tissues which is turn limits the shelf-life of the
products. This alters the integrity of fruits bringing about negative effects on
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product quality such as browning, off-flavour development, texture breakdown and
the presence of micro-organisms on the fruit surface may compromise the safety of
fresh-cut fruits (Rojas-Grau et al., 2009).
Coatings of edible material applied as a thin layer to enhance the quality and
extend the shelf life of fresh-cut fruits can act as a barrier in reducing both
respiration and water loss (Kester and Fennema, 1986; Krochta et al., 1991;
Guilbert et al., 1996). It is applied on cut apples to produce a modified atmosphere,
which reduces decay, delays ripening and colour changes, improves appearance
and functions as a carrier of anti-microbial, anti-browning agents, texture
enhancers, nutraceuticals, flavours and volatile precursors (Olivas and Barbosa,
2005).
Polysaccharide-based coatings have been used to extend the shelf-life of fruits and
vegetables by reducing respiration and gas exchange due to selective permeability
to O2 and CO2 (Nussinovitch, 2000). Alginate is biopolymer that could be
considered for edible film and coating because of their unique colloidal properties
and their ability to form strong gel or insoluble polymer upon reaction with
multivalent metal cations like calcium (King, 1983 and Rhim, 2004).
Alginate is a polysaccharide isolated from marine brown algae (Phaeophyceae) is
finding increasing use in the food industry as texturizing and gelling agents
(Mancini and McHugh, 2000; Yang and Paulson, 2000; Lu and Ye, 2009).
Alginate is a salt of alginic acid, a polymer of D-mannuronic acid and L-guluronic
acid. Alginate has unique colloidal properties and can form strong gels or insoluble
polymers through crossed linking with Ca2+
by post-treatment of CaCl2 solution.
Such biopolymer-based films can keep good quality and prolong shelf life of foods
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by increasing water barrier, preventing microbe contamination, maintaining the
flavour and texture of the fresh-cut fruits.
Many studies have been conducted in order to understand the postharvest factors
that influence star fruit quality. However, information is limited on the preharvest
and mechanical processing aspects that influence fruit physiology especially for
fresh-cut fruit. Fresh-cut fruit products, including star fruit (Averrhoa carambola
L.), have limited marketability due to cut surface browning attributed to phenolic
compound oxidation by enzymes, such as polyphenol oxidase (PPO). Carambola
(Averrhoa carambola L.) is a fruit with great possibilities as a fresh-cut product.
Carambola slices have great potential for use in salads and as garnishes for drinks
or cocktails (Oslund and Davenport, 1983).
According to Watada et al., (1996) the use of film wraps or edible coatings can
modify the internal atmosphere, which had been shown to be beneficial in
extending shelf life. However, extensive modification of the atmosphere can cause
injury to tissue, thus further study is need to determine the recommended
atmosphere.
1.2 Significance of study
The use of polysaccharide-based coating (alginate) and honey treatment in this
study is to form a safe and edible coating film for fresh-cut star fruits. The fresh-
cut star fruits have been chosen because it is well known that easily to deteriorate
due to several factors like mechanical processing, improper handling and present
of oxidative browning enzymes and others. Significantly, the use of coating and
dipping treatment is to minimize the lost of nutrient by minimal processed. The
fruits also are widely recognised for their contribution to human nutrition and
health benefits. Besides, the results of this study will be useful in order to give
information about the formulation of edible coating and dipping treatments for
fresh-cut fruit as compared to the fresh-cut fruit without treatments.
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1.3 Objectives of study
The main intentions of this study are:
1. To compare the effectiveness of edible coating treatment and dipping in
maintaining keeping quality of fresh-cut star fruit.
2. To determine the effect of Alginate-based coating and honey dips treatment on
the changes of keeping quality attributes of fresh-cut star fruits up to 12 days of
storage at 5°C.
3. To identify the most suitable formulation for Alginate-based coating and honey
dips treatment for fresh-cut star fruits.
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CHAPTER 2
LITERATURE REVIEW
2.1 Background of star fruit
Star fruit or its scientific name Averrhoa carambola L. is classified in the division
Magnoliophyta, class Magnoliopsida, order Geraniales, family Oxalidaceae (The
Columbia Encyclopaedia, Sixth Edition, 2008). It believed to originate in Sri
Lanka, the Moluccas, India and Indonesia then it has been cultivated in Southeast
Asia and Malaysia for many centuries but now it cultivated in the United States.
Averrhoa carambola is a small, evergreen, multi-stemmed tree 3 to 5m high or
rarely 10m high, attaining 15cm diameter at the base; bark light brown, smooth or
finely fissured. Leaves alternate, pinnate, 15 to 25cm long, disposed more or less
in a horizontal plane, shortly petiolate with 7 to 9 pendant leaflets; leaves have the
peculiarity of being sensitive to touch in the same way as certain Mimosa species.
Inflorescence in panicles 2 to 5cm long in the axils of old leaves; flowers
pentamerous, with a calyx of 5 pink sepals surrounding the purple corolla;
androecium contains 5 fertile stamens and 5 staminoids; gynoecium bears 5
slender united styles. Fruit a large, indehiscent berry, 5 to 8cm long; with a
characteristic shape in cross-section resembling a 5-pointed star; yellowish-green,
becoming orange-yellow when ripe. Each cell of the fruit contains five arillate
seeds (Campbell, 1989).
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In Malaysia it closely relative called “belimbing”. Other names include carambola,
Chinese star fruit, star apple and quite appropriately, five-angled fruit. This scented
fruit named after a twelfth century Arabic physician and philosopher, Averrhoes.
The fruit, with its sweet-sour taste is a popular delicacy here, most often eaten raw.
The fruit displays an attractive star-shape when cut, thus its popular name. It has a
waxy, golden yellow to green colour skin with a complicated flavour combination
that includes plums, pineapples, and lemons (Nakasone and Paull, 1998).
2.1.1 Varieties of star fruit
According to Nakasone and Paull (1998) there are two types of star fruit are
grown, tart and sweet. Tart varieties typically have narrowly spaced ribs, while
sweet varieties tend to have thick, fleshy ribs. The tastes between the two are
hardly distinguishable, as the tart variety still has some sweetness. There are
several cultivars of star fruits introduced in the markets.
There are two main types distinguished by bearing either sour or sweet fruits. The
sweet types contain up to 5% sugars and sour types have as much as 1% acid. A
Chinese type, “Fuang Tung” is very sweet, while “Brazilian” ones are full of
vitamin C. Exotic types of star fruit from Hawaii called “Golden Star”, Taiwan
called with “Tean Ma” and “Min Tao” and the famous star fruits cultivar from
Columbia is “Icambola” (Faciolla, 1990).
2.1.2 Nutritional value of star fruit
Star fruits are an excellent source of vitamin C, naturally sodium and cholesterol
free. A small whole star fruit will provide approximately 2/3 cup sliced. Star fruit
is very low in saturated fat, cholesterol and sodium. It is also a good source of
pantothenic acid and potassium, and a great source of dietary fibres, vitamin C and
copper. One medium size of star fruit contains about 40 calories. Consuming about
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five daily servings of fruits lowers the chances of cancer. A recent study found that
eating nine or ten servings of fruits and vegetables combined with three servings of
low fat dairy products are very effective in lowering blood pressure (Hung et al.,
2004).
Table 2.1 Nutritional information of star fruits
Serving size: 1 cup (132g), cubed
Amount per serving
Calories 41 kcal Calories from Fat 4 kcal
% Daily Value*
Total Fat 0g 1%
Cholesterol 0mg 0%
Sodium 3mg 0%
Total Carbohydrate 9g 3%
Dietary Fibres 4g 15%
Sugars 5g
Protein 1g
Vitamin A 2% Vitamin C 76%
Calcium 0% Iron 1%
*Percent Daily Values are based on a 2000-calorie diet. Your daily values may be higher or low
depending on your calorie needs.
Source: PMA‟s Labelling Facts (2008).
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2.2 Harvesting
Seedlings of star fruits take about four to five years to produce fruit. Star fruit tree
flowers three to four times a year follow by crops, the fruiting is especially heavy
over summer, other peak seasons are November to December, and March to April,
continuous harvesting is possible year-round in tropical regions. The best to know
for ripeness is to eat one to taste how sweet the fruit is. The average of 300 pounds
of fruit can be harvesting from a healthy grown tree per year (Anon, 1996).
2.2.1 Selection and storage of star fruit
Fruits are hand harvested carefully to avoid scratching the skin that might affect
the quality of the star fruits. High quality star fruit will give firm, shiny skinned
even colour fruit. Star fruit suffers from fruit fly maggots, particularly Dacus
dorsalis (Southeast Asia), and fruit-piercing moth (Othreis spp., Australia);
bagging prevents infestation but post harvest rots are more serious: the slightest
blemish invites infection by Ceratocystis, Colletotrichum, and Dothoriella and
Phomopsis fungi (Watson et al., 1987).
However, star fruits will ripen at room temperature and have lightly brown edges
on the ribs when it is ripe. Unripe star fruit should be turn often, until they are
yellow in colour and ripe with light brown ribs. Star fruit can be stored at room
temperature for two to three days or unwashed, and refrigerated, in a plastic bag
for up to one week. The storage length of star fruit varies with ripeness when
placed in chiller. Lower relative humidity (RH) of the storage may result in more
severe rib edge browning if the star fruit held at 20°C (68°F). However, the star
fruits are extremely perishable where it shelf life at room temperature ranges from
three to four days depending on the storage atmosphere (Kader, 1999).
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2.2.2 Post harvest of star fruit
Star fruit (Averrhoa carambola L.) is commercially harvested at colour-break to
reduce susceptibility to mechanical injury during handling. Sugar levels remain
constant during storage, although star fruits will continue to lose chlorophyll and
develop carotenoids after harvest. Acidity can decline during storage, and this is
often undesirable as it can be associated with blandness (O'Hare, 1993). The
carambola has the characteristics of a non-climacteric fruit. Increases in carbon
dioxide and ethylene production rates occur after the fruit is consider ripe and
these tend to be relating to microbial decay or tissue senescence.
A storage temperature of 5°C is capable of maintaining fruit with a minimum of
physiological changes for at least 6 weeks, provided moisture loss is controlled.
Storage life is largely limited by disease, which commonly develops from lesions
either present at harvest like insect damage or occurring during product handling
(O'Hare, 1993).
2.2.3 Physiological and physical disorders
The previous study by Kader (1999), shows chilling injury can be determine by
some observation. The symptoms include surface pitting where the pits are either
small (<1mm), deep and dark brown or large (1-2mm), superficial, and light
brown, and rib-edge browning. These symptoms have been reported in some
carambola cultivars after two weeks at 0°C (32°F) or six weeks at 5°C (41°F)
followed by two days at 20°C (68°F).
Other than that, the physical damage also may occur by post-harvested fruit where
the rib-edge browning and stem-end browning can result from surface abrasions
and other types of bruising. The browning intensity increases with water loss from
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the fruits. Handling star fruits with care to minimize bruising is essential to
reducing post harvest losses (Watson et al., 1987).
Other types of defects that might be occurring are shrivelling and heat
damage. Symptoms for shrivelling is the star fruit become visible when it lose
about 5% or greater of their weight due to water stress. However, symptoms of
heat damage shows the skin browning and flesh softening may occur when star
fruit are expose to heat treatments such as 46°C (115°F) for 35 to 55 minutes for
insect control to satisfy quarantine requirements. Better alternatives may be cold
treatment and/or irradiation.
Post harvest diseases of star fruit may be caused by Altenraria
alternata (especially on chilled fruits), Cladosporium cladosporioides, or
Botryodiplodia theobromae. These usually occur at physically damaged sites on
the fruits during prolonged storage. Minimizing physical damage throughout the
harvesting and post harvest handling operations and prompt cooling to 5°C (41°F)
can greatly reduce incidence and severity of post harvest diseases on star fruit
(O'Hare, 1993).
2.3 Maturity of star fruit
Maturation is the stage of development leading to attainment of physiological and
horticultural maturity. Maturity at harvest is the most important factor that
determines the storage life and quality of star fruit. Immature fruits are more
subject to mechanical damage and are of inferior flavour quality when it ripe.
However, overripe fruits are likely to become soft and mealy with insipid flavour
soon after harvest (Kader, 1992).
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Normally, colour is use as an index to determine the maturity of the fruits. Star
fruit maturity are based on the colour changes from green to yellow which is
accompanied by an increase in soluble solids including sugars for it sweetness.
Star fruit should be picking when fully yellow to assure good eating quality. The
colour break (1/2 to 3/4 of fruit is yellow) is used as the commercial maturity index
because these fruits are firmer and easier to handle (Kader, 1999). Some indexes
have been proposing to determine the maturity of the star fruits.
Index 1: Dark Green.
Not suitable for
harvest.
Index 2: Green
overall with stripes of
yellow. Suitable for
export by sea.
Index 3: Green
overall with yellow.
Suitable for export by
sea.
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Figure 2.1 Star fruit Maturity Index
Source: Federal Agricultural Marketing Authority (FAMA), (2010).
2.4 Grading standard
The Malaysia Federal Agriculture and Marketing Authority, (FAMA) established
three grades for golden yellow star fruit belonging to Averrhoa carambola L.
genus. The grades are FAMA no.1, FAMA no. 2 and FAMA no. 3 are determined
Index 4: Yellow
green. Suitable for
export by air.
Index 5: Yellow
overall with little
green. Suitable for
local consumption.
Index 6: Yellow to
orange overall. Ripe
fruit. Suitable for
local consumption.
Index 7: Dark yellow
to orange overall.
Ripe fruit. Suitable
for local
consumption with
limited storage life.
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by qualitative and quantitative criteria stated by FAMA. The star fruit should be
around 635–15cm long and approximately 9cm wide. It should have 4 to 6 pointed
stars that run from top to bottom. However, its colour should be translucent green
or orange-yellow with minimum darkening or other discoloration defects. The top
grade star fruits are allowed little variation in these quality characteristics, while
the lower grade is allowed greater variation and degradation.
Generally, star fruits of the same variety do not show significant variation in sizes
and weights (Abdullah et al., 2006). This is the FAMA grading standards as
summarised in Table 2.2 below. Following FAMA standards, the fruit‟s colour
was used to estimate the degree of ripeness while the fruit‟s shape was used to
determine the overall quality feature.
Table 2.2 Grading standards of ordinary star fruits based on quantitative and
qualitative evaluation
Grade Quantitative/Qualitative Features Tolerances (%)
FAMA
no. 1
- Uniform in colour
- Freshness (flesh firmness or texture)
- Damage due to mechanical injuries,
bruises, diseases, damage by insects
affecting more than 25% of fruit surface
- Defect (abnormal shape including
discolouration affecting 10% to 25% of
fruit surface
- Uniform in size (weight >200g)
5
5
5
5
5
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