Transcript Meat and Poultry

Food Biotechnology
Dr. Kamal E. M. Elkahlout
Fruits and Vegetables
• Classification:
– Botanically – parts of the plants
• Fruits:
– various combinations of tissues that may include an
expanded ovary, the seed, and other parts such as
the receptacle (apple, strawberry), bract and
peduncle (pineapple)
• Vegetables:
– Do not specifically represent any specific botanical
groupings, thus exhibit a wide variety of plant
structures
Compositions: Fruits
• Water-varies from 75-90% has soluble substances like
salts, sugars organic acids water soluble pigments and
vitamins.
• Carbohydrates-include sugars & starches as well as
cellulose, hemicellulose and pectic substances
• Proteins-low in protein
• Fat-low in fruits except avocados and olives
• Minerals-low in Ca,P &Fe
• Vitamins-most fruits are low in B vitamins. Most fruits are
excellent sources of vit. C Yellow/orange fruits eg
pawpaw, mango are good sources of vit. A. Orange is
good source of folate.
• Organic acids-contribute to the taste of fruits eg citric
acid-in citrus fruits, tomatoes, pineapple, malic acid in
grapes, apples, pineapple
• Ripening:
– A chemical process that changes the physical and
chemical compositions and characteristics of fruits:
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Texture – from hard to soft
Colour- green to pink, yellow, red, violet, etc (more appealing)
Flavour-sour to sweet
Less edible to more edible
Aroma- no aroma to sweet smell, etc
– Stages of a plant’s life that are influence by hormone
ethelene (gas created by plants from methionine AA.
– Fruits- differ depending on variety and ripeness
Ripening
Composition :vegetables
• Most veg are good sources of CHO.
• Fibre-veg are better source of fibre than fruits
• Minerals- thin, dark green leafy veg are high in Fe,Green leaves
of goosefoot family are good sources of Ca.However oxalic acid
present in spinach binds Ca in an insoluble form.
• Vitamins-Dark green veg are good sources of riboflavin, vitamin
C and carotene (vitamin A)
• Veg are also good sources of thiamine.
• Organic acids-veg contain a number of organic acids however
the content is lower in veg than fruits. tomatoes has highest
con. of acids
Managing vegetables after harvest
– Fresh fruits and vegetables:
• living tissues
• continue to breathe
• composition and physiology continue to change after harvest
• continue to ripen and, finally, they begin to die
• cellular breakdown and death (senescence) are inevitable, slowed with
optimal storage conditions
• need low temperatures (32 to 55°F or 0 to 13 0C) and high relative humidity's
(80 to 95 percent) to lower respiration and to slow metabolic and
transpiration rates
By slowing these processes, water loss is reduced and food value, quality
and energy reserves are maintained.
Storage of fruits and vegetables
• Once a crop is harvested, almost impossible to improve its
quality.
• Loss from improper storage and handling can range from 10 to
40 percent.
• Bruises in fruits rich in phenolics cause undesirable
discolouration called enzymatic browning (undesirable
browning):
– Enzyme responsible for enzymatic browning, ortho-diphenol:
• oxygen oxidoreductase, is also known as
– catecholase, tyrosinase, phenolase, and polyphenol
oxidase.
Storage temperature
• Proper storage conditions—temperature and
humidity needed to lengthen storage life and
maintain quality once the crop has been cooled
to the optimum storage temperature.
• Each fruit or vegetable has its own ideal set of
conditions at which it will store most successfully
for a max length of time.
Storage temperature
• Some fruits and vegetables should be
stored only at room temperature due to
damage by low tempt (3.3-5.6 0C) e.g.
banana.
• While other fruits need to be stored in the
refrigerator to maintain in quality and to
prevent the loss of vitamins eg vit C
Cooking or Heating
• destroys enzymes and micro-organisms
• reduces bonds on the pectin molecules, making more
sites available for cross-bonding thus
– increase firmness in some fruits e.g. potato pectin
methyl esterase (PME) is active at 50-700C
• PME -catalyses removal of methyl grps from pectin
molecules which increase the no. free COOH.
• intracellular ions e.g. ca & mg come in contact and
react with cell wall components e.g. free COOH
forming bridges that strengthens the tissue:
– this helps resist degradation during heating
Blanching
– is heating in water or steam for a short time and then
cooled on trays
– destroys enzymes and prevents changes in colour, flavour
and texture during storage but does not preserve the food
and vegetables
– to be further processed by drying to achieve a longer shelf
life
– steam blanching retains more nutrients (water soluble
nutrients not lost into the water) compared to water
blanching.
Treatments
NaHCO3(baking soda)
– Added to blancher water retains colour or brighten green
colour of leafy vegetables, peas etc.
CaCl2
– Firming agent in fruits and vegetables which acts on pectin,
which exists as a firm gel around fibrous tissues and
prevents their collapse.
– During food processing, CaCl2 (ions) forms a calcium
pectate gel that strengthens the pectin complex, increasing
firmness and crispness.
– Thus there is greater support for tissues helps protect
against softening during processing.
Sulphuring
– For most fruits, 350-400g sulphur are used per 100 kg fruit,
burning for 1-3 hours.
– Sulphur dioxide prevents browning in foods such as apple,
banana and coconut (should not be used with red fruits as it
bleaches the colour).
– Sulphuring (gas) is achieved by exposing pieces of cut or
shredded fruits to burning sulphur in a sulphuring cabinet.
– Amount of sulphur used and the time of exposure depend on
the type of fruit, its moisture content and limits placed by law in
some countries on the residual amounts of sulphur dioxide in
the final product or by commercial limits set by importers
Sulphiting
– In sulphiting, the sulphur dioxide is dissolved in water
– Sodium sulphite, sodium metabisulphite or potassium
metabisulphite are made into solutions, either by adding one of
them to the blanching water or more often, by soaking the food
for 5-10 minutes in a sulphite dip.
Canning or bottling
– Vegetables and fruits can be canned/bottled in syrup, brine or
acid. Acidic fruits require mild heat treatment for pastuerisation
while less acidic fruits require severe heat sterilazation to
destroy food poisoning bacteria, yeasts and molds
– Time and temperature of canning are critically important and
must be carefully controlled.
– under-processed cans pose a risk of serious food poisoning
and even death from a type of micro-organism named
Clostridium botulinum.
– over-processed cans of vegetables lose much of their texture,
colour, vitamins and flavour and are not saleable.
Frying
– Starchy fruits, including jackfruit, breadfruit and banana
are fried and eaten as snack foods.
– Heat during frying removes moisture from the food,
destroys microorganisms and increases shelf of the
product. E.g potato chips
– However :
» very hot oil can splash onto operators when wet fruit
is immersed
Frying
» When oil is heated too much, it exceeds its smoke
point and a blue haze appears above the oil.
» a sign of oil breaking down chemically and it will then
begin to get more viscous and develop an unpleasant
flavour.
» flavour is transferred to the product, making it
unacceptable.
» When the oil thickens, more is retained on the
product and there is a higher cost in buying more oil
than is needed. Too much oil on the product also
reduces its shelf life.
Dry heat
• Drying removes most of the water from fruits and
vegetables to extend their shelf life and to
increase their convenience and value.
Air dry
• Air dried products are the most common type of
dried fruit and vegetables.
• Freeze drying (expensive method) may be used.
• Before preserving products may be
blanched/sulfited to preserve the natural color of
fruits and veg.
Salt and drying
• The high salt concentration preserves the
food by both drawing out water by osmosis
and by the anti-microbial properties of the
salt. High salt con.
• Also prevent the action of enzymes thus
preventing loss of quality of fruits/veg. Veg
are usually washed to remove the salt
before they are eaten.