4. is a chemical process which occurs in fruits
and vegetables by the enzyme
polyphenoloxidase, which results in brown
pigments
Polyphenol oxidase acts as a catalyst to
speed up the process which can occur rapidly
at warm temperatures when the pH is
between 5.0 and 7.0. Polyphenol oxidase is a
copper-containing enzyme that catalyzes or
causes the oxidation of phenol compounds
contained in plant tissues
5. Molecular weight (128,00)
Enzymatic browning occurs when plant
tissue is exposed to air resulting in a brown
colored pigment, melanin, being produced
as a result of a series of biochemical
reactions.
Phenolases which are enzymes found
outside the cell wall come in contact with
colorless phenols which are found inside
the cell causing the brown color to appear.
6. Melanin
is any of a group of brown or black pigments
occurring in plants and animals. Melanin provides
the color in the skin of humans
Diseases caused due to difiecncy of melanin are
Yellow oculocutaneous albinism (These people
have white hair and white skin at birth but may
develop normal pigmentation as they reach infancy
and childhood)
7. Deafness
Neurodegenerative (lack of neuromelanin in
the brain areas)
Oculocutaneous albinism (absence of
melanin in the hair, skin and eyes)
It is generally accepted that two kinds of PPO
enzyme exist in nature
catechol oxidase
laccase
8. Catechol oxidase
which oxidizes o–diphenols to quinones
(catecholase activity) and also hydroxylates
monophenols to o–diphenols
Laccase
capable of oxidizing both o–and p–diphenols.
Other than these PPO enzymes
9. Polyphenols is a main component in
enzymatic browning
It is also called phenolic compounds,are
group of chemical substances
They are substrate for the browning enzymes
Phenolic compounds are responsible for the
colour, taste and flavour
Polyphenols can be divided into
Anthocyanins (colours in fruits)
Flavonoids (catechins, tanins in tea and wine)
11. When fruits and vegetables tissues are
exposed to oxygen then its colour become
brown
Such oxygen exposure occurs when the
pealing, cutting and bruising of fruits and
vegetables
Additionally, using copper or iron pans,
length of exposure to air, and humidity
increase this process
12.
13. The main cause of enzymatic browning by
which the oxidation of phenolic substrate
occurs during
Handling
Ripening
Storage
and processing of fruits and vegetables
14. It is known that the final product melanin has
antimicrobial properties, which prevents any
infection and inflammation to the plant or fruits
Melanin also has antibacterial, antioxidant, and
anticancer properties
Enzymatic browning in some food it is beneficial
because it increase colour and flavour like in
cocoa, tea, coffee, raisins, and prunes.
15. Nutritional qualities
Sensory qualities like bad odour, taste and
flavour
Unappealing to consumer
Decrease shelf life
16. Blanching (temp between 70 c° and
100 c°)
It has two types
Blanching in steam
Control enzymatic browning in canned
and frozen fruits and vegetables
Microwave blanching
Microwave energy can be used for
blanching because it causes an
inactivation of enzymatic systems in
foods
17. Refrigeration
Prevent spoilage of fruits and vegetables
Temp should be below 7 c
Freezing
Freezing is a technique often used to stop
browning reactions in fruit. Indeed, freezing
causes a decrease in available water for
enzymatic reactions
Change pH
By lowering the pH to 4.0 by addition of citric
and ascorbic acid
18. In homes lemon juice or vinegar should
sprinkled can inhibit enzymatic browning
Dehydration
Common methods for dehydration is
Freezing drying
By removing the moisture by sublimation
(change from solid to gas) under vacum
Lowering water activity
19. By adding water binding chemicals like salts
(Nacl), sucrose, honey and syrups
Irradiation
This process is used for killing bacteria and
inhibit enzymes activity
Several types are X-rays and gamma rays
High pressure treatment
Food is subjected to elevated pressures (500-
700) atmosphere
20. Reducing agents such as sulphiting agents
ascorbic acid and analogs, cysteine,
glutathione
Chelating agents such as phosphates, EDTA,
organic acids
Acidulants such as citric acid and phosphoric
acid
21. Treatment with supercritical carbon dioxide
(SC-CO2)
Supercritical carbon dioxide (fluid carbon
dioxide at high pressure) treatment is mostly
applied to destroying micro-organisms but
can also be applied for enzyme inactivation,
especially for inactivation of PPO in shrimps,
lobsters and potatoes
22. Removal of reactive textile dyes
Removal of phenolic contaminants from
waste water, effluents and contaminated soil
23. Guo, Y., Z. Zhou, Y. Yuan and T. Yue. 2013.
Survey of patulin in apple juice concentrates
in Shaanxi (China) and its dietary intake. Food
Control., 34(2): 570-573.
Es-Safi, N.-E., et al. 2003. "Implication of
phenolic reactions in food organoleptic
properties." J.Food Composition and Analysis
16(5): 535-553.
Houška, M., et al. 2006. "High pressure and
foods—fruit/vegetable juices." J.Food Eng.,
77(3): 386-398.
24. Lacroix, M. and B. Ouattara. 2000. "Combined
industrial processes with irradiation to assure
innocuity and preservation of food products—a
review." Food research inter., 33(9): 719-724.
Mcevily, A.J., R. Iyengar and W.S. Otwell. 1992.
Inhibition of enzymatic browning in foods and
beverages. Critical reviews. Food Sci. and Nutr.,
32(3): 253-273.
Zhang, L., et al. 2006. "Effect of γ irradiation on
quality-maintaining of fresh-cut lettuce." Food
Cont., 17(3): 225-228.
