Enzymatic browning in foods

3.  Introduction
 Occurrence of enzymatic browning
 Advantages
 Disadvantages
 Prevention of enzymatic browning
 Commercial aspects
 References

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)

10.  Fruits (Apples, pears, peaches, apricots, and
bananas)
 Vegetables (Potatoes, lettuce, brinjal)
 Cereals (wheat flour, rice)
 Sea foods (shrimps, spiny lobsters and crabs)

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

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.