This document discusses different types of browning reactions that can occur in foods, including enzymatic and non-enzymatic browning. Non-enzymatic browning includes caramelization, which occurs when sugars are heated and undergo a series of reactions to turn brown. It also includes Maillard browning, which is the reaction between reducing sugars and amino acids or proteins. Enzymatic browning is caused by phenolase enzymes and can be prevented by maintaining an acid pH, using sulfites or antioxidants, reducing oxygen contact, or blanching to denature the enzymes.

1. Browning Reactions
in Foods
Amandeep Singh
Assistant Professor
Department of Biotechnology
GSSDGS Khalsa College Patiala

2. Browning
• process of becoming brown, especially referring to food.
• may be desirable or undesirable.
• Browning has an important economic cost, causing deterioration of the
value of products in the market of food.

3. Types of browning reactions

4. Non-enzymatic browning
• Brown color in foods without the activity of enzymes
• usually involve sugar or related compounds
• Colour and flavour that are often :- desirable as in the crust of bread
or- undesirable as in the discoloration of dried milk products.

5. The two main forms of non-enzymatic
browning

6. Caramelization
• Caramelization or sugar browning occurs
when any of the different types of sugars are
heated over their melting points.
• When heated by dry heat, granulated sugar
will melt at approximately 160°C with
continued heating the melted sugar will
gradually turn brown to form Caramelized
sugar.
• The extreme heat pulls water out of the sugar
molecule to form furfural derivatives that
undergoes a series of reactions that are
polymerized to brown colour.

7. Maillard browning
• The Maillard browning reaction or carbonyl amine browning is
the reaction of the carbonyl group of a reducing sugar and an
amino acid or amino group of a protein or peptide.
• The reducing sugars, in order of decreasing reactivity are;
galactose, glucose, lactose and maltose the most reactive amino
acids are lysine, typtophan and arginine.

8. Maillard browning reaction

9. Enzymatic Browning

10. Enzymatic Browning
• Phenolases are found in many plants with especially high amount in
potatoes, mushrooms, peaches, banana, avocado and tea leaves.
• However, the browning that occurs in tea leaves is beneficial as it
imparts their characteristic colour.
• The term tannin describes the polyphenolic compounds that participate
in enzymatic browning and also contributes to an a stringent flavor.

11. Methods used to deter enzymatic browning
1.Maintaining an acid pH:
• retard the activity of the phenoloxidase enzyme :highest at a pH of 7
and diminishes as the pH decreases below 4.
• The lack of activity of this enzyme is seen in fruits that are very acidic
such as oranges and grape fruits.
• Cut fruits may be dipped in acid solution such as lemon juice and
orange juice.

12. 2. Use of sulphur:
• Sulphur is a chemical commonly used to
prevent the darkening of foods. E.g. use of
Pineapple juice
• prevent melanin formation. Cut lettuce for
salad are dipped in a weak sulphur solution to
retard browning.
3. Reducing contact with oxygen:
• done by coating fruits with sugar or
immersing them in sugar solutions.
• become very mushy, sugar or salt solutions are
necessary due to their osmotic pressure.

13. 4. Antioxidants
• Antioxidants, such as ascorbic acid
are also effective in reducing
browning
• they keep the substrate in a
reduced state, thereby interfering
with the remaining series of
reaction that produce brown
pigments
• Ascorbic acid is found in citrus
fruit juices and is available as a
commercial product that is
sprinkled on the fruit.

14. 5. Denaturing the enzyme by blanching
• Rapidly heating foods by dipping briefly
in boiling water will destroy or denature
the phenolase enzymes responsible for
the reaction with the polyphenolic
compounds.
• This destruction of enzymes allows
frozen foods to retain their color for a
longer period of time.
• Blanching treatment is done mostly in
vegetables such as amaranths, spinach
etc.