Food technology
Properties of Food
Date: 7th Feb
Prepared By:Sandesh Neupane
BROWNING REACTIONS
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.
Types of browning reactions
(i)Nonenzymatic
browning
(ii)Enzymatic
browning
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
The two main forms of non-
enzymatic browning
Caramelization Maillard browning
Caramelization
-Caramelization or sugarbrowning 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 160oC 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
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.
Enzymatic Browning
-Enzymatic browning is a chemical process, involving
polyphenoloxidase, catechol oxidase, and other enzymes that create
melanins and benzoquinone from natural phenols, resulting in a brown
color.
-In general, enzymatic browning requires exposure to oxygen, for
example the browning that occurs when an apple is cut.
-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.
What type of Browning involved
in Bake product????
Methods used to deter enzymatic browning :
1.Maintaining an acid pH:
• retard the activity of the phenoloxidaseenzyme :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
2.Use of sulphur:
•Sulphur is a chemical commonly used to prevent the
darkening of foods.
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.
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.
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.
