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Module 1: Aditivos alimentarios

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XSIQ
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Chemistry - Antioxidants

Antioxidants

Antioxidants are chemicals added to food to prevent it reacting with
atmospheric oxygen. Fruits such as apples and bananas start to go brown as
soon as the skin is broken because components react with atmospheric
oxygen. The reaction with atmospheric oxygen (oxidation) can be prevented
or delayed by adding ascorbic acid (vitamin C) to the fruit. Vitamin C acts
an antioxidant by reacting preferentially with atmospheric oxygen. Lemon
juice is effective in preventing the browning of freshly-cut bananas
because it contains vitamin C. Another natural antioxidant is vitamin E,
which is added to edible fats and oils. Although a high ratio of
polyunsaturated fats to saturated fats is desirable in our foods, C=C
double bonds are subject to attack by atmospheric oxygen. Vitamin E is a
stronger reductant than the C=C groups and so reacts preferentially with
atmospheric oxygen.

However, vitamin E is heat-sensitive and cannot be added to oils used for
deep-frying. If antioxidants are not added to products containing fats and
oils, these products may become rancid. Rancidity is caused by atmospheric
oxygen attacking the C=C double bonds in the fatty acid chains. This causes
the fatty acid chains to split, producing smaller, more volatile molecules
with a rancid taste and smell.

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