Due to the more types of antioxidants, antioxidant action mechanism is not the same, in summary, there are mainly the following:
1. is to reduce the oxygen content in the food system through the reducing effect of antioxidants;
2. is to interrupt the chain reaction in the oxidation process and prevent the oxidation process from proceeding further;
3. is to destroy and weaken the activity of oxidative enzymes, so that they can not catalyse the oxidation reaction;
4. is to be able to catalyse and cause the oxidation reaction of the material closed, such as complexation can catalyse the oxidation reaction of metal ions. The following is a brief introduction to the mechanism of antioxidants with the examples of automatic oxidative rancidity of fats and oils and enzymatic oxidative browning of foodstuffs.
Inhibition of oil and fat oxidation by antioxidants
When natural oils and fats are exposed to air, they will spontaneously undergo oxidation reactions, generating low-grade fatty acids, aldehydes, ketones, etc., resulting in bad acidic odour and deterioration of taste, which are the main reasons for the deterioration of oils and fats and oil-containing foods. The auto-oxidation of fats and oils follows the free radical (also known as free radical) reaction mechanism. Firstly, fat molecules (expressed as RH) are activated by heat, light or metal ions and other free radical initiators, and then decomposed into unstable free radicals R- and H-.
When molecular oxygen is present, the free radical reacts with oxygen to form a peroxide radical, and this peroxide radical reacts with the fat molecule to form hydroperoxide and radical R-, which is then passed on through the chain reaction of radical R- until the combination of free radicals and free radicals or free radicals and free radical inactivators (denoted by x) produces a stable compound, and then the reaction ends.
This process produces many short-chain carbonyl compounds such as aldehydes, ketones, and carboxylic acids, which are the main substances that produce rancidity and poor taste, and the presence of large quantities of peroxides, which can also produce adverse results in the human body.
The mechanism of action of antioxidants is most importantly to terminate the transmission of chain reaction, the pattern is as follows (with AH for antioxidant): antioxidant radical A- is inactive, which can not cause the chain reaction, but can participate in some termination reactions. For example: A- A-→AA A- ROO-→ROOA_.
Oleoresin antioxidants mainly include butylhydroxyanisole (BHA), dibutylhydroxytoluene (BHT), propyl gallate (PG), tert-butylhydroquinone (TBHQ), tocopherol (vitamin E), etc. They all belong to phenolic antioxidants, which are more stable after the formation of free radicals, and the reason for this can be explained as follows: the unpaired singlet electrons on the oxygen atoms can act with the π-electron cloud on the benzene ring, which occurs a Conjugation effect. The result of this conjugation is that the paired electrons are not fixed on the oxygen atom, but are partially distributed to the benzene ring. In this way, the energy of the free radicals is reduced and no longer triggers a chain reaction, providing an antioxidant effect.
Inhibition of enzymatic oxidative browning of food
Enzymatic oxidative browning is a class of reactions in which phenol oxidases in foods catalyse the oxidation of phenolic substances to form quinones and their polymers. As the reaction produces melanin-like substances, the colour of the food is deepened, thus affecting the appearance and quality of the food.
Enzymatic oxidative browning requires three conditions: phenol oxidase, oxygen, and appropriate phenolic substances. Therefore, the inhibition of enzymatic browning of food can be considered from these three conditions. Since it is not possible to remove phenolic substances from food, the main measures that can be used are to destroy and inhibit the activity of phenol oxidase and to eliminate oxygen. The addition of appropriate amounts of antioxidants to foodstuffs，By consuming the oxygen in the food system through reduction, it serves to prevent enzymatic oxidative browning of food.
