Food Business Network News Food antioxidants and preservatives are used for food quality and storage, but preservatives are aimed at the inhibition and inhibition of microbial growth and enzyme activity, and the fundamental purpose of antioxidants is to delay the deterioration caused by food oxidation. And the test of the use effect is also different from the preservative, and the antioxidant effect is determined by examining parameters such as peroxide value, acid value, and carbonyl change. In addition, antioxidants are also different from pharmaceuticals or health supplements and are only added as excipients to processed foods or raw materials.
â– The mechanism of action of antioxidants
The mechanism of action of antioxidants is complex and there are many possibilities.
Consumption of residual oxygen
Such antioxidants reduce the oxygen content of the food system and the surrounding environment by means of a reduction reaction, which can be said to suppress oxidation from the source. That is to say, the antioxidant itself is highly oxidizable, so when there is a factor of food oxidation (such as light, oxygen, heating, etc.), the antioxidant first reacts with oxygen in the air to avoid oxidation of the food. For example, ascorbic acid can scavenge oxygen in foods, which itself is oxidized to dehydroascorbic acid.
Chelated metal ion
The oil contains traces of metal ions, especially divalent or high valence heavy metal ions. They have a suitable redox potential, which can shorten the initiation period of the radical chain reaction and accelerate the oxidation rate of the ester compound. Such antioxidants can reduce the promotion of oxidation of metal ions by chelation of metal ions. Such as EDTA, citric acid and the like.
Absorbing free radicals
The most effective means of blocking lipid oxidation is to scavenge free radicals. This type of antioxidant can combine with the oxidation intermediates in the oxidation process to convert the free radicals produced by the oxidation of the oil into stable products, thereby preventing the oxidation reaction from proceeding. Such antioxidants are butylated hydroxyanisole, propyl gallate, vitamin E and the like. In general, oxygen in the air first combines with fat molecules to produce ROO·free radicals, and the radical absorbent provides hydrogen donor AH, that is, the ROO·free radicals absorb to form hydroperoxides.
Practice has proved that the free radicals generated by the reaction of phenolic antioxidants with lipid radicals are relatively stable. The free radical A of the antioxidant has no activity, it does not cause a chain reaction, but it can participate in some termination reactions. Another free radical R· produced by lipid oxidation can be eliminated by the electron acceptor of the radical absorber. In biological tissues, vitamin K is an electron acceptor that directly eliminates R·free radicals.
Interrupt peroxide
These antioxidants are capable of binding to the peroxide produced during the oxidation of the oil and are cleaved into new stable compounds such as dilauryl thiodipropionate.
Destruction of oxidase activity
Antioxidants can prevent or attenuate the activity of oxidases, which can scavenge superoxide radicals. In organisms, various types of free radicals oxidize ester compounds and produce peroxides. Enzyme antioxidants such as xanthan oxidase can react with the generated peroxide to form superoxide radical O2, which is then acted upon by superoxide dismutase to form hydrogen peroxide. Hydrogen peroxide is in turn converted to oxygen and water by catalase.
â– Classification of antioxidants
At present, there is no uniform standard for the classification of food antioxidants. Due to the different classification criteria, different classification results will result.
Antioxidants can be classified into synthetic antioxidants (such as BHA, BHT, PG, etc.) and natural antioxidants (such as tea polyphenols, phytic acid, etc.) by source.
Antioxidants can be classified into three types: oil-soluble, water-soluble, and lyophilic. Oil-soluble antioxidants include BHA and BHT; water-soluble antioxidants include vitamin C and tea polyphenols; and comminuted antioxidants include lipoic acid.
Antioxidants can be classified into carotenoid antioxidants, vitamin antioxidants, polyphenol antioxidants, flavonoid antioxidants, and enzyme antioxidants according to their chemical structures.
The antioxidants can be classified into a radical absorbent, a metal ion chelating agent, an oxygen scavenger, a peroxide decomposing agent, an enzyme antioxidant, a UV absorber or a singlet oxygen quencher according to the mode of action.
The radical absorbent mainly refers to a substance capable of blocking a radical chain reaction in the oxidation of fats and oils, and they are generally phenolic compounds having an electron donor function such as butylhydroxyanisole, tert-butyl hydroquinone, Tocopherol and so on.
Enzyme antioxidants include enzymes such as glucose oxidase, superoxide dismutase (SOD), catalase, and glutathione oxidase, which can remove oxygen (such as glucose oxidase) or eliminate food. Peroxide (such as SOD) and so on. At present, such enzyme antioxidants have not been included in the range of food antioxidants in China, but are incorporated into the enzyme preparation part.
â– The principle of selection of antioxidants
Antioxidants that can be used in food should have the following conditions:
First, it has excellent antioxidant effects. Food antioxidants have outstanding activity and large antioxidant capacity, and their antioxidant capacity is high, which can achieve high-efficiency antioxidant activity at low concentrations.
Second, both the product itself and the decomposition products are non-toxic and harmless. The safety of food antioxidants is an important indicator to be considered. The toxicological requirements are low, harmless to the human body, and not digested and absorbed is the primary principle for selecting food additives.
Third, it has good stability and can coexist with food, and has no effect on the sensory properties (including color, aroma, taste, etc.) of the food.
The fourth is easy to use and cheap. According to different grades of food and type and antioxidant effect, the choice of cheap and effective antioxidants is beneficial to reduce the cost of processed foods.
â– Precautions in the use of antioxidants
Choose the right time to add
It can be seen from the mechanism of action of antioxidants that antioxidants can only hinder lipid oxidation and delay the time when food begins to deteriorate, and cannot change the consequences of deterioration. Therefore, antioxidants should be added as soon as possible to exert antioxidant effects.
Choose the right amount of use
Unlike preservatives, the amount of antioxidant added and the antioxidant effect are not always positively correlated. When it exceeds a certain concentration, it not only enhances the antioxidant effect, but also has the effect of promoting oxidation. The dosage of antioxidants is generally not more than 0.02%, and the concentration of water-soluble antioxidants is generally not more than 0.1%, in accordance with the requirements of national food additive standards.
Use of compound antioxidants
Due to the complexity of the ingredients in the food, sometimes it is difficult to achieve optimal antioxidant action with a single antioxidant. At this time, a plurality of antioxidants can be used in combination. When two or more antioxidants are used in combination, the antioxidant effect is often greater than the sum of the single uses. This phenomenon is called the synergistic effect of antioxidants. It is generally believed that this is due to the fact that different antioxidants can terminate the chain reaction of lipid oxidation at different stages.
evenly distributed
Antioxidants are generally used in small amounts in foods, and can only be effectively used if they are sufficiently dispersed in foods.
Proper use of antioxidant synergists
The use of antioxidant synergists can significantly increase the antioxidant effect. The synergist itself has no antioxidant effect, or the antioxidant effect is relatively weak, but when used in combination with an antioxidant, its antioxidant effect is better than using an antioxidant alone. Commonly used synergists are citric acid, phosphoric acid, Ascorbic acid, ethylenediaminetetraacetic acid, and the like.
Raw material processing
Transition element metals, especially those having a suitable redox potential, are trivalent or multivalent transition metals (cobalt, copper, iron, manganese, nickel) which have a strong effect of promoting fat oxidation and are called prooxidants. Therefore, it is necessary to avoid mixing these ions into the food material. However, these ions are often contained in the food due to the presence of soil or contamination of the processing container. In food processing, these endogenous oxidation promoters should be removed to avoid or reduce traces of metals, plant pigments or peroxides. High-quality raw materials should be used as much as possible to reduce the entry of exogenous oxidation promoters into food.
Control the effects of light, heat, oxygen and other factors
While using antioxidants, it is also necessary to pay attention to some factors that promote fat oxidation, such as light, especially ultraviolet light, which can easily cause oxidation of fat. Light-proof packaging materials such as aluminum composite plastic bags can be used to preserve fat-containing foods.
The high temperature in processing and storage promotes the oxidation of fat on the one hand, and increases the volatilization of antioxidants on the other hand. Some antioxidants are heated, especially after high temperature, such as frying, and are easily decomposed or volatilized to lose antioxidant effect.
The presence of a large amount of oxygen accelerates the oxidation, and in fact, as long as it is exposed to the air, the grease is automatically oxidized. It is extremely important to avoid contact with oxygen. If the food is left in contact with a large amount of oxygen, even if a large amount of antioxidant is added, it is difficult to achieve the desired antioxidant effect.
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