1. Research scope of antioxidants
Research efforts on antioxidants have focused on the following three areas.
(1) Screening of natural antioxidant substances, such as VE and TP (tea polyphenols)
(2) Research on the structure-effect relationship of antioxidants. Different structural types of antioxidants have different activities, and even the activity of the same structural type of antioxidant is affected by the number and position of substituents. Weng Xinchu and Zhao Baolu revealed the effect of structure on antioxidant activity from the perspectives of experiment and quantum mechanical calculation, respectively.
(3) Research on the synergistic effect among antioxidants. Compared with single antioxidants, compound antioxidants are favored by virtue of their high activity, so the study of synergism has become a new hot spot in the field of antioxidant research. People now have a preliminary understanding of the synergistic effect, a more in-depth study will provide a theoretical basis for the composite antioxidant components and concentration ratio, has a broad application prospects.
I will explain in detail why antioxidants can inhibit oxidation of fats and oils?
Effective inhibition of oxidation is the purpose of the use of antioxidants, due to their own structure and nature, antioxidants play a role in a variety of ways, the mechanism can be summarized as follows three.
(1) Scavenging free radicals
The oxidation reaction of lipid compounds mainly involves the chain reaction of free radicals, in order to inhibit oxidation, in addition to the use of packaging to isolate air and light, the most effective means is to add antioxidants. Antioxidants play a role in scavenging free radicals, so they are called free radical terminators. Most antioxidants, including EQ, BHA, BHT, TBHQ, VE, TP, etc. which are commonly used in the past are effective free radical terminators. They mainly act as hydrogen donors and react with lipid radicals, so that the free radicals are transformed into inactive or stable compounds, thus interfering with or delaying the chain growth step in the chain reaction, and thus achieving the purpose of inhibiting oxidation.
A- Free radicals formed by the antioxidant itself after hydrogen supply
Phenolic compounds react with lipid radicals to form radicals that are more stable due to the fact that unpaired electrons can be distributed off-domain on the benzene ring.
Therefore, the conditions that an effective radical terminator must have are:
1.1 The ability to rapidly supply hydrogen atoms to the lipid radical.
1.2 The stability of the newly generated radical A- should be higher than that of ROO- and RO-.
(2) Chelation of metal ions
Many oxidation processes take place with the participation of metal ions. Metal ions play the role of transferring electrons in the process of valence change, which can shorten the time of chain initiation period, thus accelerating the rate of oxidation of lipid compounds. Therefore, the removal of metal ions is important to inhibit the oxidation reaction.
Citric acid and phosphoric acid derivatives can form inert complexes with metals and inhibit the decomposition of hydroperoxides, thus serving the purpose of antioxidant. According to Katherinel et al, citric acid and sodium polyphosphate can inhibit oxidation by chelating metal ions. Kemin products.
It should be pointed out that the metal ion chelator inhibits the generation of free radicals by chelating the substance that initiates the chain reaction, and can not be directly combined with the free radicals, thus playing an indirect antioxidant effect, so the antioxidant effect is often poor when used alone, so it is often used in combination with other antioxidants.
(3) Oxygen scavenging
This kind of antioxidant mainly inhibits oxidation through its own redox reaction. Such as VC due to molecular 2, 3 position on the existence of two adjacent enol hydroxyl, has a strong reducing properties, can effectively reduce the peroxide in the oil, consume the oxygen in the oil, thereby inhibiting the occurrence of oxidation. Similarly, sulfite and its salts are easily oxidized to sulfonic acid and sulfate in food, thus playing an antioxidant role. Alkaloids can gain energy by colliding with 1O2 (high-energy oxygen, single-linear oxygen), thus inactivating 1O2 to 3O2 (basal oxygen, three-linear oxygen).