Edible oil can be divided into vegetable oil and animal oil according to **, which provides essential fatty acids for the human body, can promote the absorption and utilization of fat-soluble vitamins, and plays an important role in human health, so the quality of edible oil has been widely concerned. Oxidative rancidity is an important cause of the deterioration of edible oils, and oxidative rancidity of oils and fats can cause adverse effects on human health.
In order to ensure the quality of edible oil and prevent oxidative rancidity of edible oil in the production and storage process, in addition to effective sealed packaging, it is also the most effective treatment method to delay the oxidation of oil by adding antioxidants. At present, the antioxidants used in edible oil are mainly divided into two categories: synthetic antioxidants and natural antioxidants.
Mechanism of action of antioxidants
Auto-oxidation, photo-oxidation and enzymatic oxidation are the three main ways of oil oxidation. Auto-oxidation is the main cause of oxidative rancidity in oils and fats. The automatic oxidation of oils and fats usually consists of three stages: chain initiation, chain elongation and chain termination.
Antioxidants can achieve the effect of inhibiting oil oxidation by blocking or inhibiting a certain stage in the oil oxidation process, and the mechanism of action mainly includes scavenging free radicals, chelating metal ions, reducing oxygen concentration and quenching singlet oxygen.
Source: Internet.
1) Scavenging free radicals.
Such antioxidants mainly include polyphenols, tocopherols, tert-butylhydroquinone (TBHQ) and other antioxidants containing phenolic structures, which can be used as hydrogen donors to provide hydrogen atoms to lipid free radicals, so that the free radicals are converted into inactive or inert free radicals, thereby delaying or interfering with the chain growth stage in the free radical chain reaction and blocking the oxidation reaction.
2) Chelation of metal ions.
Metal ions are present in the oil and processing process, and the metal ions are involved in many oxidation processes. Metal ions in the divalent or more ** state can transfer electrons to catalyze the formation of hydroxyl radicals by hydrogen peroxide through the Feton reaction, which shortens the time of the chain initiation stage and leads to the acceleration of the oxidation rate of lipid compounds.
Citric acid, phytic acid, phosphoric acid derivatives and other chelating agents can be complexed with metal ions to form complexes, inhibit the decomposition of hydroperoxides, stabilize the oxidation state of metal ions, so as to achieve the purpose of inhibiting the oxidation of oils and fats. Because metal ion chelators indirectly inhibit lipid oxidation by chelating substances that initiate chain reactions, the antioxidant effect is poor when used alone, and they need to be mixed with other antioxidants.
3) Clear oxygen. The oxygen in the air can oxidize with the oil, reduce the oxygen concentration or remove the oxygen, which can effectively delay the oxidation rate of the oil. Commonly used oxygen scavengers mainly include carotene, ascorbic acid and its derivatives, etc. These antioxidants are redox and can slow down or terminate the free radical chain reaction by forming stable phenoxy radicals through proton transfer and scavenging reactive oxygen species.
Types of antioxidants and**
At present, there is no unified standard for the classification of antioxidants, so the classification basis is different, and the classification method is also different. According to **, it can be divided into synthetic antioxidants and natural antioxidants.
Source: Internet.
1) Synthetic antioxidants.
Synthetic antioxidants have the characteristics of economy, high yield, high temperature resistance and strong oxidation resistance, and are the main antioxidants used in edible oils. At present, there are hundreds of synthetic antioxidants developed in the world, but only a dozen are approved and allowed as additives by various countries, and the commonly used ones are butyl hydroxyanisole (BHA), propyl gallate (PG), bht, and tert-butylhydroquinone (TBHQ).
2) Natural antioxidants.
Natural antioxidants** are a wide range of natural antioxidants and can be extracted from plants, animals and their metabolites. Compared with synthetic antioxidants, natural antioxidants have the characteristics of high safety, strong antioxidant capacity, and can be preservative.
At present, it has been found that there are many kinds of natural substances with antioxidant activity, which can be divided into two categories according to their solubility: water-soluble and oil-soluble. Common water-soluble natural antioxidants include ascorbic acid, tea polyphenols, grape seed extract, etc.;Common oil-soluble natural antioxidants include vitamin E, carotene, lycopene, etc.
According to GB2760-2014, the natural antioxidants that are currently allowed to be added to oils and fats mainly include tea polyphenols, tea polyphenol palmitate, vitamin C, vitamin E, rosemary extract, phytic acid, etc.
Source: Network References: 1 Zeng Yingnan, Gu Yuhang, Liu Jia, et al. Research Progress of Natural Antioxidants in Oils and Fats JAnhui Agricultural Science Bulletin,2019,25( 2):21-23-2 Zhu Zhenyi, Feng Min, Xiong Huaxuan, et al. Research progress on the application of antioxidants in food and their detection technology JChemical Analysis & Metrology, 2013, (5): 104-108-3 Zuo Yu, Zhang Guojuan, Hui Fang, et al. Research Progress on Food Antioxidants JGrains and Oils,2018,31( 5):1 3 4 Zhang Yanan, Liang Peng, Xie Jingyi, et al. Research Progress on Antioxidants in Natural Foods JChina Food and Nutrition, 2019, 25(1): 67-71