1. The mechanism of action of antioxidants
The mechanism of antioxidants is relatively complicated, and there are many possibilities. If any antioxidants are easily oxidized themselves, they first react with oxygen to protect food. Such as VE. Some antioxidants can release hydrogen ions to decompose and destroy the peroxides generated in the auto-oxidation process of fats, so that they cannot form aldehydes or ketone products such as dilauryl thiodipropionate. Some antioxidants may combine with the peroxides they produce to form hydroperoxides, which interrupt the oxidation process of oils, thereby preventing the oxidation process from proceeding. They themselves form antioxidant free radicals, but antioxidant free radicals can form stable Dimer, or ROO- with peroxide radicals. Combines to form stable compounds.
2. Several commonly used fat-soluble antioxidants
   • BHA: Butyl hydroxyanisole. Because it has good effect retention after heating and is effective in preserving food, it is one of the antioxidants widely used internationally, and it is also one of the commonly used antioxidants in China. It has a synergistic effect with other antioxidants, and when used with synergists such as citric acid, its antioxidant effect is more significant. It is generally believed that BHA has little toxicity and is relatively safe.
   • BHT: dibutyl hydroxytoluene. Compared with other antioxidants, it has higher stability, good heat resistance, little effect at ordinary cooking temperature, and good antioxidant effect. It is very effective for long-term preservation of foods and baked goods. It is a cheap antioxidant widely used internationally, especially in aquatic processing. It is generally used in combination with BHA, and citric acid or other organic acids are used as synergists. Compared with BHA, the toxicity is slightly higher.
   • PG: Propyl gallate. Relatively stable against heat. The antioxidant effect of PG on lard is stronger than that of BHA and BHT, and its toxicity is lower.
   • TBHQ: tert-butyl hydroquinone. It is a newer class of phenolic antioxidants, and its antioxidant effect is better.

These substances can produce sulfur dioxide (SO2), and sulfur dioxide will form sulfurous acid (H2SO3) when it meets with water. In addition to bleaching, it also has antiseptic effects. In addition, due to the strong reducing properties of sulfurous acid, it can consume oxygen in fruit and vegetable tissues, inhibit the activity of oxidases, and prevent the oxidative destruction of vitamin C in fruits and vegetables.
Sulfite can be metabolized into sulfate in the human body, which is excreted in the urine through the detoxification process. Compounds such as sulfites are not suitable for animal foods to avoid unpleasant odors. Sulfite has a destructive effect on vitamin B1, so foods with high B1 content such as meat, grains, dairy products and nuts are not suitable. Because it can cause allergic reactions, its use in the United States and other countries is strictly restricted.

Also known as pigments, it is a class of substances that make foods colored and improve their sensory properties. According to their nature and source, food coloring can be divided into two categories: natural food coloring and synthetic food coloring.

1. Edible synthetic pigments are artificial synthetic pigments. The characteristics of edible synthetic pigments: bright colors, stable properties, strong coloring power, high firmness, any color can be obtained, plus low cost, easy to use. However, most synthetic pigments are harmful to the human body. Some of the toxicity of synthetic pigments are that their chemical properties are directly toxic to the human body; some may produce harmful substances in the metabolic process; they may also be contaminated by arsenic, lead or other harmful compounds during the production process.
2. Food natural pigments. Food natural pigments are mainly pigments extracted from animal and plant tissues. However, the composition of natural pigments is more complex, and the purified natural pigments may have different effects from the original ones. And in the process of refining, its chemical structure may also change; in addition, in the process of processing, there is the possibility of contamination, so it cannot be considered that natural pigments must be pure and harmless.

Synthetic food coloring is the same as other food additives. In order to achieve the purpose of safe use, strict toxicological evaluation is required. include

• Chemical structure, physical and chemical properties, purity, existence form in food, degradation process and degradation products;
• Retention distribution, metabolic transformation and excretion status in tissues and organs after the accompanying food is absorbed by the body;
• The biological changes caused by itself and its metabolites in the body, as well as the possible toxicity to the body and its mechanism. Including acute toxicity, chronic toxicity, effects on reproduction, embryo toxicity, teratogenicity, mutagenicity, carcinogenicity, sensitization, etc.

1. The hair color principle and other functions of color retention agent:
   • Color protection: In order to make the meat products bright red, nitrate (sodium or potassium) or nitrite is added during processing. Nitrate is reduced to nitrite under the action of bacterial nitrate reductase. Nitrite will generate nitrous acid under acidic conditions. At room temperature, it can also be decomposed to produce nitroso groups (NO). At this time, the generated nitroso groups will quickly react with myoglobin to form a stable, bright, bright red nitrosated myoglobin. Therefore, the meat can be kept stable and bright.
   • Bacteriostatic effect: Nitrite has a certain effect on inhibiting the proliferation of microorganisms in meat products.
2. Application of color retention agent
Nitrite is one of the most acutely toxic substances in additives. It is a highly toxic drug that can turn normal hemoglobin into methemoglobin, lose the ability to carry oxygen, and cause tissue hypoxia. Secondly, nitrite is a precursor of nitroso compounds, and its carcinogenicity has attracted international attention. Therefore, all aspects require the addition of nitrate and nitrite to be limited to the minimum while ensuring color protection. level. Ascorbic acid has a high affinity with nitrite and can prevent nitrosation in the body, thereby almost completely inhibiting the formation of nitroso compounds. Therefore, adding an appropriate amount of ascorbic acid when marinating meat may prevent the formation of carcinogens. Although the use of nitrate and nitrite has been greatly restricted, they are still being used at home and abroad. The reason is that nitrite has a special effect on maintaining the color, aroma and taste of cured meat products, so far no ideal substitutes have been found. The more important reason is the inhibitory effect of nitrite on Clostridium botulinum. However, there are strict requirements on the food used and its usage and residues.

Enzyme preparations refer to substances extracted from organisms (including animals, plants, and microorganisms) with biocatalytic enzyme properties. Mainly used to speed up food processing and improve the quality of food products.
The enzyme preparations allowed in China are: papain-extracted from the latex of immature papaya; and proteases made from Aspergillus oryzae, Bacillus subtilis, etc.; α-amylase-mostly from Bacillus subtilis; saccharification type Amylase-The strains used in China to produce this enzyme preparation include Aspergillus niger, rhizozyme, monascus, and endosporin; pectinase produced by Aspergillus niger, Aspergillus oryzae, and Aspergillus flavus.

Refers to substances that supplement, enhance, or improve the original taste or taste in food. Some are called umami agents or taste agents.
The flavor enhancers allowed in China are sodium glutamate, disodium guanylate and 5′-inosinic acid disodium 5′-taste disodium nucleotide, disodium succinate and L-alanine.
Sodium glutamate is monosodium L-glutamate containing one molecule of crystal water. Easily soluble in water, it loses crystal water at 150°C, pyrrolidonizes at 210°C to produce pyroglutamic acid, and decomposes at about 270°C. Stable to light, racemization occurs when heated under alkaline conditions, and the taste is reduced. When heated under acidic conditions with a pH of 5 or less, pyrrolidone can easily be converted into pyroglutamic acid, and the taste will be reduced. Heating rarely changes when it is neutral.
Glutamic acid is a low-toxic substance. Under normal dosage conditions, there is no toxicity problem, and nucleotide series of flavor enhancers are widely present in various foods. No special regulations are required.
Over the years, many meat extracts, yeast extracts, hydrolyzed animal protein and hydrolyzed vegetable protein have been developed.

1. Acid type preservative
Commonly used are benzoic acid, sorbic acid and propionic acid (and their salts). The antibacterial effect of these preservatives mainly depends on their undissociated acid molecules, and their effectiveness depends on the pH. The greater the acidity, the better the effect, and it is almost ineffective in an alkaline environment.
• Benzoic acid and its sodium salt: Benzoic acid is also known as benzoic acid. Because of its low solubility in water, its sodium salt is often used. low cost. After benzoic acid enters the body, most of it is synthesized with glycine to synthesize hippuric acid within 9 to 15 hours and is excreted from the urine, and the remaining part is combined with glucuronic acid to detoxify. However, due to the certain toxicity of sodium benzoate, it has been gradually replaced by sodium sorbate.
• Sorbic acid and its salts: also known as sorbic acid. Due to its limited solubility in water, its potassium salt is often used. Sorbic acid is an unsaturated fatty acid that can participate in the body’s normal metabolic process and is assimilated to produce carbon dioxide and water. Therefore, sorbic acid can be regarded as a food ingredient and can be considered harmless to the human body according to the data.
• Propionic acid and its salts: weaker antibacterial effect, higher usage. It is often used in bread and pastry, and the price is relatively low. Propionic acid and its salts have low toxicity and can be considered as a normal component of food and a normal intermediate product of metabolism in the human body.
• Dehydroacetic acid and its sodium salt: It is a broad-spectrum preservative, especially for fungi and yeast, which is 2-10 times that of sodium benzoate. The product can be quickly absorbed by the human body and distributed in the blood and many tissues. However, it has the effect of inhibiting a variety of oxidases in the body, and its safety is suspected, so it has been gradually replaced by sorbic acid, and its ADI value has not yet been specified.
2. Ester type preservative
Including parabens (A, B, C, isopropyl, butyl, isobutyl, heptyl, etc.). higher cost. It has a wide range of antibacterial effects on molds, yeasts and bacteria. It has a strong effect on molds and yeasts, but has a poor effect on bacteria, especially gram-negative bacilli and lactic acid bacteria. The mechanism of action is to inhibit the activity of microbial cell respiration enzymes and electron transfer enzymes, and to destroy the microbial cell membrane structure. Its antibacterial ability increases with the increase of the alkyl chain; the solubility decreases with the increase of the carbon chain length of the ester group, but the toxicity is opposite. But the compound use of ethyl p-hydroxybenzoate and propyl ester can increase its solubility and have a synergistic effect. It can be quickly and completely absorbed in the gastrointestinal tract, and is hydrolyzed into p-hydroxybenzoic acid and excreted in the urine without accumulating in the body. China is limited to the use of propyl and ethyl esters.
3. Biological preservatives
Mainly nisin. Nisin is a metabolite of microorganisms belonging to the genus Nisin, which can be obtained by fermentation and extraction of Streptococcus lactis. The advantage of nisin is that it can be degraded by proteolytic enzymes in the human digestive tract, so it is not absorbed into the body in its original form. It is a relatively safe preservative. It will not change the normal intestinal flora like antibiotics, and cause resistance to other commonly used antibiotics, let alone cross-resistance with other antibiotics. Other preservatives include sodium diacetate, which is both a preservative and a chelating agent. It can prevent the growth of mold on cereals and soy products. Sec-butylamine, this product should not be added to processed foods, only used for preservation during the storage period of fruits and vegetables. Commercially available preservatives, such as Clomerin, Baoguolin, etc., are all preparations with sec-butylamine as the active ingredient. The increase in carbon dioxide and carbon dioxide partial pressure affects the use of oxygen by aerobic microorganisms, and can stop the respiratory metabolism of various microorganisms. For example, the presence of a large amount of carbon dioxide in high food can change the pH of the food surface and make the microorganisms lose the necessary conditions for survival. But carbon dioxide can only inhibit the growth of microorganisms, not kill them.

1. Natural sweeteners are divided into sugar alcohols and non-sugars. in
• Sugar alcohols include: xylitol, sorbitol, mannitol, lactitol, maltitol, isomalt, erythritol;
• Non-sugars include: stevioside, licorice, kiwifruit, mogroside and thaumatin.
2. Artificially synthesized sweeteners, among which sulfonamides are: saccharin, sodium cyclamate, potassium acesulfame. Dipeptides are: aspartame methyl (also aspartame), 1-a-aspartyl-N-(2,2,4,4-tetramethyl-3-sulfide Base)-D-Alaninamide (also known as Alitian). The derivatives of sucrose are: sucralose, isomalt (also known as palatinose), new sugar (fructose oligosaccharide).

In addition, sweeteners can be divided into nutritive and non-nutritive sweeteners according to their nutritional value. For example, sucrose, glucose, fructose, etc. are also natural sweeteners. Since these sugars not only impart sweetness to foods, but also are important nutrients that provide heat to the human body, they are usually regarded as food raw materials and are generally not controlled as food additives.

1. Saccharin
   The scientific name of saccharin is o-sulfonyl benzoyl. It is a synthetic sweetener widely used all over the world. It is low in price and has a high sweetness. Its sweetness is equivalent to 300 to 500 times that of sucrose. The solubility is low, so its sodium salt (sodium saccharin) is specified in the Chinese Additive Standards, which exhibits a bitter taste when the amount is large. It is generally believed that saccharin sodium is not decomposed or used in the body, and most of it is excreted in urine without damaging kidney function. Does not change the activity of the enzyme system in the body. Saccharin has been widely used throughout the world for decades, and no harmful effects on the human body have been found.
2. Sodium cyclohexyl amine sulfonate (cyclamate)
   In 1958, it was listed as a “generally considered safe substance” and widely used in the United States, but it was reported to have carcinogenic effects on animals in the 1970s. The FAO/WHO report in 1982 proved that it was non-carcinogenic. The US FDA’s long-term experiment declared non-carcinogenic in 1984. However, the National Research Council of the United States and the National Academy of Sciences still believe that it has cancer-promoting and possibly carcinogenic effects. Therefore, it is still banned from food in the United States.
3. Aspartame 
   The sweetness of aspartame is 100~200 times that of sucrose, and the taste is close to that of sucrose. It is a dipeptide derivative, which is decomposed into corresponding amino acids in the body after consumption. According to Chinese regulations, it can be used for foods other than canned foods, and the amount should be used in appropriate amounts according to production needs.
   In addition, many dipeptide derivatives containing aspartic acid have also been discovered, such as alitame, which is also an amino acid sweetener, which is synthesized from natural raw materials and has high sweetness.
4. Acesulfame Potassium
   Acesulfame potassium is stable to light and heat (225°C), the sweetness lasts for a long time, and the taste is better than that of saccharin sodium. After being absorbed, it is quickly eliminated from the urine and does not accumulate in the body. It is 1:1 with aspartame Combined use has obvious synergistic effect.
5. Sugar alcohol sweeteners
   Sugar alcohol sweeteners belong to a class of natural sweeteners, whose sweetness is similar to that of sucrose, and are mostly low-calorie sweeteners. There are many varieties, such as sorbitol, xylitol, mannitol and maltitol, some of which are found in natural foods, and most of them are obtained by hydrogenating the corresponding sugars. The precursors are derived from natural foods. Because sugar alcohol sweeteners have a low glycemic index and do not produce acid, they are mostly used as sweeteners for patients with diabetes and obesity and have the effect of preventing dental caries. Most of these substances have a certain degree of water absorption, and have certain effects on improving the rehydration of dehydrated food, controlling crystallization, and reducing water activity. However, due to the low absorption rate of sugar alcohols, especially xylitol, it has a certain ability to cause diarrhea when consumed in large quantities.
6. Stevioside
   Stevioside is a strong sweetness component contained in stevia and is a diterpene-containing glycoside. The sweetness is about 300 times that of sucrose. However, the taste of stevioside is poor, with licorice flavor, and bitterness when the concentration is high. Therefore, it is often mixed with sucrose, fructose, glucose, etc., and combined with citric acid, malic acid, etc. to reduce the bitter taste or through fructosyltransferase or α- Glucosyltransferase makes it change its structure to correct its shortcomings. Many countries have done a large number of toxicity tests on it, and none of them showed toxic effects. In countries where it has been consumed for a long time, such as Paraguay, the product has been used for 100 years, and Japan has also used it for more than 15 years, and no adverse side effects have been reported.