I、Mechanism of action of food antioxidants
Meat products in the processing, storage, transport and other aspects of oxidation and rancidity is mainly caused by the oxidation and decomposition of unsaturated fatty acids in meat products, the causes of which are mainly three kinds, one is its own enzyme; the second is the microorganisms; and the third is the automatic oxidation. Therefore, meat products in the processing, storage and transport process to add the appropriate amount of antioxidants and the use of appropriate packaging methods to prevent the oxidative decomposition of unsaturated fatty acids.
There are many types of food antioxidants, antioxidant mechanism is not the same, but most of them are based on its reducing effect, the role of food antioxidants is mainly: food antioxidants can provide hydrogen atoms to block the chain reaction of food oils and fats auto-oxidation, thus preventing the oxidation of the food deterioration; food antioxidants are oxidised themselves, consume the food and the environment of the internal oxygen so that the food The food antioxidant itself is oxidised, consuming the oxygen inside the food and in the environment so that the food is no longer oxidised; the food antioxidant prevents the food from oxidative deterioration by inhibiting the activity of oxidative enzymes.
1.Oil soluble antioxidants
Oil-soluble antioxidants are suitable for foods with high lipid content to avoid the lipid substances and nutrients in them from being oxidised and rancidised or decomposed during processing and use, so that the overall food becomes tasteless and rancid.
(1) Butyl hydroxyanisole
Butyl hydroxy anisole, also known as tert-butyl-4-hydroxy anisole, hydroxy anisole, molecular formula C11H6O2, BHA sold on the market is mainly 3-BHA and a small number of mixtures of 2-BHA. BHA is a colourless to yellowish waxy crystalline powder, with phenolic specific odour and irritating flavour; the melting point varies with the mixing ratio of 3-BHA, 2-BHA, e.g., the melting point is 62℃ when 3-BHA accounts for 95%, the boiling point is 264-270℃. BHA accounted for 95%, the melting point is 62 ℃, boiling point of 264 ~ 270 ℃; BHA is insoluble in water, can be soluble in oil and organic solvents; BHA is highly stable to heat, in the weakly alkaline conditions are not easy to destroy, has a good ability to last, can use this feature will be used in baked goods; BHA can be alkaline-earth metal ions with the role of the pink colour; BHA has a certain degree of volatility, can be BHA is volatile and can be distilled by water vapour, it is easy to be lost in high temperature products, especially in boiled products, BHA can be used in food packaging materials.
The use of BHA as a food antioxidant began in 1954, and its antioxidant effect on animal fats is more effective than that on vegetable oils.
As a fat-soluble antioxidant, BHA is suitable for use in oily and fat-rich foods, and can be used under frying or baking conditions due to its good thermal stability. In addition, BHA has a strong antioxidant effect on animal fats and a poor antioxidant effect on unsaturated vegetable fats; BHA can be used in combination with sodium tripolyphosphate and ascorbic acid to delay frozen pork chops from rotting and deteriorating; BHA can also slightly prolong the shelf-life of spray-dried whole milk powder and improve the shelf-life of cheese; BHA stabilises the colour of chilli peppers and chilli powders, and prevents oxidisation of peanuts, walnuts and other foods; BHA added to baking oil and salt can maintain the aroma of baked goods and salty peanuts, extending the shelf life of baked goods; BHA can be used in combination with other fat-soluble antioxidants, which has a better effect, for example, the use of BHA and BHT compounding can protect chicken, carp, pork chops and frozen slices of smoked pork and so on.
(2) Dibutylhydroxytoluene
Dibutyl hydroxytoluene, also known as 2,6-dibutyl-p-cresol, molecular formula C15H24O, colourless crystals or white crystalline powder, odourless, tasteless, melting point of 69.5-70.5 ℃, boiling point of 265 ℃; BHT is insoluble in water and glycerol, soluble in ethanol and various fats and oils; BHT is chemically stable, quite stable to heat, good antioxidant effect, and the reaction with the metal is not coloured, with a Monophenol-type characteristics of sublimation, when heated with water vapour volatility; BHT antioxidant effect is stronger, there is no such as PG as the shortcomings of the reaction with metal ions colouring, and there is no BHA’s specific odour, and the price is inexpensive, but its toxicity is relatively high.
The oral LD50 of BHT in rats is 1.7-1.97g/kg, and the oral LD50 in mice is 1.39g/kg. The acute toxicity of BHT is slightly greater than that of BHA, but it is not carcinogenic, and its acceptable daily intake (ADI) is 0-0.125mg/kg.
The use of BHT as fat-soluble antioxidant is basically the same as that of BHA, BHT can effectively delay the oxidative rancidity of vegetable oils, such as shortening, and improve the storage period of fried fast food, but its antioxidant effect is not as good as that of BHA when it is used alone, and in addition, BHT can be used together with citric acid, which can also improve the antioxidant effect.
(3) Propyl Gallate
Propyl gallate, also known as propyl gallate, with molecular formula C10H12O5, is white to light yellow-brown crystalline powder, or milky white needle-like crystals, odourless, slightly bitter, aqueous solution has no flavour; PG is easily soluble in organic solvents such as ethanol, slightly soluble in oils and water; PG is relatively heat-stable, with a good effect of antioxidant, easy to have a chromogenic reaction with copper and iron ions to change into purple or dark green; PG is hygroscopic, unstable to light and easy to decompose, with strong antioxidant ability for oils and fats, and with strong antioxidant ability for citric acid, or with copper and iron ions. PG is hygroscopic, unstable to light and easy to decompose, it has strong antioxidant ability to oil and grease, and its antioxidant ability is even stronger when used with citric acid or compounded with BHA and BHT as synergist.
The oral LD50 of PG in rats is 3.8g/kg, and the ADI is 0-0.2mg/kg.
As a fat-soluble antioxidant, PG is suitable for use in vegetable fats and oils, and its antioxidant effect on animal fats is more prominent than that of BHA and BHT, whereas PG is not as effective as BHA and BHT on noodle products containing vegetable oils.The antioxidant effect of PG will be better when it is used in conjunction with potentiostat, and also its antioxidant effect will be better when it is used in conjunction with BHA and BHT. Since PG and iron ions will form purple complexes and cause food discolouration, it is better to use PG together with appropriate metal chelating agents.
(4) tert-butyl hydroquinone (tert-butyl hydroquinone, TBHQ) tert-butyl hydroquinone, also known as tert-butyl hydroquinone, molecular formula for the C10H14O2, for the white powder crystals, has a special smell, easily soluble in ethanol, acetic acid and ether, and soluble in animal and plant fats and oils; slightly soluble in water, and does not form a coloured substance with iron, copper ions, but in the light or alkaline conditions. It is slightly soluble in water, does not form coloured substances with iron and copper ions, but will be pink in light or alkaline conditions.
According to China’s Hygienic Standard for the Use of Food Additives, TBHQ can be used in edible oils and fats, fried foods, dried fish products, biscuits, instant noodles, quick-cooked rice, canned dried fruits and cured meat products, with a maximum use level of 0.2 g/kg. For meat products, TBHQ can effectively prolong the time for the frozen patties to produce a rancid odour.
TBHQ heat resistance is poor, should not be used in frying, baking conditions, can be used together with BHA to improve the effect of inhibiting the oxidation of vegetable oils and fats in the storage process at room temperature, in addition, TBHQ also has a certain bacteriostatic effect, TBHQ has a synergistic effect on the other antioxidants and chelating agents. In vegetable oil and animal oil, TBHQ is generally used in combination with citric acid. When the oxidative stability of lard is determined by the method of reactive oxygen species, TBHQ is equal to BHA and exceeds BHT and PG, and TBHQ can be effectively inhibited from oxidative deterioration of lard when it is doped into packaging materials.
(5) Other oil-soluble antioxidants
Dilauryl thiodipropionate (DLTP) DLTP is white crystalline flakes or powder, with special sweet fragrance, ester-like odour, insoluble in water, soluble in most organic solvents.DLTP can be used in animal and vegetable fats and oils, the use of alone is not as good as the effect of PG, BHA, BHT, generally used in conjunction with other fat-soluble antioxidants. DLTP can be used in animal and vegetable oils and fats.
L-ascorbyl palmitate (ascorbyl palmitate) L-ascorbyl palmitate, also known as ascorbic acid-6-palmitate, ascorbyl stearate, white or yellowish white powder, slightly citrus odour, very soluble in water or vegetable oil, soluble in ethanol.
L-ascorbyl palmitate is soluble in water, but still used as fat-soluble antioxidant, suitable for use in animal and vegetable fats and oils and many kinds of food. Generally mixed with PG, BHA, BHT.
Anoxomer (anoxomer) Anoxomer is a discrete off-white powder, insoluble in water, glycerol and propylene glycol, soluble in ethanol and vegetable oils, and very soluble in diethyl ether, chloroform and benzene. Arnoxolomide is a new type of fat-soluble antioxidant with high safety, it can be used in all kinds of oil or fat-containing food, the use limit is 5g/kg in terms of the amount of oil in food.
2、Water-soluble antioxidants
Water-soluble antioxidants can be dissolved in water, mainly used to prevent oxidation and discolouration of food, water-soluble antioxidants are mostly used in processing or storage of fruits and vegetables to eliminate or slow down the browning and other deterioration phenomena caused by oxidation.
(1) L-ascorbic acid
L-ascorbic acid, also known as VC, molecular formula C6H8O6, white or slightly yellow crystals or powder, odourless, acidic taste; the colour gradually darkens when exposed to light, the dry state is relatively stable, but its aqueous solution is quickly oxidized and decomposed, especially in neutral or alkaline solution; L-ascorbic acid is easily dissolved in water, insoluble in benzene, ether and other solvents; aqueous solution is easily oxidized by heat. L-ascorbic acid is easily soluble in water, insoluble in benzene, ether and other solvents; the aqueous solution is easily destroyed by heat, light and so on, especially in the presence of alkaline and metal ions, which will promote its destruction, so care must be taken to avoid mixing metals in the containers or contacting with the air when it is in use.
Normal dose of ascorbic acid has no toxic effect on human, ADI is 0～15mg/kg. ascorbic acid can be used in fruit juice and carbonated drinks to prevent their oxidation and deterioration; ascorbic acid is used in canned fruits to avoid deterioration and discolouration and flavour change due to oxidation, and to maintain the quality of canned fruits, and the dosage is 0.025%～0.06%; most of the canned vegetables do not add ascorbic acid, only mushrooms and canned cauliflower do. Only canned mushrooms and cauliflower add ascorbic acid in order to prevent browning or blackening during heating, and the dosage of ascorbic acid is 0.1%; ascorbic acid can be used in frozen food, which can prevent enzyme browning and deterioration of flavour in frozen fruits, prevent oxidative discolouration of water-soluble pigments, and maintain the flavour, colour and quality of frozen food; ascorbic acid can be used in wine to maintain the original flavour of wine, and can be added 0.01-0.0% when filtering in beer. Add 0.01-0.02g/kg ascorbic acid when filtering to prevent oxidative browning; used in meat products, it can be used as the pigment stabilizer of fresh meat and the colouring agent of cured meat; used in aquatic products, it can prevent the formation of dimethylamine and can delay the blackening of shrimps.
(2) L-ascorbic acid sodium
L-ascorbic acid sodium molecular formula for the C6H7O6Na, for the white or slightly yellowish-white crystals or crystalline powder, which is stable in the dry state, hygroscopicity is strong; L-ascorbic acid sodium than L-ascorbic acid is soluble in water, it is extremely difficult to dissolve in ethanol; the colour of the light is gradually becoming darker, and its antioxidant effect and L-ascorbic acid. The toxicity of sodium L-ascorbate is the same as that of L-ascorbic acid, and the method of using it is basically the same, but because of the acidity of L-ascorbic acid, it can be used instead of L-ascorbic acid in the food which is not suitable for the addition of acidic substances; for meat products, sodium L-ascorbate can be used as a coloring auxiliary, and at the same time it can also keep the flavor of the meat and increase the elasticity of the meat products.
(3) Isoascorbic acid
Isoascorbic acid molecular formula for C6H8O6, is a stereoisomer of VC, chemical properties similar to VC, for the white to light yellow crystals or crystalline powder, odourless, acidic taste; light gradually darken the colour, the dry state in the air is quite stable, and in solution when exposed to air is rapidly deteriorating; isoascorbic acid is very soluble in water, insoluble in glycerol, insoluble in benzene, ether; isoascorbic acid heat resistance is poor, strong reduction, but its antioxidant properties are better than ascorbic acid, but its antioxidant properties are better than ascorbic acid, but metal ions can promote its decomposition. Isoascorbic acid has poor heat resistance, strong reducibility, metal ions can promote its decomposition, but its antioxidant performance is better than ascorbic acid, and the price is cheap.
In sausage, ham and other meat cured products, isoascorbic acid can promote nitrite in the curing process of colour development, to extend the shelf life of the product; isoascorbic acid and nitrous acid used in conjunction with the meat products, can prevent discolouration of meat products, but also to improve the effect of the colour of the meat products, but also to enhance the ability of nitrite resistance to Clostridium botulinum and can reduce the production of nitrosamine, in the meat products, isoascorbic acid In meat products, the amount of isoascorbic acid is 0.5-0.8g/kg; isoascorbic acid can be used in fish products, fish and shellfish cured products and frozen products; isoascorbic acid can also be used in fruits, vegetable products, beer, glucose, carbonated beverages, frozen products, etc. in order to prevent oxidation and discolouration and deterioration of flavour.
(4) Sodium erythorbic acid
The molecular formula of sodium erythorbic acid is C6H7O6Na-H2O, it is white to yellowish-white crystal or crystalline powder, odourless, slightly salty, quite stable in air in dry state, but in aqueous solution, it is easy to be oxidised when it meets with air, metal, heat and light; sodium erythorbic acid is easy to be dissolved in water, almost insoluble in ethanol, and the antioxidant performance of sodium erythorbic acid is the same as that of sodium isoascorbic acid.
(5) Disodium ethylenediaminetetraacetic acid (EDTA-2Na)
The molecular formula of disodium ethylenediaminetetraacetic acid is C10H14N2O3Na2-2H2O, it is white crystalline particles or powder, odourless, tasteless, very soluble in water, very difficult to dissolve in ethanol. It is an important chelating agent, can chelate the metal ions in the solution, the production often use its chelating effect to maintain the colour, aroma and taste of food, to prevent oxidation and deterioration of food.
The ADI of disodium EDTA is 0~2.5mg/kg, according to China’s ‘Hygienic Standard for the Use of Food Additives’, disodium EDTA can be used in canned aquatic products, canned chestnuts in sugar water, etc., and the maximum use level is 0.25mg/kg, which can maintain the colour, aroma and taste of canned food; for canned aquatic products such as crabs and prawns, the addition of disodium EDTA can prevent the glassy-like crystals –For canned crab, shrimp and other aquatic products, the addition of disodium ethylenediaminetetraacetic acid can prevent the precipitation of glass-like crystals and ensure the quality of processed products.
3. Natural antioxidants
(1) Tocopherol
Tocopherol is VE, natural VE is widely found in the tissues of higher plants and animals, it has the function of preventing the oxidative deterioration of fat-soluble components in plant and animal tissues. It is known that natural tocopherol has α-, β-, γ-, δ-, ε-, ζ- and η- isomers of 7 kinds. The tocopherol blend concentrate used as an antioxidant is a mixture of the 7 isomers of natural VE.
Tocopherol mixed concentrate is yellow to brown transparent viscous liquid, almost odourless, insoluble in water, soluble in ethanol, and can be freely mixed with acetone, ether, oil and grease; it is heat-stable, and will not be destroyed even if it is heated up to 200°C under anaerobic conditions; it is acid-resistant but not alkali-resistant, and it is very sensitive to oxygen, and it will be oxidised slowly and turn black in the air and in the light conditions.
Vegetable oil contains more tocopherol, has a certain stability, but after refining the tocopherol content has been reduced, about 70% of the original, when the tocopherol content of vegetable oil is close to the natural content, has a high antioxidant capacity, if the content is too high, on the contrary, it will play the role of auxiliary oxidation, animal fats and oils seldom contain tocopherol and other natural antioxidant, so tocopherol as an antioxidant is mostly used for Therefore, as an antioxidant, tocopherol is mostly used in animal fats and oils such as lard and butter and their processed products.
Tocopherol added to food not only has antioxidant effect, but also has nutritional enhancement, and many countries have no restrictions on the amount of its use. Tocopherols are suitable for use as antioxidants and nutritional enhancers in baby food, therapeutic food and dairy products. Some research results in recent years have shown that tocopherol also prevents the production of carcinogens (nitrosamines) in salted meat products. Foreign countries also use this product for fried foods, whole milk powder, cream and margarine, powdered soups and so on.
(2) tea polyphenols
Tea polyphenols, also known as polyphenols, is a class of polyphenol compounds, including: catechins, anthocyanins, phenolic acids, flavonoids, 4 types of compounds, of which the content of catechins is the largest, accounting for about 60% of the total amount of tea polyphenols to 80%, but also tea polyphenols antioxidant effect of the main components.
Tea polyphenols are antioxidants extracted from tea, light yellow or light green powder, with tea flavour, easily soluble in water, ethanol, ethyl acetate; stable in acidic and neutral conditions, the optimal pH value of 4.0-8.0; tea polyphenols and citric acid, malic acid, tartaric acid, ascorbic acid, tocopherol has a good synergistic effect, and the synergistic effect of citric acid is the best. The method of use is to dissolve tea polyphenols in ethanol, add a certain amount of citric acid or other acids to formulate a solution, and then used in food in the form of spraying or adding.
Tea polyphenol is a natural antioxidant, high security, when used in its dissolved in water, directly add the use; for fats, fish and meat food can be first dissolved in ethanol after adding tea polyphenol, tea polyphenol antioxidant with the increase in temperature and enhancement of the use of heated food; tea polyphenol is generally stronger than the antioxidant effect of animal food and plant food. In addition, tea polyphenols can also be used as an auxiliary preservative.
Tea polyphenols can be used in fats and oils, with a maximum dosage of 0.4g/kg; in sauces, with a maximum dosage of 0.1g/kg; in confectionery, fried foods, instant noodles, with a maximum dosage of 0.2g/kg; and in meat and fish products, with a maximum dosage of 0.3g/kg.
(3) Phytic acid
Phytic acid is widely distributed in higher plants, also known as inositol hexakisphosphate, cyclohexanol hexakisphosphate, molecular formula C6H18O24P6, light yellow or brown viscous liquid, phytic acid is easily soluble in water, 95% ethanol, propylene glycol and glycerol, slightly soluble in anhydrous ethanol, benzene, ethanol and chloroform, and is stable to heat.
Phytic acid has been widely used in aquatic products, wine, fruit juice, oil and fat food, as antioxidant, stabiliser and preservative. Phytic acid in food processing applications are mainly: on the one hand, can be used as an antioxidant oil, add 0.01% of phytic acid in vegetable oils, can obviously prevent the rancidity of vegetable oils, its antioxidant effect varies depending on the type of vegetable oils, for peanut oil is the best effect, soybean oil is the second worst, cottonseed oil is poorer; on the other hand, used in aquatic products can prevent the generation of magnesium ammonium phosphate, can prevent the blackening of canned shellfish and canned crab meat to prevent blue spots. Prevent canned crab meat from blue spots, preventing fresh shrimp from turning black, etc.; In addition, phytic acid can remove copper, iron, calcium, magnesium and other ions in beverages; delay fish, meat, quick-cooking noodles, bread, cakes, salads and other shelf life.
(4) Guaiac resin
Guaiac resin is the resin of the guaiac tree native to Latin America, and its main components are α-guaiac lipoic acid, β-guaiac lipoic acid, guaiac wood acid, and a small amount of keratin, essential oils and so on.
Guaiacum resin is greenish brown to reddish brown glass-like lumps, its powder gradually turns into dark green in the air, with the smell of balsam, slightly pungent; easily soluble in ethanol, ether, chloroform and alkaline solution, insoluble in carbon dioxide and benzene, insoluble in water; guaiacum resin has a good antioxidant effect on the oils and fats. The oral LD50 of guaiacum resin in rats is 7.5g/kg, and the ADI is 0-2.5mg/kg.
Guaiacum resin is one of the earliest natural antioxidants used, and is also recognised as a safe antioxidant with antiseptic effect. Guaiacum resin is used for the antioxidant of butter, cream and other easily rancid food, generally only need to add 0.005% that is effective.
(5) nordihydroguaiaretic acid
nordihydroguaiaretic acid molecular formula C18H22O4, for the white-grey to white crystalline powder, soluble in ethanol, ether, glycerol and propylene glycol, slightly soluble in hot water, insoluble in cold water; nordihydroguaiaretic acid has good antioxidant effect, but also has a certain mildew ability, and citric acid, ascorbic acid has a synergistic effect. Synergistic effect with citric acid and ascorbic acid.
The oral LD50 of n-dihydroguaiaretic acid in rats is 2-5g/kg. n-dihydroguaiaretic acid is added to lard by 0.01%, and it does not change colour and rancidity after 19 months at room temperature and under sunlight, but due to the high price of n-dihydroguaiaretic acid, it is only used in high-grade food or military food.
(6) Licorice antioxidants
Licorice antioxidants are mainly composed of flavonoids and flavonoids, brown or tan powdery fat-soluble substances, with the characteristic odour of licorice, insoluble in water, soluble in organic solvents such as ethanol. Licorice antioxidant features can inhibit the photo-oxidation of fats and oils, licorice antioxidant has good heat resistance, can effectively inhibit the elevation of carboxyl valence in high-temperature frying oils, and can play its strong antioxidant role in the range from low to high temperature.
(7) Rice branin
Rice branin is also known as glutamate, is a mixture of several kinds of ferulic acid ester with trienol as the main one, it is white to light yellow powder or crystalline powder, odourless, soluble in ethanol and acetone, insoluble in water, oil solubility is good, it has good antioxidant effect for oil and grease. In addition to the oil-soluble antioxidant, it can also be used in pharmaceuticals.
(8) Quercetin
Quercetin for oak bark contains substances, molecular formula for C15H10O7-2H2O, for a kind of containing two molecules of water of crystallisation of yellow crystals, can be used as food yellow pigment; Soluble in water, anhydrous ethanol and glacial acetic acid, its ethanol solution is bitter; Quercetin for five hydroxyflavonoids, its molecule 2, 3 position between the double bond, 3, 4 position at the two hydroxyl groups, has a metal chelating or grease, such as antioxidant process Generate free radical acceptor function, can also be used as oil, ascorbic acid antioxidant.
(9) Rosemary, cinnamon and clove extracts
The extracts of rosemary, cinnamon and cloves have significant antioxidant effects with the advantages of being purely natural, efficacious and non-toxic, and are used in fruit and vegetable products, pickle products, oil and fat products, meat products, water-cultivated products, bakery products, dehydrated processed foods, transparent packaged foods and beverages.
Meat and poultry products do not contain natural antioxidants per se. When pre-cooked, sliced, grinded, boned, frozen and grilled, the muscle tissue cells rupture and release bound iron and enzymes, which when combined to form a catalyst trigger oxidative reactions within the muscle. The antioxidant mechanisms of rosemary, cinnamon and clove extracts include the bursting of singlet oxygen, the trapping of free radicals and the cutting off of the chain reaction of lipoid auto-oxidation; and the synergistic effect of chelating organic acids and metal ions. It has a strong antioxidant effect on the oxidation of many complex lipids. For example, adding 0.3% of fresh rosemary stems and leaves in beef burgers can improve the taste and prevent oxidative loss.
(10) Other natural antioxidants carnosine
carnosine is a natural dipeptide widely found in animal muscle, with antioxidant, chelating with metal ions, scavenging of free radicals and oxygen- and electron-donating activities, and has a high content in animal muscle tissue. Xing Zixin et al. found that myostatin can prolong the preservation time of cold meat, and the preservation time of cold meat added with myostatin increased from 9d without preservative to 15d, which was better than ascorbic acid, and in addition, the beef pre-cooking liquid of myostatin can also prolong the storage time of cold meat.
Chitosan
and its derivatives chitosan and its derivatives of meat and meat products have antibacterial and antioxidant properties, if the combination of radiation preservation methods with better results. Lan Fengying et al. studied the effect of chitosan on the organoleptic quality and fat oxidation resistance of Chinese sausage, the results show that the addition of 0.4% chitosan in Chinese sausage can significantly inhibit the oxidation of fat in the process of storage, chitosan concentration increases, the inhibitory effect is enhanced, and chitosan also has a certain role in the protection of colour.
Lecithin
Lecithin is light yellow to brown transparent or translucent viscous liquid or light brown powder or particles, odourless or slightly nutty smell and taste, partially soluble in water, but easy to form emulsion with water, oil-free phospholipids can be soluble in fatty acids and difficult to dissolve in non-volatile oils.