1. Common food preservatives
In recent years, the commonly used preservatives in food are: benzoic acid, which is a kind of food preservative allowed by all countries in the world. It is easy to be excreted with excrement in animals, does not accumulate, has low toxicity and low price, and currently occupies most of the domestic preservative market; Butyl hydroxyanisole (BHA) is one of the antioxidants widely used in the world at present, and it has strong antimicrobial effect. It is mainly used in edible oils and fats, with the maximum dosage of 0.2g/kg, but the disadvantage is high cost. Dibutylhydroxytoluene (BHT) is one of the largest antioxidants produced in China at present, and its price is low, which is 1/5~ 1/8 of BHA, but its oxidation resistance is not strong, and its application range is the same as that of BHA, but its disadvantage is high toxicity. Propyl gallate (PG) has stronger antioxidant activity than BHA and BHT, and is mainly used in fried food, instant noodles and canned food. The maximum dosage is 0. 1g/kg, but its disadvantage is that it reacts with metal ions. Isoascorbic acid is used for antioxidation and antisepsis of general foods, and is non-toxic; Tert-butyl hydroquinone (TBHQ) is very effective for oils and unsaturated crude vegetable oils, stable at high temperature, and less volatile than BHA and BHT, so it is very suitable for foods that need to be heated during processing and eating.
2. Natural food preservative
In order to adapt to people's idea of advocating nature and health, the development and application of efficient and safe food preservatives has become an important research field of food preservatives in the world today. According to relevant data, the toxicity of natural preservatives in foods that people eat for a long time is far lower than that of synthetic preservatives. Therefore, in recent years, the research on seeking natural preservatives from nature has attracted great attention of scientists all over the world. A large number of natural preservative products developed by various countries are widely welcomed by people.
3. New food preservative
3. 1 Nisin is a small peptide produced by Lactococcus lactis, which consists of 34 amino acids, among which the basic amino acid content is high, so it has a positive charge. Nisin and lysozyme have synergistic effect; Combined with other sterilization measures, food spoilage can be prevented more effectively. Nisin mainly acts on the cell membrane, and its mechanism of action is probably that after being inserted into the cell membrane, a membrane channel with a certain aperture is formed on the cell membrane, which leads to the leakage of cytoplasm and the death of cells. Nisin is mainly used for preserving foods with high content in protein, such as meat and bean products, and cannot be used in foods with low content in protein, otherwise, it will be used as nitrogen source by microorganisms.
3.2 POly-lysine (abbreviated as PLL) is a new broad-spectrum preservative developed in Japan. It is a fermented product produced by Streptomyces, which is separated, extracted and refined. It is a new natural preservative after Nisin. Its monomer lysine is an essential amino acid, so its safety is high. Polylysine has high thermal stability and good water solubility, and has good antibacterial effect in the neutral to slightly acidic range, but the effect is not good in the acidic and alkaline pH range.
3.3 Protamine is isolated from fish testis and has broad-spectrum bactericidal effect. protein has the advantages of good thermal stability, safety and non-toxicity, and wide pH range (better bactericidal effect under neutral or alkaline conditions). However, protamine is difficult to be used in ordinary food because of its high price and large addition.
3.4 Lysozyme This enzyme can hydrolyze the B- 1, 4-glycosidic bond of peptidoglycan in bacterial cell wall, leading to autolysis and death of bacteria, and even the denatured lysozyme has bactericidal effect, because it is an alkaline protein, so it can be used for food preservation. When lysozyme is used together with EDTA, EDTA can complex the calcium ions necessary for lipopolysaccharide to maintain its structure and destroy its structure, so that lysozyme can act on its cell wall. It is often used in combination with glycine to preserve foods such as noodles, cooked aquatic products and salads.
4. Synthesize safe food preservative.
In addition to natural food preservatives, some synthetic non-toxic and efficient food preservatives also have broad development prospects. In contrast, it is cheaper and easier to synthesize non-toxic and pollution-free food preservatives.
Extended reading: types of food preservatives
Fresh fruits, vegetables, eggs, meat and aquatic products can keep their moisture, color, fragrance, taste and nutrients unchanged for a long time. Usually, some chemicals are used to achieve the purpose during storage. This kind of chemicals is called preservative. There are many kinds of preservatives because of different objects, and different preservatives have different preservation mechanisms, which can be generally divided into two categories: one is to maintain the stability of their chemical composition by inhibiting respiration; The second is to inhibit or kill microorganisms that cause food deterioration. Therefore, general antistaling agents usually also have antiseptic function. Fresh vegetables, fruits and eggs can also be preserved by some physical methods, such as freezing, cold storage and drying. The effect will be better if chemical method is combined with physical method.
1. Fruit preservative
Fruit preservation is an early developed and widely used field. The preservatives used include bactericide, fumigation preservative, ethylene absorbent, coating agent and antioxidant. The dosage forms of antistaling agents are aqua, wettable powder, tablets and other types.
(1) Fungicidal preservatives Fungicidal preservatives mainly include carbendazim and TBZ. Among them, carbendazim is produced by the reaction of lime nitrogen, water and methyl chloride to obtain methyl cyanocarbamate, which is then condensed with o-phenylenediamine.
(2) Fumigation antistaling agent The fumigant of tetrabromochloroethane successfully developed in China can be used for the preservation of oranges, and it has obvious inhibitory effects on Penicillium digitatum, Oomycetes citricola and Aureobasidium pullulans, which cause citrus rot. The rotten rate of citrus treated with bromochloroalkane is only about 2% after 3 months storage. At low temperature, it also has a good preservation effect on litchi and kiwifruit. Bromochloroalkane can be prepared from ethylene by bromination and chlorination, and the reaction formula is as follows:
(3) Apple, an antioxidant preservative, often suffers from a physiological disease tiger skin disease when stored at about 0℃. The symptom is that the peel and subcutaneous tissue produce irregular brown spots. It was found that the main reason was that a- farnesene in pericarp tissue was oxidized by air or directly entered cells to form an airtight film, which inhibited the normal respiratory exchange and produced the disease. A- farnesene is a hydrocarbon compound with 4 double bonds and 15 carbon atoms, which is extremely unstable in nature and easy to be oxidized, so antioxidants can be used to prevent its oxidation and produce lesions. The commonly used antioxidant is Hupiling (ethoxyquin).
Hupiling is a 50% emulsifiable concentrate used for apple preservation. When it is used, the emulsifiable concentrate is diluted to a specified concentration, wrapped in paper or directly wrapped in fruit, and the disease prevention effect is over 90%.
2. Oxygen-isolating preservative
Oxygen-isolating preservative is actually a coating agent. When used in food, it plays a role in quality, freshness and glazing; When used in fruits and vegetables, it can inhibit water evaporation, regulate respiration and prevent microbial invasion to maintain freshness. Coating agents can be divided into natural coating agents and synthetic coating agents according to their sources.
(1) natural oxygen-isolating preservative
Natural oxygen-isolating preservative mainly includes beeswax and shellac (lac). Shellac is a complex mixture of hydroxyl fatty acids mainly composed of aleuritic acid, hydroxyl fatty acids mainly composed of shellac acid and their esters. Shellac is a brown transparent sheet or powder with a special smell. It has a melting point of115 ~120℃ and a softening point of 70 ~ 80℃. It is soluble in ethanol and alkaline aqueous solution, but insoluble in water.
Shellac is made from resinous substances secreted by shellac parasitic on leguminous or Moraceae plants. The raw materials are crushed, screened, washed, dried into granules, dissolved in alcohol, filtered, and vacuum concentrated into sheets to obtain insect film.
Shellac can be used for glazing coatings of apples and oranges, as well as for glazing and coloring chewing gum, roasted coffee and substitutes. GB 2760-86 can also be used for coating chocolate candy and puffed chocolate, and its maximum limit is 0.20g/kg.
(2) synthesizing an oxygen-isolating preservative
① Morpholine fatty acid salt Morpholine fatty acid salt is yellowish to yellowish brown oily or waxy substance. With the different carbon chain length of fatty acids, their properties are different. Higher fatty acids are solid and lower fatty acids are liquid. The substance has ammonia odor, is miscible in acetone, benzene and ethanol, and is soluble in water. When it is dissolved in water, it is gel-like, and is mainly used for coating citrus. When in use, the fatty acid salt is mixed with wax, water and emulsifier to prepare mixed emulsion.
Synthesis method: ethylene glycol amine and hydrochloric acid are heated to 200 ~ 210℃ for dehydration, and after cooling, excessive calcium chloride is added for dry distillation. The distillate was dehydrated and distilled with granular sodium hydroxide, and the fraction of126 ~129℃ was collected to prepare morpholine. Then adding water to prepare a 90% solution, adding fatty acid with the same amount of substance, standing at 20-30 DEG C, and evaporating to remove water to obtain the product.
The commodity of coating agent is usually emulsion, which contains 3% morpholine fatty acid salt, 0/2% wax/kloc-and 85% water. The product is only for coating, and is inedible. After entering the human body, it is decomposed into morpholine and fatty acids.
(2) ethylene oxide higher fatty alcohol ethylene oxide higher fatty acid. The emulsion prepared by emulsifying with sodium oleate has strong adhesion, and a very thin molecular film can be formed on the surface of plants after coating. When it is used, it is made into milky white viscous emulsion. The ratio of OED- 100 is: ethylene oxide higher fatty acid 109g, sodium oleate 3g, a small amount of preservative and water lOOML. When the emulsion is diluted by10 ~ 20 times with water and sprayed on the surfaces of apples, oranges, bananas, peaches, plums, cherries and tomatoes, a film permeable to oxygen and carbon dioxide can be formed without affecting the respiration of fruits, and the evaporation of water molecules can be effectively prevented.
The product is produced by transesterification of docosahexaenoic fatty acids and erucic acid rich in rapeseed oil to produce fatty acid methyl ester, which is then reduced to higher alcohols and reacted with ethylene oxide at120 ~130℃ in the presence of acid clay catalysts.
In addition to the above-mentioned oxygen-isolating preservative, sucrose ester and mannan can also be used for film preservation.
3. Deoxidation preservative
Deoxidation preservative, also known as free oxygen absorbent or free oxygen remover, is a kind of substance that can absorb oxygen. When the deoxidizing preservative is sealed in the same packaging container with the food, the oxygen released in the container and existing in the food is absorbed by chemical reaction, so as to prevent the food from oxidative deterioration, and at the same time, the formed anoxic conditions can effectively prevent the food from mildew and pests.
There are many kinds of deoxidizing preservatives, which can be basically divided into two categories: organic and inorganic deoxidizing preservatives. Organic compounds include glucose plus glucose oxidase and alkaline sugar. Inorganic compounds can be divided into metal powder type (Fe,Cu,Zn,Al powder), iron compound type (iron carbide, carbon-based iron carbide, iron silicide, ferrous oxide, ferrous sulfate, ferrous hydroxide), palladium catalytic type and dithionite type. At present, the widely used deoxidizing and antistaling agents are mainly special iron powder, sodium dithionite and alkaline sugar preparation.
4. Egg preservative
Fresh-keeping curd is a common preservative for poultry eggs. It is a water-soluble paste-like colloidal substance, which consists of hydrophobic substances (paraffin, animal and vegetable oils), water-soluble polymers (dextrin, gelatin, polyvinyl alcohol, etc.), emulsifiers (commonly sucrose fatty acid esters, Tween and Span) and fungicides (benzoic acid, etc.).
Firstly, the oil-phase hydrophobic substance is heated to be liquid, added to the water-soluble polymer which has been dissolved in water under stirring, emulsified by adding emulsifier, and finally added with bactericide to obtain fresh-keeping curd. If animal and vegetable oils and fats are used, antioxidants (such as vitamin C) should also be added.
When in use, the curd can be diluted to a certain concentration by adding water to keep the eggs fresh. The product can also be used for fruit preservation.
A Chinese herbal antistaling agent for poultry eggs is composed of traditional Chinese medicines with the function of blocking the stomata of poultry eggs, such as bletilla striata; Traditional Chinese medicine with protein coagulation function, such as alum; Traditional Chinese medicine with disinfection and sterilization function, such as borax. At least one of the three kinds of traditional Chinese medicines is prepared into powder according to a certain proportion, and the eggs can be kept fresh for 6 months by soaking them in its water diluent for half an hour, with low cost, no residue, good fresh-keeping quality and simple use.
5. Vegetable preservative
Controlling microbial spoilage is the key to keep vegetables fresh. In order to prevent vegetables from losing water and wilting, it is necessary to maintain high humidity in the environment, and appropriate humidity is the necessary condition for mold propagation, so mildew prevention and preservation has become the first choice. The mildewproof agents used in vegetable preservation are sec-butylamine (2- aminobutane), o-phenylphenol and its sodium salt, thiazole benzimidazole (TBZ) and so on.
British Emile Food and Agriculture Company has developed an edible preservative for fruits and vegetables. It is a translucent film made of sugar, starch, fatty acid and poly-AK, which can be sprayed, dipped and painted on the surfaces of apples, pears, oranges, bananas or tomatoes. Because this preservative forms a sealed film on the surface of fruits and vegetables, it can prevent oxygen from entering the interior of fruits and vegetables, inhibit the ripening process of fruits and vegetables, and play a fresh-keeping role. This preservative can be eaten with fruits and vegetables without harm, and the preservation period can reach160 ~ 220 days.