For agricultural products, food additives are mainly for preserving, preserving freshness and color protection. According to the Ministry of Agriculture, "agricultural packaging and labeling management", preservatives for agricultural products is to prevent the spoilage of agricultural products, chemical synthetic substances or natural substances; agricultural preservatives are to maintain the fresh quality of agricultural products, reduce circulation losses, extend the storage time of synthetic chemicals or natural substances; agricultural additives are to improve the quality of agricultural products and color, fragrance, taste and processing performance The addition of synthetic chemical substances or natural substances. Because the current standard is not clear, the preservatives and preservatives used in agricultural products include both pesticides and food additives. If a certain distinction is made, then food additives are mainly for the improvement of food color, flavor, taste and other qualities, as well as for the preservation and processing process needs to be added to the food compounds or natural substances, including preservatives, bleaching agents, color protectors, acidity regulators, bleaching agents, coloring agents, such as chitosan, fruit wax is often used as a film agent for fruit and vegetable preservation, nitrite, sulfite, etc. commonly used in meat products and aquatic products color protection, corrosion protection.
Due to the constant news of health hazards caused by the abuse of food additives, people have more or less prejudice and resistance to food additives, believing that pure and natural food should not add any preservative and antioxidant. But in fact, food additives are indispensable to the food industry - all processed and packaged food on the market, in order to prevent spoilage, are treated with preservatives, only the method is different.
If a large number of grain and oil, fruits and vegetables, meat and poultry are only roughly processed into the market, then the post-production losses will be very large. First of all, the food itself still has physiological activities, will continue to age, vegetables stored for too long will increase harmful substances, fruits stored for too long, not only the flavor decline, and cell tissue separation, for microbial growth to create the conditions. Secondly, fresh agricultural products are gradually oxidized by air, light and heat during storage and begin to change flavor. Oil and fat produce hydrolysis and fatty acid oxidation and rancidity, not only produce off-flavor, but also the oxidation products of the rancidity process have a destructive effect on human enzyme system. Thirdly, food in the production, storage, transportation, packaging and other aspects are vulnerable to infection by microorganisms in the environment. In addition to easily observed mold, meat is infected by bacteria is a hidden danger that should not be underestimated. Therefore, food additives are an essential part of the chain from production to sales of agricultural products. Understanding food additives and using them rationally and legally is the only way to scientifically enrich our table and add bricks to our health.
1.Preservation preservatives
1.1 Chitosan
Film coating preservation technology is coated on the surface of fruits and vegetables with a layer of natural sugars, proteins, oils and fats as raw materials of polymeric liquid edible substances, to be dried to form a uniform film to isolate fruits and vegetables and air, to prevent the physiological and biochemical processes of fruits and vegetables, thereby maintaining the freshness and fullness of fruits and vegetables, reducing the decay caused by bacterial infiltration, thus achieving the purpose of preservation.
Among them, chitosan derivatives are widely concerned because of high film-forming rate, strong antibacterial properties, good preservation effect and other advantages. Chitosan is the only natural alkaline polysaccharide found in the biological world at present. It is the product of deacetylation by chitin - chitin is widely present in shrimps, crabs and other crustaceans and spiders and other arthropods surgical or wings for the maintenance and protection of the carcass of linear amino polysaccharide, in fungi algae and other microorganisms cell wall also exists, is a resource that exists widely in nature. Compared with other membranes, it is non-toxic, odorless, and can be decomposed by living organisms, making it a renewable resource. The unique structure of chitosan determines that it has a variety of unique physicochemical properties, such as: very high viscosity, good water absorption, moisture retention, film formation, thickening, gelation, etc. These unique physicochemical properties have an important role in the preservation quality of fruit. In addition, chitosan coating treatment can make the activity of superoxide dismutase in fruits at a high level, which is conducive to the removal of superoxide anion radicals, and can also reduce the peroxidation of membrane lipids and ethylene generation, thus playing a role in preservation.
1.2 Sodium metabisulfite
Sodium metabisulfite is a widely used additive in the food industry, the key to its role is to form sulfite. Sulfite is a strong reducing agent, which can reduce the coloring material to fade when being oxidized, so that the food can keep the bright color, and also can inhibit the oxidation enzyme to prevent the food from deteriorating. Due to its reducing effect, it can block the normal physiological oxidation process of microorganisms and inhibit the reproduction of microorganisms, thus playing a preservative role. It is a common practice to add sodium metabisulfite to agricultural products, such as bamboo shoots and lotus roots soaked in sodium metabisulfite will look white and fresh; mushrooms soaked in sodium metabisulfite can inhibit the activity of polyphenol oxidase and prevent browning; bean sprouts soaked in sodium metabisulfite can prevent blackening and rotting; water chestnuts bleached with sodium metabisulfite; ginger soaked in sodium metabisulfite can make its color bright and flesh feel tender.
1.3 Chlorine Dioxide
Chlorine dioxide (ClO2) is a strong oxidant with strong sterilization ability, while the sterilization process does not produce harmful substances, no odor residue, does not affect the flavor and appearance of food quality, is a broad-spectrum, efficient and safe chemical disinfectant of A1 level, is currently recognized internationally as the best performance, the best effect of food preservation agent. Chlorine dioxide can quickly and effectively stop the decomposition of methionine inside fruit and vegetable tissues, eliminate ethylene and other substances, and at the same time can control the generation of spoilage bacteria, and does not react with fatty acids, slowing down the aging and spoilage process of fruits and vegetables without affecting the quality of food. Chlorine dioxide has good adsorption and permeability to the cell wall of bacteria and other microorganisms, and can react with some amino acids in proteins by redox reaction, so that amino acid decomposition and destruction, and then control the synthesis of microbial proteins, and finally lead to the death of microorganisms. At the same time, in addition to killing general bacteria, it has a better killing effect on budding spores, viruses, algae and fungi.
1.4 ε-Polylysine
As a natural antibacterial peptide, ε-polylysine is widely used in the food industry for its excellent antibacterial activity, stability and safety. It is especially used for the preservation of aquatic products. It has good inhibitory effect on common specific spoilage bacteria in aquatic products, which can effectively maintain the sensory quality of aquatic products, effectively inhibit protein degradation and lipid oxidation during storage, and prolong the shelf life of aquatic products.
1.5 Nisin
For the preservation of fruits and vegetables, the common methods are low-temperature refrigeration and pharmaceutical treatment. Although the use of chemical agents is effective, its toxic side effects and residual problems have been plagued by people. The use of natural anti-microbial peptide itself has good anti-bacterial effect, spraying the solution containing natural anti-microbial peptide substances or packaging outside the fruit and vegetables containing anti-microbial peptide cling film can play a good preservative effect, which is also the current food preservative research hot spot. Streptococcus lactis (Nisin) belongs to the bacterial source of natural anti-microbial peptide, as a food preservative, its advantage is that it is a natural protein, which can be quickly digested into amino acids by protein hydrolytic enzymes after consumption, and will not produce resistance and allergic reactions. And it has no cross-resistance with some other antibiotics such as penicillin, erythromycin, etc., and will not cause bacteria to be resistant to these antibiotics.
2.Colorant protector
2.1 Nitrite
Nitrite is a particularly important additive in meat products, the color of meat products is particularly important to the sensory judgment of consumers, in order to keep the meat bright rose-red, nitrite can be added during processing, and the lactic acid in the meat to produce a complex decomposition reaction to form nitrite. In addition to color protection, nitrite also has antibacterial effect and antioxidant effect. It can inhibit the growth and reproduction of some pathogenic bacteria such as Clostridium botulinum, Staphylococcus aureus, Bacillus cereus and Pneumocystis carinii. The antioxidant effect of nitrite is one of the important factors to ensure the long preservation of meat cured foods, which can enhance the stability of fat in meat through the double bond reaction of carbon-carbon. Moreover, nitrite has the effect of flavor enhancement.
But nitrite, as an inorganic compound, can be very harmful to the human body. The intake of a certain amount of nitrite can cause methemoglobinemia, which leads to lack of oxygen in human tissues. If a person absorbs a lot of nitrite in a short period of time, there is a high probability that it will cause poisoning, and in serious cases, it may even lead to cancer. Therefore, people are actively looking for alternatives to nitrite, including natural food additives such as red yeast pigment, chitosan, which was introduced earlier, and myostatin, a natural food antioxidant called "liquid ultrasound knife".
2.2 Ascorbic acid
E - isoascorbic acid (erythorbic acid) is also known as erythorbic acid, isovitamin C. Isoascorbic acid and its sodium salt is a safe and effective food additive, in meat, aquatic products, vegetables in the curing process, adding sodium isoascorbic acid, can replace nitrate coloring, but also can prevent the production of carcinogenic substances such as amyl nitrite. In the preservation of fruits and vegetables, it can inhibit the activity of oxidative enzymes of fruits and vegetables, so it can prevent the occurrence of browning of fruits and vegetables. Adding isoascorbic acid to meat products can make the coloring agent nitrite produce more nitrogen oxide, which can reduce orthoferric myoglobin to myoglobin, and then combine into red nitro-myoglobin to prevent meat oxidation and taste, and reduce the production of nitrosamines. At the same time isoascorbic acid also has the effect of strengthening sodium nitrite against botulinum toxin.
Ascorbic acid (L-ascorbic acid, AA), also known as vitamin C, has strong reducing properties due to its alkenediol structure, which is chemically unstable and easily oxidized. It is having this good antioxidant ability that makes it play an important role in the food field. It scavenges oxygen and inhibits the oxidation of oxygen-sensitive food components; shifts the redox potential of the system to the reducing range; acts as a phenolic or lipid-soluble antioxidant; maintains sulfhydryl groups in the reducing form; acts as a synergist for chelating agents and reduces harmful oxidation products.
