Natural food preservatives generally refer to a kind of substances directly separated from animals and plants or separated from their metabolites. Natural preservatives have many advantages over synthetic preservatives, such as strong antibacterial activity, safety, non-toxicity, good water solubility and wide range of action. With the improvement of people's living standards and the progress of science and technology, people pay more and more attention to natural food preservatives. Natural food preservatives can be divided into three categories according to their sources: plants, animals and microorganisms;
1, extracting preservatives from natural plants.
(1) pectin decomposition products
Pectin mainly exists in apples, grapes, oranges and other fruits and vegetables. The enzymatic hydrolysate of pectin has a strong antibacterial effect, which is especially suitable for inhibiting Escherichia coli. Pectin decomposition products are effective under acidic conditions, and the antibacterial activity is the strongest when PH is less than 6. At present, it is widely used in the preservation of pickled vegetables, salted fish and other foods abroad, and it is used in conjunction with other natural preservatives.
(2) Agar oligosaccharide
Agar extracted from seaweed is mainly composed of agarose, and its enzymolysis product is agarose oligosaccharide, which has strong antibacterial and starch retrogradation and anti-aging effects, and can effectively reduce colony formation when the concentration reaches 3. 1 1%. At present, it is widely used in dried noodles, bread and cakes.
(3) Chinese herbal medicine extract
Allicin and allicin in garlic can effectively resist Portugal; Perilla leaf extract has broad-spectrum antibacterial effect and good inhibitory effect on various cocci and bacilli; Forsythia suspensa extract can effectively inhibit a variety of Gram-positive bacteria and negative bacteria, and prolong the shelf life of food. In addition, tea polyphenols, konjac extract mannan and corn stigma extract all have good antibacterial effects.
2. Natural preservatives from animals
(1) propolis
Propolis has a strong antibacterial effect, and its antibacterial effect is equivalent to that of various chemical preservatives. It is generally believed that the preservation mechanism of propolis is firstly that propolis can kill a variety of bacteria, fungi, viruses and protozoa, and secondly that propolis has a good film-forming effect, and the film formed can reduce the pollution of micro-disputes and reduce the exchange of food with external gas. Propolis extract can be directly added to human milk, health oral liquid and beverage, which has good antiseptic and fresh-keeping effect. At present, the price of raw propolis powder is around 300 yuan per kilogram.
(2) Chitosan
Shellfish polysaccharide, also known as carapace rope, is a polysaccharide extracted from crab shells and shrimp shells. The principle of chitosan and its derivatives as preservatives is similar to that of propolis, mainly due to its good film-forming ability and strong antibacterial ability. Chitosan is effective against bacteria, yeast and mold. The research shows that it can be used to keep drinks, sauces, fruits and vegetables fresh, and it is the best candidate for natural antibacterial preservatives at present.
(3) lysozyme
Generally, protein contains about 0-3% lysozyme, so it can be extracted from protein. At present, egg white lysozyme is put into commercial production. Under the conditions of PH 7 and temperature 50℃, lysozyme has a strong bacteriolytic effect on Gram-positive bacteria, Bacillus subtilis, Bacillus and aerobic Bacillus. Because hydroxyl and acid in food will affect the activity of lysozyme, it is generally used with wine, phytic acid, glycine and other substances. It has been widely used in the preservation of aquatic products, meat products, fresh seafood, cakes, alcohol and other beverages, but the price is relatively high, about 2400 yuan per kilogram.
(4) Protamine
Protamine is a polycationic peptide existing in fish sperm, which has broad-spectrum antibacterial activity, can inhibit the growth of Bacillus subtilis, Bacillus megaterium and Bacillus licheniformis, and also has obvious inhibitory effects on gram-positive bacteria, yeast and mold. The action mechanism of protamine destroys microbial cell wall, dissolves cell membrane and causes cell leakage. When protamine is combined with other natural additives, glycine, sodium acetate, etc. The antibacterial effect is better, and it is applicable to a wider range of food preservation. At present, the price of food-grade protamine is around 600 yuan per kilogram.
3. Natural preservatives from microorganisms
(1) Streptococcus lactis (nisin)
Nisin has a strong inhibitory effect on Gram-positive bacteria, especially bacteria that can form spores, but has no effect on Gram-positive bacteria, yeasts and molds, and can inhibit Staphylococcus, Streptococcus, Micrococcus and most Clostridium and Bacillus spores. Nisin has strong activity under acidic conditions and pH value.
(2) Natamycin
Natamycin can kill and inhibit almost all yeasts and molds, but it has no effect on bacteria and protozoa. The antibacterial spectrum of natamycin is just complementary to nisin, and they can be used together. The antibacterial effect of natamycin is 50~300 times stronger than that of commonly used sorbic acid, and1.0 ~ 6.0 mg L-1can inhibit most molds. Natamycin is usually used for the surface treatment of cheese and dried sausages, and also for the preservation of yogurt, wine and juice.
Second, chemical food preservatives.
1, benzoic acid and its sodium salt
Benzoic acid and its sodium salt are one of the most commonly used preservatives in China's food processing industry, which are mainly used to preserve liquid foods such as beverages (such as soda, juice, soy sauce, canned food, alcohol, etc.). ). Benzoic acid, also known as benzoic acid, has a molecular formula of C7H6O2. Benzoic acid is a monobasic aromatic carboxylic acid. Benzoic acid has strong lipophilicity, which easily penetrates into cells, thus interfering with the permeability of microbial cell membranes and inhibiting the absorption of amino acids by cell membranes. Benzoic acid molecules entering cells ionize and acidify alkaline substances in cells, which can inhibit the activity of cellular respiratory enzymes and strongly prevent the condensation reaction of acetyl-CoA, thus playing a role in preserving food. Benzoic acid has a broad antibacterial spectrum in acidic environment, and has strong inhibitory effect on bacteria, but weak inhibitory effect on yeast and mold. The optimum pH value of anticorrosion is 2.5 ~ 4.0. Because benzoic acid is insoluble in water, sodium benzoate is often used instead in practical application. Sodium benzoate can only play an antiseptic role in the case of free benzoic acid, and it has a good antiseptic effect in foods with strong acidity. Benzoic acid and its sodium salt are relatively safe food chemical preservatives. According to the Hygienic Standard for the Use of Food Additives, no toxic or side effects have been found.
2. Sorbic acid and its potassium salt
Sorbic acid is 2,4-hexadienoic acid, also known as sorbic acid, and its molecular formula is C6H8O2. Sorbic acid (potassium sorbate) is the most commonly used preservative, which is used in most countries. Sorbic acid is an unsaturated fatty acid, and its bacteriostatic mechanism is that it uses its own double bond to combine with sulfhydryl groups of enzymes in microbial cells to form * * * valence bonds, which make it lose its activity and destroy the enzyme system. In addition, sorbic acid can also interfere with the transmission function, such as the transmission of cytochrome C to oxygen and the energy transmission function of cell membrane, and inhibit the proliferation of microorganisms, thus achieving the purpose of anticorrosion. Sorbic acid and its potassium salt can effectively inhibit mold, yeast and aerobic spoilage bacteria, but it is almost ineffective against anaerobic bacteria and lactic acid bacteria. The antiseptic effect of sorbic acid decreases with the increase of pH value, but its applicable pH value range is wider than that of benzoic acid, and it is applicable below pH 5 ~ 6, and it is also an acidic preservative. Sorbic acid can participate in the normal metabolism of human body, and is eventually oxidized into CO2 and water, which is basically harmless to human body and has no adverse effect on food flavor. It is one of the safest food chemical preservatives recognized internationally at present. However, because the price of sorbic acid is higher than that of benzoic acid, its application is limited, and it is only used in high-end food at present.
3. Propionic acid and its salts
Propionic acid is a monocarboxylic acid, colorless oily liquid. It plays an antibacterial role by inhibiting the synthesis of β -alanine by microorganisms. Propionates mainly include sodium propionate and calcium propionate, and their antiseptic mechanism is the same, and they are all converted into propionic acid in human body. Monomer propionic acid molecules can form high osmotic pressure outside mold cells, dehydrate mold cells, lose fertility, penetrate mold cell walls, and inhibit intracellular activity. Propionic acid is an intermediate product of normal metabolism of human body, which can be metabolized and utilized, and is safe and non-toxic. Propionate is an acidic preservative, which can only produce antibacterial effect in acidic environment. At present, it is mainly used in bread and cakes, which can play a good role in mildew prevention.
4. P-hydroxybenzoate (nipagin ester)
The parabens include methyl paraben, ethyl paraben, propyl paraben, isopropyl paraben, butyl paraben, isobutyl paraben and heptyl paraben. The bacteriostatic mechanism of parabens is to inhibit the activities of respiratory system and electron transfer enzyme system of microbial cells, which can destroy the structure of microbial cell membrane and thus play an antiseptic role. The antiseptic effect of p-hydroxybenzoate does not change with the change of pH value, and it has good effect in the range of pH value 4 ~ 8, and has broad-spectrum antibacterial effect on mold, yeast and bacteria, but it has poor effect on gram-negative bacilli and lactic acid bacteria. The antibacterial activity of p-hydroxybenzoate is related to the length of alkyl chain, and the longer the alkyl chain, the stronger the antibacterial effect. The antibacterial effect of p-hydroxybenzoate is stronger than benzoic acid and sorbic acid, and its toxicity is lower than benzoic acid but higher than sorbic acid. The biggest disadvantage is that they have a special smell and are insoluble in water, so they are usually dissolved in sodium hydroxide, acid and ethanol before use. In order to give full play to the anti-corrosion effect, it is best to mix two or more of these esters.
5. dehydroacetic acid and its sodium salt dehydroacetic acid
The molecular formula C8H8O4 It and its sodium salt are white or yellowish crystalline powder, which has strong antibacterial ability, especially for mold and yeast. It is an acidic preservative, which is basically ineffective for neutral foods. It is stable to light and heat, degrades into acetic acid in aqueous solution, and is non-toxic to human body. It is a broad-spectrum preservative, widely used in the preservation of meat, fish, vegetables, fruits, beverages and cakes.
6. Sodium lactate
Colorless or yellowish transparent liquid, odorless, slightly salty and slightly bitter, easily soluble in water, ethanol and glycerol. The general concentration is 60%-80%, and the maximum usage limit of 60% concentration is 30g/KG. Sodium lactate is a new preservative, which is mainly used in meat and poultry products and has a strong inhibitory effect on bacteria in meat food. Such as Escherichia coli, Clostridium botulinum and Listeria. By inhibiting food pathogenic bacteria, food safety is improved. Enhance and improve the flavor of meat and prolong the shelf life. Sodium lactate has good dispersibility in raw meat and good water adsorption, thus effectively preventing dehydration of raw meat and achieving the functions of preservation and moisture retention. Mainly suitable for barbecue, ham, sausage, chicken, duck and poultry products and sauce and halogen products. The reference formula of meat preservation: sodium lactate: 2%, sodium dehydroacetate: 0.2%.
7. Dimethyl fumarate
It is a new anti-mildew preservative developed vigorously at home and abroad, which can inhibit more than 30 kinds of molds and yeasts, and its antibacterial performance is not affected by pH value. It has the advantages of high efficiency, broad spectrum, high safety and low price. It has excellent comprehensive antibacterial and antiseptic properties and strong biological activity. Because sublimation has fumigation effect, it has dual functions of contact sterilization and fumigation sterilization. With low toxicity, it will soon become fumaric acid, a normal component of human metabolism, and has good application repeatability. Dimethyl fumarate is also widely used in vegetables, fruits, Chinese herbal medicines, tobacco, cosmetics, textiles, films, tapes, floppy disks, leather, paper and books. Dimethyl fumarate has great application value and good economic benefits in food preservation. Especially under the condition of high temperature and high humidity, it can avoid food deterioration, dry aging and poor taste, which seriously affects production and market sales.
8. Inorganic salt preservative
It mainly includes nitrate and nitrite containing nitrogen and sulfur. The toxicity of nitrate is mainly caused by its reduction to nitrite in food, water or body. Nitrite is one of the most toxic substances in food additives. After ingestion, it can combine with hemoglobin to form methemoglobin, losing its oxygen-carrying function. In severe cases, it will suffocate. The lethal dose to human body is 4~6g/kg body weight. It can be transformed into nitrosamines with strong carcinogenicity under certain conditions. This preservative is mainly used for the preservation and color protection of meat food. Sulfite and pyrosulfite contain sulfur, and its effective component is sulfite molecule. The sterilization mechanism of sulfurous acid is mainly to consume O2 in food to kill microorganisms that need oxygen due to lack of oxygen and inhibit the activity of enzymes in some microbial physiological activities. Because the residual sulfur dioxide after using these salts will cause allergic reactions, especially for asthma patients, it is generally only contained in special preservatives. For example, Guangxi local standard DB45/3 19- 2007 "Quality and Safety Requirements for Fresh and Wet Rice Noodles" stipulates that the SO2 residue in rice noodles should be lower than the method detection limit.
In view of the problems existing in the use of food preservatives and people's misunderstanding of preservatives, the purpose of adding preservatives to food is to ensure the non-deterioration, health and safety of food. In fact, it is a friend of our human beings, but the premise of using it must be the varieties allowed by the state, the addition range is in line with the regulations, and the addition dose is within the allowable range. All the food additives not recorded in GB 2760-20 14 National Food Safety Standards-Catalogue of Standards for the Use of Food Additives are non-additives. Excessive use is also illegal. ? Consumers can't tell whether excessive preservatives have been added from the appearance, color, shape and taste of food, so they can use Guanyu Instrument's multifunctional food additive detector to quickly detect sulfur dioxide, sulfite, potassium bromate, phosphate, indigo, brilliant blue, carmine, pyrophosphate, sodium dihydrogen pyrophosphate and tripolyphosphate. , which can effectively prevent excessive and bad illegal addition.