Food preservation has been closely related to human life since ancient times. Human beings have been utilizing methods such as pickling and soaking in wine for food preservation since long ago. With the rapid development of social and economic and the rapid growth of food demand, a large number of foods need to be transported over long distances and reprocessing, simple traditional preservation methods no longer meet the needs of food preservatives also came into being. Food preservatives can inhibit the growth and reproduction of microorganisms, thus preventing food spoilage and prolonging the preservation time of food.

The mechanism of food preservatives

It is generally believed that the preservative function of food preservatives is realized by destroying the cell structure of microorganisms or interfering with their physiological functions. For example, the cell wall, as well as the plasma membrane, metabolic enzymes, nucleic acids and proteins system and other structural integrity and the normal operation of the function are necessary for the growth and reproduction of microorganisms, the lack of which is essential, so food preservatives as long as to interfere with any of these links can make microorganisms to die or to stop growing.

Types of food preservatives

According to the source, food preservatives can be divided into two categories: chemical preservatives and natural preservatives.

2.1 Chemical preservatives

Preservatives synthesized through chemical reaction are called chemical preservatives. Chemical preservatives are characterized by high efficiency, convenience and cheapness, and are the most widely used type of preservatives in China, including acid-type, lipid-type and inorganic salt preservatives.

2.1.1 Acid preservatives

Commonly used acid preservatives are benzoic acid, sorbic acid and propionic acid, as well as their salts and so on…. Acid preservatives in acidic conditions through the undissociated molecules and the role of bacterial inhibition, its preservative effect is related to pH. The reason why acid preservatives can inhibit and prevent bacteria is that they will interfere with the enzyme system of microorganisms, so that they can not exercise normal metabolic functions. At the same time, acid preservatives have a barrier effect on the permeability of the cell membrane, which will inhibit the growth and reproduction of microorganisms.

Benzoic acid, one of the acid preservatives, is inexpensive and is widely used in everyday products such as soy sauce and cosmetics, but the toxic side effects of benzoic acid and its salts have been controversial. Sorbic acid has a strong inhibitory effect on molds and yeasts, and is recognized as a highly efficient and low-toxicity preservative, which has no effect on the flavor of food and is usually used in foods processed from flour, fish, eggs and poultry.

2.1.2 Ester preservatives

Ester preservatives are nipagin esters, which are commonly used in China, such as p-hydroxybenzoic acid, ethyl ester and propyl ester. The action mechanism of ester preservatives is to destroy the cell membrane of microorganisms, so that the protein inside the cell is denatured and inactivated, thus destroying the normal physiological balance of microorganisms. Ester-type preservatives are mainly used in the preservation of fruits and vegetables, the bactericidal effect is stronger than acid-type preservatives, and its preservative effect will not be changed because of the change of pH, it can be quickly and completely absorbed in the gastrointestinal tract and hydrolyzed into p-hydroxybenzoic acid, which can be discharged from the urine without accumulation in the body, so the toxicity is also relatively low.

2.1.3 Inorganic salt preservatives

Commonly used inorganic salt preservatives include nitrates, nitrites and sulfites containing sulfur. These preservatives mainly inhibit the activity of microbial respiratory enzymes and cause microorganisms to die of anoxia. Inorganic salt preservatives not only keep food fresh, but also increase the color. For example, nitrite can not only inhibit the growth of Clostridium botulinum, but also preserve the freshness and color of fish and meat, which is mainly used in the marination of meat food.

2.2 Natural preservatives

Natural preservatives are generally isolated and extracted from animals, plants and microorganisms or their metabolites, which have antimicrobial and antiseptic effects, and are safer than chemical preservatives, and they mainly include three types of natural preservatives of animal, plant and microbial origin.

2.2.1 Animal-derived natural preservatives

Natural preservatives of animal origin refer to the substances with antiseptic effect artificially extracted from the body of certain animals or their metabolites, such as ichthyocyanin, chitin and propolis. Ichthyosperm is mainly a molecule in which polyarginine or polyarginine and a few other amino acids are bound to the cell wall of bacteria in a certain structure or form and inhibit the formation of the cell wall, thus inhibiting the metabolism of the cell and causing the cell to die. At present, it is mainly used in milk and bread.

2.2.2 Natural preservatives of plant origin

Plant-derived natural preservatives refer to substances with antibacterial and antiseptic effects extracted from the roots, barks and seeds of plants, such as spices, certain herbs and essential oils of plants. Due to the unique geographical environment of China, Chinese herbs are very rich in resources, and the extraction of substances from Chinese herbs that can be used as preservatives has a broad research prospect in China. Among them, plant essential oils contain a large number of secondary metabolites, which have the effect of delaying or inhibiting the growth of bacteria, yeasts and molds. They are mainly used in the preservation of beef, fruits and vegetables.

2.2.3 Natural preservatives of microbial origin

Certain microorganisms or their metabolites in nature have bacteriostatic and antiseptic effects and can be used as preservatives, such as lactic acid streptococcusin and tretinoin. Streptococcus lactis can be digested into amino acids by protein hydrolysis enzymes in the digestive tract after being consumed by human beings, with high safety, and it is the first antibiotic used in food preservation in the world, and it is mainly used in the preservation of all kinds of dairy products; tretinoin has the effects of scavenging free radicals, enhancing the vitality of cells, and protecting the color of food, and it has been widely used in the field of pharmaceuticals and foodstuffs.