An Introduction to Food Preservation Techniques
Generally speaking, the deterioration of food during storage and transportation is mainly caused by microorganisms, enzymes contained in the food, life activities, oxidation or light. And food preservation is achieved by controlling or inhibiting external contaminants and/or internal biological reactions that may alter the sensory and nutritional quality of food.
At present, the commonly used food preservation techniques in actual production can be divided into three categories: physical, chemical and biological preservation technologies. However, considering that chemical preservation is easy to result in chemical residues, in recent years, people have paid more attention to biological preservation technology and physical preservation technology. In particular, the non-thermal technique in physical preservation can inactivate microorganisms at or near normal environment temperatures, thereby avoiding the adverse effects of heat on the flavor, color and nutritional value of food, which is the reason why people focus on and research it. The following is a brief introduction to these three types of preservation technologies.
1. Physical Preservation Technology
Common physical preservation techniques include low-temperature preservation, heat treatment, modified atmosphere packaging and vacuum preservation, as well as some relatively advanced non-thermal technologies, such as ultra-high pressure preservation, ultrasonic preservation, ionizing radiation preservation, magnetic field preservation, etc.
The low-temperature preservation method is to use cryogenic technology to reduce the temperature of food and maintain it at a low temperature to prevent food from spoilage and prolong its shelf life. Heat treatment uses high temperatures to kill microorganisms and some spores and inactivate enzymes, but excessive heat treatment can also lead to protein denaturation, non-enzymatic browning, and loss of vitamins and volatile flavor compounds.
Modified atmosphere packaging refers to changing the gas composition around the product or replacing it with inactive gas before the product is sealed in the container or package, thus inhibiting the reproduction of bacteria. For fruits and vegetables, it can also effectively inhibit their respiration.
Vacuum preservation is to use a vacuum method to remove the air in the packaging bag, and then use the sealing technology to isolate the food from the external environment, so as to effectively prevent fat oxidation and the growth of aerobic microorganisms, inhibit the enzyme activity and prolong the shelf life.
Ultra-high pressure is a low-temperature pasteurization method that inactivates vegetative microbial cells by disrupting non-covalent bonds and cell membranes for extended shelf life and pathogen reduction. Ultrasound uses the energy generated by sound waves, which vibrate at least 20,000 times per second, and these mechanical shocks can destroy the structural and functional components of cells until the cell lysis. Ionizing radiation reduces or eliminates spoilage and disease-causing microorganisms by fragmenting DNA.
These advanced technologies have not been widely used in actual production. This is because of the high cost, and these technologies also have certain problems. For example, ultra-high pressure can change the structure of proteins and polysaccharides, resulting in changes in food's texture, appearance and function. And higher doses of ionizing radiation may cause slight changes in the color of beef, pork and poultry.
2. Chemical Preservation Technology
Chemical preservation is mainly to keep food fresh through chemical preservatives. For fruits and vegetables, chemical preservatives include adsorption preservatives, solution immersion preservatives, fumigation preservatives, waxes and coating agents. For meat, chemical preservatives include preservatives, antioxidants, colorants, and quality improvers. But the disadvantage of chemical preservation is the toxicity and residue of chemical preservatives. It was reported that in 2012, nearly 50 different types of chemicals were detected in strawberries in California.
Since long-term use of traditional chemical preservatives will adversely affect human health and the environment, some more environmentally friendly chemical preservatives, such as ozone, have emerged. Ozone can react rapidly with endoenzymes, nuclear material, envelope components, sporozoites or viral capsids of microorganisms. It breaks down quickly with no trace of oxidation and no residual toxic by-products, and does not alter the chemical composition of food. In addition, nano-emulsion, acidic electrolyzed water and other chemical products are gradually applied to food preservation.
3. Biological Preservation Technology
The general mechanism of the biological preservation technique is to isolate the contact between food and air and delay oxidation, or the biological preservation material itself has a good antimicrobial activity, so as to achieve the effect of preservation. Common biological techniques include natural antimicrobial agents, bacteriophages, and bioprotective microorganisms.
Natural antibacterial agents contain substances with good antibacterial properties extracted from plants, such as the essential oil, lysozyme, antimicrobial peptides, chitosan, lipids extracted from animal bodies, and microbial fermentation products, including nisin and catechin. Bacteriophage, a novel, environmentally friendly and effective biological preservation method, can specifically and effectively infect and multiply in the respective host bacterial cells, so it is harmless to humans, animals and plants, and considered as a new and environmentally friendly alternative to chemical disinfectants. Bioprotective microorganisms avoid microbial growth by introducing other competing microorganisms that are beneficial to humans, such as lactic acid bacteria. It has a long history of safe use in food as a natural flora of meat, milk, vegetables and fish.