Types of fermented foods

(1)Metabolite fermentation Fermentation with metabolites as products is the most numerous, the largest output and the most important part, and the products include primary metabolites, intermediate metabolites and secondary metabolites. Various amino acids, nucleotides, proteins, nucleic acids, lipids, sugars, alcohols and acids are primary metabolites or intermediate metabolites. Secondary metabolites are synthesized from intermediates or products of primary metabolism, and some secondary metabolites inhibit or kill microorganisms (e.g., antibiotics), some are special enzyme inhibitors, and some are growth promoters.

(2) Enzyme fermentation Enzymes are commonly found in plant and animal cells and microbial cells, it can be said that all biological cells contain enzymes. The use of fermentation to prepare and extract a variety of enzymes produced by microorganisms has been an important part of today's fermentation industry. At present, most of the enzymes for industrial use come from enzymes produced by microbial fermentation. For example: α-amylase, β-amylase, glucosidase, debranching enzyme, invertase, glucose isomerase, cellulase, alkaline protease, acid protease, neutral protease, pectinase, lipase, rennet, catalase, penicillin acylase, cholesterol oxidase, glucose oxidase, aminocarbamoylase and so on. In addition, the production of various curves applied in the production of brewing industry, traditional brewing industry, etc. is also equivalent to the production of enzyme preparations.

(3)Biotransformation Fermentation Biotransformation refers to the biochemical reaction of using one or more enzymes in biological cells to act on specific parts (groups) of some compounds to transform them into compounds with similar structure but greater economic value. The end product of biotransformation is not produced by the metabolism of a biological cell using nutrients. Growing cells, resting cells, spores or stem cells are all capable of carrying out transformation reactions, and immobilized cells or immobilized enzymes are increasingly being used in order to increase the efficiency of the transformation, reduce the cost and minimize impurities in the product. In the transformation reaction, the role of biological cells is only equivalent to a special biological catalyst, which only causes a reaction at a specific site. And the conversion reactions it can perform include dehydrogenation, oxidation, dehydration, condensation, decarboxylation, hydroxylation, amination, deamination, and isomerization. Bioconversion reaction has many advantages compared with chemical reaction, such as simple process, convenient operation, mild reaction conditions, and less pollution to the environment. The most obvious characteristic of biotransformation reaction is the strong specificity of the reaction, including reaction specificity (reaction type), structural position specificity (position in the molecular structure) and stereospecificity (special enantiomers), in which the stereospecificity of the reaction is particularly important.