What bacteria is used to ferment soy sauce?

Soy sauce is fermented by Aspergillus oryzae.

The raw materials of soy sauce are protein and starch. Vegetable protein is taken from bean cake after soybean oil extraction or soybean meal after solvent extraction, and also replaced by peanut cake and broad bean.

In traditional production, soybean is the main product; Wheat and bran are widely used as starch raw materials, and some of them are replaced by broken rice and corn. Flour is the main raw material in traditional production. Steaming and cooling the raw materials, inoculating pure cultured Aspergillus oryzae seeds to make sauce koji, transferring into a fermentor, fermenting with brine, and extracting soy sauce after the fermented grains are mature.

The purpose of koji-making is to make Aspergillus oryzae fully grow and develop on koji, and to produce and store a large number of needed enzymes, such as protease, peptidase, amylase, glutaminase, pectinase, cellulase and hemicellulase. In the process of fermentation, the formation of taste is based on the action of these enzymes.

For example, protease and peptidase hydrolyze protein into amino acids to produce umami flavor; Glutaminase turns tasteless glutamine into delicious common glutamic acid; Amylase hydrolyzes the precipitate into sugar to produce sweetness; Pectinase, cellulase and hemicellulase can completely break the wall and make protease and amylase hydrolyze more thoroughly.

At the same time, in the process of koji-making and fermentation, yeast and bacteria falling from the air also reproduce and secrete a variety of enzymes. Pure cultured lactic acid bacteria and yeast can also be added.

Lactic acid bacteria produce proper amount of lactic acid, while yeast produces ethanol. The raw materials and metabolites of Aspergillus produce alcohol, acid, aldehyde, ester, phenol, acetal, furanone and other components, which are mostly trace, but can constitute the compound aroma of soy sauce.

In addition, tyrosine in the raw protein is oxidized to produce melanin, and the classical mildew amylase in the sediment is hydrolyzed to produce glucose to produce melanin-like substances, which react with amino acids to make soy sauce produce bright and shiny reddish brown.

The umami, sweet, sour, alcoholic and ester flavors produced by a series of extremely complicated biochemical changes in the fermentation process are mixed with the salty taste of salt water, and finally soy sauce with unique color, fragrance and taste is formed.

Extended data:

Aspergillus oryzae is a common fungus in Hemiptera, Myxomycetes, Myxomycetes, Cladosporium and Aspergillus. Aspergillus oryzae is a strain that produces complex enzymes. Besides protease, it can also produce amylase, glucoamylase, cellulase, phytase and so on.

Aspergillus oryzae is an ideal vector for producing eukaryotic bioactive proteins that Escherichia coli cannot express. Using the information contained in the genome of Aspergillus oryzae, we can find the most suitable conditions for Aspergillus oryzae fermentation, which will help to improve the production efficiency and product quality of food brewing industry.

Under the action of amylase, amylose and amylopectin in raw materials are degraded into dextrin and various low molecular weight sugars, such as maltose and glucose.

Under the action of protease, the indigestible macromolecular protein is degraded into peptone, polypeptide and various amino acids, and the indigestible substances such as crude fiber and phytic acid in auxiliary materials are also degraded, which improves the nutritional value, health care efficacy and digestibility. Widely used in food, feed, kojic acid production, wine-making and other fermentation industries, it has been safely used 1000 years.

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