The Role of Acid Protease in Alcohol Fermentation

Protein, composed of amino acids, is one of the most complex organic compounds found in nature. It is broken down by hydrochloric acid and protease into amino acids that are easily absorbed by the intestinal tract of higher animals and the cell membrane of microbial organisms. Every animal, including humans, must have enough protein to sustain their own growth to produce the amino acids necessary for every cell. Some special proteins are also functional composition elements of some special cells, glandular secretions, enzymes and hormones. Proteases are enzymes that have a catalytic function that can hydrolyze (break) proteins, so they are also called proteolytic enzymes. Proteolytic enzymes play an important role in many physiological and pathological processes and are also widely used in the food and dairy processing industries. Acid protease refers to the lower optimal pH of the protease, rather than the presence of acidic groups in the active site of the enzyme. The optimal pH of the acid protease is from about 2 (pepsin) to 4. From the enzyme activity-PH curve analysis, one or more carboxyl groups are contained in the active site of the enzyme. The most thoroughly studied of this class of proteases is pepsin. Acid protease can effectively hydrolyze proteins under low pH conditions, and is widely used in alcohol, liquor, beer, brewing, food processing, feed addition, leather processing and other industries. Acid protease action products are amino acids, the best nutrients for yeast growth and fermentation promoters. In addition to containing a large amount of starch in corn raw materials, it also contains a certain amount of crude protein that is closely bound to starch, which affects the rate of starch hydrolysis. Adding acidic protease during the fermentation process, through hydrolysis of protein, releases some starch that is difficult to hydrolyze, creating conditions for the saccharification of amylase, and also providing fermented yeast with richer nutrition. Specifically, acid protease has the following enzymatic functions during alcohol fermentation: 1. Promote the dissolution of raw material particles Acid protease is very soluble in the particulate matter of the brewing raw materials, which creates favorable conditions for saccharification and fermentation. In addition to its ability to dissolve particulate matter, the acid protease can release the adsorbed α-amylase, so that the saccharification and fermentation can proceed smoothly. 2. Conducive to microbial proliferation Acid proteases of molds have an important effect on microbial proliferation. Because it decomposes and produces L-amino acid, it can be directly extracted and utilized by microorganisms. In alcohol fermentation, the addition of acid protease can better decompose the protein in the raw materials, provide more free amino acids to the yeast, and shorten the fermentation time. 3. Promote alcohol fermentation The reason that acid protease promotes alcohol fermentation is to increase the FAN level in the mash, promote the growth and reproduction of yeast, and reduce the substrate loss and energy consumption caused by the use of bacteria for the synthesis of amino acids. 4. Effect on the viscosity of fermentation mash The acid protease has a certain effect on the viscosity of the fermentation mash. The research shows that the increase of the acid protease increases the viscosity of the fermentation mash. Due to the decrease in the viscosity of the fermentation mash, the pump efficiency and the effect of plate heat exchange and cooling can be improved, and the separation effect of the hydraulic filtration of the stillage after distillation is improved. 5. Provide fragrant precursor substances and flavor substances Acidic protease hydrolyzes raw protein into amino acids in the acidic environment of wine making. Amino acids are the prerequisite substances for the production of flavor components of liquor. 6. Degradation of yeast protein bacteria Acid protease can effectively decompose the bacterial protein of the yeast, and has the ability to decompose the dead yeast, and has no effect on the live yeast. After a large number of dead yeasts are decomposed by acid protease, it is not only a good nutrient for microorganisms, but also can effectively provide precursor substances for the flavor components of liquor.