Yeast-based organic nitrogen source and its application in fermentation industry
December 18, 2019
Nitrogen sources refer to nutrients that make up the source of nitrogen in microorganism and its metabolites. Commonly used nitrogen sources can
Yeast-based organic nitrogen source and its application in fermentation industry
December 18, 2019
Nitrogen sources refer to nutrients that make up the source of nitrogen in microorganism and its metabolites. Commonly used nitrogen sources can be divided into two categories: inorganic nitrogen sources and organic nitrogen sources. Inorganic nitrogen sources include ammonium sulfate, nitrate, ammonia and urea, and organic nitrogen sources include soybean meal, peanut meal, cottonseed meal, corn pulp, peptone, yeast extract and fish meal. Generally speaking, inorganic nitrogen sources only contain single composition which can be quickly assimilated but organic nitrogen sources have the following characteristics:
1. More complicated components and nutrients;
2. The rate of utilization by bacteria is different;
3. The utilization of amino acids in organic nitrogen sources by microorganisms is always selectiveness;
4. It is the crucial influencing factor of fluctuations in fermentation.
As the cultivation conditions of recombinant bacteria in the field of microbial fermentation are becoming increasingly severe, the requirements for culture media are becoming higher and higher. The search for natural, stable and applicable organic nitrogen sources has become a limiting factor in the development of fermentation industry. Under the demand of huge market, yeast-based organic nitrogen sources have emerged as the times require, and their natural, pollution-free, high stability and high applicability are accepted by the majority of fermentation enterprises.
1. Yeast-based organic nitrogen sources
Yeast-based organic nitrogen sources have high protein content (proteins account for more than 50% of the total try weight of yeast), contain 18 types of amino acids completely, as well as be rich in vitamins and minerals. That means, it is a kind of high quality organic nitrogen sources for microbial fermentation and cell culture. For example, yeast extract has been widely used as the raw materials for seed and fermentation media in a broad range of microbial fermentation applications. Actually, due to the growth needs of different strains, the products currently used in the field of biological fermentation mainly include: yeast powder (inactive dry yeast), autolyzed yeast, yeast extract and yeast peptone.
At present, the raw materials for producing yeast extract mainly come from brewer’s yeast and baker's yeast. Among them, baker’s yeast is the target of many researchers. Angel Yeast Co., Ltd. is the main player of baker’s yeast. However, some of yeast extracts also use spent brewer’s yeast as raw materials, such as the United States A-B beer company, Japan Sapporo, Kirin, etc. In Japan, dried spent brewer’s yeast is used to produce yeast extract.
2. Application of yeast-based organic nitrogen source in fermentation industry
(1) Fermentation of Lactic acid bacteria.
Lactic acid bacteria refers to a class of spore-free and Gram-positive bacteria whose main metabolites is lactic acid after fermenting sugars. Lactic acid bacteria is a kind of chemotrophic microorganism. Most lactic acid bacteria require complicated nutrients for their growth and acid production. Yeast extracts are rich in amino acids, peptides, amino acids, vitamins, nucleotides, etc., and are often used as key component of fermentation media for lactic acid bacteria. Zhang Ya and Leng Yifei used response surface methodology to optimize the growth medium of Lactobacillus acidophilus, in which the nitrogen source was yeast extract and the dosage was 8.682%. Using the optimized medium, the cell density can reach 16. 49 × 10^9 cfu / ml, which is 20.61% higher than the number of viable bacteria in classic MRS medium. Meanwhile the cost was reduced by 30%.
Hu Chengyuan selected 5 kinds of yeast extracts produced by famous enterprises for component content analysis, used them as nitrogen sources for the culture medium on 2 strains of Lactobacillus (Lacobacillus helveticus and Lactobacillus rhamnosus). The results showed that: in the cultivation of Lactobacillus helveticus, one type of Angel yeast extract was better than other three yeast extracts produced from Europe and US; In the cultivation of Lactobacillus rhamnosus, the performance of 4 types of yeast extracts was not obvious difference.
In the solid-state fermentation process of Chinese traditional liquor, lactic acid bacteria can promote Maillard reaction, improve the fermentation performance of liquor, and maintain the micro-ecological environment of liquor. Ding Haimei and Zhang Zhimin optimized the acid production medium of Lactobacillus casei by orthogonal experiments. The optimal organic nitrogen source in the obtained medium was casein peptone, beef extract and yeast extract, and the dosage of yeast extract was 0.5%.
(2) Steroid drugs.
Steroid hormones are a class of compounds containing a nucleus of cyclopentane polyhydrophenan