酶制剂在酵母水解物中的应用

With the continuous development of the feed industry and the continuous improvement of yeast technology, yeast hydrolysates have become one of the protein raw material alternatives in the feed industry. In September 2018, in the face of the new situation in which the Ministry of Agriculture has explicitly ordered a suspension of the use of pig blood products in pig feed, yeast hydrolysate products have become even more popular and are playing an even more important role.

Yeast hydrolysate is a product obtained by autolysis or exogenous enzyme catalysed hydrolysis of the mycelium obtained by liquid fermentation using Saccharomyces cerevisiae as the strain. The soluble yeast is not extracted, and the crude protein content is not less than 35%. The main types of production strain used today are: one is beer yeast filtered after fermentation, with a protein content of 42-47%. The quality of the product varies with the beer fermentation process, the taste is bitter and has a beer flavour, and the cost is low; the other is brewers’ yeast fermented with molasses, with a protein content of 50-60%. The quality of the product is stable, the taste is fresh and fragrant, and the cost is high.

Yeast hydrolysates are produced mainly by activating endogenous and exogenous enzymes. Different yeast fermentation can lead to high or low activity of endogenous enzymes. By adding exogenous enzymes, the indicators of the product in all aspects can be improved.

The quality indicators of yeast hydrolysate generally include crude protein, nucleic acids, amino acid-based nitrogen, amino acids, acid-soluble proteins, small peptide nucleotides, etc. Crude protein and nucleic acids are determined by the fermentation strain, and these two indicators are different for different species and different mutant strains.

During autolysis, some companies add cell wall hydrolases to help break down the yeast cell wall, accelerate the dissolution of intracellular substances, and improve the utilization rate of active ingredients. This also facilitates protein and nucleic acid hydrolysis.

Adding protease can effectively hydrolyse proteins into small molecular proteins, polypeptides, small peptides and amino acids. Through the cooperation of different types of endopeptidases, the cleavage sites of enzyme preparations can be effectively increased, which can significantly increase the degree of protein hydrolysis and hydrolyse more macromolecular proteins into smaller substances. The application of compound proteases can greatly increase the product’s amino acid nitrogen, amino acids, acid-soluble protein and small peptide content, giving the product richer nutrition that can be more easily absorbed by livestock.

During protein hydrolysis, many hydrophobic peptides and small peptides are produced. When the product has too high a degree of hydrophobicity, it can produce an unpleasant bitter taste. By adding flavour enzymes, the hydrophobic amino acids can be effectively cut, the hydrophobicity of the product can be reduced, the bitter taste can be reduced, the flavour can be enhanced, and the product can be given a better appetising effect.

Nucleic acids and nucleotides are essential for the growth of young animals. Adding exogenous nucleic acid hydrolase can degrade nucleic acids released from the nucleus into nucleotides, enrich the nutrients of yeast hydrolysate, provide young animals with sufficient energy, and promote rapid animal growth.

The addition of various types of exogenous enzymes in the production of yeast hydrolysate improves the operability of the production, enriches the nutrition of the product, modifies the taste of the product, and provides the necessary basis for the production of high-quality yeast hydrolysate. It is believed that in the near future, with the continuous development of enzyme engineering and the increasing application of special enzyme preparations, the quality of yeast hydrolysate will take off again.

The impact of enzyme preparations on the flavour of yeast extract

Yeast extract (YE) is a high-grade natural condiment made from food yeast as raw material, which is refined by autolysis, separation and other processes to degrade the proteins and nucleic acids in yeast cells. YE itself can volatilise a variety of odour-active compounds with roasted and meaty aromas such as pyrazines and thiophenes. As a flavouring agent, YE is also rich in non-volatile flavouring compounds such as amino acids, nucleotides and peptides. These volatile and non-volatile compounds together determine the flavour of a particular YE.

The factor that most strongly influences the flavour of YE is the yeast. The different strains of yeast determine the differences in yeast endogenous proteins, nucleic acids, vitamins, metabolic compounds, etc., and thus the flavour. If yeast from the same source is used to produce YE, the most influential factor is the production process. The various enzyme preparations involved in the process have a decisive influence on the flavour of YE.

Yeast is very rich in protein, accounting for about 40-65% of the dry weight of yeast. The flavouring effect of protein after hydrolysis occupies a major position in yeast extract. Many years of research have shown that after protein hydrolysis by proteases, various polypeptides, small peptides, amino acids and amides are formed, and different substances give the extract different flavours. For example, research has shown that polypeptides with a molecular weight of 2000-5000Da provide yeast extract with a mellow flavour, making the flavour more persistent and prolonging the flavour retention time of the final product. Certain small molecular peptides with cysteine or methionine residues with a molecular weight of 200-1000Da give the extract a certain meaty flavour, making it more suitable for use in savoury flavours; amino acids such as glutamic acid, aspartic acid, phenylalanine, alanine, glycine and tyrosine give the extract a strong umami flavour; yeast also contains abundant RNA, which, after enzymatic hydrolysis, produces sodium salts of IMP and GMP, giving yeast extract an extreme umami flavour. All of the substances that give the extract its flavour can be obtained by targeted enzymatic hydrolysis of enzyme preparations.

With the development of modern fermentation technology, enzyme preparations have become increasingly diverse. In the preparation of yeast extract, the peptide distribution of yeast proteins is controlled to a reasonable range through controlled enzymatic hydrolysis technology, thereby controlling and enhancing the mellow taste of the product. Through the combination of complex enzymes and flavour enzymes, the bitterness of the yeast extract is reduced while flavour peptides with a certain taste are formed, and various free free amino acids, enriching the flavour of the product; through the action of glutamine and asparagine enzymes, glutamine and asparagine are converted into the flavourful glutamic acid and aspartic acid, enhancing the umami flavour of the product; through the hydrolysis of RNA by nucleic acid enzymes and the conversion of AMP by deaminase, GMP and IMP can be formed, giving the product an ultimate umami flavour.

The continuous development of modern enzyme preparations has promoted continuous innovation in the yeast extract industry, making yeast extract products increasingly diverse, with more and more diverse applications, and benefiting an ever wider range of industries.

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