In this century, people advocate green foods and health foods, and they are eager to replace antibiotics and other drugs with green additives to produce health foods that are truly suitable for people's consumption. Microbial feed additives produced using biotechnology are one type of such additives. Yeast cultures in such additives are discussed herein.
1. Production of yeast culture
1.l Nutritional ingredients
A yeast culture generally refers to a mixture of a culture and a yeast which is fermented by a fermenting bacterium in a solid or liquid medium, and is rich in nutrients and rich in B vitamins. Minerals, digestive enzymes. Growth-promoting factors and more complete amino acids are feed additives that integrate nutrition and health care. The average VK content in yeast culture was determined to be 40-142 mg/kg. The phytase activity of a yeast culture was determined to be 1400 units/kg, which is consistent with the higher activity of the phytase contained in the yeast. A red yeast found in the study is rich in carotenoids, which can enhance the coloring effect of animal products.
1.2 Production Process
Yeast cultures produced by fermentation of fermentation broth alone in liquid or solid medium are not ideal, so liquid solid state combined fermentation processes are currently generally employed. It adopts liquid strain, solid-state fermentation, solidification and ripening of medium, increasing liquid inoculum, reasonable drying process, shortening fermentation cycle, greatly reducing the degree of contamination of bacteria, and effectively preserving the organisms in the product. Active substance. The product produced by this process contains about 25% of crude protein, and pays attention to preserving yeast active cells, digestive enzymes, vitamins and yeast metabolic end products, belonging to the type of microecological preparation, and is a biologically active feed compound additive. Taking Xi'an Aipu'an Biotechnology Co., Ltd.; the company's yeast culture as an example, the production methods are as follows: l) adding liquid medium to promote yeast metabolism, starting to produce nutrient metabolites; 2) grain medium and liquid fermentation broth The mixture is mixed to form a wet mixture, and the fermentation process continues; 3) the wet mixture is extruded into a soft noodle shape, and the fermentation process continues. In the process, the yeast cells continue to use the medium to produce more nutrient metabolites; 4) fermentation The noodle-like yeast culture is dried, ground, and then packaged.
2, the difference between yeast and yeast culture
2.l Yeast (active dry yeast)
Yeast and yeast cultures are two completely different substances. Yeast is a microbial fungus belonging to a single-celled organism. People have long recognized the nutritional value of yeast, which is a very good source of protein and amino acids. Among yeast products, active dry yeast (95% of the substance content) is the most common practical yeast product in the feed industry and is used in many feeds in the form of live yeast. Active dry yeast is metabolite-free, and it is almost impossible if active yeast is to produce metabolites in animals. Because living yeast cells are difficult to survive in the stomach of animals, they are attacked by other microbial bacteria in the stomach, and they are killed in the future when they produce metabolites. Therefore, it is impossible to obtain all the beneficial ingredients contained in the yeast culture simply by feeding the yeast cells.
2.2 Yeast Culture
Yeast cultures are microecological products formed by yeast after extensive fermentation on a specially prepared medium under the control of specific process conditions. It consists of yeast cell metabolites and a medium that has been mutated after fermentation, as well as a small amount of inactive yeast cells. In the production of yeast cultures, yeast cells are only a tool used to produce cellular metabolites. A yeast culture is a complex product that contains not only nutrients in yeast cells, but also yeast cell metabolites formed after fermentation. It is these metabolites that stimulate microbial bacteria in the stomach of animals and promote healthy growth of animals, thereby achieving the goal of improving feed utilization and improving animal productivity. Long Ling (2001) believes that yeast culture is a unique yeast product that must be evaluated as a fermented product containing “known growth factorsâ€, but not based on its “known nutrients†(proteins, vitamins and The composition of amino acids, etc.) is measured.
3, the application of yeast culture
Yeast cultures used as feed additives began in the mid-20th century and were first used as protein supplement feeds for ruminants. At present, yeast culture is mainly used in ruminants and aquaculture, and plays a dual role of nutrition and health care. A large number of studies at home and abroad have proved that yeast culture plays an important role in promoting animal growth, improving feed utilization, preventing diseases, improving immunity and improving the environment.
3.l Nutritional role
The yeast culture is used as a feed additive, and its nutritional function is mainly to optimize the nutritional value of the feed. Yeast culture is a pure natural feed ingredient that improves feed palatability and digestibility. Good palatability can maintain a stable feed intake; better feed digestibility allows the animal to absorb more nutrients to promote production performance.
Recent studies have shown that yeast cultures stimulate the proliferation of rumen cellulose bacteria and lactic acid bacteria, change the rumen fermentation mode, reduce the rumen ammonia concentration, increase the rumen microbial protein production and feed digestibility. Under the domestic feeding conditions, the effect of yeast culture on the milk production and milk composition of Holstein cows was 60 g/small. The results showed that the milk yield increased by 0.9 kg/d. It was as high as 1.77 kg/d in five days, and significantly increased the content of milk fat and lactose. In the experiment, 60 small head yeast culture was added to the cow ration, which had obvious milk-increasing effect on the early lactating cows, which made the average daily milk production. The amount increased by 0.48- 1.74kg, and the daily average milk increased by 1.13 kg. However, the effect of yeast culture on dairy cows was affected by the nutritional level of the diet and the physiological state of the animals. It is reported that yeast culture is more effective than early stage in early lactation; It is believed that the effect of adding milk to the yeast culture is higher, and the effect is better. When the cow is fed the first clear grass and the wheat is added, the effect is not obvious.
The reason why the yeast culture shows a significant milk-increasing effect on the cow is that the culture is a metabolite of yeast, which promotes rumen fermentation and causes a large number of ammonia bacteria, protein-synthesizing bacteria and fiber bacteria to multiply and grow, thereby improving the feed. Crude fiber digestibility and the efficiency of bacteria using NPN (non-protein nitrogen) to synthesize bacterial proteins.
In order to study the effect of yeast culture on fish feed, feeding experiments with tilapia showed that yeast cultures had a tendency to reduce the feed coefficient and increase the weight gain rate.
The use of yeast cultures in monogastric animals has been shown to have improved feed digestibility and reproductive performance. Experiments with pigs and chickens have shown that not only the growth rate and feed remuneration are increased, but also some of the fiber components in the energy feed are also more digestible after the yeast culture is added to the high fiber diet. Adding 8 % peanut shell or bean hull to the growing diet reduces the daily gain and feed intake of the pig, while supplementing the yeast culture can reduce the adverse effects of the crude fiber and increase the daily gain. It was found that the addition of yeast culture to low-phosphorus diets increased pig daily weight gain by 10% and increased feed intake. Experimental studies have shown that adding 2% yeast culture to broiler diets can promote growth, while adding 4% yeast culture seriously affects the growth rate. Adding yeast culture to poultry feed can reduce stress response and improve Feed efficiency.
3.2 Health Care
Recent evidence suggests that a portion of the beneficial effects of yeast cultures are related to their cell walls. Studies by many researchers around the world have shown that a mannan oligosaccharide (MOS) contained in the yeast cell wall can greatly affect the animal's immune system. MOS is a powerful improver of intestinal microflora. MOS has the ability to reduce pathogenic bacteria in the intestine and prevent colonization of pathogenic bacteria in the gastrointestinal tract. According to recent trials, animal diets contain lower levels of MOS. At the time, its immune function can be improved.
Adding yeast cultures reduces morbidity. According to reports, the yeast culture prepared by experts using agricultural and forestry waste is added to the squid feed. The test results show that after adding the yeast culture, the disease resistance is enhanced and the growth can be promoted, and the suitable addition amount is about 5%. A trial in Canada injected glucose from the yeast cell wall into the squid and found it to be an effective immune stimulator that significantly reduced fish mortality in fish farms. It is reported that the yeast cell wall is a kind of feed immune enhancement source, which can adsorb, phagocytose, destroy and absorb toxic substances such as bacteria, molds and viruses invading the body, and enhance the immune function. A recent new area of ​​research on yeast cultures is as a natural antidote to feeds, probably because yeast cells have a combined action on toxins in the feed.
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