Guide
In recent years, with the improvement of people's living standards and consumption standards, the quality and yield of meat products have attracted widespread attention. The quality and safety of meat products, as well as the tight supply of meat products caused by the competition for human and animal food caused by the reduction of per capita arable land area, are urgently needed. Therefore, the full and effective development and utilization of various available resources as feed ingredients, optimization of feed processing technology and technology, and vigorous development of fermented feed have become a recent research hotspot of animal husbandry, and are considered to have broad development prospects in order to achieve feed utilization. And the continuous increase in the rate of food conversion.
The widespread application of fermentation technology in feed production is of great significance for improving the quality and yield of the diet. In order to further promote the wide application of fermentation technology in feed production and make its process technology more perfect, it is necessary to control and optimize the relevant technical conditions in the fermentation process. The temperature, pH, moisture content, fermentation time, and inoculum size of the fermentation system are all key control parameters that need further optimization.
1 temperature
Incubation of the cells in a suitable temperature range allows them to undergo normal growth and metabolism activities. Temperatures that are too high or too low may affect the normal growth and metabolism of the cells. If the temperature is too high, the microorganisms may grow too fast, and the nutrients in the fermentation system are excessively consumed, so that the fermentation cannot be performed normally. Too low a temperature may cause the cells to grow too slowly, which may result in a decrease in fermentation yield.
A large number of experiments have been conducted to explore and discuss temperature control during feed fermentation. Gu Bin used solid-state fermentation of rapeseed meal by Bacillus subtilis and Geotrichum candidum to produce polypeptides. It was found that too low temperature affected the normal growth of Bacillus subtilis, and excessive temperature affected the normal growth of Geotrichum candidum. The formation of the polypeptide is most advantageous in the temperature range, so the optimum temperature is determined to be 32 to 34 °C. When Wang Yuan used solid bacteria to carry out solid-state fermentation of soybean meal, it was found that when the temperature was 40 °C, the fermented soybean meal samples had the highest lactic acid content, and the soybean protein had the highest degree of hydrolysis; when the temperature was higher than 40 °C, the "burning" appeared. "Phenomenon, the color of the soybean meal sample is brown. When Zhang Cuimian used the composite bacteria to ferment corn stover powder, it was also found that with the increase of temperature, the microorganisms in the fermentation system gradually increased and the pH showed a downward trend, but when the temperature rose above 30 °C, the number of bacteria decreased. At the same time, a suitable ambient temperature can also effectively shorten the fermentation cycle. Li Long used compound probiotics to carry out solid-state fermentation of rapeseed meal, corn, wheat flour and soybean meal mixed in a certain proportion. It was found that the number of bacteria of lactic acid bacteria also showed an increasing trend with the increase of temperature, and the pH was Reduce accordingly. Compared with the lower temperature, the color, odor and texture of the feed are better when the temperature is suitable, and the suitable fermentation temperature is finally determined to be 35 °C.
The fermentation temperature will affect the normal growth and metabolism of microorganisms and the activity of enzymes. The suitable fermentation temperature can effectively increase the fermentation yield. Therefore, when the feed is fermented, it is necessary to control the temperature of the system to avoid it being too high or too low.
The pH of the fermentation system also has a certain effect on the fermentation. During the fermentation of the feed, the pH affects the activity of the enzyme. At the same time, since pH affects the dissociation of certain intermediate metabolites, the formation of fermentation products is inhibited.
Feng Zhen et al. cultured Lactobacillus under different pH conditions and found that when the pH of the fermentation system was 6.0, the fermentation activity of the cells was the highest. When Tang Xiaopeng used solid state fermentation of cassava residue by Aspergillus niger, the pH was controlled between 3 and 4, which ensured that the activity of carboxymethyl cellulase was significantly higher than that of other pH treatment groups, and the crude protein content was also significantly higher. In other pH treatment groups. Sun Lin used solid microbial fermentation of rapeseed meal to find that the low pH inhibited the growth of various bacteria, hindered the normal fermentation, and finally determined that the composite strain had a rapeseed meal at pH 6.0. Fermentation works best.
Therefore, the suitable pH in the fermentation system is more conducive to the normal growth and metabolism of the cells, maintaining a higher fermentation vigor, so that the fermentation is carried out with high efficiency, thereby increasing the fermentation yield.
3 water content
A large number of tests have shown that the moisture content is also a major factor affecting the fermentation effect. Too low or too high a water content will have an effect on the normal fermentation.
When Hu Rui et al. used optimized probiotics to ferment soybean meal, the temperature, pH and true protein content in the fermentation system showed an increasing trend with the increase of water content. Lin Biaosheng and other conventional feeds were sealed and fermented. It was found that the higher the water content of the material, the faster the strain grew and the better the fermentation effect. Zhou Mengjia and others used Lactobacillus to carry out solid-state fermentation of the basic feed. The results showed that the water was too high or too low to be detrimental to the pH. As the moisture content increased, the dry matter recovery rate of the fermented feed gradually decreased. When Liu Qiang and others carried out the fermentation test of rapeseed meal, the pH gradually decreased with the increase of water content. Zhao Hua et al. 'When performing solid-state fermentation of sweet potato slag, it was found that when the water-to-feed ratio was 1.3:1, the fermentation effect was the best.
Therefore, in the fermentation process, if the water content is too low to meet the needs of the microorganisms, the intake of nutrients by the microorganisms is inhibited, and the growth and metabolism of the microorganisms cannot be performed normally. Excessive water may deteriorate the permeability of the matrix, affect the ventilation, and also inhibit the growth of microorganisms. At the same time, due to excessive moisture, the drying cost may increase, and the possibility of contamination by bacteria may also increase. Sex. Therefore, the moisture content can be reasonably controlled during the fermentation process to avoid excessive or too low, and the fermentation can be effectively ensured.
4 fermentation time
Fermentation time refers to the time from the start to the end of the fermentation. The fermentation time also requires good control during the fermentation process, and too long or too short fermentation time is not desirable.
Gao Aiqin et al. found that in the fermentation test of soybean meal feed, after the fermentation was carried out until the sixth day, the protein, cellulose and the like in the soybean meal had been degraded in a large amount, the substrate concentration decreased, and the hydrolysis rate became slow. At the same time, due to the non-starch polysaccharide Degraded to produce a large amount of acid, the normal growth and metabolism of microorganisms are also affected. Zhang Pei et al. used the rice husk powder for solid-state fermentation to produce protein feed. It was found that the protein content increased the most from the third day to the fourth day. On the fifth day, the protein content reached the maximum, and after the fifth day, the protein content decreased. This may be related to the phenomenon of autolysis in the decline of the species, and the consumption of nutrients may also inhibit the formation of proteins. Sun Lin et al. used the mixed strains to ferment rapeseed meal. The 24th to 48th hour of fermentation was the most active period of fermentation activity of mixed bacteria. After that, the anti-nutritional factors such as sulfur and tannin decreased gradually. .
In the fermentation process, the substrate feed in the early stage of fermentation contains sufficient nutrients for microbial fermentation, and the microorganisms can make full use of the nutrients provided, and the growth is vigorous. If the fermentation is terminated too early, the fermentation yield will decrease; When the fermentation time is too long, most of the nutrients in the fermentation system are consumed, so that the growth rate of the microorganisms tends to be slow, the microorganisms may also have autophagy, and the fermentation cost is also increased, so that the appropriate fermentation time is determined, and the high fermentation yield is achieved. Have an important role.
5 inoculum
In the fermentation process, the excessive inoculum of fermenting microorganisms may cause an increase in oxygen consumption, resulting in a relative shortage of oxygen supply, affecting the normal growth and metabolism of microorganisms, and also causing waste of materials. Too small an inoculum may slow the growth of microorganisms and reduce the fermentation efficiency.
Xu Yunhe and others used Bacillus subtilis to ferment soybean meal in a solid state, and the inoculum amount became larger, and the hydrolysis ability of the strain on the protein was also enhanced. In the study of mixed-stock solid-state fermented corn stover, Yan Hongshan found that the yield of the obtained fermentation product was the highest when the inoculum amount was 8%. In the experiment of using Aspergillus niger to ferment soybean meal, Yan Hesong found that the protein in the fermentation product gradually increased with the increase of inoculum, but the inoculum increased to 1%, and its protein yield became saturated.
Therefore, too small inoculum will prolong the fermentation cycle and reduce the fermentation efficiency; if the inoculum is too large, the excessive product produced may inhibit the normal growth and metabolism of microorganisms in the fermentation system, and the fermentation will end prematurely.
In addition to the above points, parameters for optimizing the fermentation process technology include many other influencing factors such as substrate feed size, fermentation strain ratio, bacterial density, and aeration. In the process of solid-state fermentation, the substrate feed has a small particle size, which can increase the contact area with the raw material, but the particle size is too small, prone to agglomeration, which is not conducive to heat transfer and affects the normal growth of microorganisms, so the substrate The size of the feed size may also affect the fermentation effect. In the study of solid-state fermentation of corn stalks by composite bacteria, Yan Hongshan found that the ratio between different strains and the ratio of raw materials in solid medium affected the fermentation products obtained. Kim et al. found that during liquid fermentation, the cell density increased with the increase of ventilation in the fermentation system. Zhang Pei et al. used the solid-state fermentation of rice hull powder to produce protein feed. It was found that the addition of urea increased the protein content in rice husk powder and had a significant effect on the fermentation results. In the solid-state fermentation test of soybean meal, Qiao Li found that adding proper amount of corn flour can improve the fermentation effect, which may be related to the growth and metabolism of microorganisms in corn flour-promoting fermentation system.
7 application prospects of fermented feed
As fermentation technology becomes more mature, fermentation will be more and more widely used in pig feed and rearing production practices. After the growth and fattening pigs were fed the fermented feed, the daily gain and daily feed intake increased. Zhao Zhengxing used fermented feed to feed the finishing pigs and found that the daily gain and feed compensation were improved, and the fermented feed had a significant effect on the improvement of pork quality. Wei Jintao and other fertilized feeds were used to feed the weaned piglets. It was found that the growth performance of the piglets was improved and the stress caused by weaning was relieved. A large number of experimental studies have shown that fermented feed has shown good results in actual pig production, especially in the feeding process of weaned and fattening pigs.
Although there are still some problems in the application of fermentation technology in feed production, the optimization of related processes still requires a lot of exploration, but the fermented feed has shown great development prospects. According to the key points of the fermentation process, a more detailed and effective fermentation process scheme can be established for different strains, substrate feeds and pigs of different growth stages. With the continuous development of science and technology, the fermentation technology continues to mature, the fermentation feed technology system will be more and more perfect, and this will definitely have great significance for the efficient and sustainable development of the pig industry.
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Source: Pig Industry Science; Author: Wang Jian, Cao Yunhe, Lu Wenqing, Wang Chunlin
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