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Assessing and selecting feed enzymes involves many factors and is more complex than ordinary industrial enzymes. General industrial enzymes, such as amylase and saccharification, have relatively fixed pH values, temperature, substrates, and reaction times, and have clear enzyme components. However, for feed enzymes, due to the diversity of feed raw materials, processing requirements, and animal digestive tract pH, there are many and complex factors to consider.
Phytase enzyme A has a peak value at pH 5.5, while its activity is low under other pH conditions. It has no activity after the pH value drops below 3.5. However, Phytase enzyme B not only has a peak value at pH 5.5, but also has a peak value at pH 2.5. Its range of action is much broader than that of Phytase A, and its use effect is better than A's. Obviously, to achieve the same effect, the amount of Phytase enzyme A must be higher than that of B.
Xylanase is the second largest feed enzyme, and there is more research on it. Relatively speaking, the structure of xylanase is more complex than that of phytase enzyme, and there are more influencing factors. Xylanase mainly has two types: papermaking xylanase and feed xylanase. The substrate for the determination of papermaking xylanase is birch xylan, while the substrate for the determination of feed xylanase is oat xylan. Therefore, it is more reasonable to choose Xylanase A as the feed enzyme.
The acid stability of animal feed enzymes is also an indicator of assessing the quality of feed enzymes. When using two feed xylanases for animal feeding tests, one is black Aspergillus fermentation product and the other is rice Aspergillus fermentation product. When used in piglet and cattle feed, the effect of black Aspergillus fermentation product is better than that of rice Aspergillus fermentation product. However, it was found that rice Aspergillus fermentation product was better than black Aspergillus fermentation product when added to growing pig feed. In the stomach acid environment of growing pigs, the activity loss of black Aspergillus fermentation product is larger, and the enzyme activity is retained very little after entering the intestine. However, the enzyme activity loss of rice Aspergillus fermentation product is less, and the time and segment of its effectiveness are much larger.
Currently, almost all companies producing feed enzymes by liquid fermentation advertise that liquid fermentation products are better than solid fermentation products, and many researchers in animal nutrition research also support this view. In fact, this argument is very one-sided. Solid-state fermentation production exists in developing countries such as China, India, Brazil, and is highly valued in some developed countries such as Japan and the Netherlands (mainly because of low energy consumption and less pollution) . The quality of solid fermentation products is also good. Feed raw materials contain many non-starch polysaccharides, and breaking down these non-starch polysaccharides requires the joint cooperation of one or more enzyme systems. The non-starch polysaccharide enzymes produced by solid-state fermentation usually contain multiple subunits or even multiple enzyme systems. The substrate for solid-state fermentation is basically agricultural and sideline products (mainly wheat bran), and the inducibility of the substrate makes the enzyme system produced by fermentation more targeted. Under the condition that enzyme activity test values are equal, the effect of the enzyme produced by solid-state fermentation production in feed is often more significant than that of the enzyme produced by liquid-state fermentation production.
Heat resistance and stability need to consider two situations, one is the heat resistance of dry matter, and the other is the stability in aqueous solution (or high humidity conditions). Some reports say that certain feed enzymes have good heat resistance and can withstand high-temperature granulation of feed without losing activity. This argument is not comprehensive. Some enzymes have good stability under dry matter conditions, but they will quickly lose activity in high-temperature aqueous solutions (or materials with high water content). Testing a xylanase, under the condition of dry powder (water content not exceeding 10.0%), keeping it at 105℃ for 2 hours, the enzyme activity loss should not exceed 10.0%; but at 80℃ in aqueous solution, the enzyme activity loss exceeds 40.0% after keeping it for 5 minutes. Further experiments found that the vitality loss of this xylanase in the high-temperature granulation process of feed (85-90℃) usually exceeds 24.0%. Of course, if high-temperature granulation is not considered, it is recommended to prioritize the selection of powdery feed enzymes that are relatively inexpensive and have higher activity.
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