Xylanases account for the largest share of world enzyme sales (Bedford and Schulze, 1998), and their use allows high viscosity wheat to be added to poultry diets as feed ingredients without adverse effects. Perhaps due to its economic importance, the reports on the stability of xylanase in the scientific literature are much more reported than the reports on the stability of β-glucanase.
Xylanases can be produced by a variety of fungi and bacteria, and the optimal conditions for their enzyme activities vary, which is not surprising, as each organism has a specific adaptation environment. A review by Bedford and Schulze (1998) shows that many fungi and bacteria produce xylanases with an optimum temperature of 30 to 105 degrees Celsius and an optimum pH of 2.0 to 10. Pickford (1992) compared the stability of three commercial enzyme preparations without providing information on the enzyme activity type of the enzyme. The results showed that at the granulation temperature of 80 degrees Celsius, the activity of the first enzyme preparation retained 85%, the activity of the second enzyme preparation retained 55%, and the activity of the third enzyme preparation retained only 33%. At the granulation temperature of 95 degrees Celsius, the activity of all three enzyme preparations was lost. Extrusion at a short time and high temperature also caused a large loss of activity of the three enzyme preparations, and the difference in enzyme activity loss was similar to the above.
Studies by Pettersson and Rasmussen (1997) have shown that xylanases isolated from Thermomyces, Humicola and Trichoderma differ in thermal stability. The xylanase isolated from Trichoderma is significantly inactivated at 75 ° C. The xylanase isolated from the mold and the rot fungus retains 80% at 85 ° C. The above activity. Among them, the xylanase isolated from the high temperature mold retains more than 70% of the activity even at a temperature of 95 degrees Celsius. Gibson (1995) observed variations between nine xylanase preparations, seven of which were commercial enzyme preparation products at the start of the experiment. The results showed that after processing at 90 degrees Celsius, one of the enzyme preparations retained more than 90% of the enzyme activity, and the other seven retained enzyme activities were less than 10%. The report is not sufficient to show how much of the variation is due to the source of the enzyme, and how much is due to the stabilization of the enzyme. Perez-Vendrell et al. (1999a) determined the in vitro stability of eight commercial enzyme preparations (including smeared or coated products) after conditioning at 65-70 degrees Celsius, 75-80 degrees Celsius and 85-90 degrees Celsius. The results show that even at the lowest tempering temperature, the enzyme activity of most products is still lost at least 30%; at the highest tempering temperature, the enzyme activity can be lost by 90%. Esteve-Garcia et al. (1997) reported that, as found in the β-glucanase study, the enzyme activity of fine-grained xylanase preparations was not inactivated at quenching and granulating temperatures close to 80 °C. .
Several protection methods have been mentioned above that are protected from heat treatment. The most basic method of enzymatic protection is the method proposed by Pettersson and Rasmussen (1997) in its study to separate heat-producing enzymes from heat-resistant microorganisms. Another method of enzymatic protection is to spray the enzyme preparation on the feed pellets after granulation cooling, but this requires additional processing equipment and processing steps (Perez-Vendrell et al., 1999b).
The dried enzyme preparation product can also be stabilized to increase its thermal stability and can be added to the feed prior to granulation without significant loss of enzyme activity. The method of stabilization is the method mentioned above. The inactivation of the enzyme is caused by the steam used for quenching and tempering. Therefore, the stabilization of the enzyme preparation is mainly to protect the enzyme preparation from steam by adsorbing the enzyme preparation onto a carrier or by applying a hydrophobic substrate to the enzyme preparation (Cowan, 1996). Pickford (1992) provides an example of a stabilization treatment that increases the enzyme activity retained by the enzyme preparation after granulation at 75 degrees Celsius from 48% to 76%, increasing the enzyme activity retained after granulation at 95 degrees Celsius from 12% to 34%. Obviously, even enzymes that are stabilized are thermally stable. Steen (1999) suggested that if the feed is to be processed at temperatures above 90 degrees Celsius, even the enzymes that are stabilized should be added to the feed after processing.
In vitro enzyme activity assays are a valuable means of determining enzyme loss. The test results show that even a relatively low temperature can cause a significant loss of enzyme activity. However, in vitro testing is only one of them. Obviously, under the conditions of treatment and digestion of the feed, the activity of the enzyme preparation in the buffer at the optimum pH only provides very limited information on the enzyme activity. In fact, most researchers (Vukic-Vranjes et al., 1994; Pettersson and Rasmussen, 1997; Perez-Vendrell et al., 1999a; etc.) have recognized the importance of interaction between enzymes and feed, and have determined compound feeds. Enzyme activity. Determination of the viscosity of feed extracts (Spring et al., 1996; Bedford et al., 1997) provides an indicator of the effect of assessing enzyme activity prior to feed intake by poultry. Preston et al. (1999) confirmed the existence of this effect. The results show that even if the enzyme activity is completely lost in the final product of the feed, the supplemental enzyme preparation can significantly improve the performance of the poultry production.
In order to clarify the effect of feed processing on the enzyme, it is necessary to determine the enzyme addition effect and heat treatment effect in the feed through poultry production performance. Enzyme inactivation is not always directly reflected by differences in poultry production performance (Bedford et al, 1997; Perez-Vendrell et al, 1999a; Silversides and Bedford, 1999). Bedford et al. (1997) found that as the processing temperature increased from 65 degrees Celsius to 105 degrees Celsius, the percentage of enzyme inactivation changed linearly, while the performance of broilers (body weight gain, weight gain ratio) was 81 to 83 degrees Celsius. The processing temperature is optimized. Silversides and Bedford (1999) also confirmed this effect of heat treatment, as shown in Figure 15-1. As the processing temperature increased, the activity of the enzyme decreased linearly (R2 = 0.97), and the body weight of the broiler showed a quadratic curve (R2 = 0.84). Mapping the results of the weight gain ratio yielded similar results (R2 = 0.98). The maximum weight and the lowest weight gain ratio are obtained at processing temperatures between 80 and 85 degrees Celsius. There are two possibilities for producing such a result: one possibility is that the enzyme performs its function almost in the conditioner, so that the analytical value after granulation is irrelevant; the other may be the analytical method used. Enzyme activity cannot be measured efficiently.
The enzyme data obtained from the high temperature mildew coated with the protective layer and the enzyme data obtained from the uncoated protective layer of Trichoderma or Aspergillus do not appear to be of the same type, which may be due to the absence of the former between the enzyme and the feed matrix. Work. In this case, the enzyme is more easily extracted, and the correlation between the recovered enzyme activity and the poultry production performance is also confirmed (Cowan and Rasmussen, 1993; Pettersson and Rasmussen, 1997; Andersen and Dalboge, 1999). These contradictory results indicate that there is no single way to determine the performance of a poultry based on the analytical value of the feed sample if the properties of the enzyme are unknown.
Increasing the performance of poultry as a result of decreased enzyme activity in vitro indicates a risk of relying solely on enzyme activity assays, but may not be as contradictory as shown. In addition to affecting enzymes, heating affects many other aspects (Pickford, 1992). Moderate heating can promote the gelation of starch, accelerate the breakage of cell walls, improve the utilization of nutrients, and improve the performance of poultry. This is one of the basic reasons for granulating the feed. Higher processing temperatures also increase the solubility of non-starch polysaccharides, thereby increasing the viscosity of the intestinal contents of the poultry and reducing the performance of the poultry, which in turn increases the need for exogenous enzymes. Silversides and Bedford (1999) have shown that in the absence of exogenous xylanase in wheat basal diets, the viscosity of the intestinal contents of broilers increases significantly with increasing processing temperatures (Figure 15-2). When the xylanase is added to the diet, the viscosity of the intestinal contents of the broiler can be lowered even at a higher processing temperature, and the viscosity actually decreases at the highest temperature. At higher processing temperatures, the enzyme can still play a larger role, probably because the enzyme can get more substrate at this time. The enzyme may be active before or during processing, thereby reducing viscosity measurements in vitro and in vivo. Higher processing temperatures reduce the performance of poultry, not only due to increased viscosity of the intestinal contents and weakened effects of exogenous enzymes, but also due to inactivation of vitamins and other enzymes, as well as starch and protein digestibility. Decline. With the commercialization of heat-resistant or stabilized enzyme preparations, the destruction of vitamins and other nutrients by heating will also limit the processing temperatures used in production.
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The activity of the enzyme in solution may be reduced at temperatures below 60 degrees Celsius. The enzyme is somewhat protected by the feed ingredients in the mixed feed, and most of it may be very stable at slightly lower temperatures. However, at processing temperatures of up to 95 degrees Celsius, there is a serious loss of enzyme activity. In order to reduce the adverse effects of heat treatment, several methods have been employed or recommended, including protecting the enzyme from vapor infiltration, using heat resistant enzymes or adding liquid enzymes after processing. Feed enzymes may have some activity before the animal feeds the feed, so the total loss of enzyme activity in vitro may not always mean a total loss of benefit. This seems to depend in part on the enzyme and its analytical method. In some cases, in vitro analytical values ​​are misleading; in other cases, there is a significant correlation between enzyme content and animal performance. Since vitamins, proteins, and starches may be more sensitive to heat treatment than exogenous feed enzymes, increasing the processing temperature increases the damage to these nutrients, so the general processing temperature cannot be increased without limitation. The further development of heat-resistant enzymes and the role of enzymes in feed processing or before being eaten by animals may be a promising route for the feed industry to maximize the benefits by adding enzymes.
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