Introduction
In many countries around the world, enzymes are often added to the feed of monogastric animals. This is obviously due to the fact that the enzyme has a certain improvement effect on the production performance of monogastric animals, but it has not been easy to prove that there is an enzyme in the commercial feed, and many studies have been conducted so far. The enzyme is a protein that, like all other feed proteins, is very sensitive to feed processing. However, feed protein functions in units of amino acids, so there is no need to maintain the configuration, and the feed enzyme either undergoes irreversible denaturation during feed processing or does not function anymore. Therefore, it is necessary to detect the activity of the enzyme in the compound feed. The focus of this paper is not to discuss the existing methods for measuring enzyme activity, but to describe the characteristics of the enzymes used in the feed, including the differences between the enzymes of different sources on the thermal stability in vitro, and the analysis bands due to the interaction between the enzyme and the feed matrix. The problems that come (and the ways to eliminate this effect), the data on feed processing trials, and future trends.
Most pig and poultry feeds require a certain degree of processing. Some feeds need to be granulated. The process is to first temper the feed mixture through steam and then extrude it into granules by pressing. Granulation can increase the nutrient concentration of the feed, improve the storage characteristics of the feed, and reduce the microbial content of the feed. The granulation temperature is generally 65 to 90 degrees Celsius (Gibson, 1995), such high temperatures can destroy heat sensitive nutrients (including enzymes).
In the past few years, concerns about feed-derived pathogens and factors affecting granulation quality have prompted feed producers to increase the temperature, time and pressure of feed processing and to secondary granulation or puffing of feed (Pickford, 1992). . The enhanced processing of feed processing makes the stability of the enzyme more important. Several approaches have been taken to overcome this problem, including by adding liquid enzymes after the feed pellets have cooled to avoid the effects of processing together on enzyme activity. Although enzymes can be added after granulation, feed enzymes are generally added to the powdered feed prior to processing. The effect of heat treatment on the enzyme activity can be reduced by using a hydrophobic coating or by using a more heat resistant enzyme.
Research data on feed enzyme activity retention rates published to date are still limited (Chesson, 1993). However, the stability of the enzyme is extremely important to the feed manufacturer and it must be ensured that the enzyme is evaluated in the laboratory prior to the sale of the enzyme preparation. Since 1993, a number of research results have been reported in newspapers or conference proceedings. There are also several test results in the critical scientific literature. Obviously, in vitro determination of enzyme activity, whether in solution or in feed, is extremely important. Recent studies have shown that in vitro enzyme activity measurements must be verified by in vivo effects.
Phytase
Since phytase usage accounts for about 20% of the amount of commercial enzyme preparations, there are quite a few reports on the thermal stability of phytase (Bedford and Schulze, 1998). The reason for this concern may be that many plant-based feed ingredients contain phytic acid, which is difficult to absorb due to the presence of phytic acid (Cheryan, 1980; Eeckhout and dePaepe, 1994; Ravindran et al., 1995). . However, endogenous phytase deficiency activity or activity in monogastric animals is low (Pallauf and Rimbach, 1997). More complicated is that plants of the same phytic acid source also contain considerable amounts of phytase, and the nutritional problems of phosphorus digestion are intertwined with environmental pollution problems caused by the accumulation of phosphorus in the soil. Phosphorus pollution has become a limiting factor in the production of intensive livestock and poultry production areas.
Phytase has a wide range of sources and its properties vary. Liu et al. (1998) reviewed the literature before 1998. The results showed that the optimum activity temperature of phytase from bacteria, fungi, yeast and plants was 45-77 degrees Celsius, and the difference was as high as 32 degrees Celsius. Dvorakova et al. (1997) describe phytase properties isolated from Aspergillus niger. The phytase is active at a temperature range of 25-65 degrees Celsius, and its optimum temperature is 55 degrees Celsius; its incubation at 60 degrees Celsius for 10 minutes can reduce the initial activity by 5%, while at 80 degrees Celsius for 10 minutes. Initial activity lost 80%. As part of the search for thermostable enzymes, Wyss et al. (1998) studied the thermal denaturation of purified phytase isolated from A. fumigatus and A. nige. These two sources of phytase are denatured down to 55 degrees Celsius. However, when the temperature was raised to 90 degrees Celsius, the phytase from A. fumigatus was again folded into an active configuration, but the phytase from A. nige did not change. Certainly, certain heat-resistant phytase classes will be put into commercial use in the near future.
The inactivation of the enzyme in the solution does not indicate that the enzyme in the feed is also inactivated by heat, because the enzyme in the feed interacts with the feed matrix. In fact, feed ingredients protect enzymes from steam or high temperatures in a short period of time (Chesson, 1993). Determination of phytase activity in pelleted feeds provides more accurate data for the commercial evaluation of the extent of phytase inactivation in feed. Simons et al. (1990) added phytase to "general swine feed" which was heated to 50 degrees Celsius or 65 degrees Celsius prior to granulation. The results show that heating to 50 degrees Celsius makes the particle temperature reach 78 degrees Celsius or 81 degrees Celsius, which does not reduce the activity of the enzyme; but when heated to 65 degrees Celsius, the particle temperature reaches 84 degrees Celsius or 87 degrees Celsius, at which time the enzyme is Loss of activity was 17% or 54%. Gibson (1995) added three plant acidase preparations to the wheat basal diet and pelletized at 65-95 degrees Celsius. The results showed that two of the acidase preparations were inactivated at a granulation temperature of 65 degrees Celsius, leaving only one phytase preparation to retain a considerable amount of activity at a granulation temperature above 85 degrees Celsius. In addition to studying the stability of the enzyme in solution, Wyss et al. (1998) also added phytase isolated from Aspergillus fumigatus and Aspergillus niger to commercial feed prior to granulation (75 degrees Celsius or 85 degrees Celsius). The results showed that the activity of the two phytase enzymes in the pellet feed was similar at the granulation temperature of 75 ° C. However, when the granulation temperature was 85 ° C, the phytase activity from Aspergillus niger was higher than that from the smoke. Aspergillus phytase activity is lost more, which also supports their findings on denaturing kinetics. Eeckhout et al. (1995) added commercial phytase preparations to feeds and showed that phytase activity was lost by 50% to 65% at granulation temperatures of 69-74 °C.
Inactivation not only affects the action of microbial enzymes added to the feed, but also affects the action of naturally occurring enzymes in the feed ingredients. Gibson (1995) found that granulation at temperatures above 85 degrees Celsius would inactivate a large amount of endogenous investigative phytase activity in wheat. Eeckhout and dePaepe (1994) reported in a survey of phytase activity in different feeds that wheat bran is rich in phytase, but the phytase activity of the granulated samples is only 56% of the ungranulated samples. Jongbloed and Kemme (1990) found through three experiments that granulation at near 80 degrees Celsius reduced phytase activity in pig feed, which was formulated on feed ingredients rich in or lacking phytase activity. of. They further conducted experiments to determine the effect of granulation on the apparent absorption of phosphorus. In two of these experiments, they found that granulation of feeds rich in phytase reduced the rate of phosphorus uptake, which is consistent with the endogenous phytase inactivation.
Research institutions and the feed industry are concerned about the stability of phytase research due to the increasing processing temperatures currently used and the increasing absorption of phosphorus due to nutritional and environmental factors. The addition of envelopes or granules to exogenous enzymes provides a means of protecting enzymes from thermal damage. A more basic approach may be the separation of thermostable enzymes or reduction to the active configuration after enzymatic denaturation. It is also regrettable that none of these methods can prevent the destruction of endogenous enzymes contained in feed ingredients by high temperatures.
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