Broderick G A, Craig W M
J Nutr. 1980 Dec;110(12):2381-9. doi: 10.1093/jn/110.12.2381.
The effect of heat treatment of ruminal protein degradation and escape was studied using in vitro incubations with autoclaved and commercial cottonseed meal (CSM) samples. Incubations using high ratios of protein to ruminal fluid appeared to overestimate ruminal degradation of CSM protein relative to casein. A biexponential model, assuming CSM contained two protein fractions degraded at two different rates, was used to interpret data from in vitro incubations conducted using ratios of protein to ruminal fluid similar to those expected in vivo. The first fraction was degraded at rates (0.68-1.19/hour) which were 2--3 1/2 times greater than that of casein (0.34/hour). Degradation rates of the second fraction were much slower (0.011-0.093/hour). The effect of heat treatment was to decrease the proportion of the rapidly degraded fraction and to both increase the proportion and to decrease the degradation rate of the more slowly degraded fraction. Estimated ruminal escape increased with each increment of heat treatment. Intestinal protein digestibility (ruminal escape times true digestibility) increased to maximum at 60 minutes autoclaving, and then declined. Estimates of intestinal protein digestibility averaged 30.6 and 50.3% for solvent-extracted and screw-press CSM, respectively. These and previous results suggest heat treatment decreases ruminal degradation partly by blocking reactive sites for microbial proteolytic enzymes and partly by reducing protein solubility.
采用体外培养法，使用经高压灭菌的和市售的棉籽粕（CSM）样品，研究热处理对瘤胃蛋白质降解和逃逸的影响。相对于酪蛋白，使用高蛋白与瘤胃液比例的培养方法似乎高估了CSM蛋白质的瘤胃降解率。采用双指数模型（假设CSM含有以两种不同速率降解的两个蛋白质组分）来解释使用类似于体内预期的蛋白质与瘤胃液比例进行的体外培养数据。第一组分的降解速率（0.68 - 1.19/小时）比酪蛋白（0.34/小时）的降解速率高2 - 3.5倍。第二组分的降解速率则慢得多（0.011 - 0.093/小时）。热处理的效果是降低快速降解组分的比例，同时增加较慢降解组分的比例并降低其降解速率。估计瘤胃逃逸率随热处理程度的增加而增加。肠道蛋白质消化率（瘤胃逃逸率乘以真消化率）在高压灭菌60分钟时增加到最大值，然后下降。溶剂萃取CSM和螺旋压榨CSM的肠道蛋白质消化率估计平均值分别为30.6%和50.3%。这些结果以及之前的结果表明，热处理部分通过阻断微生物蛋白水解酶的反应位点，部分通过降低蛋白质溶解度来减少瘤胃降解。
