Craig W M, Broderick G A
J Anim Sci. 1981 Feb;52(2):292-301. doi: 10.2527/jas1981.522292x.
Effects of heating cottonseed meal (CSM) protein were quantitatively assessed by determination of true digestibility (TD), in vitro proteolysis, N solubility and fluorodinitrobenzene (FDNB) available lysine. Flaked, dehulled cottonseed was extracted with hexane and desolventized at 25 C, then autoclaved (121 C, 1.1 kg/cm(2)) for 0, 15, 30, 60, 90 or 120 minutes. Free gossypol was subsequently extracted, and TD was determined in weanling rats. Metabolic fecal N (the fecal N excreted by rats fed a basal diet containing 4% casein protein) was 1.84 +/- .10 mg N/g dry matter intake. TD and FDNB-available lysine (percentage of total) were 91 and 89%, respectively, in the unheated meal. TD and FDNB-available lysine were reduced to 84 and 78% after 60 min of autoclaving, and to 71 and 44% after 120 min of autoclaving. The effect of heat treatment on TD was described by the equation: % TD = 100 - 9.28e(.0096t) (r = .998), where t = minutes of autoclaving. This indicated an accelerated decline in TD as heating time increased. No more than 40% of the loss in FDNB-available lysine was attributable to gossypol binding. In vitro release of total amino acids from autoclaved CSM samples during pepsin-pancreatin incubations was highly correlated to TD (r = .996), but N solubility in .02 N NaOH was poorly correlated to TD. In samples of solvent-extracted and screw-pressed CSM, TD (estimated from pepsin-pancreatin incubations) ranged from 80 to 85% and FDNB-available lysine ranged from 73 to 85%, and both were only slightly lower in screw-pressed than in solvent-extracted meals. Intake of FDNB-available lysine was correlated (r = .902) to weight gain in rats fed diets containing the CSM that were more severely autoclaved. Results suggest that heat treatment must be more severe than that which normally occurs in commercial CSM processing to cause substantial, selective loss in lysine availability.
通过测定真消化率（TD）、体外蛋白水解、氮溶解度和氟二硝基苯（FDNB）可利用赖氨酸，对加热棉籽粕（CSM）蛋白的效果进行了定量评估。将轧片、脱壳棉籽用己烷萃取并在25℃脱溶，然后在121℃、1.1kg/cm²条件下高压灭菌0、15、30、60、90或120分钟。随后提取游离棉酚，并在断奶大鼠中测定TD。代谢粪氮（饲喂含4%酪蛋白的基础日粮的大鼠排出的粪氮）为1.84±0.10mg氮/克干物质摄入量。未加热粕中TD和FDNB可利用赖氨酸（占总量的百分比）分别为91%和89%。高压灭菌60分钟后，TD和FDNB可利用赖氨酸分别降至84%和78%，高压灭菌120分钟后降至71%和44%。热处理对TD的影响可用以下方程描述：%TD = 100 - 9.28e(0.0096t)（r = 0.998），其中t为高压灭菌分钟数。这表明随着加热时间增加，TD加速下降。FDNB可利用赖氨酸损失中不超过40%归因于棉酚结合。在胃蛋白酶-胰蛋白酶孵育过程中，高压灭菌CSM样品中总氨基酸的体外释放与TD高度相关（r = 0.996），但在0.02N NaOH中的氮溶解度与TD相关性较差。在溶剂萃取和螺旋压榨CSM样品中，TD（根据胃蛋白酶-胰蛋白酶孵育估算）范围为80%至85%，FDNB可利用赖氨酸范围为73%至85%，螺旋压榨粕中的两者仅略低于溶剂萃取粕。在饲喂经更严重高压灭菌的含CSM日粮的大鼠中，FDNB可利用赖氨酸摄入量与体重增加相关（r = 0.902）。结果表明，热处理必须比商业CSM加工中通常发生的更剧烈，才能导致赖氨酸有效性出现显著的选择性损失。
