Qiao Y, Lin X, Odle J, Whittaker A, van Kempen T A T G
Department of Animal Science, North Carolina State University, Raleigh 27695, USA.
J Anim Sci. 2004 Jun;82(6):1669-77. doi: 10.2527/2004.8261669x.
Typically, in vitro methods used for estimating the amount of ileal digestible AA do not exhaustively digest samples, and arbitrary methods for separating digestible from indigestible protein are used. This may lead to over- or underestimation of digestibility coefficients. A method that exhaustively digests proteins using pepsin and pancreatin was developed, and the first objective of this research was to confirm that exhaustive digestion was indeed appropriate and to determine the fractionation method for separating digestible from indigestible proteins. For this, three homoarginine-labeled animal proteins were prepared. Samples were subsequently digested in vivo and in vitro to determine which fraction should be considered indigestible, and in vitro followed by in vivo to determine whether the extent of digestion in vivo was improved by predigestion. In vivo, soluble but unabsorbed peptides were smaller than 1 kDa, suggesting that the size of soluble peptides is not what prevents their absorption. Thus, all in vitro-soluble proteins should be considered digestible. In vitro, 88 +/- 3% of the soluble peptides were smaller than 1 kDa, with the remainder between 1 and 5 kDa, suggesting that in vitro digestion is less complete. Predigested samples were digested in vivo to the same size distribution as the nonpredigested samples. The second objective was to test whether in vitro digestibility assays based on these principles equaled in vivo digestibility. For this, digestibility data for 25 animal proteins were compared. Results showed a lack of correlation between lysine digestibility coefficients; however, across samples, the extent of digestion did not differ for lysine (P = 0.71), threonine (P = 0.26), methionine (P = 0.18), or valine (P = 0.66), whereas in vitro digestibility coefficients were lower for (the less water-soluble) histidine (P = 0.05), isoleucine (P < 0.01), leucine (P < 0.01), and phenylalanine (P = 0.05). In conclusion, in vitro digestibility assays should exhaustively digest proteins to mimic in vivo digestibility. All in vitro-soluble peptides could be considered digestible, because in vivo, no large soluble peptides were observed whose size prevented them from being absorbed. However, an in vitro assay based on these principles lacked precision for highly water-soluble AA, and underestimated digestibility for other AA. Better solubilization of the digesta and more replicates may improve the in vitro assay further.
通常，用于估计回肠可消化氨基酸量的体外方法并不能完全消化样品，而是采用任意方法将可消化蛋白质与不可消化蛋白质分离。这可能导致消化率系数的高估或低估。本研究开发了一种使用胃蛋白酶和胰酶完全消化蛋白质的方法，该研究的首要目标是确认完全消化确实合适，并确定将可消化蛋白质与不可消化蛋白质分离的分级方法。为此，制备了三种高精氨酸标记的动物蛋白。随后将样品在体内和体外进行消化，以确定应将哪一部分视为不可消化的，并先在体外后在体内进行消化，以确定预消化是否能提高体内的消化程度。在体内，可溶性但未吸收的肽小于1 kDa，这表明可溶性肽的大小并非阻碍其吸收的因素。因此，所有体外可溶的蛋白质都应被视为可消化的。在体外，88±3%的可溶性肽小于1 kDa，其余介于1至5 kDa之间，这表明体外消化并不完全。预消化样品在体内消化后的大小分布与未预消化样品相同。第二个目标是测试基于这些原理的体外消化率测定是否等同于体内消化率。为此，比较了25种动物蛋白的消化率数据。结果显示赖氨酸消化率系数之间缺乏相关性；然而，在所有样品中，赖氨酸（P = 0.71）、苏氨酸（P = 0.26）、蛋氨酸（P = 0.18）或缬氨酸（P = 0.66）的消化程度没有差异，而对于（水溶性较低的）组氨酸（P = 0.05）、异亮氨酸（P < 0.01）、亮氨酸（P < 0.01）和苯丙氨酸（P = 0.05），体外消化率系数较低。总之，体外消化率测定应完全消化蛋白质以模拟体内消化率。所有体外可溶的肽都可被视为可消化的，因为在体内未观察到因大小而阻碍吸收的大的可溶性肽。然而，基于这些原理的体外测定对于高水溶性氨基酸缺乏精确性，并且低估了其他氨基酸的消化率。更好地溶解消化物并增加重复次数可能会进一步改进体外测定。
