Huang Xuewei, Zhang Huihua, Yu Peiqiang
Department of Animal and Poultry Science, College of Agriculture and Bioresources, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
College of Life Science and Engineering, Foshan University, Guangdong, China.
PLoS One. 2017 Feb 16;12(2):e0170173. doi: 10.1371/journal.pone.0170173. eCollection 2017.
The objectives of this study were: (1) To investigate the effects of conditioning temperature (70, 80, 90°C), time (30, 60 sec), and interaction (temperature × time) during the pelleting process on internal protein molecular structure changes of the co-products; (2) To identify differences in protein molecular structures among pellets that were processed under different conditions, and between unprocessed mash and pellets; 3) To quantify protein molecular structure changes in relation to predicted energy and protein utilization in dairy cows. The final goal of this program was to show how processing conditions changed internal feed structure on a molecular basis and how molecular structure changes induced by feed processing affected feed milk value in dairy cows. The hypothesis in this study was that processing-induced protein inherent structure changes affected energy and protein availability in dairy cattle and the sensitivity and response of protein internal structure to the different pelleting process conditions could be detected by advanced molecular spectroscopy. The protein molecular structures, amides I and II, amide I to II ratios, α-helix structure, β-sheet structure, and α to β structure ratios, were determined using the advanced vibrational molecular spectroscopy (ATR-FT/IR). The energy values were determined using NRC2001 summary approach in terms of total digestible nutrients, metabolizable and net energy for lactation. The protein and carbohydrate subfactions that are related to rumen degradation characteristics and rumen undegraded protein supply were determined using updated CNCPS system. The experiment design was a RCBD and the treatment design was a 3x2 factorial design. The results showed that pelleting induced changes in protein molecular structure. The sensitivity and response of protein inherent structure to the pelleting depended on the conditioning temperature and time. The protein molecular structure changes were correlated (P < 0.05) with energy values and protein subfractions of the pelleted co-product. The results indicated that the protein internal molecular structure had significant roles in determining energy and protein nutritive values in dairy cows. Multi-regression study with model variables selection showed that the energy and protein profiles in pelleted co-products could be predicted with the protein molecular structure profiles. This approach provides us a relatively new way to estimate protein value in dairy cows based on internal protein molecular structure profile.
（1）研究制粒过程中的调质温度（70、80、90°C）、时间（30、60秒）以及相互作用（温度×时间）对副产品内部蛋白质分子结构变化的影响；（2）确定在不同条件下加工的颗粒之间以及未加工的粉料与颗粒之间蛋白质分子结构的差异；（3）量化与奶牛预测能量和蛋白质利用率相关的蛋白质分子结构变化。该项目的最终目标是展示加工条件如何在分子基础上改变饲料内部结构，以及饲料加工引起的分子结构变化如何影响奶牛的饲料产奶价值。本研究的假设是，加工诱导的蛋白质固有结构变化影响奶牛的能量和蛋白质可利用性，并且可以通过先进的分子光谱检测蛋白质内部结构对不同制粒工艺条件的敏感性和响应。使用先进的振动分子光谱（ATR-FT/IR）测定蛋白质分子结构、酰胺I和II、酰胺I与II的比率、α-螺旋结构、β-折叠结构以及α与β结构的比率。能量值根据总可消化养分、泌乳代谢能和净能，采用NRC2001总结方法测定。使用更新的CNCPS系统测定与瘤胃降解特性和瘤胃未降解蛋白质供应相关的蛋白质和碳水化合物亚组分。试验设计为随机区组设计，处理设计为3×2析因设计。结果表明，制粒诱导了蛋白质分子结构的变化。蛋白质固有结构对制粒的敏感性和响应取决于调质温度和时间。蛋白质分子结构变化与制粒副产品的能量值和蛋白质亚组分相关（P<0.05）。结果表明，蛋白质内部分子结构在决定奶牛能量和蛋白质营养价值方面具有重要作用。通过模型变量选择的多元回归研究表明，可以根据蛋白质分子结构特征预测制粒副产品中的能量和蛋白质概况。这种方法为我们提供了一种基于蛋白质内部分子结构概况估计奶牛蛋白质价值的相对新方法。
