热处理对生鲜乳及复原乳蛋白质体外消化特性的影响

通过体外模拟消化的方法对不同热处理的牛乳样品进行检测,研究热处理对鲜牛乳及复原乳营养价值的影响。通过聚丙烯酰氨凝胶电泳、尺寸排阻高效液相色谱、扫描电镜及质谱分析等多种方法进行检测。结果表明:经过胃液消化后,牛乳中的部分蛋白被消化,其中酪蛋白消化最为明显,鲜牛乳中酪蛋白在胃液中的消化水平高于其他热处理样品;而经过肠液消化后,牛乳中蛋白消化完全,生成游离氨基酸及小肽。乳中蛋白质经消化主要生成分子质量低于1 500 Da的肽段,易于人体消化吸收。通过扫描电镜可以看出,热处理程度越大,乳蛋白变性,发生聚集现象,粒径增大,其中加热复原乳的粒径较其他乳制品大;通过质谱检测及高效液相色谱分析,热处理程度越大,蛋白质美拉德反应程度升高。

Effect of Heat Treatment on in Vitro Digestibility of Raw and Reconstituted Milk Protein

The effect of heat treatment on the nutritional value of fresh raw milk and reconstituted milk were studied by in vitro simulated digestion method. The treated samples were detected by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), size exclusion high performance liquid chromatography, scanning electron microscopy and mass spectrometry. The results showed that some milk proteins were broken down during simulated gastric digestion, and casein showed the highest degree of breakdown. The level of digestion of casein in fresh milk by the gastric juice was higher than that of other heat-treated samples. After digestion with the intestinal juice, milk proteins were completely broken down into free amino acids and small peptides, and the digestibility of fresh milk was higher than that of other heat-treated samples. Milk proteins were mainly digested into peptides with molecular weight of less than 1 500 Da, which can be easily absorbed by the body. It was observed by scanning electron microscopy (SEM) that heat treatment induced denaturation and aggregation of milk proteins and that the particle size of reconstituted milk was larger than that of other milk samples with increasing heating temperature. Analysis by mass spectrometry (MS) and high performance liquid chromatography (HPLC) revealed that greater degree of heat treatment resulted in higher reaction degree in Maillard reaction.