牛乳中之乳脂肪球係外圍生物膜包覆中心之三酸甘油酯所構成，而此生物膜則稱為乳脂肪球膜 (milk fat globule membrane; MFGM)，蛋白質約佔膜總組成份之70%，其中某些蛋白質對於乳脂肪球之分泌與穩定極為重要。然而，牛乳加工過程中之均質處理會明顯改變乳脂肪球膜之構成，而酪蛋白 (casein) 與乳清蛋白 (whey protein) 會成為新的乳脂肪球膜主要成分。本研究之目的在於探討生乳、 HTST 鮮乳以及均質 HTST 鮮乳進行體外模擬腸道或胃腸道消化，於胰蛋白?存在與否之條件下檢測胰解脂?對乳脂肪之水解情形。體外模擬腸道消化試驗結果指出，不論胰蛋白?存在與否，均質 HTST 鮮乳所釋出之游離脂肪酸濃度均高於生乳及 HTST 鮮乳，但模擬胃腸道消化結果則無顯著差異。體外胃腸道消化試驗中，經胃蛋白?消化後之生乳、HTST 鮮乳以及均質 HTST 鮮乳於解脂作用前期之乳脂水解率均會提高，再添加胰蛋白?則無法更進一步提高乳脂消化前期脂水解率。於含有胰蛋白?之體外腸道消化試驗中，HTST 之鮮乳和均質 HTST 鮮乳於解脂作用前期之乳脂水解率高於無蛋白?處理之組別。綜上所述，胃腸之蛋白?於體外乳脂肪消化過程中扮演一輔助角色，可提高牛乳脂肪於消化初期之水解率。 Milk fat globules are composed of a triglyceride core and a natural biological membrane, milk fat globule membrane (MFGM). Proteins account for 70% of MFGM. Certain of those proteins are important for the secretion and structural stability of milk fat globule. However, composition of MFGM is restructured after homogenization, and the newly formed membrane mainly consists of caseins and whey proteins. The aim of this study was to examine the lipolysis of milk fat in raw milk, HTST milk, and homogenized HTST milk by pancreatic lipase during in vitro intestinal and gastrointestinal digestion, with and without the presence of trypsin. The results of in vitro intestinal digestion indicated that whether presence trypsin or not, homogenized HTST milk showed higher level of free fatty acids release than raw milk and HTST milk. Releasable free fatty acids were not significantly different among raw milk, HTST milk, and homogenized HTST milk on gastrointestinal digestion. During in vitro gastrointestinal digestion, the hydrolysis rate of milk fat in raw milk, HTST milk, and homogenized HTST milk increased on early stage of lipolysis after pepsin digestion. However, trypsin treatment could not further increase milk fat hydrolysis rate on gastrointestinal digestion early stage of lipolysis. Homogenized HTST milk and HTST milk fat hydrolysis rate on early stage of trypsin presence in vitro intestinal digestion were higher than trypsin absence in vitro intestinal digestion. In conclusion, gastrointestinal proteases play a coordinative role to increase fresh milk fat hydrolysis on early stage of in vitro digestion.
