黃嘌呤氧化? (xanthine oxidase々XO) 普遍存在於牛乳中，於牛乳中主要存在於乳脂肪球膜 (milk fat globule membrane々MFGM) 內，其活性會因加工過程之處理程序而有所改變。本研究旨在探討生乳均質化 (homogenization) 以及不同程度熱處理之乳油 (cream) 於標準化 (standardization) 後經HTST (high temperature short time) 熱殺菌處理其乳中黃嘌呤氧化?活性變化情形。藉由硫酸銨分離純化出牛乳中黃嘌呤氧化?，再經光電比色儀偵測單位時間內黃嘌呤被轉換為尿酸含量，以作為黃嘌呤氧化?活性之高低。結果顯示，均質生乳與無均質組無顯著差異，脫脂乳與乳油以低階HTST (72℃, 15sec) 處理其尿酸生成量顯著低於其他熱處理組 (P<0.05) 。當乳油經低階或高階HTST (89℃, 15sec) 處理後回填至脫脂生乳標準化之結果，均質組之尿酸生成量會高於無均質組，且高階HTST處理組會高於低階HTST組 (P<0.05) 。綜上所述，將乳油分離後以低階HTST或UHT熱處理後回填至脫脂生乳中，經標準化後，均質或不均質再經HTST處理製成鮮乳其黃嘌呤氧化活性可降至最低，惟仍無法完全使其完全失活。然而，本研究可供業界欲製造低黃嘌呤氧化?活性牛乳且不大幅變動其生產線流程之參考。 Xanthine oxidase (XOase) is one of components of milk fat globule membrane (MFGM) which presents in bovine milk. The enzyme activity of XOase varies with thermal intensity under dairy processing. The aims of this study were to observe the effect of homogenized treatment on XOase activity in raw bovine milk, and followd by the variation of XOase activity in HTST standardized-milk which composed of raw skim milk and different heat-treated cream. The XOase was purified from bovine milk through ammonium sulphate fractionation and the enzyme activity was detected by UV-spectrophotometer at 285 nm wavelength in measuring uric acid formation. The results showed that whether raw milk was treated with homogenization or not, there was no difference in XOase activity. As for HTST standardized-milk, low-level HTST (72℃, 15sec) treated cream samples had the lowest formation of uric acid catalyzed by XOase (p<0.05). Furthermore, XOase activity was significant increase in HTST standardized-milk underwent homogenized processing as compared with un-homogenized treatment (p<0.05). Under homogenized HTST standardized-milk, the activity of XOase was higher in high-level HTST (89℃, 15sec) treated cream than in low-level HTST treated cream samples (p<0.05). In conclusion, based on this study, we recommended that separating cream was subject to low-level HTST thermal treatment alone, and then mixed with skim milk to bring out standardized-milk, then went through homogenization or better not to homogenized before HTST pasteurization further to produce low XOase activity milk. This work flow could be availably introduced to dairy industry under slightly alteration in existing dairy production line.
