Milk is a source of antimicrobial systems such as xanthine oxidoreductase, which has been proposed to modulate the oral and gut microbiota of infants. Heat treatments are applied to milk to ensure its microbial safety, however, the effects of heat on this antimicrobial enzyme are not known. The effects of batch pasteurization (BP), high-temperature short time (HTST), and ultra high temperature (UHT) on kinetics of inactivation of xanthine oxidase and its antimicrobial properties were determined. Xanthine oxidase activity was preserved by HTST (100%). Partial (8%) and nearly complete (95%) enzyme inactivation were observed for BP and UHT milks, respectively. K_m values of 100 μM and V_max values of 6.85, 5.12, 6.31, and 0.40 μmol/min/mg were determined for xanthine oxidase in raw, BP, HTST, and UHT milks, respectively. These results demonstrate that xanthine oxidase maintains apparent affinity and activity for its substrate when milk is treated by BP and HTST and yet the enzyme is inactivated with UHT. To investigate heat treatment-induced alterations in the biological activity of xanthine oxidase, heat treated milks were compared to raw milk for their ability to inhibit the growth of S. aureus. Raw, BP, and HTST milk xanthine oxidase efficiently inhibited S. aureus growth. However, these antibacterial properties were lost when milk was subjected to UHT. These results demonstrate that HTST and BP preserves bovine milk xanthine oxidase activity compared with UHT and that, the judicious selection of thermal treatments could be exploited to preserve the antimicrobial properties of bovine milk.

牛奶是抗微生物系统的来源，例如黄嘌呤氧化还原酶，已被提议用来调节婴儿的口腔和肠道菌群。对牛奶进行热处理以确保其微生物安全性，但是，加热对这种抗微生物酶的影响尚不清楚。确定了分批巴氏灭菌（BP），高温短时间（HTST）和超高温（UHT）对黄嘌呤氧化酶失活动力学及其抗菌性能的影响。黄嘌呤氧化酶活性被HTST（100％）保留。对于BP和UHT牛奶，分别观察到部分（8％）和几乎完全（95％）的酶失活。K _m值为100μM和V _max测定原奶，BP，HTST和UHT牛奶中的黄嘌呤氧化酶的值分别为6.85、5.12、6.31和0.40μmol/ min / mg。这些结果表明，当用BP和HTST处理牛奶时，黄嘌呤氧化酶对其底物保持明显的亲和力和活性，而UHT使该酶失活。为了研究热处理引起的黄嘌呤氧化酶生物学活性的变化，将热处理过的牛奶与生牛奶的抑制金黄色葡萄球菌生长的能力进行了比较。原料，BP和HTST牛奶黄嘌呤氧化酶可有效抑制金黄色葡萄球菌生长。但是，当牛奶经过超高温灭菌后，这些抗菌性能便丧失了。这些结果表明，与UHT相比，HTST和BP保留了牛乳黄嘌呤氧化酶的活性，可以明智地选择热处理方法来保留牛乳的抗菌性能。