Proteolytic side activity of the lactase preparations (LPs) intended for ultra-high temperature hydrolyzed-lactose milk (UHLM) production induces changes in the product quality during shelf-life. The problem is particularly relevant when the enzyme is added aseptically in the packaging (“in pack” process), while the negative quality effects can be mitigated following the “in batch” process adding the LP before thermal sterilization. In this study, we monitored the quality over time of UHLM produced “in batch” and stored at 4, 20, 30 and 40 °C focusing on proteolysis, volatiles organic compounds (VOCs) formation and color changes. The goal was to identify the key reactions and compounds relevant for the product quality. An increase in storage temperature determined significant changes in the free amino acids profile increasing Strecker aldehydes and methyl ketones formation. At 30 and 40 °C, Maillard reaction and lipid oxidation ended up in a modification of the milk color, whereas at 4 and 20 °C no significant alteration was observed. Altogether, the results suggested a coordinate involvement of Maillard reaction, protein and lipid oxidation to milk browning and off-flavors formation in UHLM.

旨在用于超高温水解乳糖牛奶（UHLM）生产的乳糖酶制剂（LP）的蛋白水解副活性会导致货架期产品质量发生变化。当将酶以无菌方式添加到包装中时（“分装”过程），该问题尤为重要，而在热灭菌之前“分批”添加LP后，可以减轻负面的质量影响。在这项研究中，我们监测了“分批”生产的UHLM随时间推移的质量，并分别存储在4、20、30和40°C下，重点关注蛋白水解，挥发性有机化合物（VOC）的形成和颜色变化。目的是确定与产品质量有关的关键反应和化合物。储存温度的升高确定了游离氨基酸分布的显着变化，从而增加了Strecker醛和甲基酮的形成。在30和40°C时，美拉德反应和脂质氧化最终改变了乳色，而在4和20°C时未观察到显着变化。总之，结果表明UHLM中美拉德反应，蛋白质和脂质氧化与牛奶褐变和异味形成协调相关。