从新疆传统发酵乳中筛选出具有蛋白水解活性的酵母菌，对其发酵乳进行蛋白水解和体外自由基清除活力测定；并与商业酸奶发酵剂（保加利亚乳杆菌CICC6047和嗜热链球菌CICC6038）复配，研究其在发酵以及冷藏过程中发酵剂活力、蛋白水解、质构变化、酸化能力和体外自由基清除活力的影响。结果发现，菌株0807-39具有较高的蛋白水解活性，亮氨酸含量达到0.34 mg/mL，显著高于其他菌株（P<0.05）；其发酵乳具有较高的ABTS和DPPH自由基清除率，分别为68.13%和74.24%；菌株0807-39不产生有害生物胺，对抗生素耐药敏感，且不具备溶血性，是安全性菌株；经过26S rDNA测序，鉴定为马克思克鲁维酵母菌（K. marxianus DPUL-F15）。K. marxianus DPUL-F15增加了发酵过程中乳酸菌活菌数量、乳蛋白的水解；在冷藏过程中，K. marxianus DPUL-F15显著促进发酵乳中α-酪蛋白和β-酪蛋白的降解（P<0.05），分别降低了0.24 mg/mL和1.23 mg/mL；发酵乳中游离氨基酸的含量增加了0.1 mg/mL；加速了发酵乳后酸化，冷藏21 d时酸度达到120.56 T°；冷藏14 d时，有最高ABTS和DPPH自由基清除活性，分别为68.87%和71.1%；同时对质构特性有一定影响。因此，K. marxianus DPUL-F15具有作为一株附属发酵剂的潜力，提高发酵乳的蛋白水解。

A yeast strain with proteolytic activity was screened from traditional fermented milk from Xinjiang and its proteolytic activity and in vitro free radical scavenging activity determined before combination with the commercial yogurt starter (Lactobacillus delbrueckii subsp. bulgaricus. CICC6047 and Streptococcus thermophilus CICC6038) for study of the starter activity, proteolysis, texture change, acidification ability, and in vitro free radical scavenging activity during fermentation and cold storage. The results showed the highest proteolytic activity for strain 0807-39, which had a significantly higher leucine content than other strains at 0.34 mg/mL (P<0.05), with free radical scavenging rates of 68.13% and 74.24% obtained for ABTS and DPPH, respectively. Strain 0807-39, which was not associated with any harmful biogenic amines, was found sensitive to antibiotic resistance and did not show hemolysis, indicating that the strain is safe. Identification by 26S rDNA sequencing indicated the strain as K. marxianus, and it was found to promote the number of live lactic acid bacteria and increase the hydrolysis of milk protein during fermentation. During cold storage, K. marxianus DPUL-F15 significantly promoted the degradation of α-casein and β-casein in fermented milk (P<0.05), which decreased by 0.24 mg/mL and 1.23 mg/mL respectively. The content of free amino acids in the fermented milk increased by 0.1 mg/mL. The post-acidification of fermented milk was accelerated, with acidity reaching 120.56 T° after 21 days in storage, and the highest scavenging activities of 68.87% and 71.1% were observed for ABTS and DPPH free radicals, respectively, after 14 days in cold storage. The strain was also found to influence the texture characteristics. The results indicate that K. marxianus DPUL-F15 has the potential to be used as an auxiliary starter that can improve proteolysis in fermented milk.

兵团重大科技项目（2018AA009-02）