Luo Jie, Jiang Chenbo, Zhao Liang, Zhang Ming, Wang Fang, Sun Erna, Ren Fazheng
Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China; College of Chemistry and Biological Engineering, Changsha University of Science and Technology, Changsha 410114, China.
Key Laboratory of Functional Dairy, Co-constructed by Ministry of Education and Beijing Government, China Agricultural University, Beijing 100083, China.
J Dairy Sci. 2018 Nov;101(11):9725-9735. doi: 10.3168/jds.2018-14760. Epub 2018 Sep 7.
3-Methylbutanal is one of the primary substances that contribute to the nutty flavor in cheese. Lactococcus strains have been shown to have higher aminotransferase and α-keto acid decarboxylase activities compared with other microbes, indicating that they might form a higher amount of 3-methylbutanal by decarboxylation. Several dairy lactococcal strains have been successfully applied as adjunct cultures to increase the 3-methylbutanal content of cheese. Moreover, compared with dairy cultures, the nondairy lactococci are generally metabolically more diverse with more active AA-converting enzymes. Therefore, it might be appropriate to use nondairy lactococcal strains as adjunct cultures to enrich the 3-methylbutanal content of cheese. This study thereby aimed to select a nondairy Lactococcus strain that is highly productive of 3-methylbutanal, identify its biosynthetic pathway, and apply it to cheese manufacture. Twenty wild nondairy lactococci isolated from 5 kinds of Chinese traditional fermented products were identified using 16S rRNA sequence analysis and were found to belong to Lactococcus lactis ssp. lactis. The nondairy strains were then screened in vitro for their production of 3-methylbutanal and whether they met the criteria to become an adjunct culture for cheese. The L. lactis ssp. lactis F9, isolated from sour bamboo shoot, was selected because of its higher 3-methylbutanal production, suitable autolysis rate, and lower acid production. The enzymes involved in the catabolic pathway of leucine were then evaluated. Both α-keto acid decarboxylase (6.96 μmol/g per minute) and α-keto acid dehydrogenase (30.06 μmol/g per minute) activities were detected in nondairy L. lactis F9. Cheddar cheeses made with different F9 levels were ripened at 13°C and analyzed after 90 d by a combination of instrumental and sensory methods. The results showed that adding nondairy L. lactis F9 significantly increased 3-methylbutanal content and enhanced the nutty flavor of the cheese without impairing its textural properties. Thus, nondairy L. lactis F9 efficiently enhanced the biosynthesis of 3-methylbutanal in vitro and in manufactured cheese.
3-甲基丁醛是构成奶酪坚果风味的主要物质之一。与其他微生物相比，乳球菌菌株已被证明具有更高的转氨酶和α-酮酸脱羧酶活性，这表明它们可能通过脱羧作用形成更多量的3-甲基丁醛。几种乳制品乳球菌菌株已成功用作辅助培养物，以增加奶酪中3-甲基丁醛的含量。此外，与乳制品培养物相比，非乳制品乳球菌通常在代谢上更加多样化，具有更活跃的氨基酸转化酶。因此，使用非乳制品乳球菌菌株作为辅助培养物来增加奶酪中3-甲基丁醛的含量可能是合适的。本研究旨在筛选出高产3-甲基丁醛的非乳制品乳球菌菌株，确定其生物合成途径，并将其应用于奶酪生产。通过16S rRNA序列分析对从5种中国传统发酵产品中分离出的20株野生非乳制品乳球菌进行了鉴定，发现它们属于乳酸乳球菌乳酸亚种。然后在体外筛选这些非乳制品菌株的3-甲基丁醛产量以及它们是否符合成为奶酪辅助培养物的标准。从酸笋中分离出的乳酸乳球菌乳酸亚种F9因其较高的3-甲基丁醛产量、合适的自溶速率和较低的产酸量而被选中。然后评估了参与亮氨酸分解代谢途径的酶。在非乳制品乳酸乳球菌F9中检测到了α-酮酸脱羧酶（6.96微摩尔/克每分钟）和α-酮酸脱氢酶（30.06微摩尔/克每分钟）的活性。用不同水平的F9制作的切达干酪在13°C下成熟，并在90天后通过仪器分析和感官方法相结合进行分析。结果表明，添加非乳制品乳酸乳球菌F9显著增加了3-甲基丁醛的含量，并增强了奶酪的坚果风味，同时不影响其质地特性。因此，非乳制品乳酸乳球菌F9在体外和制成的奶酪中均有效地增强了3-甲基丁醛的生物合成。
