Liang Jiahui, Yoo Michelle Ji Yeon, Seale Brent, Grazioli Gianpaolo
School of Science, Faculty of Health and Environment Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand.
Giapo Research Kitchen, 12 Gore Street, Auckland CBD, Auckland 1010, New Zealand.
Foods. 2021 Nov 30;10(12):2944. doi: 10.3390/foods10122944.
In this study, thermo-tolerant strain of () was developed using gradual increase in temperature to induce Adaptive Laboratory Evolution (ALE). Viable colony count of 1.87 ± 0.98 log cfu/mL was achieved at 52 °C, using MRS agar supplemented with 2% lactose. Changes in bacteria morphology were discovered, from rod (control) to filament (52 °C) to cocci after frozen storage (-80 °C). When milk was inoculated with thermo-tolerant , lactic acid production was absent, leaving pH at 6.84 ± 0.13. This has caused weakening of the protein network, resulting in high whey separation and lower water-holding capacity (37.1 ± 0.35%) compared to the control (98.10 ± 0.60%). Significantly higher proteolytic activity was observed through free amino acids analysis by LC-MS. Arginine and methionine (237.24 ± 5.94 and 98.83 ± 1.78 µg/100 g, respectively) were found to be 115- and 275-fold higher than the control, contributing to changing the aroma similar to cheese. Further volatile analysis through SPME-GC-MS has confirmed significant increase in cheese-aroma volatiles compared to the control, with increase in diacetyl formation. Further work on DNA profiling, metabolomics and peptidomics will help to answer mechanisms behind the observed changes made in the study.
在本研究中，通过逐渐升高温度诱导适应性实验室进化（ALE），开发出了（）的耐热菌株。在添加2%乳糖的MRS琼脂培养基上，52℃时的活菌计数达到1.87±0.98 log cfu/mL。发现细菌形态发生了变化，从杆状（对照）变为丝状（52℃），冷冻保存（-80℃）后变为球菌。用耐热菌接种牛奶后，未产生乳酸，pH值为6.84±0.13。这导致蛋白质网络弱化，与对照（98.10±0.60%）相比，乳清分离率高，持水能力低（37.1±0.35%）。通过LC-MS分析游离氨基酸，观察到显著更高的蛋白水解活性。发现精氨酸和蛋氨酸（分别为237.24±5.94和98.83±1.78μg/100 g）比对照高115倍和275倍，有助于改变奶酪般的香气。通过SPME-GC-MS进行的进一步挥发性分析证实，与对照相比奶酪香气挥发物显著增加，二乙酰形成增加。进一步开展DNA谱分析、代谢组学和肽组学研究将有助于解答本研究中观察到的变化背后的机制。
