School of Life Science and Biotechnology, Korea University, Seoul 136-701, Republic of Korea.
J Agric Food Chem. 2010 Aug 11;58(15):8738-47. doi: 10.1021/jf101994u.
Meju, a brick of dried fermented soybean naturally inoculated with microorganisms, is a starter used for producing traditional Korean fermented soybean products such as soybean paste (doenjang) and soy sauce (ganjang). In order to reduce aging time during production of soybean paste and soy sauce, high pressure (HP) treatment was applied to the meju starter at 500 MPa of pressure for 10 min at 15 degrees C. Fermentative behaviors of normal and HP-treated meju were assessed and compared through physicochemical and (1)H NMR-based metabolomic analysis. All mejues were incubated for 3 weeks at 30 degrees C. At 1 week of incubation, total bacterial population decreased mainly due to a reduction of water content by spontaneous evaporation during the incubation period. As the incubation time increased, glutamate, proline, betain, choline, and phosphocholine levels increased in both normal and HP-treated mejues, indicating that microorganisms in the mejues synthesize these metabolites to endure intracellular hyperosmotic stress induced by the reduction in water content. Through 3 weeks of incubation, the amino-type nitrogen contents and neutral protease activities in HP-treated meju were significantly higher (p < 0.05) than in normal meju, even though total bacterial content in HP-treated meju was 2 or 3 times lower. Moreover, marked increases in glycerol, acetate, tyrosine, and choline levels were observed in HP-treated meju compared to normal meju. In particular, higher levels of tyrosine in HP-treated meju were consistent with the increased neutral protease activities compared to normal meju, indicating an improvement in enzyme stability with HP treatment. These findings highlight a new or better understanding of the influence of the HP or physical treatments on fermentative products in food processing, such as those associated with soybean paste and soy sauce, regarding metabolic behaviors in fermentative starter induced by HP treatment.
美居，一种由微生物自然接种的干燥发酵大豆砖，是用于生产传统韩国发酵大豆制品（如豆瓣酱和酱油）的发酵剂。为了缩短豆瓣酱和酱油生产过程中的老化时间，将美居发酵剂在 15°C 下以 500 MPa 的压力处理 10 分钟。通过物理化学和基于 1H NMR 的代谢组学分析评估和比较了正常和 HP 处理的美居的发酵行为。所有的美居都在 30°C 下孵育 3 周。在孵育的第 1 周，由于在孵育期间自发蒸发导致水分减少，总细菌数量减少。随着孵育时间的延长，谷氨酸、脯氨酸、甜菜碱、胆碱和磷酸胆碱的水平在正常和 HP 处理的美居中都增加，这表明美居中的微生物合成这些代谢物以忍受由水分减少引起的细胞内高渗应激。经过 3 周的孵育，HP 处理的美居中的氨基酸态氮含量和中性蛋白酶活性显著高于（p < 0.05）正常美居，即使 HP 处理的美居中的总细菌含量低 2 或 3 倍。此外，与正常美居相比，HP 处理的美居中甘油、乙酸盐、酪氨酸和胆碱的水平明显增加。特别是，与正常美居相比，HP 处理的美居中酪氨酸水平更高，表明 HP 处理可提高中性蛋白酶的稳定性。这些发现强调了对食品加工中发酵产品（如豆瓣酱和酱油）的高压或物理处理对代谢行为的影响的新的或更好的理解，这些影响与高压处理诱导的发酵剂的代谢行为有关。
