米曲霉优良菌株的筛选及在制曲发酵西瓜黄豆酱中的应用

为获得蛋白酶、淀粉酶活性优良的米曲霉菌株，采用牛津杯双层平板法初筛、制曲分析酶活性复筛的方法，从制酱用成品曲中获得1?株淀粉酶活性优良菌株CS3.04和1?株蛋白酶活性优良菌株CS3.22，结合形态特征，ITS?rRNA序列分析鉴定为米曲霉。将2?株米曲霉分别进行单一菌种制曲及混合菌种制曲发酵西瓜黄豆酱，与商业米曲霉菌株制曲发酵进行对比，结果显示：不同制曲方式发酵西瓜黄豆酱的理化指标变化趋势保持一致，混合菌种制曲发酵样品的还原糖及氨态氮含量最高，分别为107.37、6.76?g/kg，比接种商业米曲霉菌株制曲发酵的样品分别提高了11.02%、5.56%；采用液液萃取-气相色谱-质谱联用技术定性及定量分析西瓜黄豆酱的挥发性风味物质，发现混合菌种制曲发酵具有产醛类、醇类、酮类及短链酯类物质的优势，而接种CS3.04单一菌种制曲发酵更有利于产酸类及酚类物质；混合菌种制曲发酵样品整体感官评分优于单一菌种制曲发酵，且在香气与滋味上占有优势。混合菌种制曲发酵工艺因CS3.04和CS3.22的酶系互补作用，有效地提升了西瓜黄豆酱的品质。

Screening and Application of Aspergillus oryzae in Koji-making for Manufacturing of Fermented Watermelon-Soybean Paste

A strain with high amylase activity, designated as CS3.04, and another strain with high protease activity, designated as CS3.22, were isolated from koji for fermented soybean paste by the Oxford-cup double-layer plate method. Both strains were identified as Aspergillus oryzae by morphological characterization and internal transcribed spacer (ITS) rRNA sequence analysis. The two strains were used to make single-strain and mixed-strain koji for the manufacturing of fermented watermelon-soybean paste. Commercial A. oryzae was served as the control. The results showed that physicochemical indexes of the fermented product exhibited a consistent trend with fermentation time. The contents of reducing sugar and ammonia nitrogen in the mixed-strain fermented product were the highest, which were 107.37 and 6.76 g/kg and increased by 11.02% and 5.56% compared with that fermented by commercial A. oryzae, respectively. The qualitative and quantitative analysis of volatile flavor compounds was performed using liquid-liquid extraction and gas chromatography-mass spectrometry (GC-MS). It was found that the mixed-strain fermentation was superior to the single-strain fermentations in producing aldehydes, alcohols, ketones and short-chain esters, while fermentation with CS3.04 alone was more conducive to the production of acids and phenols. Moreover, the mixed-strain fermentation resulted in higher overall sensory score and better aroma and taste. We concluded that the mixed-strain fermentation improves the quality of fermented watermelon-soybean paste through the complementary effect between the enzymes of strains CS3.04 and CS3.22.