Most current studies on Lactococcus lactis subsp. lactis are focused on its application in bovine milk, but few studies have been conducted on its application in soymilk. The fermentation characteristics of Lactococcus lactis subsp. lactis in soymilk were analyzed by metabolomics and sensory evaluation in the present study. The results showed that Lactococcus lactis subsp. lactis strains DYNDL21-2, DYNDL1-2 and FJNDD18M8 showed good sucrose metabolism capacity, growth and acid production ability. The abundance of hexanal and various heterocyclic compounds such as furan in fermented soymilk was significantly down-regulated by DYNDL21-2 and FJNDD18M8, which effectively reduced the intensity of beany odor. Fermentation with FJNDD18M8 significantly up-regulated the abundance of acetaldehyde, acetoin and 2,3-butanedione in soymilk, enhancing the milky aroma and creamy flavor and improving the overall flavor. In conclusion, Lactococcus lactis subsp. lactis has excellent fermentation characteristics and strong metabolic capacity during soymilk fermentation, but there are some differences among strains.

Processing parameters are important factors influencing the physical properties and microstructure of processed cheese spreads. This work researched the influence of processing parameters on the texture, meltability, apparent viscosity and microstructure of processed cheese spreads. Results showed that shearing speed, heating temperature and heating time had significant influence on the texture and meltability of cheese samples (P < 0.05). When the shearing speed increased from 800 to 1 400 r/min, the hardness, spreading work and adhesiveness did not significantly increase. Appropriately elevating the melting temperature and prolonging the melting time enhanced the emulsifying capacity. Emulsification appeared after 2.9 minutes of shearing. The optimum processing parameters were determined as follows: preheating at 85 ℃ for 4 min under static conditions, and shearing at 800 r/min for 2.9 min. The product prepared using these conditions tasted refreshing and smooth, and had a gentle flavor, good meltability, medium hardness and good spreadability. Its sensory quality was similar to that of a commercial product.