Screening And Application Of Microorganism In Huizhou Traditional Hairy Tofu

Huizhou hairy tofu is very popular with people because of its unique flavor,which is mainly formed during the production of hairy tofu with the participation of microorganisms in fermentation.At present,hairy tofu production is mainly manual workshop production,fermentation is mainly by natural inoculation,the bacterial community structure is very unstable.In this study,proteinase producing Mucor strains and proteinase producing lactic acid bacteria strains were screened by using Huizhou traditional hairy tofu and sour milk water as the isolation sources.Response surface methodology was used to optimize the culture conditions of Mucor.Orthogonal experiment was used to optimize the culture conditions of lactic acid bacteria and preliminarily explore the application of the strain in Huizhou hairy tofu industrial production.The main results are as follows:(1)Four samples of hairy tofu(D1 the Wang of Xiong village,D2 one family soybean products industy,D3 the Luo of Chengkan and D6 Fangxinyu of Lantian)and three samples of yellow pulp water(H2 one family soybean products industy,H3 the Luo of Chengkan and H4 Fangxinyu of Lantian)were screened as high quality separation sources by mycelial density,spore quantity and texture.A strain of protease producing fungus LMM1 was screened by the diameter of the hyaline circle and protease activity of the strain.Molecular biological identification showed that LMM1 was closely related to Mucor mucedo(99.93%),so it was named Mucor mucedo LMM1.A strain of lactic acid bacteria with high protease yield was screened.Molecular biological identification showed that the lactic acid bacteria LMX1 was closely related to Lactobacillus paracasei(98.00%)and named as Lactobacillus paracasei LMX1.(2)Using protease activity as the index,the results of single factor and response surface test showed that the optimal culture conditions of Mucor mucedo LMM1 were as the starting liquid medium pH of 6.1,42?constant temperature culture for 48 h.Under these conditions,the protease activity was 16.591 U,which was 28.7%higher than that of the unoptimized conditions for LMX1 bacteria.The results of single factor experiment and L₉(3³)orthogonal design showed that the optimal culture conditions of Lactobacillus paracasei LMX1 were as follows:initial liquid medium pH was 6.5 and constant temperature was placed at 37?for 60 h.Under these conditions,the content of protease could reach 3.373 U,and the activity of protease increased by 16.2%compared with the unoptimized conditions for LMX1.(3)The quality ratio of Mucor mucedo LMM1 and Lactobacillus paracasei Lmx1 was1:1 to prepare the fermentation agent,which was artificially inoculated on the surface of the hairy tofu,and cultured at 16?for 3 days.The quality of the rough tofu was relatively good.