Abstract:
This study aimed to evaluate method for the production of active concentrated starter culture of Zygosaccharomyces rouxii for use in the culture starter production process for soy sauce fermentation. Initially, the methods for Z. rouxii TISTR 5044 cultivation to prepare the concentrated starter culture were evaluated. The cultivations were divided into 4 methods. They were; (1) YM broth containing 1%NaCl (2) YM broth containing 5%NaCl (3) YM broth containing 5%NaCl for the first batch and YM broth containing 10%NaCl for the second batch (4) YM broth containing 5%NaCl for the first batch and soy sauce (SS) containing 5%NaCl for the second batch. The cultures form all methods were subjected to evaluation of their ability to grow in soy sauce containing 10%NaCl and 1.5% sugar. Thus result showed that yeast cultivated in the fourth method had the highest growth rate (µ = 0.13 generation/hour). Thus, the fourth method was selected for the evaluation of the effect of added sugar on the growth rate of the yeast. The result revealed that added sugar did not associate with the growth rate. Consequently, concentrated cells prepared by the fourth method were further evaluated for the ability to grow in a bioreactor using SS containing 10%NaCl and 1.5%sugar as the cultivation media, relative to concentrated cells form the fourth method and further cultivation in SS containing 10%NaCl. It was found that the growth rate of concentrated cells of the both methods were not different (µ = 0.14). According to this study, cultivation of cells in YM broth containing 5%NaCl in the first batch and SS containing 5%NaCl in the second batch was found as an appropriate method for the production of active concentrated starter culture of Z. rouxii TISTR 5044. Then, concentrated cells were kept in retort pouch using three protectants (10%glycerol, SS containing 1%NaCl and 8%soy protein isolate) at ratio 8 log CFU per ml of protectant under three temperatures (-20, 0 and 4°C). The survival rate in the pouch and growth rate of concentrated cells in SS containing 10%NaCl and the contamination of yeast&mold, coliforms and E. coli were determined every week for 1 month. During storage, the concentrated cells kept in 10%glycerol under 4°C was found as an appropriate condition. Under this condition, viable cells and the growth rate of concentrated cell was not different from the initial week (8 log CFU per ml and µaverage=0.15). The morphology of the storaged concentrated cells different from the normal cell. In addition, no contamination were found in the storaged concentrated cells. Then, fermentative activity of the storaged concentrated cells in moromi were evaluated compared to fresh concentrated cells prepared from the same cultivation method. The fermentative ability of the both concentrated cells were not different. Thus, the concentrated cells production method obtained from this study is potential to apply in industrial moromi fermentation