Soy sauce decolorization using autochthonous isolates

Abstract

The aim of this study was to explore autochthonous strains having properties in reduction of brown color in moromi and evaluate their potential as biological mean for de-colorization of soy sauce. The autochthonous microbes associated to moromi fermentation under different manufacturing conditions were evaluated using both the culture plating and Reverse transcriptase-nested PCR-DGGE (RevT-nested PCR-DGGE) methods. By culture plating, Bacillus (43.17%) and Staphylococcus (33.09%) were isolated from every fermentation stages of all samples. Yeast Candida spp. was frequently detected (46.67%) in most samples. RevT-nested PCR-DGGE revealed the different results, as 29.73% of major bacterial DGGE band belonged to lactic acid bacteria (LAB) while equal proportion of 18.92% were Bacillus spp. and Staphylococcus spp., and including unidentified bacteria. Candida spp. was generally detected (56.00%) as the main fungal, following by Saccharomycetales (24.00%), while Z.rouxii, known as soy sauce yeast was identified as low as 4.00%. Through the RNA-based DGGE analysis, Bacillus and Staphylococcus demonstrated their roles in the reduction of browning generation rate. Total isolates of 139 bacteria and 105 yeast were further screened based on sugar utilization. Five isolates having co-metabolic activity of xylose and glucose in synthetic medium, in addition with containing either total browning or melanoidin degradable activities, were obtained. The two isolates of Staphylococcus sp. SSB48 and B. amyloliquefaciens strain SSB6 with the highest xylose utlilizability (39.09 and 40.08%, respectively), and total browning decolorizability (27.04% and 26.11%, respectively) were selected as potential strains. The ability in browning color reduction of potentials were tested in moromi in order to preliminary optimize decolorization process. The optimal condition of the potentials in de-colorization was inoculation of single candidates at final stage of moromi fermentation and incubation for another 1 month.