[P004] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P02-176] Growth inhibition of wild lactic acid bacteria in low-salt shoyu production.

○Alican Erdogan¹, Taiki Terasaka¹, Jun Yoshikawa¹, Kenji Maehashi¹ (1. Tokyo University of Agriculture (Japan))

Keywords:

soy sauce,wild lactic acid bacteria,growth inhibition,Tetragenococcus halophilus,low salt

Soy sauce, or shoyu, is a popular condiment widely consumed in Asian countries and is gaining attraction in countries in Europe or North America. Shoyu is made primarily from soybeans, wheat, Aspergillus oryzae, water and salt and typically contains a salt content of around 17% (w/v). While health consciousness is gaining popularity, the average salt intake still exceeds the recommended intake set by the Japanese government. Based on National surveys, a great part of the average daily salt intake was from shoyu. Low salt shoyu may be suitable to reduce the salt intake, but it often has an inferior flavor profile compared to that of normal shoyu and that can be often attributed to the post fermentation methods used, which can also remove essential flavor components. An alternative method to producing low salt shoyu is using a brine with a lower salt concentration, but this poses risks as it allows for the growth of undesirable microorganisms. Tetragenococcus halophilus can produce biogenic amines (BA). When overly consumed, BAs can cause adverse health effects. To manage this risk in shoyu with a brine of 10% NaCl (w/v), an alternative fermentation method has been implemented by combining the addition of 1% (v/v) lactic acid (LA) and a large amount of yeast cells (Zygosaccharomyces rouxii). This condition was compared to both yeast and LA addition at 23% (w/v) NaCl and lastly compared to the addition of yeast and T. halophilus at 23% (w/v) NaCl. For both LA addition conditions, the pH stayed stable for the course of 55 days at 4.7, while the T. halophilus condition had an initial pH of 5.7, it progressively decreased to a final pH 4.7. After 55 days, glutamic acid was lower in the low salt moromi compared to control, 0.82% versus 0.87% (w/v), respectively. Moreover, the microbiota was compared between modified fermentation and control. During 30 days of fermentation, Tetragenococcus spp. was absent only in the low salt moromi. Furthermore, Weisella spp, could not grow when LA was added to the moromi, indicating a lack of acid tolerance and Lactobacillus spp. reached a relative abundance of 95% after 30 days while it was not detected in control. To increase enzyme activity of koji in an acidic environment, an alternative koji making method was explored by soaking soybeans in a solution with LA. Soybeans soaked in 5% (v/v) LA produced an acidic koji with a pH of 4.6. Preliminary results indicate that acid protease activity was approximately 1.4-fold higher in 5% LA condition, a-amylase and glutaminase activity being lower by 0.8-fold approximately after 8 days. The addition of lactic acid and yeast during the fermentation phase indicate potential as microbial control strategy, however alternative methods need to be explored for increasing the enzyme activity of various protein and peptide degrading enzymes at an acidic environment to make this new fermentation method viable to produce high grading shoyu.