Pseudovitamin B12 producing Loigolactobacillus coryniformis enhances soy milk fermentation by Lactobacillus delbrueckii subsp. bulgaricus

Abstract

Background: Fermenting soy milk with lactic acid bacteria is challenging. Generally, carbohydrates are added to enhance the acid production in soy milk. However, the yoghurt starter Lactobacillus delbrueckii subsp. bulgaricus did not succeed in fermenting soy milk supplemented with carbohydrates. If this yoghurt starter could be used with soy milk, it is expected that it would produce a yoghurt-like flavour, making soy yoghurt more appealing. In this study, we aimed to ferment soy milk using Lb. delbrueckii subsp. bulgaricus and pseudovitamin B₁₂-producing lactic acid bacteria.

Results: Loigolactobacillus coryniformis SAB01 was found to produce corrinoid in soy milk, with the highest production being observed at 20 °C. The produced corrinoid was identified as pseudovitamin B₁₂ using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Another bacterial strain, Lb. delbrueckii subsp. bulgaricus NBRC 13953, was examined for its ability to produce lactic acid in soy milk. Compared with soy milk supplemented with glucose or cyanocobalamin alone, the highest lactic acid production was observed in soy milk supplemented with both glucose and cyanocobalamin. These findings indicate that the combined addition of glucose and cyanocobalamin enhances lactic acid production by strain NBRC 13953 in soy milk. We accordingly examined lactic acid production in soy milk inoculated with strains SAB01 and NBRC 13953, and found that a substantial quantity of lactic acid was produced when glucose was added to soy milk.

Conclusions: Our findings in this study indicate that the growth of Lb. delbrueckii subsp. bulgaricus NBRC 13953 was promoted by the pseudovitamin B₁₂ produced by Loigolactobacillus coryniformis SAB01, thereby suggesting a novel symbiotic relationship between these two lactic acid bacteria in soy milk. © 2025 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Keywords: fermentation; pseudovitamin B12; soy yoghurt; symbiosis.