Study Shows Rhizopus Nigricans Enhances Doenjang Quality Safely

A novel study focused on the use of a Rhizopus nigricans-based starter culture to enhance the quality of doenjang, a traditional Korean fermented soybean product. The research aimed to develop a consortium of effective microorganisms for preparing doenjang. Different ratios of microbial strains were selected to produce doenjang with improved quality attributes. The microbial strain combinations were mixed at varying ratios to prepare different doenjang samples.

The study analyzed various parameters such as free amino acids, free sugars, volatile and non-volatile organic acids, cellular antioxidant activity, presence of biogenic amines, aflatoxins, and microbial counts in the prepared doenjang samples. Results showed that total free amino acids responsible for the sweet taste were highest in specific samples. Total volatile organic acid content varied among the preparations, with different levels of biogenic amines detected in each sample. The aflatoxin and microbial counts were found to be below toxic levels in all tested samples.

Historically, doenjang is a protein-rich traditional Korean food product produced by fermenting soybeans. The preparation of doenjang involves the fermentation of soybeans by various microorganisms. The taste and color of doenjang are key factors influencing its acceptability, dependent on the starter culture and oxygen presence. Traditional doenjang is made through a fermentation process lasting over two months.

The study’s findings suggest that using multiple microbial strains in combination with R. nigricans as a starter culture could be an effective approach to enhance the nutrition and safety of fermented soybean food products like doenjang. The research also evaluated the cellular antioxidant activity of a selected doenjang sample, demonstrating its potential against oxidative stress induced by reactive oxygen species.

The analysis of microbial counts in the doenjang samples revealed the absence of specific foodborne pathogens, ensuring good hygienic conditions. Additionally, the study determined that the aflatoxin levels in the samples were below the hazardous limit. Overall, the research highlights the potential benefits of utilizing a novel starter culture for improving the quality and safety attributes of traditional fermented soybean products like doenjang.