Isolation and analysis of molds from soy sauce koji in Thailand

Area of Science:

• Microbiology
• Food Science
• Biotechnology

Background:

• Protease-producing fungi are crucial in food fermentation, particularly for soy sauce production.
• Contamination by mycotoxigenic fungi, such as those producing aflatoxins, poses a significant food safety concern.
• Screening for novel fungal strains with high enzymatic activity and low toxicity is essential for improving fermentation processes.

Purpose of the Study:

• To compare the proteolytic activity of different Aspergillus and Mucor isolates.
• To identify a superior protease-producing fungal strain for potential use in food fermentation.
• To assess the aflatoxin production and efficacy of the selected strain in soy sauce production.

Main Methods:

• Comparative analysis of proteolytic activity of six fungal isolates (five Aspergillus, one Mucor) and a commercial Aspergillus oryzae strain on wheat bran.
• Identification of the most potent protease-producing isolate.
• Aflatoxin production assessment on glutinous rice and soybean substrates.
• Preliminary evaluation of the selected fungus as a koji mold in a traditional soy sauce factory.

Main Results:

• One Aspergillus isolate, identified as Aspergillus flavus var. columnaris, exhibited superior protease production compared to other tested strains.
• This isolate showed no detectable aflatoxin production on glutinous rice or soybean substrates.
• Soy sauce produced using Aspergillus flavus var. columnaris as a koji mold was of superior quality compared to conventionally produced soy sauce.

Conclusions:

• Aspergillus flavus var. columnaris is a promising candidate for industrial applications due to its high protease activity and absence of aflatoxin production.
• The use of this strain can potentially improve the quality of fermented foods like soy sauce.
• Further research is warranted to optimize its application in large-scale food fermentation.