Food safety considerations in the production of traditional fermented products: Japanese rice koji and miso

Abstract

While established in Asia, rice koji and miso are fermented foods that are becoming more popular in western countries. They have been shown to contain a variety of microorganisms, consisting of bacteria, yeasts, and fungal species. Many contemporary miso varieties are not pasteurized as consumers are looking for more natural products, and/or have the desire to consume fermented foods containing live microorganisms. While correctly prepared fermented foods are rarely associated with food safety outbreaks, incidences have been recorded. On these occasions, pathogenic, or spoilage microorganisms were introduced into the products from external sources such as the raw material or the processing environment. Consequently, hygiene and fermentation conditions need to be carefully monitored to ensure food safety. Furthermore, many of the production steps during koji and miso manufacture do not fit into contemporary food safety guidelines for foods. Although pH is a required food safety hurdle for fermented foods, this does not apply to nonacidic foods such as koji or miso. This review focuses on control of microbial pathogens and discusses the processes of miso fermentation, and how fermentation of rice koji and miso fits with current food safety hurdles in western countries.

Novel misos shape distinct microbial ecologies: opportunities for flavourful sustainable food innovation

“…Enterotoxin expression is favoured by environmental conditions such as optimal temperature growth for S. aureus (37°C) and neutral pH (between 6-7.5). Misos are typically fermented at a lower temperature (often room temperature or cooler in traditional production; these misos were kept at 28°C to expedite the process), and they typically begin at a pH lower than this range, often starting around pH 6 and dropping to around pH 5 (Allwood et al ., 2023). Our misos exhibited a lower pH range, starting between pH 4.52 and pH 5.64 (mean=5.32, SD=0.38) and ending between pH 3.32 and pH 5.02 (mean=4.02, SD=0.45; Table S1 ).…”

“…All but three ended at a pH below 4.6, the general threshold for safety recognised by the FDA (2007). Even the highest was at the lower range of typical misos (Allwood et al ., 2023). While salt is less of a deterrent for production of these toxins (Schelin et al ., 2011), which could still be produced at the 5% concentration of these misos, their low pH makes it unlikely.…”

Exploring the culinary and health significance of fermented foods: A comprehensive review

“…Once the miso reaches the desired level of fermentation, it can be transferred to clean jars and stored in the refrigerator to slow down further fermentation. Miso can be used as a seasoning or flavoring agent in soups, marinades, sauces, dressings, and other dishes, adding depth and complexity to the flavor profile [51][52][53][54].…”

Carbon stable isotopes of glucose during the degradation of rice by the koji fungus Aspergillus oryzae

“…Saccharification mediated by the filamentous fungus Aspergillus oryzae is a cornerstone process in the production of traditional East Asian fermented foods [ [1] , [2] , [3] , [4] , [5] ]. During koji production, A. oryzae grows on steamed rice ( Oryaze sativa ) and secretes hydrolytic enzymes, including α-amylase and glucoamylase, that degrade starch into fermentable sugars [ 6 , 7 ].…”