Microflora and Flavor of Wild Rice Fermented Under Different Conditions

Changes in number and types of microorganisms in fermenting wild rice were studied. The effect of various microorganisms on keeping quality of wild rice during fermentation and on flavor of wild rice was also determined. Addition of microbial cultures and/or nutrient solutions did not increase the storage life of fermenting wild rice held at 21 or 5°C. Refrigeration of rice greatly increased the effective keeping time of the unprocessed grain. Periodic addition of a 0.1% (w/v) (NH₄)₂SO₄ solution apparently decreased the acceptable storage life of refrigerated (5°C) rice. Although unprocessed rice could not be kept beyond 10-14 d at 21 °C without obvious changes in organoleptic quality, rice stored at 5°C remained acceptable for 7 weeks. Steaming wild rice for 15 min before fermentation generally caused a marked reduction in microbial load during the first few days of storage. Rice inoculated with Streptomyces sp. in a circulating nutrient medium to produce an "earthy" flavor was rapidly spoiled by microorganisms indigenous to rice. Cultures of Pseudomonas perolens and Pseudomonas taetrolens inoculated into rice stored at 5°C gave only mild methoxylated-pyrazine (green-earthy) flavors to resulting processed rice. In most treatments, bacteria and molds generally increased during the first week of fermentation, maintained a rather constant number for most of the remainder of the fermentation, and often decreased near the end of storage. Gram-negative, rod-shaped bacteria were the microorganisms most commonly isolated from fermenting wild rice. Many psychrotrophic bacteria were isolated from refrigerated (5°C) rice. Low-temperature storage greatly increased the keeping quality of rice, but unacceptable organoleptic changes eventually occurred at this temperature. Many bacteria isolated from wild rice were facultatively anaerobic Enterobacteriaceae . Although rice contained large populations of various types of microorganisms, the potentially hazardous Bacillus cereus and Pseudomonas aeruginosa were not found.