Ecology of controlled soyabean acidification for tempe manufacture

Abstract

During the traditional Indonesian tempe manufacturing process, spontaneous and uncontrolled fermentations of soyabeans take place during the soaking stage prior to fungal fermentation. Often, such fermentations result in an acidification of the beans. A comparison of industrial tempe processes suggested that fermentative acidification during soaking inhibits the multiplication of spoilage causing bacilli. The acidification during soaking could be controlled by recycling part of the soak water from a previous batch as an inoculum, resulting in a soak water pH of 4·1–4·9 depending on soaking temperature and recycling rate. Soaks at 19°C and 25°C were dominated by Lactobacillus plantarum. Isolates of L. plantarum added as an inoculum to freshly started soaks were able to acidify the beans to pH ≤ 4·30 yielding tempe of good quality in which bacilli and Enterobacteriaceae could not be detected. Yeasts, notably Saccharomyces dairensis, present in soaks at 19°C and 25°C, did not contribute to the acidification and could not prevent early spoilage of tempe. Pediococcus spp. dominated soaks at 37°C, and though able to acidify soyabeans, inhibited the growth of Rhizopus oligosporus; hence no tempe could be formed. Our findings indicate that a simple recycling process can result in predictable acidification during soaking of soyabeans, contributing to the shelf-life and safety of tempe.