Colour and pH changes of tempe during extended fermentation

Tempe is a nutritious food, prepared mostly from soybeans and was originated in Indonesia. Tempe is sometimes collected beyond its maturity age for culinary purpose. The studies of overripe tempe ranged from microbiology, chemical and nutritional changes, functionality and safety, to sensorial aspect. Study which follows pH and colour changes of tempe during fermentation, however, is scarce. The objectives of this study were to investigate and model the colour and pH changes of tempe and the mould mycelia during extended fermentation with Rhizopus spp. up to 156 hours. Our investigation revealed that both lightness soybeans and mycelia of the tempe decreased with increasing fermentation time while pH of the tempe increased. The decrease of both lightness followed simple cubic equations whilst the pH increased linearly with increasing time. The other a values of tempe decreased by one point in the first 72 h of fermentation and tended to increase later however did not reach the initial a value, The b value decreased by approximately two points during the first 24 h of fermentation and the changes during the rest of fermentation time were not significant. The colour changes were believed to be the results of increased numbers of Rhizopus spp which entered the death phase, increased amount of linoleic and linolenic unsaturated fatty acids which were prone to oxidation, and formation of red coloured vitamin B12. Meanwhile, the increase of pH was majorly because of protein break down which led to increased ammonia production. The utilisation of lactic acid for mould growth also contributed to the alkalinisation, however to a much lesser extent. The lactic acid was previously formed during the soaking which resulted in decrease in pH of initial soybeans.