Gas producton by Clostridium perfringens as a measure of the fermentability of carbohydrates and processed cereal-legume foods

A new and improved method was developed for the in vitro measurement of gas produced by Clostridium perfringens, in an attempt to determine the fermentability of pure carbohydrates, processed legumes and cereal-legume mixtures. The bacterial strain, inoculum and substrate concentrations and type of carbohydrate all proved to be important factors affecting in vitro gas production by Clostridium perfringens. Increasing glucose concentrations resulted in increased gas production, but only up to 2%, above which it became inhibitive. A 10-fold dilution of the active inoculum reduced the rate of gas production, whilst a 50-fold dilution produced no gas in 24 h. Strain NCTC 8239 was able to ferment a wide range of carbohydrates, with the exception of xylose. Arabinose, ribose and raffinose were, however, only moderately fermented. Native starch was also poorly fermented but, after heating, was fermented with vigorous gas production. Cooked, lactic-fermented cereal-legume composite doughs produced less gas compared to cooked non-fermented doughs. Soaking resulted in decreased fermentability of cowpea and pigeon pea, but the opposite effect was observed with soaked mungbean and soya bean. Fungal fermentation (with Rhizopus oligosporus) into tempe also had varying effects on fermentability, depending on the legume. Fungal-fermented cowpea, groundnut and pigeon pea produced more gas than similarly treated mungbean and soya bean. Steaming these products again had contrasting effects, with cowpea and pigeon pea showing reduced fermentability whilst the fermentability of mungbean and soya bean increased.