Tempeh fermentation improves the nutritional and functional characteristics of Jack beans (Canavalia ensiformis (L.) DC)

The effect of two processing methods of Jack beans (i.e. cooked bean (CB) and cooked tempeh (CT)) on
the in vitro digestibility of protein and starch, as well as the production of short chain fatty acids (SCFAs),
γ-aminobutyric acid (GABA), and tryptophan (Trp) metabolites after in vitro colonic fermentation, was
investigated. CT was obtained by fungal fermentation after cooking under acidic conditions. CT had significantly higher protein, lower digestible starch, lower total fiber, higher free phenolic compounds, and
higher ash content compared to CB. CT exhibited better in vitro protein digestibility than CB and less
glucose release during in vitro digestion than CB. A comparable concentration of total SCFAs and GABA
was produced after in vitro fermentation of CB and CT, but CB produced more indole than CT, resulting
in higher amounts of total Trp metabolites. In summary, our findings show that tempeh fermentation
improves the nutritional quality of Jack beans and describe the impact of fermentation on the digestibility
of nutrients and the formation of metabolites during colonic fermentation.