Comparative Studies on the Effect of Fermentation on the Nutritional Compositions and Anti-nutritional Levels of Glycine max Fermented Products: Tempeh and Soy-Iru

Aims: A comparative study of fungi and bacteria fermentation of soybean (Glycine max) was carried out to determine the effect of fermentation on the nutritional composition of their fermented products: tempeh and ‘soy-iru’.

Study Design: The experiment was carried out in the Department of Microbiology, Ekiti State University, Ado Ekiti, Nigeria, between August, 2017 and July 2018.

Methodology: Soybean was processed into ‘soy-iru’ (bacterial fermentation) and tempeh (fungal fermentation) and the microbial load, physico-chemical properties, proximate composition, levels of anti-nutritional components (trypsin inhibitor and phytic acid), anti-oxidants (total phenol, total flavonoid and DPPH), in-vitro protein digestibility and vitamins (A, B, C, D, and E) were analyzed.

Results: The microbial load, pH increased progressively during fermentation, while there was a decrease in the titratable acidity (TTA) of the two products. The protein(%), ash(%) and fat(%) contents of the Glycine max cotyledons increased from 29.56, 1.86 and 24.36 in unfermented substrate to 33.61, 2.21 and 26.90, respectively, after 24hrs of fermentation to produce tempeh. However, there was a reduction in the crude fibre(%) and carbohydrate(%) content from 2.94 and 41.29 in unfermented substrate to 2.53 and 32.57, respectively, after 24hrs of fermentation. Similar trends were observed during the production of ‘soy-iru’, however the change in proximate composition was not as significant as observed in tempeh. There was significant decrease in the trypsin inhibitor and phytic acid levels of the two products. The levels of anti-oxidants, vitamins B, D, E and protein digestibility increased significantly, in both bacterial and fungal-fermented products.

Conclusion: This research has therefore shown that fungal fermentation of Glycine max seeds into tempeh may be a better alternative to ‘soy-iru’ which was obtained from bacterial fermentation, because of the significant lower level anti-nutritional factors in the former.