This study investigated the effect of fermentation time (24 and 48 h) on the pH, titratable acidity (TTA), phytochemicals, antioxidants, phenolic compounds, colour, functional, pasting, and thermal properties of flours from selected legumes (mung beans, haricot beans, butter beans, and black beans). The pH dropped significantly (p ≤ 0.05) after 48 h (6.61–4.91) of fermentation, with a corresponding increase in TTA, which ranged from 0.3 to 1.28 g lactic acid/100 g sample. Colour analysis showed that fermentation caused a decrease in L* values (2.97–23.86% reduction), with the highest reduction observed in black bean flour (23.86% at 24 h), along with an increase in the browning index. The total phenolic content increased significantly (p ≤ 0.05) in all the samples, with the most pronounced increase observed in mung bean 24 h (6.85 mg GAE/g). Similarly, the values for total flavonoid increased from 2.26 to 6.48 mg QE/g, and antioxidant activities such as DPPH ranged from 45.04 to 74.51%, FRAP from 1.65 to 8.03 Mm TE/g, and ABTS from 60.86 to 90.01%. Ultra-high performance liquid chromatography–photodiode array quantification of the targeted phenolic compounds showed a significant increase, with the highest notable increase for trans-ferulic acid in mung bean (330% after 48 h). Water absorption capacity generally showed an increase, whereas bulk density ranged from 0.55 to 0.91 g/cm3 and decreased in all legumes. There were differences in the pasting properties of the selected legumes. The peak time of unfermented butter bean was 33.08 min and remained constant at 33.15 min at 24 and 48 h of fermentation. Thermal analysis indicated the alteration of gelatinization parameters, with a decrease in peak temperature, whereas higher gelatinization enthalpy was observed. Findings from this study show that fermentation with the starter cultures can significantly improve the bioactive compound and functional properties of legume flours and thus act as potential ingredients in functional food development.
Mpho Brian Molimi (Wed,) studied this question.