Effects of soaking and malting on thermal, functional and antinutritional properties of finger millet (Eluesine coracana L. Gaertn) flour

MSC in Food Science and Technology

Department of Food Science and Technology

In sub-Saharan Africa and India, finger millet (Eleusine coracana L. Gaertn) is a crucial food crop, holding the sixth position in cereal productivity, just after maize, wheat, rice, and sorghum. Despite its nutritional value, the underutilisation and neglect of finger millet have been widely documented. This research explored how soaking and malting impact the colour, pasting behaviour, thermal properties, crystallinity, and functional characteristics of both light and dark brown finger millet, along with sorghum (Sorghum bicolor) (included as reference). A central composite rotation design was applied with Design Expert software, focusing on soaking and malting durations of 24, 48, and 72 h. Sorghum flour exhibited high values for b*, c and hue, while the dark brown finger millet flour (DBFM) showed the highest L* value. The light brown finger millet flour (LBFM) recorded the highest redness (a) value. Gelatinisation onset temperatures were highest in LBFM, reaching 110.67°C, compared to 109.67°C for DBFM and 109.24°C for sorghum flour (SF), indicating slight thermal variation among the flours. The highest peak viscosity was observed in DBFM after 18 h of soaking and 24 h of malting. Tannin content ranged from 0.06 to 0.62 mg/100 g in LBFM, 0.15 to 0.84 mg/100 g in DBFM, and 0.21 to 0.77 mg/100 g in SF. Oxalic acid levels varied from 0.64 to 1.93 mg/100 g in LBFM, 0.93 to 1.56 mg/100 g in DBFM, and 0.50 to 1.45 mg/100 g in SF. Significant tannin models were identified in LBFM and SF, while all oxalic acid models were statistically significant across all flour varieties. Regarding functional properties, DBFM exhibited the highest pH, titratable acid (TTA), loose bulk density, and dispersibility. Sorghum flour demonstrated higher oil absorption capacity (OAC) and water absorption capacity (WAC), whereas LBFM exhibited the highest packed bulk density. Results indicated that soaking and malting significantly influenced the pasting properties and crystallinity of the flours. Scanning electron microscopy revealed structural modifications due to enzymatic activity during processing. Surface plots were generated, and ANOVA and regression analyses were performed to assess the data. These results offer important information for food processors on improving the colour characteristics, pasting behaviour, thermal and overall functional quality of finger millet and sorghum throughout processing. The models developed to evaluate these properties were dependable, as the lack-of-fit tests were not significant, and the coefficients of determination (R²) were relatively high, ranging from 0.3403 to 0.8721 on functional properties of the flour, indicating strong model performance. These results emphasise that soaking and malting have a considerable impact on the microstructure and functional properties of finger millet and sorghum flours. By optimising these processing conditions, the bioavailability of nutrients and beneficial compounds can be improved, leading to better flour quality for diverse uses.