Nutritional quality, microstructural properties and consumer acceptability of biscuits obtained from fermented finger millet (eleusine coracana) flours

Abstract

Finger millet (FM) (Eleusine coracana) is one of the most important minor cereal grains. Its fibre and ash contents are higher than that of major cereals such as wheat and rice. The grains are gluten-free therefore, they should be incorporated in the diet of celiac patients. The objective of this study was to determine the nutritional quality, microstructural properties, and consumer acceptability of biscuits prepared using spontaneously fermented FM flours. The FM grains were fermented at Different period (24, 48 & 72 h) of fermentation. The mineral content of FM flours used in biscuits making, as well as their functional, thermo-pasting, and microstructural properties were investigated. Biscuits were subjected to nutritional quality analyses (proximate composition & minerals), antioxidant, microstructural and sensory properties analyses. The results obtained showed that spontaneous fermentation (SF) decreased the packed bulk density (PBD), swelling capacity (SC), and increased water absorption capacity (WAC), and oil absorption capacity (OAC) of FM flours. The loose bulk density (LBD) values showed that SF had no effect, as no significant differences (p < 0.05) were noted. The LBD, PBD, WAC, OAC and SC of FM flours were within the range of 0.47 to 0.56 g/g, 0.71 to 0.79 g/g, 1.96 to 2.14 g/g, 1.24 to 1.44 g/g, and 13.33 to 14.33 mL, respectively. The cooked paste viscosity of FM flours decreased with increasing period of SF, ranging from 253.67 to 421.67 cP. The process of SF also induced changes in the thermal properties of FM flours as an increment of gelatinization temperatures and gelatinisation enthalpy with increasing time of SF was observed. The onset, peak, and conclusion temperature of FM flours ranged from 69.42 to 82.47 °C, 70.98 to 84.48 °C, and 78.24 to 86.39 °C, respectively. The gelatinisation temperature range and gelatinisation enthalpy of FM flours were within the range of 3.01 to 9.59 °C and 2.99 to 5.07 J/g, respectively. The reduction in the peak viscosity (PV), trough viscosity (TV), and final viscosity (FV) and increment in the breakdown viscosity (BDV), setback viscosity (SV), peak time (Pt), peak temperature (PT) of fermented FM flours were observed. The PV, TV, BDV, FV, SV, PT, and Pt ranged from 1709.67 to 2876.67 cP, 1349.67 to 2739.7 cP, 102.00 to 360.00 cP, 1616.33 to 2959.00 cP, 105.33 to 349.33 cP, 5.11 to 6.80 min, and 74.82 to 75.73°C, respectively. The enhancement in the mineral compositions of FM flours as SF time increased was noted. The microstructural changes in the starch granules as SF time increased were also observed. As for the biscuits, the decrease in moisture, ash, crude fiber, and crude fat contents as well as total phenolic and flavonoids contents as SF time increased was observed. Protein content, carbohydrates content, antioxidant activity, and mineral compositions of FM biscuits increased as SF time increased. The colour attributes such as lightness (L*), showed a significant increase as fermentation time increased in light brown FM biscuits, however dark brown FM biscuits showed no significant differences (p < 0.05). The hue angle and total colour differences (ΔE) iii of FM biscuits increased with increasing time of SF. The reduction in the physical properties of FM biscuits including diameter, weight, spread ratio and an increment in thickness and texture as SF time increased were also observed. The diameter, thickness, weight, spread ratio and hardness of FM biscuits were within the range of 4.54 to 4.76 cm, 0.66 to 0.76 cm, 11.99 to 12.77 g, 6.05 to 7.25 and 689.61 to 2372.23 g, respectively. Spontaneous fermentation also induced changes on the microstructure of FM biscuits. Among the fermented FM biscuits, panellists preferred 24 h gluten-free fermented FM biscuits since they had better sensory properties. Overall, SF enhanced the functional properties, thermo-pasting properties, mineral compositions, and nutritional value of FM flours, as well as the potential health benefits of eating gluten-free FM biscuits.