Protein Profile and Carbohydrate-Degrading Enzymes Activities during Malting of African Finger (Eleusine coracana) and Pearl (Pennisetum glaucum) Millets

Abstract

Malting is a process of controlled partial germination of cereal seeds involving hydration (steeping), incubation in an environment suitable for seed germination and early seedling growth, and then heating and drying (kilning). In this study, an approach towards the malting process optimization of African Finger Millet (Eleusine coracana) and Pearl Millet (Pennisetum glaucum) was sought for its improved potential as alternative cereals in the infant food formulation, brewery and beverage process. The influence of pH stress and heat stress on the amylolytic, proteolytic, and cytolytic properties as malting quality parameters of the two cereals was investigated. Hundred grams (100 g) each of the African Finger and Pearl millet was micro-malted at low salt concentration of acidic pH stress (pH 3.0) and alkaline pH (pH 9.0) stress conditions and germinated under heat stress conditions of 30 and 40 ᵒC. Distilled water steeping condition served as the control. α-Amylase, β-amylase and β-glucanase activities as well as β-glucan and total protein as indices of malting quality were monitored daily for four days (96 h). Differential hordein protein expressions of the malted millets after 96 h of germination at 30 and 40 ᵒC were analyzed by discontinuous SDS-PAGE. There were significant increases in α-amylase and β-amylase activities, as indicators of malting progress, at acidic pH (3.0) and alkaline pH (9.0) stress conditions compared to the control. The Pearl millets malted at 30 ᵒC gave optimum α-amylase (191.04±0.16 U/g) and β-amylase (2.73±0.20 U/g) activities at 96 h under alkaline pH stress. The malted Finger Millets also gave optimum α-amylase (238.04±0.20 U/g) and β-amylase (2.27±0.20 U/g) activities under the same conditions. There was a positive correlation between β-glucanase activity and β-glucan content during the malting process and suggesting reduction in malting viscosity. The significant decrease in protein content under the alkaline and acidic pH stress conditions at 30 ᵒC indicates an improvement in the malting performance of the millets. The hordein protein profile of the malted millet grains showed up-regulated expressions of the B hordein protein at 30 ᵒC and down

regulated expressions at 40 ᵒC. This could suggest the involvement of the B hordein proteins as molecular chaperones for the diastatic enzymes in the course of malting at 30 ᵒC heat stress condition but might be ineffective at higher temperature. The results from this study have shown that alkaline pH stress and 30 ᵒC heat stress are the best malting optimization conditions; and, α-amylase is the best predictor of diastatic power.