Response surface methodology approach of inducing amylolytic enzymes from Digitaria exilis and Digitaria iburua grains

Abstract

In this study, amylolytic enzymes were induced and extracted from the grains of Digitaria exilis (Acha) and Digitaria iburua (Iburu) which  are underutilized African cereals. These findings can aid in determining the suitability of enzymes from the grains as a suitable alternative  to enzymes from other tropical cereals. Whole grains of Digitaria exilis and Digitaria iburua (100 g) were steeped in water and  water containing phosphate salt for 24 h at room temperature and germinated in a locally constructed malting chamber for six (6) days.  The most appropriate pH and temperature conditions for the induction of amylolytic enzymes in the grains were selected based on the  central composite design of response surface methodology (RSM). The amylolytic activities of crude extracts from harvested malts of D.  exilis and D. iburua were measured by assaying the reducing sugar released from starch the using dinitrosalicylic acid method and soluble  proteins were quantified by the Bradford method. The highest amylolytic enzyme activities were 17,948 and 24,337 units/mg  protein for D. exilis and D. iburua respectively on day two (2) of the malting process. RSM showed that the maximum induction of amylolytic activity in grains of D. exilis and D. iburua was achieved by steeping in water containing phosphate salt at pH 6.5 and  temperature of 22.5°C.The study concluded that grains of D. exilis and D. iburua were rich sources of amylases and could be of valuable  for various biotechnological applications through studies of their physicochemical properties.