Partial purification and characterisation of β-amylase isolated from malted pearl millet (Pennisetum glaucum)

Abstract

The industrial use of enzymes in the degradation of starch has become predominant over conventional methods of acid starch hydrolysis. As such, cheap sources of starch hydrolysing enzymes are being sought for. β-amylase, an exo-hydrolase which releases maltose by hydrolysing starch from the non-reducing end, is one of such important enzymes found to be common to the seeds of higher plants such as cereal grains. In this research, β-amylase was extracted from malted Pearl Millet grains and partially purified by ammonium sulphate precipitation (0-60%). The activity of β-amylase peaked at 72h of malting (7.40 ìmol/min/mL) with specific activity of 1.84 ìmol/min/mg. The enzyme extract at 72h was purified for characterization assays, giving a 1.33 purification fold and a yield of 9.28% after extensive dialysis against extraction buffer. Enzyme characterisation assays showed pearl millet β-amylase has optimal activity at pH 5.0 and 50 °C while a K_m value of 10 mg/mL and V_max value of 11.11 ìmol/min/mL were obtained when corn starch was used as substrate. The enzyme also showed significant activity over a wide temperature and pH range, indicating its potential as an industrial enzyme. The results from this study show that malted Pearl Millet is a cheap source of β-amylase with favourable kinetics and the desired characteristics of activity at low pH and elevated temperatures.

Keywords: Partial Purification, Pearl Millet, β-amylase, Starch, Malting, Industrial Potential