Characterization of an Alkaline Thermostable Pectin Lyase from Newly Isolated Aspergillus niger _WHAK1 and Its Application on Fruit Juice Clarification

Abstract

Pectin lyase degrades pectic substances that are complex polysaccharides of middle lamella and primary cell walls of plants. In this study, alkaline thermostable pectin lyase from Aspergillus niger strain_WHAK1 was produced on wheat bran and citrus pectin in submerged culture. Pectin lyase was purified by ammonium sulfate fractionation, gel filtration and ion-exchange chromatography, and 76.5 purification fold was obtained. Optimum pH and temperature values of pectin lyase were 8.0 and 40°C at 60min, respectively. The enzyme was stable for 17 months at 4°C. Km and Vmax values were found to be 5.2mg/mL and 0.2(mmol/min)−1 mL, respectively. Molecular weight of pectin lyase was nearly 23.3 kDa. Effects on PL activity of metal ions (NaCl, KCl, CaCl2, MgCl2, CoCl2, CuCl2.H2O, FeCl3.6H2O, ZnSO4.7H2O, (NH4)2SO4, MnSO4), amino acids (l-tryptophan, l-cysteine hydrochloride monohydrate, l-arginine monohyd rate), ascorbic acid, citric acid monohydrate, EDTA and resorcinol were studied. The presence of FeCl3, CaCl2 and ascorbic acid significantly enhanced relative pectin lyase activity (%). The purified pectin lyase induced viscosity reduction in fruit juice samples, and it was effective for clarification of fruit juices. Pectin lyase showed substrate preference against fruit juice samples.