Abstract
Dextran is a high molecular weight polysaccharide formed in sugarcane during post harvest staling resulting in loss of sucrose as well as quality of sugar. Information regarding the removal of polysaccharides from the sugarcane milled juice is limited. In the present study, enzyme dextranase was produced from Paecilomyces lilacinus by submerged fermentation using Mandel medium and substrate dextran. The crude enzyme was partially purified by 80 % ammonium sulphate saturation followed by DEAE-cellulose column chromatography. Two isoforms of dextranase D-I and D-II each with optimum pH 5.0 and temperature 50 °C were identified. Both the isoforms were most efficient kinetically at pH 5.0 and temperature 50 °C and were found to be thermostable in the temperature range 0–50 °C. The pKa values of ionizing groups in free enzyme and enzyme-substrate complex were found to be between 4.1 and 5.8 indicating the possible participation of carboxylate groups of aspartate/ glutamate and imidazolium group of histidine in dextranase catalysed hydrolysis of dextran by both the isoforms. Activation energy (Ea) values for D-I and D-II were 22.07 and 31.68 kJ/mol and corresponding enthalpy change (ΔH) values were 17.01 and 8.70 kJ/mol, respectively. Cu2+ activated whereas Mg2+, Ca2+, Mn2+, Fe2+ and Pb2+ inhibited the activity of dextranase. With the application of 5, 10 and 15 units of partially purified dextranase per 100 mL of juice, dextran content decreased by 56.39, 73.88 and 80.27 %, respectively as compared to the control (with no dextranase added) after 24 h of storage of cane juice.
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