Optimized Application of Dextranase at Low Doses and Retention Times to Hydrolyze Dextran in Sugarcane Juices

Abstract

Dextranase (endo 1 → 6-α-glucan hydrolase; EC 3.2.1.11) enzyme is applied in sugarcane factories to hydrolyze dextran (α-1 → 6-D-glucan) into smaller, more manageable molecules which can improve crystallization rates, reduce crystal elongation problems, and prevent dextran penalties in the raw sugar. The efficiency of the factory application of dextranase depends on the pH, Brix, temperature, retention time, agitation, type, activity and dose of the applied dextranase, and the enzyme/substrate ratio. Reported optimum conditions for the factory application of concentrated dextranase are: Brix < 25%, temperature 50 °C, pre-limed juice pH 5.90, 1:10 working solution of concentrated dextranase up to 5 mg/mL dosage, retention time 10 min, and 39 rpm agitation. Because (i) some factories have < 10 min juice retention time available and (ii) the relatively high cost of adding dextranase, this small study was undertaken to evaluate and predict dextran hydrolysis in sugarcane juice (3950 mg/kg Haze dextran content) following the optimum conditions with ≤ 5 mg/mL of concentrated dextranase (92,330 DU/mL) and retention times ≤ 5 min. For dextranase concentrations of 4 to 80 mg/L, most of the dextran hydrolysis occurred in the first 1 min after which there were diminishing techno-economic returns with an increase in retention time and dextranase concentration. Reactions of ≤ 5 mg/L dextranase in the juice for 1, 2, 3, and 4 min of reaction time were fitted with either linear or polynomial curves and the equations used to calculate the percent hydrolysis of dextran for low dextranase concentrations from 0.5 to 5 mg/mL for 1 to 4 min. At a very low dose of 0.5 mg/L dextranase, little dextran hydrolysis was gained from 1 to 4 min reaction time, i.e., 3.1 to 6.7%. Approximately 18–19% hydrolysis of dextran was gained by adding 1.5 mg/L for 4 min or 2 mg/L for 3 min. Approximately 25% hydrolysis of dextran was gained by adding 2 mg/L enzyme for 4 min or 3 mg/L for 3 min. Adding 4 mg/L or 5 mg/L caused hydrolysis of up to ~ 44 and 51%, respectively, after 4 min.