FURTHER STUDIES ON ENZYMIC HYDROLYSIS OF DEXTRAN IN MILL JUICES BY DEXTRANASE AND FUNGAL a-AMYLASE

The kinetics of dextranase activity were studied using dextran-containing samples of mixed juice taken from mills in Puerto Rico and Jamaica. Mean values of the initial enzyme velocity (V) were 0,063 and 0,173 mg dextran hydrolysed/min/unit enzyme in Puerto Rico and Jamaica respectively. Mean substrate concentrations, expressed as dextran % w/v juice determined by the haze analysis technique, were 0,064 and 0,080% w/v respectively. Estimated values of the kinetic constants Vmax (apparent) and Km (apparent) were significantly greater in Jamaica than in Puerto Rico. This indicated that differences existed in the nature of the substrates between the two countries, and suggests that each location for dextranase treatment should be considered individually. In both locations the initial enzyme velocity was dependent on substrate concentration. Fungal a-amylase showed little activity in hydrolysis of "dextrans" in Puerto Rican juices, whereas in Jamaica its mean activity was about 60% that of dextranase at similar enzyme concentrations. This suggested that the so-called "dextran" determined by haze analysis comprised a variable and heterogenous mixture of polysaccharides. Mixtures of dextranase and fungal cc-amylase exhibited additive rather than synergistic effects. No economic advantage would be incurred by using mixtures of the two enzymes. Calculations based on experimental data showed that a dextranase dosage of 6-7 units/100 ml juice would be needed to hydrolyse + of the dextran in mixed juice containing moderate-to-high dextran levels, within 20 minutes at 50 C. Treatment costs (enzyme only) were estimated to be f0,5/ton sugar.