Laccase-gum Arabic conjugate for preparation of water-soluble oligomer of catechin with enhanced antioxidant activity

Catechin was oligomerized using free laccase and laccase-gum Arabic conjugate. The process of oligomerization was optimized with respect to solvent, ratio of solvent to buffer (0.2:10 to 1:10), pH of buffer (3-10), enzyme (575-18,400 U/mg) and substrate concentration (1-7 mM). Maximum production of oligomer was observed in methanol at ratio 0.6:10 of methanol:buffer of pH 5 using 2300 U/mg of laccase and 5 mM of catechin. The laccase-gum Arabic conjugate showed lower activity but higher stability than free laccase in methanol. Free laccase produced cross linked water-insoluble oligomer, whereas conjugated laccase produced linear water-soluble oligomer. The linear water-soluble oligomer showed higher antioxidant activity, as determined by the DPPH assay, and reducing power as compared to monomer making it suitable for biological applications. The molecular weight of the linear oligomer was found to be 13.14 kDa, which suggested it to be composed of 45 monomer units. Further characterizations of linear and cross linked oligomer were done using FTIR and differential scanning calorimetry.