Papaya peel valorization for production of acidic pectin methylesterase by Aspergillus tubingensis and its application for fruit juice clarification

Production of an extracellular, acidic pectin methylesterase was carried out by a newly isolated fungal strain identified as Aspergillus tubingensis using dried papaya peel under solid state fermentation. Response Surface Methodology involving Box-Behnken Design was employed for the optimization of process parameters viz. moisture content, period of fermentation, inoculum size and particle size of papaya peels. Maximum yield of pectin methylesterase was 246.83 U/g dried substrate, obtained by inoculating 10 g of papaya peel with 1×107 spores/ml, at initial 86% moisture content and particle size 2 mm after 120 h of fermentation period. The nearly same optimized values (R2=0.99) and experimental values (R2=0.96) indicated the validity of the statistical model. Under these experimental designs, the yield of pectin methylesterase increased 3.39 fold, which was much efficient and economical than “one factor at a time” methodology. Crude pectin methylesterase showed maximum activity at 50 °C and pH 4.6. Addition of partially purified enzyme increased the pineapple juice clarity as indicated by an increase in % transmission at 650 nm from 3.1 to 19.5 and decrease in pH from 4.3 to 3.0.