Pineapple peel carboxymethyl cellulose/polyvinyl alcohol/mesoporous silica SBA-15 hydrogel composites for papain immobilization

Hydrogel composites based on pineapple peel carboxymethyl cellulose, polyvinyl alcohol and mesoporous silica SBA-15 were synthesized by an eco-friendly method of repeated freeze-thaw cycles for the application of papain immobilization. The experiment was optimized to obtain an efficient papain immobilization carrier. Simultaneously the immobilization conditions, including enzyme concentration, pH, crosslinker concentration and cross-linking time were optimized. The immobilized papain had maximum activity at low reaction temperature of 40 °C and showed pH-sensitivity by exhibiting a rapid decrease of activity within a narrow range from pH 7.0 to pH 7.5. Compared with the free papain, the immobilized papain revealed enhanced pH, thermal and storage stability. After 2 h incubation at 80 °C, the immobilized papain retained 56% of its initial activity while the free papain only retained 16%. After 10 days of storage, 79% of the initial activity was retained for the immobilized papain while only 27% for the free papain.