Re-recycling agro-industrial waste: exploiting activated carbon from cocoa shells after solid-state fermentation as a support for endoglucanase immobilization

Endoglucanases have been increasingly applied in industrial processes but have high production costs and recovery difficulties. Using agro-industrial waste as an alternative growth media and employing immobilization techniques for enzyme reuse and stabilization may greatly reduce production expenses. We examined the potential of reusing cocoa shells, an alternative growth medium and abundant agro-industrial waste in the north and northeast regions of Brazil, as a substrate for enzyme immobilization. Endoglucanase from Penicillium roqueforti was immobilized on activated carbon derived from cocoa shells pretreated by solid-state fermentation with P. roqueforti (ACPr) or Aspergillus niger (ACAn) and without fermentation pretreatment (ACC). At 80 °C and pH 6–13, immobilized endoglucanase showed high catalytic activity, whereas approximately 90% of enzyme activity was lost in solution. The immobilized enzyme maintained its activity for 120 days of storage at 4 °C (> 80% activity on all supports); 10% of the enzymatic activity was maintained in solution. After reusing the immobilized enzyme for three reaction cycles, endoglucanase activity remained above 50% on all immobilization supports; after five cycles, the relative enzyme activities for ACPr, ACAn, and ACC were 30%, 33% and 32%, respectively. Thus, endoglucanase from P. roqueforti can be immobilized on activated carbon from cocoa shells to maintain its activity at high temperature and various pH levels and can be reused for up to five cycles with a four-fold longer storage time. This simple adsorption protocol can reduce production costs and increase industrial applications of the biocatalyst, enabling reuse of agro-industrial waste after solid-state fermentation in fermentable sugar production.