Optimization of glucose production from liquid pineapple waste using immobilized invertase in PVA- alginate-sulfate beads

Abstract

Pineapple (Ananas cosmosus) waste is known as a byproduct of the pineapple processing industry and typically consists of residual pulp, peels and skin. The liquid pineapple waste used in this study consists of sucrose (76.8%), glucose (12.6%) and fructose (10.5%). Through an enzymatic hydrolysis process, the sucrose in the waste can be converted into glucose and fructose. In this study, the conversion of sucrose to glucose was performed with the help of invertase enzyme. PVA-alginate-sulfate beads were used as an entrapment matrix to immobilize invertase using entrapment-crosslinking method. RSM comprising Box-Behnken design was successfully applied in this study as a tool to evaluate the interactive effects and to obtain the optimum operating conditions for the enzymatic hydrolysis. Four parameters were varied which was pH (4-6), temperature (40-60oC), agitation rate (100-200 rpm) and amount of immobilized beads (3-6 g). Results revealed that the highest sugar content in the liquid pineapple waste was sucrose which was 79.6 g/L. While for the cations content, potassium had the highest composition which was 2195.0 mg/L whilst phosphorus was the highest anion content with the value of 79.23 mg/L. Meanwhile, the pH of the pineapple waste was 4.0. Hydrolysis of the liquid pineapple waste showed that 95% of sucrose content in the waste was hydrolyzed to glucose after 3 hours of hydrolysis and the overall glucose generated from the hydrolysis was approximately 1131% of its original content. The optimum operating conditions derived via RSM were: pH 4.74, temperature 50.11oC, agitation rate of 147.68 rpm and amount of immobilized beads used were 4.45 g. The experimental yield of glucose was found to be 111.42 g/L (850.5%) and sucrose 25.70 g/L (32.3%) under optimum conditions, which correlated well with the maximum predicted value of glucose and sucrose 110.13 g/L (840.7%) and 25.93 g/L (32.6%) respectively.