Enzymatic clarification of orange juice in continuous bed reactors: Fluidized-bed versus packed-bed reactor

Abstract

In this study, a commercial enzyme cocktail designed for fruit juice clarification was immobilized on chitosan beads activated with glutaraldehyde and used for setting-up continuous packed-bed and fluidized-bed reactors. Firstly, the enzyme cocktail concentration in the immobilization process was tested to get maximum biocatalyst activity in the reaction. Then, the effect of pH and temperature on the free and immobilized enzyme cocktail stability and activity were studied. Despite the low enzyme cocktail activity recovery after immobilization (1 %), the stability of immobilized enzyme was greater compared to free enzyme, even under extreme reaction conditions. For example, when activity was measured at 90 °C and pH 4.8, the immobilized enzyme cocktail retained 80 % of its initial activity while the free enzyme retained only 35 %. Finally, the clarification capacity of the biocatalysts using orange juice was tested, providing clearer juices when performed in the fluidized-bed reactor, showing 60 % of its initial clarification capacity after 72 h of continuous use. Otherwise, the clarification rate in the packed-bed reactor decreased linearly during 54 h, probably due to the formation of dead zones and preferential paths along the bed. Pectinase immobilized on chitosan particles and used in fluidized-bed reactor seems to be a good alternative for large scale application on juice clarification.