Characteristics of immobilised β-glucosidase and its effect on bound volatile compounds in orange juice

In this study, bound volatile compounds were isolated and extracted with Amberlite XAD-2 resin and then hydrolysed by free or immobilised beta-glucosidase. The released bound volatiles were analysed by GC-MS. In addition, the optimisation of immobilisation method on sodium alginate and the characteristics of immobilised beta-glucosidase were studied. The results showed that crosslinking-entrapment was the best method. The optimal conditions of this method were as follows: sodium alginate concentration 3.5%, glutaraldehyde concentration 1%, crosslinking time 3 h, immobilisation time 2 h and CaCl2 concentration 3%. The optimum temperature for beta-glucosidase (65 degrees C) was decreased by 10 degrees C after immobilisation, while the optimum pH values for free and immobilised beta-glucosidase were both at pH 5.0. The K-m values of free and immobilised beta-glucosidase were 14.89 and 0.59 m, respectively. In total, thirteen and six bound volatile compounds were detected in orange juice hydrolysed by free and immobilised beta-glucosidase, including benzenic compounds, terpenic compounds, hydroxy esters, C-13-norisoprenoids and alcohols.