Title : Grapefruit debittering by simultaneous naringin hydrolysis and limonin adsorption using immobilized naringinase
Naringin and limonin are the two main bitter compounds of citrus products such as grapefruit juice. To reduce or remove bitterness in citrus juices below the threshold level for consumer acceptability, several physicochemical and biochemical strategies have been developed; however, up to now the problem has not been completely solved. The aim of this investigation was to evaluate a single strategy that incorporates the advantages of physical and biochemical approaches for citrus juice debittering. The proposed strategy was based on the design of an immobilized biocatalyst of nariginase able to simultaneously hydrolyze naringin and adsorb limonin, reducing their concentration in grapefruit juice below their thresholds. Naringinase was covalently immobilized in the heterofunctional supports butyl-glyoxyl agarose (BGA) and octyl-glyoxyl agarose (OGA) through glyoxyl groups of carriers, while the alkyl chains of the supports were utilized for limonin adsorption. The immobilized biocatalysts were characterized in terms of optimal pH and temperature and were compared with soluble enzyme. Debittering of grapefruit juice was evaluated using soluble enzyme, enzyme-free supports, and immobilized catalysts. Enzyme immobilized in BGA reduced naringin and limonin concentrations in 54 and 100%, respectively; while the use of catalyst immobilized in OGA allowed a reduction in 74 and 76%, respectively, obtaining a final concentration of both bitter component under their detection threshold. The use of OGA biocatalyst presented better results than when soluble enzyme or enzyme-free support were utilized. Biocatalyst was successfully applied in juice debittering along five repeated batch of 24 h each, and the final residual activity of biocatalyst was over 60%. These results show the potential of this strategy for citrus juice debittering and could offer a technical and economic advantage in relation to the processes currently utilized.
Acknowledgement: This research was funded by Chilean Fondecyt Grant 11180726.
- The new advances in support functionalization allows us to use the carrier not only for the improvement of enzyme performance but also to adsorbed undesired molecules.
- The improvement of debittering process by a single strategy that incorporates the advantages of physical and biochemical approaches, being possible to compare three strategies: free enzyme; enzyme-free support; immobilized enzyme.
- A single strategy that effectively combines both principles could offer the technical and economic advantage of reducing the number of operations required for citrus juice debittering.