Evaluation of the Effect of High Pressure on Naringin Hydrolysis in Grapefruit Juice with Naringinase Immobilised in Calcium Alginate Beads

The reduction of bitterness in citrus juices would increase their acceptance by the consumer. This reduction in grapefruit juices can be achieved as a result of an enzymatic process, with improved commercial value and maintenance of health properties. The use of a cheap, simple and effective immobilisation method combined with high pressure can be a key asset in the debittering of citrus juices. The aim of this study is the debittering of grapefruit juice under high pressure, with naringinase immobilized in calcium alginate beads. Naringinase, an a-rhamnopyranosidase, hydrolyzes naringin (a flavanone glycoside and primary bitter component in grapefruit juice) to naringenin, which is tasteless. High pressure can activate or inhibit enzymatic activities depending on the proteins and conditions. The hydrolysis of naringin was first evaluated in model solution (acetate buffer 0.02 M, pH=4.0) and then in grapefruit juice. In model solution, at 160 MPa and 37 °C, a 50 % increase in the concentration of reducing sugars was obtained when compared to the reaction at atmospheric pressure. The higher naringenin concentration (33 mg/L) was obtained at 54 °C under high pressure of 200 MPa, which corresponds to a naringin reduction of 72 % in model solution, while at atmospheric pressure (0.1 MPa), the naringin reduction was only 35 %. The decrease in naringin content can be directly correlated with the reduction in bitterness. From the concentration of residual naringin, the percentage of reduction in bitterness was evaluated. In grapefruit juice, a debittering of 75 % occurred with a pressure of 160 MPa at 37 °C for 20 minutes.