Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
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 α-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.Smanjenjem gorčine sokova citrusa povećala bi se njihova prihvatljivost za potrošače. Gorčina soka grejpfruta može se smanjiti enzimskim procesom koji poboljšava komercijalnu vrijednost soka, a ne smanjuje njegov pozitivan utjecaj na zdravlje. Uporaba jeftinih, jednostavnih i djelotvornih metoda imobilizacije, kombiniranih uz primjenu visokoga tlaka, ključni su za odgorčavanje sokova citrusa. Svrha je ovog istraživanja smanjiti gorčinu soka grejpfruta primjenom visokoga tlaka i naringinaze imobilizirane u kapsulama kalcijeva alginata. Naringinaza, tj. α-ramnopiranozidaza, hidrolizira naringin (flavanon glikozida što je osnovna gorka komponenta soka grejpfruta) u naringenin koji nema okus. Visoki tlak može aktivirati ili inhibirati aktivnost enzima ovisno o sastavu proteina i uvjetima hidrolize. U radu je najprije istražena hidroliza naringina u modelnoj otopini (acetatni pufer 0,02 M; pH=4,0), a zatim u soku grejpfruta. U modelnoj je otopini pri 160 MPa i 37 °C postignuto 50 %-tno povećanje koncentracije reducirajućih šećera, u usporedbi s reakcijom pri atmosferskom tlaku. Veća koncentracija naringenina (33 mg/L) postignuta je pri 54 °C i visokom tlaku od 200 MPa, što odgovara 72 %-tnoj redukciji narinigina u modelnoj otopini, dok je pri atmosferskom tlaku (0,1 MPa) redukcija naringina iznosila samo 35 %. Smanjenje koncentracije naringina može se povezati sa smanjenjem gorčine soka, tako da je postotak smanjenja procijenjen prema koncentraciji preostalog naringina. U soku grejpfruta smanjenje gorčine od 75 % postignuto je pri tlaku od 160 MPa, na 37 °C, tijekom 20 minuta
