Limonin from citrus juices, removal

Control of Juice Bitterness. A number of advances have been reported in this field since it was last reviewed (3). A commercial application of the cellulose acetate adsorption technique for the removal of limonin from citrus juices was undertaken (49). New sorbent gel forms of cellulose esters for adsorption of limonin were developed (50). Knowledge was gained that limonoids are biosynthesized in citrus leaves and translocated to the fruit (12) and that specific bioregulators can inhibit accumulation of XIV in citrus leaves (15). Additional studies were carried out on the use of neodiosmin to suppress limonin and other types of bitterness (30,51). The influence of extractor and finisher pressures on the level of limonin and naringin in grapefruit juice was reported (34). Also, further studies were conducted on the microbial sources and properties of limonoate dehydrogenase (52), the enzyme that converts XIV to XV and can be used to prevent limonin from forming in freshly expressed citrus juices (53). 

Physical Removal During the past several years, significant progress has been made in the development of selective adsorption processes for removal of two bitter principles, limonin and naringin, from citrus juices. Adsorbents such as cellulose esters (43), cross-linked polystyrenes (44) and 6-cyclodextrins (45, 46) have been shown to reduce effectively the limonin bitterness in the juice. 

Polystyrene-divinylbenzene cross-linked copolymer adsorbent resins removed effectively both limonin and naringin from citrus juices (44). Over 85% of limonin was adsorbed from about 50 bed volume juices of grapefruit, navel orange, lemon and tangerine. Up to 70% of naringin was also removed from grapefruit juice. 

Not only analytical or preparative separations can be performed on cyclodextrin polymer columns, but also undesired components can be removed from aqueous solutions, bitter tasting substances (narin-gin, limonin) can be removed or at least their concentration can be strongly reduced after treatment of citrus juice with cyclodextrin polymers in batch or column process (65,66). Phenylalanine can be eliminated from dietetic protein hydrolysates (67), water-soluble organic substances (e.g. polychlorinated biphenyls (68), 2-naph-talenecarboxylate or phenol can be removed from aqueous solutions (e.g. from pharmaceutical wastewater) by polystyrene-cyclodextrin derivatives (69), by 8-cyclodextrin immobilized on cellulose (70) or by 6-cyclodextrin-polyurethane polymer (71). 

Cellulose acetate jels and beads were used to effectively remove limonin below the bitterness threshold from citrus juies (43). The resins can be regenerated readily by washing with a small volume of warm water. The process has been used commercially in Australia in debittering bitter orange juices (47). 

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