Citrus limonin levels

Limonin Levels of Citrus Juices. A compilation of limonin values in various citrus juices is given in (3). Limonin has been found in essentially all varieties of citrus juices examined. Although there is a considerable range of limonin values reported, certain trends are apparent. 

In the food industry, high-performance liquid chromatography (HPLC) is the most widely used technique for the determination of limonin levels in citrus juices, since it is accurate and reliable. Most of the HPLC methods developed are for the analysis of limonin in citrus juices. These methods may not work for other bitter limonoid aglycones and/or tissues. 

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). 

Limonin bitterness is especially acute in juice obtained from short maturation time fruits such as navel oranges. Juices obtained from most of the other citrus crops, such as Valencia oranges, usually do not have the limonin bitterness problem, as the concentration of limonin has decreased sufficiently by the time the processing season starts. Juices from navel oranges, particularly early- to mid-season fruits, can contain over 30 ppm of limonin, which is well above the bitterness detection threshold of 6 ppm. Grapefruit also has significant levels of limonin, which vary from 10 ppm in the early season to 1 ppm or less in the late season. 

Deoxylimonin and deacetylnomilin were found to cross-react with the limonin antibody, but the relatively low levels of these two compounds in citrus tissues should not add to the limonin values significantly. 

Essential oils obtained by cold pressing or extraction contain, in addition to volatile substances, low volatile and non-volatile substances, such as oleoresins. For example, the dry matter content in citrus essential oils is about 4%. The main components are flavonoids, such as naringin, or metabolites of bitter triterpenes of limonin type. Coumarins such as scopolaron are present at a level of 1.5%, along with furanocoumarins (psoralens), such as bergaptene and bergamottin. 

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