Limonoid glucosides, citrus

Biochemical studies carried out at the Pasadena laboratory have shown how, where and when limonoids are biosynthesized and accumulate in citrus. The recent discovery of limonoid glucosides has cleared an unanswered question of how limonoid aglycones disappear at late stages of fruit growth and maturation. 

Two limonoid glucosides, obacunone and nomilin glucoside, were extracted from Citrus tangeria and analyzed on a Cig column (A = 215nm) using a 15/85... 

Limonoid glucosides and deoxylimonin were found to cross-react with the antibodies. The relatively low levels of deoxylimonin in citrus juices should not contribute to the limonin values significantly. However, the high concentration of limonoid glucosides, which can be over 400 ppm, can give artificially high limonin values. 

Limonin has recently become commercially available from several chemical companies including Aldrich and Sigma. Nomilin is also available from Takasago (Toyko, Japan). Other limonoid aglycones and limonoid glucosides are currently only obtained by isolation from citrus seeds. See Herman et al. (1992) for extraction and isolation methods. 

Hasegawa S, Bennett RD, Herman Z, Fong CH, Ou P (1989) Limonoid glucosides in citrus. Phytochemistry 28 1717-1720... 

Raman, G., Cho, M., Brodbelt, J.S., and Patil, B.S. 2005. Isolation and purification of closely related Citrus limonoid glucosides by flash chromatography. Phytochemical Analysis, 16, (3), 155-160. 

Several limonoids are known to be bitter principles of citrus (Rutaceae). A typical example is limonin. Although fresh juice does not elicit a bitter taste, sometimes it becomes bitter after heating or storage. This is explained by the formation of bitter-tasting limonin by deglycosylation and further cyclization from limonin glucoside, which is present in citrus fruit tissue and seeds and does not exhibit bitterness.146 Recently, it was reported that limonin had antitumor activity.147 Besides limonin, nomilin and obakunone, which are considered to be... 

Limonoids are a group of chemically related triterpene derivatives found in the Rutaceae and Meliaceae families. There are two groups of limonoids the aglycones and their corresponding glucosides. A total of 36 limonoid aglycones have been isolated from Citrus and its hybrids (Table 1). Five of them are bitter in taste -limonin, nomilin, nomilinic acid, obacunoic acid and ichangin (Fig. 1). In citrus juices, limonin is the major cause of delayed bitterness. 

Breksa, A.P. and lharra, P. 2007. Colorimetric Method for the Estimation of Total Limonoid Aglycones and Glucoside Contents in Citrus Juices. Journal of Agricultural andFood Chemistry, 55, (13), 5013-5017. 

Figure 7.29 Citrus fruit are a rich source of terpenoids including the Cio diterpenes (+)- and (—)-limonene and a number of more complex limonoids which are distinctive in that the glucosides are tasteless while the aglycones have a bitter taste.

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