Bitter limonoides

Manners GD, Breksa AP III, Schoch TK, Hidalgo MB. Analysis of bitter limonoids in citrus juices by atmospheric pressure chemical ionization and electrospray ionization liquid chromatography-mass spectrometry. J Agric Food Chem 2003 51(13) 3709-3714. 

Bitterness, caused by naringin, is also removed by an enzyme, naringinase. Another possibility would be to eliminate one or more of the enzymes in the limonin biosynthetic pathway by using recombinant DNA techniques. Limonin, a triterpenoid, is probably synthesized via the mevalonate pathway, as are the monoterpenoid flavor compounds. It appears that nomilin, a precursor of limonin, is synthesized in the stems and roots of citrus and then the precursor transported to the fruit where it is converted by several enzymes to limonin and other bitter limonoids (46). 

Azadirachtin, meliacin, azadironic acid bitter limonoids (Nortriterpenoids). Nimbibin, nimbin, salanin. Sesquiterpenes. Limonoids,... 

This review paper summarizes the biochemical and biological aspects of limonoids in citrus and presents possible preharvest approaches to reduce bitter limonoids in citrus fruits. 

Limonin and nomilin are two bitter limonoids present in citrus juices. Systematic organoleptic tests showed that the bitterness threshold is 6 ppm (5) for limonin, and 6 ppm (6) or 3 ppm (7) for nomilin. The bitterness due to limonin develops gradually in juices after extraction from certain varieties of oranges, grapefruit, lemon, Natsudaidai, mandarin and some other minor citrus such as Iyokan and Ponkan. This phenomenon is generally referred to as "delayed bitterness". 

Fruits of the genus Citrus constitute one of the world s most important horticultural crops. Production is at least 45 million tons, of which about 45% is converted into a variety of processed products (Maier, 1983). After expression of citrus juices, especially orange juice, precursors that occur in the juice are converted to bitter limonoids, primarily li-... 

Nomilin, a limonoid that is approximately twice as bitter as limonin (Hashinaga et al. 1977), was found in various citrus species. Nomilin concentrations ranging from 1.6 to less than 0.1 ppm were found in commercial grapefruit juices with the greatest concentration found in early-season juices (Rouseff 1982). The concentrations in the early season exceed the detection threshold of 0.8 ppm but they are below the recognition threshold of 2.1 ppm (Rouseff and Matthews 1984). Other bitter limonoids are also present in the citrus juices, but at much lower concentrations than limonin. They do not contribute significantly to the bitterness problem. 

A variety of methods have been proposed for the detection and quantification of bitter limonoids in citrus. Most methods were developed specifically for the quantification of limonin in citrus juices. The early techniques included colorimetry, fluorimetry, and gas chromatography. 

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. 

Limonoids are a group of chemically related triterpene derivatives found in the Rutaceae and Meliaceae. Limonin, a bitter member of the group, occurs widely in citrus juices. It has commercial significance because bitterness (excessive bitterness in the case of grapefruit) reduces juice quality. Dreyer (1) and Connolly et al. (2) have reviewed the chemistry and biochemistry of limonoids. 

More recently Maier et al. (3) published a comprehensive review of the limonoid constituents of Citrus and the impact of limonin bitterness on juice quality. This paper summarizes the chemical, biochemical and juice quality aspects of limonoids in Citrus (and related genera) and presents relevant advances since previous reviews. 

While most of the limonoids of Citrus have been isolated from seeds, several occur in detectable amounts in other parts of the fruit. Minor amounts of deacetylnomilin, nomilin, obacunone, de-acetylnomilinic acid and nomilinic acid were identified in extracts of navel orange peel (37). 17-Dehydrolimonoate A-ring lactone was isolated from peel and juice of navel oranges (38) and nomilin has been reported to occur in grapefruit juice and juice vesicles (39). The only Citrus limonoids known to be bitter are limonin, VI, XII, obacunoic acid and IX (3). 

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). 

V. P. Maier S. Hasegawa R. D. Bennet L. C. Echols, Limonin and Limonoids-Chemistry, Biochemistry and Juice Bitterness. In Citrus Nutrition and Quality, S. Nagy, J. A. Attaway, Eds. ACS Symposium Series No. 143 American Chemical Society Washington, DC, 1980 pp 63-82. 

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 C2(, nortriterpenoids deriving from a C30 triterpene precursor. The best known limonoids are the Azadirachta indica (neem tree) antifeedant azadirachtin (C50L C40 C6 -C60(epoxide methylene cross-link) furan) and the Citrus species (Rutaceae) bitter antifeedant limonin (G50L G40 G6 G6 C50L(epoxide)-furan). Limonin gives a delayed bitter taste to Citrus fruit. The limonoids are typically bitter compounds with insect antifeedant activity... 

The relationship between the Simaroubaceae and limonoid bitter principles has been confirmed by showing that glaucarubolone (102) has a triterpenoid origin. ... 

Biochemistry and Biological Removal of Limonoid Bitterness in Citrus Juices... 

Bitterness due to limonoids in a variety of citrus juices is a major problem of the citrus industry worldwide and has significant negative economic impact. Recently, Maier, et al. 

Limonoids are a group of chemically related triterpene derivatives found in the plant families, Rutaceae and Meliaceae. Among 37 limonoids reported to occur in citrus and hybrids, four are known to be bitter. They are limonin, nomilin, ichangin and nomilinic acid. Limonin is the major cause of citrus juice bitterness and is widely distributed. Nomilin is also known to contribute to limonoid bitterness in grapefruit juice (4). 

Citrus ichangensis possesses an unusual distribution of limonoids (20). Unlike other species of citrus, fruit tissues and seeds of . ichangensis contain very high concentrations of nonbitter ichangensin and very low concentrations of bitter limonin. It also contains relatively high concentration of nonbitter deacetylnomilin. Quantitative analysis showed that a ratio of ichangensin to limonin in the fruit tissue is approximately 50 to 1. 

---