Limonoid analysis

Anthothecol (94) and hirtin (95) have been interrelated via the trione (96). Dysobinin (97) is a new tetranortriterpenoid from Dysoxylum binectariferum7 An intermediate in a projected limonoid synthesis has been shown to have structure (98) by X-ray analysis. ... 

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. 

BicydononanoUdes.—Utilin, C41H52O17, a complex limonoid from Entandro-phragma utile, has been shown by X-my analysis to have the structure (93) with the unprecedented feature of bond formation between one of the C-4 methyl... 

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. 

Stems are the major site of nomilin biosynthesis from acetate in citrus (26). Analysis of the phloem, the cortex and the inner core regions of the stem showed that the phloem region is the site of nomilin biosynthesis from acetate (27). Root tissues also have this capacity. Leaves, fruits and seeds are either incapable of biosynthesizing limonoids from acetate or have a very low capacity. However, these tissues are capable of biosynthesizing limonoids from nomilin. Nomilin is translocating from the stem to other locations, where it is further biosynthesized to other limonoids (26). 

The technical feasibility of an immobilized cell system was demonstrated on a laboratory scale for use in reducing limonoid bitterness of citrus juices. The treatment caused no significant adverse effect on the other juice constituents as judged by analysis of ascorbic acid, citric acid, malic acid, sucrose, glucose and fructone. 

The structure of phragmalin (75), a complex limonoid from Entandrophragma caiidatum, has been determined by X-ray analysis." It is closely related to utilin (see Vol. I, p. 177) and occurs in combination with nicotinic and isobutyric acids. 

Tetranortriterpenoids.— Two further new limonoids from Melia azedarach are ohchinolides A (44) and B (45). X-Ray analysis confirmed the structure of ohchinolide Other new limonoids reported this year are pseudrelone B (46) from Pseudocedrela kotschyii (Meliaceae), febrinins A (47) and B (48)... 

Miyake et al. (1991) found that extraction of neutral limonoids from Natsudaidai seeds depended upon the solvents used, time of extraction, and methods of sample preparation prior to extraction. Since the seeds contain high concentrations of both dilactones and monolactones with dilactones dominating, direct organic solvent extraction method yields lower values than extraction with the Hasegawa method mentioned above. The optimum extraction method was determined to be grinding the seeds in 0.1 M Tris buffer at pH 7.0 and incubating the mixture for at least 20 h at room temperature. It was followed by acidification and extraction with methylene chloride. The organic phases can then be evaporated off to concentrate the samples for analysis. 

Since the solvent system which separates the limonoids in one sample may not be satisfactory for another, several solvent systems should be tried for a particular sample in order to find the one that has the best separation. For example, Fong et al. (1992) used solvent system (A) to quantify limonin and nomilin in the extract of Valencia orange flesh, and solvent system (C) to quantifjr deacetylnomilin in the same extract. For the analysis of the extract from Valencia orange peel, system (B) was used to quantify limonin, nomilin and deacetylnomilin. 

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. 

The above HPLC methods are used for the analysis of limonin and/or nomilin in citrus juices. Herman et al. (1989) used a reverse phase HPLC method to quantify limonoids in fruits, seeds, leaves, stems and seedlings of Citrus ichangensis. The extraction procedure of Hasegawa et al. (1984) as described in Section 2.1.1 was followed. The dried extracts were dissolved in 50% methanol prior to injection. A reverse phase C-18 column (4.6 X 250 mm) was used. The column was eluted isocratically with water-methanol-acetonitrile (49 41 10) at a flow rate of 1 ml/min. Limonoids were detected by UV absorption at 210 nm. This... 

Rouseff RL, Nagy S (1982) Distribution of limonoids in citrus seeds. Phytochemistry 21 85-90 Seitz U, Oefner PJ, Nathakarnkitkool S, Popp M, Bonn GK (1992) Capillary electrophoretic analysis of flavonoids. Electrophoresis 13 35-38... 

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. 

Schoch T.K., Manners G.D., Hasegawa S. Analysis of limonoid glu-cosides from citrus by electrospray ionization liquid chromatography-mass spectrometry. Journal of Agricultural and Food Chemistry, 49 1102 1108 (2001). 

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