Limonoid content of sour orange varieties.

BACKGROUND: Modern Citrus cultivars are thought to have arisen from three parents: the pummelo, the mandarin, and citron. Taxological and genetic data support that sweet and sour oranges share a common parentage. However, as their name suggests, the organoleptic properties of the fruit from these two families is distinctly different. Analysis of the limonoid content of sour orange varieties has been limited. RESULTS: Juice samples prepared from a selection of sour orange cultivars were evaluated for their limonoid A-ring lactone, aglycone, and glucoside contents. Limonoate A-ring lactone concentrations ranged from 11.1 to 44. 9 mg L⁻¹, whereas nomilinoate A-ring lactone levels were found not to exceed 1.2 mg L⁻¹. Total limonoid aglycone and total limonoid glucoside concentrations varied from 2.4 to 18.4 mg L⁻¹ and from 149.0 to 612.3 mg L⁻¹, respectively. Limonoid glucoside profiling by liquid chromatography-mass spectrometry suggest that the sour oranges are distinctly different from sweet oranges and other citrus species. CONCLUSION: Limonoid aglycone and A-ring contents across sweet and sour oranges are similar, whereas limonoid glucoside profiles are distinctly different. Juice prepared from Citrus maderaspatana had the highest limonoid concentrations among the samples tested and could potentially be used for the isolation of limonoid A-ring lactones and glucosides.

Sonication induced intermediate in prion protein conversion.

We have observed that hamster prion protein (PrP(C)) undergoes conformational changes on exposure to heat or sonication. If a sonication induced new conformer is seeded with a small amount of its abnormal pathogenic isoform (PrP(Sc)) it undergoes a significant conversion to a proteinase-resistant isoform. This suggests the presence of a third stable PrP conformer, which may be intermediate in the conversion of PrP(C) to PrP(Sc).

Extraction methods for analysis of citrus leaf proteins by two-dimensional gel electrophoresis.

General procedures for the extraction of Citrus leaf proteins for analysis by two-dimensional electrophoresis (2-DE) were developed through the evaluation and modification of existing methods. Among the methods evaluated, the best results were obtained when Tris-HCl, KCl, and phenol extractions were followed by precipitation with organic solvents to purify and concentrate the samples. The utility of the Tris-HCl extraction method was demonstrated on the leaves of six genetically different Citrus varieties. The methods described are versatile and result in high resolution 2-DE gels of Citrus leaf proteins.

Determination of limonoate and nomilinoate A-ring lactones in citrus juices by liquid chromatography-electrospray ionization mass spectrometry.

The development of delayed bitterness in citrus products is a major problem to citrus producers and juice processors worldwide. A rapid and sensitive liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method has been developed to quantify the recognized precursors of limonoid derived delayed bitterness, limonoate and nomilinoate A-ring lactones, in a wide variety of citrus juices. The limonoid A-ring lactones were isolated by solid-phase extraction from juice samples, analyzed by negative ion LC-ESI-MS and quantified utilizing the standard addition method.

Isolation and characterization of limonoate and nomilinoate A-ring lactones.

A method combining solid-phase extraction and reversed-phase high-performance liquid chromatography is described for the isolation of two key metabolites in the limonoid biosynthetic pathway critical to citrus quality. Potassium salts of limonoate A-ring lactone and nomilinoate A-ring lactone were isolated from young Chandler pummelo seedlings and characterized on the basis of proton and carbon NMR data.