Optimization and Isolation of Grapefruit Secondary Metabolites and Their Changes Due to Production Systems and Storage

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2012-12-12

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Abstract

Grapefruits have shown a multitude of health promoting properties owing to their secondary metabolites. Modulation of production systems to increase the levels of nutrient content (secondary metabolites) in fruits and vegetables is a topic of intense scientific debate. The goal of this present research is to understand the influence of production systems and storage on grapefruit secondary metabolites and to identify and purify potentially bioactive grapefruit secondary metabolites.

The first and second studies encompass the optimization of extraction procedures for the accurate quantification of flavanones and vitamin C respectively. The grapefruit flavanones were best extracted using two times dimethyl sulfoxide with the grapefruit sample volumes. Three percent meta phosphoric acid is the best extraction solvent and 5mM of TCEP is the best reducing agent for the quantification of vitamin C in grapefruit. The optimized extraction procedures were used for the quantification of grapefruit flavanoids and vitamin C.

The third and fourth studies encompass the influence of production systems (organic or conventional) and storage on various groups of grapefruit secondary metabolites and their antioxidant properties. Vitamin C, limonoids and flavonoids were found to be higher in organic grapefruits compared to conventional grapefruits in the November 2008 harvest. However, there were no significant differences observed in the above mentioned secondary metabolites in the February 2010 harvest. In general, during storage the vitamin C losses were minor while limonoids and carotenoids losses were significant. In the 2010 sample, flavonoid levels increased during storage. The total phenolics and total antioxidant (DPPH) showed trends similar to flavanones during storage. The results of these studies suggest that organic production (might have) caused a small increase in the levels of a few secondary metabolites. However, it was the harvest season that had a greater impact that probably masked the effect of production systems in the 2010 sample.

The fifth study focused on the isolation and purification of grapefruit minor bioactive compounds. Seven coumarins and two polymethoxy flavones including Meranzin and pranferin were purified from grapefruit byproducts such as grapefruit oil and peels using solvent partitioning and flash chromatography. The purified dihydroxy bergamottin was used as a standard in the quantification of coumarins from organic and conventional grapefruits. In future, pure coumarins, especially meranzin and pranferin, produced using various isolation techniques needs to be studied to understand the mechanism of drug interaction.

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