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Lipid oxidation, especially the oxidation of polyunsaturated fatty acids, is a significant issue in the food industry impacting both food quality and health of consumers. Apple skin was investigated as a source of natural antioxidants. The phenolic compound composition and antioxidant properties of 21 selected apple genotypes were evaluated. The lipid stabilizing ability of the apple skin extracts was examined using an aqueous emulsion system of methyl linolenate. The total phenolic concentrations determined by high-performance liquid chromatography tandem mass spectrometry of methanolic extracts of skins of the apple genotypes varied from 150 to 700 mg/100 g DW. The antioxidant capacity measured by Folin-Ciocalteu (16.2 to 34.1 mg GAE/100 g DW), ferric reducing antioxidant power (1.3 to 3.3 g TE/100 g DW), oxygen radical absorbance capacity (5.2 to 14.2 g TE/100 g DW), and percent inhibition of oxidation of methyl linolenate (73.8% to 97.2%) varied among the apple genotypes. The apple skin extracts, specifically the crab apple varieties such as "Dolgo," were revealed to be effective inhibitors of oxidation of polyunsaturated fatty acid in a model system and thus can be considered as a potential source of natural food antioxidants.

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Rupasinghe, H. P. V., Huber, G. M., Embree, C. and Forsline, P. L. 2010. Red-fleshed apple as a source for functional beverages. Can. J. Plant Sci. 90: 95Á100. The potential of anthocyanin pigments in fruits and vegetables to provide protection against oxidative damage is well known. Cyanidin-3-O-galactoside is a naturally occurring red pigment commonly found in skin of apples but also present in flesh of certain crab apple and apple genotypes. The purpose of this study was to investigate the cyanidin-3-O-galactoside concentration and antioxidant capacity of juice made from 14 genotypes of red-fleshed apples in comparison to three white-fleshed apple cultivars and three commercial apple juices. Cyanidin-3-O-galactoside was found only in the juice made from red-fleshed apple genotypes with the highest concentrations (39 mg L(1 ) in a crab apple Roberts Crab. The antioxidant capacity measured using the Folin-Ciocalteu, the ferric reducing antioxidant power (FRAP), and the oxygen radical absorbance capacity (ORAC) assays were the greatest in juice prepared from the red-fleshed genotypes Babine and Malus pumila Niedzwetzkyana, a red-fleshed crab apple genotype. The antioxidant capacity measures were strongly correlated with each other; however, there was no correlation between the concentration of cyanidin-3-O-galactoside and the antioxidant capacity measures. The juice quality parameters 8Brix and titratable acidity values were not significantly different among the juices made from the redfleshed apples, commercial apples and commercial apple juice products.

Quercetin and quercetin glycosides are physiologically active flavonol molecules that have been attributed numerous health benefits. Recovery of such molecules from plant matrices depends on a variety of factors including polarity of the extraction solvent. Among the solvents of a wide range of dielectric constants, methanol recovered the most quercetin and its glycosides from dehydrated ‘Idared’ apple peels. When ultrasonication was employed to facilitate the extraction, exposure of 15 min of ultrasound wavelengths of dehydrated apple peel powder in 80% to 100% (v/v) methanol in 1:50 (w:v) solid to solvent ratio provided the optimum extraction conditions for quercetin and its glycosides. Acidification of extraction solvent with 0.1% (v/v) or higher concentrations of HCl led to hydrolysis of naturally occurring quercetin glycosides into the aglycone as an extraction artifact.