Antioxidant activity and Phenolic compounds of raw and processed cashew nuts

Chandrasekara, Chandrasekara Mudiyanselage Neel Ranjith (2010) Antioxidant activity and Phenolic compounds of raw and processed cashew nuts. Masters thesis, Memorial University of Newfoundland.

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Abstract

Roasting of cashew (Anacardium occidentale L.) nut is a commonly used processing method to improve their texture, colour, flavour and appearance. The effect of roasting on the content of phenolic compounds, antioxidant activity, and antiradical properties of cashew nuts and testa were studied. Raw whole cashew nuts were roasted at low temperature (LT; 70° C for 6 hours) and high temperature (HT; 130° C for 33 min). Raw and roasted whole cashew nuts, kernels and recovered testa were used to extract soluble phenolic compounds under reflux conditions with 80% (v/v) ethanol. The residues were used to extract insoluble bound phenolics at room temperature by alkaline hydrolysis under nitrogen. The antioxidant activity was measured using several chemical assays as well as food and biological model systems. Cashew nut oils extracted from raw and roasted whole cashew nuts were examined for their fatty acid composition, colour change and oxidative stability. The results showed that the highest antioxidant activity was achieved when nuts were roasted at HT. The contents of soluble and insoluble bound phenolic of raw, LT and HT roasted cashew nuts and testa ranged from 1.14 ± 0.43 to 348.99 ± 6.88 and 0.03 ± 0.01 to 4.53 ± 0.12 mg of gallic acid equivalents (GAE) per g of defatted meal, respectively. Roasting increased the total phenolic content while decreasing that of the proanthocyanidins. Phenolic acids, namely syringic, gallic and p-coumaric acids were identified in soluble extracts of raw, LT and HT roasted cashew nuts and testa by high performance liquid chromatography (HPLC) and amongst which syringic acid was the predominant one. Flavonoids, namely catechin, epicatechin and epigallocatechin were also identified and their contents increased with increasing temperature. -- The results of the present study showed that HT roasting effectively enhanced antioxidant activity of cashew nuts and testa. The analysis of fatty acid composition showed that oleic acid was the major monounsaturated (MUFA) fatty acid. Roasting of whole cashew nuts improved the oxidative stability of nut oil during storage. The results suggest that whole cashew and testa could be used as a potential source of natural antioxidants in food applications and for health promotion.

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