Effect of Roasting on Phenolic Content and Antioxidant Activities of Whole Cashew Nuts, Kernels, and Testa

The effect of roasting on the content of phenolic compounds and antioxidant properties of cashew nuts and testa was studied. Whole cashew nuts, subjected to low-temperature (LT) and high-temperature (HT) treatments, were used to determine the antioxidant activity of products. Antioxidant activities of cashew nut, kernel, and testa phenolics extracted increased as the roasting temperature increased. The highest activity, as determined by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, oxygen radical absorbance capacity (ORAC), hydroxyl radical scavenging capacity, Trolox equivalent antioxidant activity (TEAC), and reducing power, was achieved when nuts were roasted at 130 °C for 33 min. Furthermore, roasting increased the total phenolic content (TPC) in both the soluble and bound extracts from whole nut, kernel, and testa but decreased that of the proanthocyanidins (PC) except for the soluble extract of cashew kernels. In addition, cashew testa afforded a higher extract yield, TPC, and PC in both soluble and bound fractions compared to that in whole nuts and kernels. Phenolic acids, namely, syringic (the predominant one), gallic, and p-coumaric acids, were identified. Flavonoids, namely, (+)-catechin, (-)-epicatechin, and epigallocatechin, were also identified, and their contents increased with increasing temperature. The results so obtained suggest that HT-short time (HTST) roasting effectively enhances the antioxidant activity of cashew nuts and testa.