Variations in chemical composition, fatty acids, amino acids, oil quality and functional properties of groundnut (Arachis hypogaea) as influenced by high and low dose gamma irradiation using cobalt-60 wet storage source

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Abstract Groundnut samples were irradiated at 2.5 and 10 kGy, using cobalt-60 gamma source; the control sample was not irradiated. The parameters determined were the proximate chemical composition, mineral composition, anti-nutritional factors and functional properties, as well as amino-acid profiles, fatty acid profiles, and oil quality of the samples. The differences in the parameters among all the samples after gamma-irradiation were tested by analysis of variance at the 95% confidence level of significance (P ≤ 0.05). Irradiation did not have any significant effect on the proximate composition, except the fat content which was increased by irradiation (from 41.98 ± 0.03%dry wt. at 0 kGy to 42.06 ± 0.03% and 42.08 ± 0.05% at 2.5 and 10 kGy, respectively). The energy values of irradiated samples were 571.32 ± 0.50 and 571.76 ± 0.10 kCal at 2.5 and 10 kGy, respectively; compared with 569.32 ± 0.10 kcal at 0 kGy. The mean protein content of samples was 29.77%. Irradiation significantly (P ≤ 0.05) increased the mineral contents of groundnut. Potassium being the most abundant in groundnut (28.56 ± 0.03 mg/100g) at 0 kGy was increased to 37.56 ± 0.01 and 36.31 ± 0.01 mg/100g at 2.5 and 10 kGy respectively. Iron and sodium were low (2.05 ± 0.03 and 2.08 ± 0.03 mg/100g at 0 kGy, respectively; and 2.58 ± 0.02 and 2.82 ± 0.02 mg/100g, respectively). The oil absorption capacity for the groundnut flour samples was increased significantly (P ≤ 0.05), with increased dose of irradiation (86 ± 0.58, 87 ± 0.58, and 94 ± 0.58%) at 0, 2.5 and 10 kGy, respectively; while the foaming and emulsion capacities were decreased significantly (P ≤ 0.05), by increased dose of irradiation. However, the water holding capacity of groundnut flour was not affected by irradiation. The least gelation concentration was increased significantly (P ≤ 0.05), with increased dose of irradiation (50, 60, and 70% at 0, 2.5, and 10 kGy respectively). Peroxide and saponification values were not affected significantly at (P ≤ 0.05) by irradiation; while the iodine value was significantly reduced at (P ≤ 0.05) with increased irradiation dose; also, the acid value and free fatty acid content increased significantly. Sulphur and aromatic amino acids were reduced significantly at (P ≤ 0.05) with increased dose of irradiation. There was reduction or elimination of unsaturated fatty acids at 2.5 and 10 kGy doses, while the level of saturation was increased. Anti-nutritional factors were reduced with increased dose of irradiation. This study shows that irradiation is still suitable as a method of preservation for groundnut, although it showed reduced overall nutritional quality.

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