Effect of Local Storage on Nutritional and Antioxidant Profiles of Onion and Garlic from Northwest Nigeria

Abstract

Fruits and vegetables are important food components; they are a vital source of essential and nonessential micronutrients that are essential for wellbeing. Onion and garlic are among the most widely consumed vegetable. Their broad nutritional and pharmacological benefits arise from the diverse micronutrients and phytochemicals present in the plants. The present study investigated the effect of local preservation/storage method on the proximate composition, antioxidant vitamins and activity, pungency, mineral composition and amino acid profile of two onion varieties (red and white) and garlic collected from Northwest Nigeria. It was observed that moisture and lipid content decreased upon storage, while other proximate parameters increased. Vitamin A increased from 37.750 ± 0.050 mg/dl to 49.470 ± 0.442 mg/dl upon storage of garlic. In white onion, it decreased from 8.600 ± 0.183 mg/dl to 2.123 ± 0.125 mg/dl. Vitamin C, vitamin E, and pyruvate (a measure of pungency) generally decreased with storage.  While antioxidant activities decreased following storage, % DPPH activity for garlic increased (77.813 ± 0.156 % to 90.673 ± 3.294 %). Except for Ca, Mg and Na, mineral element composition tends to decrease with storage. A varied influence of storage on amino acid levels was observed; Glu, Asp and Arg of onion samples increased but Glu levels decreased. In garlic, Lys, Phe, Ser and Asp levels were elevated while Iso, Val, Tyr, His, and Cys dropped. Thus, preservation/storage differently affected the levels of parameters analysed.