Effects of Post-harvest Storage and Moist Heat Treatment on Carotenoids and Micronutrients in African Spinach (Amaranthus hybridus)

Abstract

The aim of this research was to investigate the nutrient composition of Amaranthus hybridus (raw,stored and as consumed) and evaluate its potentials for alleviating hidden hunger. Changes in carotenoids, selected vitamins and minerals of Amaranthus hybridus leaf during cooking (5 min,100°C) and room temperature storage conditions (29 ± 2°C, 85%RH) were determined. Carotenoids were separated by High performance liquid chromatography (HPLC) on a reversed-phase column. Lutein, β-cryptoxanthin, β-carotene and its trans-/cis-isomers were identified and quantified. Total-carotene was determined spectrophotometrically. The results indicated that the raw vegetable was rich in lutein (309.21 µg/gdwt) and β-carotene (174.86 µg/gdwt). β-cryptoxanthin was detected in relatively small amounts (11.02 µg/gdwt). Cooking significantly increased (p<0.05) the lutein (382.92 µg/gdwt) and β-carotene (208.94 µg/gdwt) contents of the leaf sample; however, it decreased the trans-β-carotene content. The contents of ascorbic acid, thiamin, niacin and riboflavin were as follows (in mg per 100 gfwt) 54.30, 0.14, 3.69 and 1.84 respectively, while phylloquinone (vitamin K1) was 122.21 µg/100 gfwt. Cooking significantly (p<0.05) decreased the contents of the vitamins except phylloquinone. The mineral contents of raw sample were (in mg/100 g fwt), potassium, 5.50, calcium, 1.15, magnesium,1.20, zinc, 1.72 and iron, 10.40 respectively. Cooking of the leaf significantly (p<0.05) decreased the contents of potassium, calcium, zinc, magnesium, but increased the content of Iron. Storage caused a non-significant decrease in the content of niacin, potassium and magnesium. Consumption of 100-200 g/day of the leaf may be adequate to meet the recommended daily allowances (RDAs) of 900 µgRAE/day, 90 mg/day, 120 µg/day 1.3 mg/day and 9mg/day for vitamin A, vitamin C, vitamin K1, riboflavin and Iron respectively. Amaranthus hybridus leaf will therefore improve the nutritional status of populations that consume adequate amount of the vegetable.