Effect of heating and refrigeration durations on ascorbic acid, β-carotene and riboflavin contents of Solanum tuberosum and selected vegetables

Abstract

Aim: It has long been established that the quality and nutritional composition of vegetables vary according to the conditions under which they are stored or prepared. For this reason, the current research was designed to probe the effect of cooking as well as refrigeration time on the β-carotene, riboflavin and ascorbic acid contents of cabbage, lettuce, pumpkin, water leaf, onions, garden egg and Irish potatoes. Methodology: The vegetable leaves and potato tuber were cooked in boiling water for 40 minutes to determine their β-carotene and riboflavin content, and 45 minutes for ascorbic acid content. Furthermore, portions of the samples were refrigerated for a period of 3 days and 7 days, and their β-carotene and ascorbic acid content assessed. Determinations were done using standard AOAC methods and methods reported by previous researchers.Results: The amount of β-carotene in untreated samples ranged between 1,200 mg/100g in potato to 17,310 mg/100g in water leaf and between 504.00 mg/100g to 10,729 mg/100g in the same samples respectively after boiling for 40 minutes. The riboflavin content ranged between 3.80 mg/100g to 130.00 mg/100g in pumpkin and onions respectively. After boiling for 40 minutes, this dropped to within a range of 2.00 mg/100g to 74 mg/100g in both samples respectively. The ascorbic acid content was generally below that of β-carotene but higher than riboflavin and ranged between 504 mg/100g to 10,729 mg/100g and 39 mg/100g to 180 mg/100g before and after boiling for 45 minutes respectively. The β-carotene in cabbage was least affected by heat treatment with a percentage loss of 21.30% whereas ascorbic acid in onions was most affected at 82.21%. Refrigeration also showed marked impact on the vitamin content with the β-carotene and ascorbic acid content completely lost in lettuce after refrigeration for 7 days, whereas it showed no impact on the β-carotene content of cabbage after 3 days. The ascorbic acid content of garden egg was reduced by 80.01% upon refrigeration for 7 days while the β-carotene and ascorbic acid contents of lettuce were completely lost after the same duration of time. Generally, the contents of the vitamins decreased with increasing refrigeration time.