Alterations in fruit and vegetable β-carotene and vitamin C content caused by open-sun drying, visqueen-covered and polyethylene-covered solar-dryers

Abstract

This study investigated the effects of three drying methods (open sun drying, visqueen-covered solar dryer and polyethylene-covered solar dryer) on β-carotene and vitamin C content of edible portions of mango fruit (Mangifera indica) and cowpea leaves (Vigna unguiculata). Commercial samples were analysed for vitamin C by titrimetry and β-carotene by spectrophotometery at 450nm. Differences in vitamin retention and loss associated with the three drying methods were assessed by analysis of variance and least significant difference (LSD) at (p<0.05. The fresh cowpea leaf β-carotene and vitamin C content was 140.9 and 164.3 mg / 100g DM respectively and decreased (p<0.05) with drying. Open sun drying method caused the greatest β-carotene and vitamin C loss (58% and 84% respectively), while the visqueen-covered solar dryer caused the least loss (34.5% and 71% respectively). Blanching cowpea leaves improved β-carotene and vitamin C retention by 15% and 7.5% respectively. The β-carotene and vitamin C content of fresh ripe mango fruit was 5.9 and 164.3 mg/100g DM respectively. Similar to effects on cowpea leaves, the mango micronutrient content decreased (p<0.05) with drying. The open sun drying method caused the greatest β-carotene (94.2%) and vitamin C (84.5%) loss, while the visqueen-covered solar dryer caused the least (73 and 53% respectively). These results show that the three solar drying methods cause significant loss of pro-vitamin A and vitamin C in dried fruits and vegetables. However, open sun drying causes the most loss and the visqueen-covered solar dryer the least, making the later a probable better drying technology for fruit and vegetable preservation. The drying technologies should be improved to enhance vitamin retention.

African Health Sciences Vol.4(2) 2004: 125-130