Vitamin and provitamin profiles of selected vegetables as affected by storage and different drying methods

Abstract

Effects of drying methods on the vitamin and provitamin compositions of selected vegetables during storage were assessed in this study. Telfaria occidentalis, Celosia argentea (green), Vernonia amygdalina, Moringa oleifera, Launaea taraxacifolia, Curcubita maxima and Celosia argentea (red) were subjected to air drying (AD), oven drying (OD) and freeze drying (FD). The experiment was a 3x7 factorial arrangement in a completely randomized design. Dried leaves were milled and assayed for vitamins (pyridoxine, riboflavin, ascorbic acid and tocopherol) and provitamins (total carotene and ergocalciferol). Samples were stored in opaque airtight containers after drying and assayed periodically at weeks 0, 3, 6, 9, 12, 15 and 18 of storage. Air-dried samples had significantly higher (P<0.05) total carotene (1177.49 μg/100g), pyridoxine (0.59 mg/100g), riboflavin (0.46 mg/100g), ascorbic acid (39.11 mg/100g), ergocalciferol (46.55 μg/100g) and tocopherol (57.52 μg/100g) compared with samples dried by other methods. Moringa oleifera leaf type had significantly higher (P<0.05) total carotene (1079.48 μg/100g), riboflavin (0.41 mg/100g), ergocalciferol (46.40 μg/100g) and α-tocopherol (58.45 μg/100g) while Cucurbita maxima had significantly higher (P<0.05) pyridoxine (0.73 mg/100g). Effects of the interaction of drying methods and leaf type were significant (P<0.05) on the vitamin and provitamin compositions of samples. The effect of the interaction of the oven drying method and leaf type was highly significant (P<0.05) on inherent vitamin and provitamin of samples. Vitamin and provitamin compositions of samples were stable until week six. Air-dried samples contained more vitamins and provitamins which were also more retained in storage.