Effects of Osmotic Dewatering and Oven Drying on β-Carotene Content of Sliced Light Yellow-Fleshed Sweet Potato (Ipomea batatas L.)

Abstract

The effects of pre-treatment in osmotic salt solution followed by oven-drying on the moisture removal, and β-carotene content of yellow-fleshed sweet potato were investigated. Potato rings of 3 cm diameter and thicknesses of 2 mm, 3 mm and 4 mm were soaked in NaCl solutions of 10, 15, 20, 25 and 30% w/v, for varying time of 20, 40, 60, 80 and 100 minutes. The pre-treated slices were then oven-dried in a convective oven at 60^oC. Moisture diffusivity was determined by the method of slopes, while β-carotene was measured by UV/VIS- spectrophotometer. Moisture diffusivity values during drying were between 3.648 × 10-7 m²/s and 1.459 × 10-6 m²/s, while losses in β-carotene ranged from 47 to 86%. The amount of water removed by pre–treatment with NaCl solution decreased significantly as the concentration and the time soaking increased, however, the water out flow was found to increase significantly with increase in thickness of the samples, where the 4 mm size had the highest (1.535 g H2O/g sample) and 2 mm the least (1.434 g H₂O/g sample) Osmotic pre-treatment in salt solution had no effect on β-carotene, but subsequent oven-drying however degraded the β-carotene.

Keywords: Sample thickness, sodium chloride solution, water out flow, moisture  diffusivity, β-carotene.