Drying characteristics and nutritional quality of Roselle (Hibiscus sabdariffa L.) leaves and calyces during infrared drying
Abstract
Roselle (Hibiscus sabdariffa L.) is a rich medicinal plant, therefore, the effects of infrared drying on the drying characteristics, colour and nutritional quality (vitamin C and carotenoid contents) of Roselle (Hibiscus sabdariffa L.) leaves and calyces were investigated. Roselle leaves and calyces were subjected to infrared drying at temperature of 80 and 110oC and infrared power of 1000W. The experimental data obtained during infrared drying were subjected to five drying models namely, Newton, Page, Wang and Singh, Henderson and Pabis, and Logarithm models. The results showed that the drying time for Roselle leaves and calyces were less than 60 and 80 min, respectively. Page model best described the drying behavior of Roselle leaves and calyces during infrared drying. The moisture diffusivity of Roselle leaves and calyces ranged from 7.49 to 1.16 m2s-1 and 6.13 to 6.91 m2s-1, respectively. As a result of the short drying time, the vitamin C and carotenoid content of Roselle leaves and calyces were significantly preserved. However, the infrared temperature led to a high total colour change of the samples, particularly at 110oC. This work therefore showed that infrared drying is a good drying technique that could be adopted by the food industries involved in the drying of Roselle leaves and calyces.
