Kinetics studies on the ascorbic acid extraction from roselle (Hibiscus sabdariffa) calyces

Abstract

The effect of processing conditions of roselle (Hibiscus sabdariffa) calyces on the vitamin C content of the extracts was studied to develop models that best describe the process. The extraction parameters are the processing time (5, 10, 15 mins), process temperature (30oC, 50℃, 75℃ and 100℃), and calyx-water mass ratio (1:50, 1:20 and 1:10). These samples were tested for ascorbic acid using the spectrophotometric method. Statistical analysis was conducted on the experimental results and regression models were developed. A total of six mathematical models were selected for the description of vitamin C extraction from the calyces. The results showed that time, temperature and calyx-water mass ratio have a linear significant effect (p ≤ 0.01); while time-temperature and temperature-ratio had a significant (p ≤ 0.05) interaction effect; time and temperature had a significant (p ≤ 0.05) quadratic effect on the vitamin C content of the extract. Pseudo-first-order gave the highest overall coefficient of determination R2 and lowest overall root mean square error (RMSE). The activation energy of vitamin C ranged from 3 to 8.4 kJ; the effective diffusion coefficient ranged from 1.5×10-9 to 5.0×10-7 m 2 s -1 ; while mass diffusivity ranged from 3.11×10-5 to 8.6×10-4 ms-1 . The Biot number calculated ranged between 33.93 and 541.94 which showed that there is an insignificant external mass transfer resistance.