Drying kinetics and effects of drying on nutritional properties of 5 varieties of aonla were investigated using cabinet dryer. Thin shreds of aonla were spread in a layer in dryer and dried at varying temperature of 40, 50 and 60 °C till constant weight attained. Thin layer Newton model was proposed to study drying kinetic of aonla varieties. Degradation in TPC (total phenolic content) and ascorbic acid content were studied at varying temperature. Total phenolic and ascorbic acid content were retained maximum at 50 °C and higher values of R2 and the lowest value of root mean square error (RMSE), Chi square and mean biased error (MBE) for all varieties indicated that Newton model appropriately described the drying curve of aonla. Among the varieties, variety Banarasi had maximum value of R2 (0.993) and the lowest values for RMSE (0.039), Chi square (0.018) and MBE (0.001) at 50 °C. Reduction was observed in ascorbic acid, reducing sugar, polyphenol content and pectin content of aonla varieties during drying process. From study, it was observed that drying of aonla at 50 °C was best in terms of higher retention of TPC and ascorbic acid and Newton model was found suitable to explain drying pattern within temperature range under study.
Keywords: Ascorbic acid; Drying kinetic; Newton model; Polyphenol.