Conventional and low-calorie rosehip leathers: Effect of several drying processes on color and ascorbic acid retention

Abstract

Conventional and low-calorie rosehip leathers were developed by several drying processes: convective and vacuum drying, both with and without a preconcentration process, and combined with a stage of microwave finish drying. The aim of this study was to reduce the processing time and to improve quality retention, in comparison with the conventional convective drying. The product temperature and moisture content as a function of time were analyzed in each case. Color and ascorbic acid content were measured in the leathers, as indexes of organoleptic and nutritional quality, respectively. Total drying times varied widely, between 120 and 870 min, while diffusion coefficients from 4.60 x10-10 to 52.3 x10-10 m2/s were fitted. The color was mostly affected by a combined time-temperature effect, while ascorbic acid retention showed a dependence on the oxygen partial pressure during drying. The concentration process carried out before drying caused no improvement on the dehydration rate of further convective or vacuum drying nor on product quality. Microwave finish drying led to the lowest processing times though it was detrimental for color and nutritional retention of leathers at an absorbed power level of about 1 W/g. Vacuum drying resulted the best option in this research, as it implied shorter processing time and higher quality retention compared with convective drying.