Effect of the dehydration method of Hibiscus sabdariffa L. calyces on the quality of their aqueous extracts

Abstract

Hibiscus sabdariffa L. is a plant from tropical climates, which produces, among other products, deep red calyces used to prepare refreshing drinks. The high humidity (85-87%) of the calyces at the time of harvest must be reduced to about 12% for handling and storage. The aim of the work was to evaluate the effect of the dehydration method of the calyces (sun drying, SD; air-drying, AD, at three temperatures: 50, 60 and 70 ºC) of three varieties of Hibiscus sabdariffa L. on the quality of their aqueous extracts. The quality was measured as a function of color), and chemical variables (titratable acidity, TA, total soluble phenols, TSP; total anthocyanins content TAC, and organic acids). The varieties used were Negra Quiviquinta (NQ) with dark red calyces, UAN-9 with light red calyces, and UAN-16, with white calyces. The dehydration method affected the quality of the extracts. The SD was the one that most affected the color and chemical variables. The color of the extracts was darker than that of the control while titratable acidity (TA) was reduced on average 40.6%. No effect of AD treatments was observed on these variables. On chemical composition, SD reduced TSP on average 15.3%, the most affected variety was UAN-16. In the varieties with red calyces, the average TAC reduction was 36.9%. Of the organic acids, the most affected were malic and succinic. As observed in physical variables, AD treatments showed little influence on chemical composition of calyces. Of the dehydration methods evaluated, the AD70°C rendered the best quality aqueous extract, in base of the variables evaluated.