Effect of water activity on extractable polyphenols and some physical properties of Hibiscus sabdariffa L. calyces

Bioactive compounds and physical properties of Roselle (Hibiscus sabdariffa L. calyces) are of interest in food, cosmetics and pharmaceutical industries. The objective of this study was to relate water activity with the extractable polyphenols and physical properties of freeze- dried calyces stored at 35 °C for 49 days. The minor changes in soluble phenols, monomeric anthocyanins, antioxidant activity and color were found at aw’s < 0.329 (near minimum integral adsorption entropy). In contrast, at higher aw’s (0.536, 0.765, and 0.846) an increase in the extractability of phenolic compounds, as well as a reduction in ABTS•+ EC50 value, were observed, as a consequence of matrix swelling and dissolution. In addition, moisture gain caused discoloration and loss of crispiness in stored calyces. However, in the aw near minimum integral entropy, an anti-plasticization effect was observed. These results suggest that the functional properties of Roselle calyces might be modified by factors such as moisture content, aw, and the physical state of the water found in them. Thus, minimum integral entropy showed to be a reliable indicator to establish the most appropriate moisture conditions to control the extractable polyphenols and physical properties of H. sabdariffa calyces during storage.