Vol.:(0123456789) 1 3 Journal of Food Measurement and Characterization https://doi.org/10.1007/s11694-018-9981-3 ORIGINAL PAPER Efect of water activity on extractable polyphenols and some physical properties of Hibiscus sabdariffa L. calyces Yanik I. Maldonado‑Astudillo 1  · Javier Jiménez‑Hernández 1  · Gerónimo Arámbula‑Villa 3  · Verónica Flores‑Casamayor 3  · Patricia Álvarez‑Fitz 2  · Mónica Ramírez‑Ruano 2  · Ricardo Salazar 2 Received: 14 September 2018 / Accepted: 12 November 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Bioactive compounds and physical properties of Roselle (Hibiscus sabdarifa 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 a w ’s < 0.329 (near minimum integral adsorption entropy). In contrast, at higher a w ’s (0.536, 0.765, and 0.846) an increase in the extractability of phenolic compounds, as well as a reduc- tion in ABTS •+ EC 50 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 a w near minimum integral entropy, an anti- plasticization efect was observed. These results suggest that the functional properties of Roselle calyces might be modifed by factors such as moisture content, a w , 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. sabdarifa calyces during storage. Keywords Hibiscus sabdarifa · Minimum integral entropy · Storage · Bioactive compounds · Water activity Introduction Roselle (Hibiscus sabdarifa) calyces, also known as red sorrel, karkadé or jamaica, are widely grown in Asia, Africa, and America [1]. The red calyces are a good source of natu- ral antioxidant anthocyanins and phenolic compounds due to their high red-pigment content, and they are commercially valuable for producing beverages, juices, jams, and syrup in the food industry. In addition, dried Roselle calyces are appreciated to obtain concentrated extracts which might be used in the food and pharmaceutical industries [2]. Traditionally, fresh hibiscus is sun-dried for preservation and is stored for long time-periods before consumption. Consumers employ decocted calyces to obtain a soft drink that can be consumed as both, cold or hot beverage. To date, the high-antioxidant properties, diuretic, anti-cholesterol, anti-diabetic, anti-bacterial, anti-hypertensive, as well as nephro- and hepato-protective efects, of hibiscus extracts, have been extensively evaluated [3]. These efects are linked to strong antioxidant activities, inhibition of angiotensin- converting enzymes, a-glucosidase and a-amylase, and a direct vaso-relaxant efect or calcium-channel modulation. Phenolic acids and anthocyanins are likely to contribute to the reported efects. It is common knowledge that the bioactive compounds found in plants are unstable during processing and storage [4] and are afected by several factors, such as pH, tempera- ture, light, oxygen, metal ions, enzymes, and sugars (see, for example: [5–9]). In this context, one additional factor that frequently exerts a signifcant efect on the stability * Ricardo Salazar rsalazarlo@conacyt.mx 1 Facultad de Ciencias Químico-Biológicas, Universidad Autónoma de Guerrero, Av. Lázaro Cárdenas s/n, Ciudad Universitaria Sur, Col. La Haciendita, 39087 Chilpancingo, Guerrero, Mexico 2 CONACyT, Universidad Autónoma de Guerrero, Av. Javier Méndez Aponte No. 1, Fracc. Servidor Agrario, 39070 Chilpancingo, Guerrero, Mexico 3 Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (CINVESTAV IPN), Unidad Querétaro, Libramiento Norponiente # 2000, Fraccionamiento Real de Juriquilla, 76230 Querétaro, Querétaro, Mexico