Effect of heat treatment on physico-chemical parameters and extractability of free radical scavengers from Hibiscus sabdarifa juice

Hibiscus sabdariffa also known as Roselle is a shrub generally measuring between one and two meters in height. After flowering, white or red calyxes appear, depending on the variety. These calyxes are highly prized by African populations for the production of drinking juice. Thus, this work was initiated to study the thermal effects on physico-chemical parameters of the juice obtained. The pH was determined using a pH meter, the conductivity using a conductivity meter. Polyphenols were quantified by the ferric chloride reaction and Folin-Ciocalteu's reagent. The antiradical activity was determined by the ABTS method and the mineral content was determined using an atomic absorption spectrometer. According to the results, the production of juice at 100°C allowed the extraction of more phytochemical compounds among which: flavonoids (66.6 mg EQ/100 g dry extract) and polyphenols (49.3 mg EAG/100 g dry extract). The results also showed a better anti-free radical capacity for the juice obtained at 100°C compared to the other juices in this study. Indeed, the highest percentage of inhibition was obtained with the lowest concentration of juice extracted at 100°C (0.446 mg/mL). Hence, this study allowed the determination of the optimal temperature for preparing hibiscus sabdarifa juice.