Hydrodynamic study of a reactor for the electrochemical processing of Hibiscus sabdariffa l. extracts

Health requirements in recent years have made food products containing preservatives or treated at high temperatures less popular, explaining the new focus on innovative and interdisciplinary technologies. The calyxes of Hibiscus sabdariffa L. are rich in antioxidants such as anthocyanins but sensitive to degradation factors such as oxygen. Several technological alternatives have been proposed to reduce its action, such as bubbling with an inert gas or adding preservatives. This work proposes a new electrochemical approach consisting of cold reduction of dissolved oxygen in aqueous extracts of Hibiscus sabdariffa. An electrochemical treatment reactor consisting of an electrolysis cell designed and dimensioned (L=9cm ; l =3.3cm ; e =1cm) in the laboratory. Knowledge of the hydrodynamic parameters is essential for technology transfer on an industrial scale, so these were determined. For a useful volume of 29.7 cm³ and a flow rate of 0.28 mL/s, the transit time of the Hibiscus extract is approximately 107 s. The flow is laminar, with a Reynolds number of 71.57, hence the need for a turbulence promoter. The reactor is a piston type (Peclet number = 3). A non-significant difference between the electro-reduced extract and the initial extract was observed, confirming that this reduction does not dilute the product and that the Hibiscus extract does not contain a supporting electrolyte. Monitoring of the anthocyanins in the electro-reduced Hibiscus extract under these conditions showed better preservation of anthocyanins compared to heat treatments. Preservation was 35% in the first month of storage at 25°C and 30% after 15 days of storage at 37°C. This new electrochemical approach preserves the original quality of the extract at low temperatures without adding antioxidants, while maintaining the same organoleptic qualities as traditional methods.