Ndiaye Khady^1,, Kane Cheikhou¹, Ayessou Nicolas¹, Cisse Mady¹, Diop Codou Mar¹

The instability of anthocyanins, the molecules responsible for the red coloration of Hibiscus sabdariffa L calyxes, remains a major problem despite the many stabilization techniques that exist. Membrane technologies have played a central role in stabilizing roselle anthocyanins. Until now, dissolved oxygen in juices has been treated by bubbling with an inert gas or by adding other molecules such as preservatives, which can cause considerable damage to human health. The electrochemical approach is a new stabilization technique that reduces dissolved oxygen in juice, cold and without adding other molecules. The reduction of dissolved oxygen on a platinum electrode is a new athermic technique using an electrolysis cell with two compartments separated by a cationic membrane. The fruit juice is stabilized by passing a reduction current through it for a specified period of time. The results obtained from bubbling reveal that it is necessary to bubble with nitrogen gas for 2 hours to obtain an anthocyanin concentration of 279.21 mg/L after storage at 37°C for 30 days, while 282.66 mg/L is obtained for the same extract treated electrochemically (30 min/-6 mA) and stored under the same conditions. Both concentrations are significantly different from the control concentration of 263.37 mg/L. Electrochemical treatment with a time/current combination of 30 min/-6 mA for 500 ml of Hibiscus sabdariffa L extract on a platinum/SCE electrode (in a batch reactor) preserved more than 10% of the anthocyanins at 25°C and 37°C after 30 days of storage, which is significantly more than the control. This had previously been problematic for other treatments. The classic Arrhenius, Ball, and Eyring models used showed the degrading effect of dissolved oxygen in the extract, with a significant difference (Ea = 4000 J/mol) between the activation energy of the electrically reduced extract and the control (untreated). This was corroborated by half-reaction time values of 24 s⁻¹ for the electrochemically treated extract and 20 s⁻¹ for the untreated control after 5 months of storage at 4°C. The activation enthalpy of the electrically reduced hibiscus extract is approximately 6 J/mol/K, and that of the control is 5.72 J/mol/K, showing that the electrochemical process occurs at low energy, i.e., 0.28 J/mol/K for a volume of approximately 250 ml.

Membrane, Stabilization, Anthocyanin, Oxygen, Electrochemistry, Hibiscus