Characterisation of Electrochemical Parameters for the Stabilisation of Anthocyanins from Hibiscus Sabdarrifa L

Abstract

The high nutritional value of Hibiscus sabdariffa L calyxes is now known almost worldwide. The multiple benefits of Hibiscus juice on human health explain the new consumer demands on the preservation techniques of the nutritional qualities of Hibiscus juice. The instability of anthocyanins, the molecules responsible for the red colouring of Hibiscus sabdariffa calyxes, remains a problem despite the numerous stabilisation techniques on the subject. Platinum electrode oxygen reduction is a new athermal technique using a two-compartment electrolysis cell separated by a cationic membrane. The fruit juice is stabilised by the passage of the reduction current for a specified time. Cyclic voltammetry was used to characterise the electroactive element, the reduction peak, which is dissolved oxygen. The electroreduced Hibiscus juice was then stored at 37°C for 30 days with an untreated control. After one month of storage, determination of the anthocyanin concentration of the electroreduced extracts and the control made it possible to retain the 30mn/-6mA couple presenting a significant difference compared to the control for the stabilisation of the juices. Bubbling with nitrogen gas not only justified the negative impact of dissolved oxygen in the Hibiscus sabdariffa juice but also confirmed that oxygen is the electroactive element in the extract. The result obtained on bubbling also reveals that it is necessary to bubble for 2 hours to obtain an anthocyanin concentration of 279.21 mg/l after storage at 37°C for 30 days, whereas 282.66 mg/l is obtained for the same extract treated electrochemically (30mn/-6mA) and stored under the same conditions; both concentrations are significantly different from the control 263.37 mg/l. The electrochemical treatment with the time/intensity couple of 30min/-6mA for 500ml of Hibiscus sabdariffa juice on platinum/ECS electrode allowed to keep more than 10% of anthocyanins at 25°C and 37°C after 30 days of storage, significant compared to the control.