TITLE:
Monitoring of Anthocyanins and Colour in Electrochemically Processed Hibiscus sabdariffa Juice
AUTHORS:
Khady Ndiaye, Cheikhou Kane, Omar Ben Khatab Cisse, Nicolas Ayessou, Codou Mar Diop
KEYWORDS:
Monitoring, Anthocyanin, Colour, Oxygen, Stabilisation, Electrochemical Nafion Membrane, Ratio
JOURNAL NAME:
Food and Nutrition Sciences,
Vol.12 No.11,
November
19,
2021
ABSTRACT: The vital role of anthocyanins in Hibiscus sabdariffa L. is now known to
most consumers. The richness of anthocyanins in antioxidants, vitamin C,
minerals, etc., provides Hibiscus juice with proven nutritional qualities. The health requirements of recent
years have made food products with added preservatives or processed at high
temperatures less popular, thus explaining the new orientations towards innovative and interdisciplinary technologies. Anthocyanins
from Hibiscus sabdariffa L. are,
however, sensitive to degradation factors such as temperature, light, enzymes
and also oxygen. The instability of anthocyanins
has long been a subject of research using classic techniques such as
heat treatment, the results of which are often limited by the rapid degradation
and above all the destruction of the nutritional and organoleptic qualities of
the product. Oxygen dissolved in juices is so far treated by bubbling with an
inert gas or by adding other molecules such as preservatives which can cause a
lot of health damage. The electrochemical approach is a new stabilisation technique that reduces the dissolved oxygen in the
juice, cold and without the addition of other molecules. The
electrolysis of Hibiscus juice was
carried out by noble electrodes (Platinum and Stainless Steel) with a well-characterised Time/Potential or Time/Intensity
couple. The electroreduced samples and the control were then stored at
4°C, 25°C and 37°C for more than 6 months. Monitoring of anthocyanins in the
first month, of the samples and the control, showed a significant difference of
10% between the electroreduced extract and the untreated control at 37°C, which
had previously been problematic for the heat treatment and even for the other
membrane techniques. Oxygen reduction on the platinum electrode/ECS allowed the
retention of more than 10% of anthocyanins after 4 weeks of storage at 25°C and
37°C. At 4°C, a significant difference of 5% between the electro-reduced Hibiscus juice and the control was
maintained until the fifth month of storage with
the 1/5 ratio (calyx/water). Non-significant losses in anthocyanin (10 mg/l), for the juice with reduced dissolved oxygen, were noted for the 1/5 and
1/15 ratios during the first month of storage at 4°C against 24 mg/l of
significant losses for the 1/20 ratio. However, the untreated control showed
significant losses for the ratios 1/20, 1/15 and 1/5. Oxygen dissolved in the
juice therefore considerably degrades the anthocyanins of Hibiscus sabdariffa L. from the first month
of storage at 4°C.