Abstract
Centella asiatica (Family: Apiaceae), also referred to as “Gotu kola” or ‘icudwane’, is a medicinal plant commonly cultivated in South Africa to manage several ailments traditionally and recently as a health supplement. Despite the anecdotal usage of Centella asiatica in South Africa for centuries, no functional food containing the health-enhancing plant is currently available. Furthermore, most commercially available extracts or preparations of C. asiatica are imported, making it less affordable for many consumers. This has discouraged its extensive use for health purposes, particularly in the potential management of chronic diseases in South African consumers. Therefore, this study aimed to develop a functional beverage locally containing indigenous C. asiatica extracts, given their well-established medicinal properties.
To achieve this, the newer and eco-friendly extraction technique, ultrasound-assisted extraction (UAE), was employed to extract the major medicinal bioactive compounds in C. asiatica leaves using three solvents – methanol, ethanol, and water, in comparison to the conventional soaking method. This was followed by the bioactive characterization of C. asiatica extracts using total polyphenols content (TPC), total flavonols content (TFC), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric ion reducing antioxidant power (FRAP). The liquid chromatography-mass spectroscopy (LCMS) technique was used to investigate the amounts of the key compounds in C. asiatica, which include triterpenes, madecassoside, asiaticoside, madecassic acid (MA), and asiatic acid (AA). Functional beverage juice was then formulated to contain 100%, 70%, or 50% of the C. asiatica extracts which were further analysed for their nutritional properties, microbiological analysis, total titratable acidity (TTA), pH, and sensory attributes.
In this study, the UAE extracts had a significantly (p < 0.05) higher yield of all the bioactive compounds when compared to the conventional soaked extracts. Additionally, the water extracts had significantly (p < 0.05) higher TPC, and TFC values as well as the antioxidant capacity indices, DPPH, and FRAP, when compared with their methanol or ethanol counterparts. However, LCMS analyses revealed that the methanol and ethanol extracts are indeed excellent sources of the medicinal triterpenes (p < 0.05) unlike the water extracts. The abundance of the triterpenes in the C. asiatica extracts was in the following order; madecassoside > asiaticoside > MA >AA. Interestingly, these bioactive compounds and antioxidant qualities were preserved during the formulation of the functional beverage from water extracts as only marginal differences (p > 0.05) were observed when compared with the raw materials (extracts) before product development.
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The changes in the TTA, pH, microbiological, and nutritional analyses in the juices from both UAE and soaking extracts were largely statistically insignificant (p > 0.05). While the 100% C. asiatica formulation had the best yield (p < 0.05) of bioactive compounds than 70% or 50%, the latter beverages may be comparatively better accepted by consumers from the sensory analyses data. An inverse relationship between TTA and pH was also observed where an increase in TTA resulted in a pH decrease. The microbial count from day 0 to day 12 increased exponentially and the functional beverages were of good microbial quality for up to 8 days when stored at 4 0C unopened.
In summary, the overall data obtained in this study indicates that C. asiatica is an excellent source of antioxidants and health-promoting triterpenes that can be utilized for functional food strategies through oral supplementation or diet enrichment to potentially assist in countering the soaring incidences of chronic diseases in the South African population. The formulated beverage from water C. asiatica extracts exhibited good nutritional, microbiological, and consumer acceptability profiles. The UAE technique provides a more eco-friendly alternative in obtaining optimum concentrations of important bioactive compounds in C. asiatica than the soaking or maceration method. The importance of the choice of solvents for the extraction of medicinal plants with hundreds or more bioactive compounds is further highlighted in this study. The extraction solvent of choice must be dependent on the targeted compounds of interest in functional food production, for example, while water was the preferred solvent for polyphenols and antioxidants in this study; methanol or ethanol was more advantageous for triterpenes. To mitigate the loss of certain class of compounds in an extract, hydroalcoholic extracts may be considered in future studies instead of using only one solvent such as water, ethanol or methanol. Furthermore, future studies are warranted to evaluate the long-term safety profile and specific health mechanisms of actions of the newly-developed beverages.
Keywords: Antioxidant, Functional foods, Gotu kola, Phyto-compounds, Ultrasound-assisted extraction.