Optimising the Polyphenolic Content and Antioxidant Activity of Green Rooibos (Aspalathus linearis) Using Beta-Cyclodextrin Assisted Extraction
2022
Lusani Norah Vhangani | Leonardo Cristian Favre | Guido Rolandelli | Jessy Van Wyk | María del Pilar Buera
Antioxidant activity associated with green rooibos infusions is attributed to the activity of polyphenols, particularly aspalathin and nothofagin. This study aimed to optimise &beta:-cyclodextrin (&beta:-CD)-assisted extraction of crude green rooibos (CGRE) via total polyphenolic content (TPC) and antioxidant activity assays. Response surface methodology (RSM) permitted optimisation of &beta:-CD concentration (0&ndash:15 mM), temperature (40&ndash:90 °:C) and time (15&ndash:60 min). Optimal extraction conditions were: 15 mM &beta:-CD: 40 °:C: 60 min with a desirability of 0.985 yielding TPC of 398.25 mg GAE·:g&minus:1, metal chelation (MTC) of 93%, 2,2&prime:-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging of 1689.7 µ:mol TE·:g&minus:1, ferric reducing antioxidant power (FRAP) of 2097.53 µ:mol AAE·:g&minus:1 and oxygen radical absorbance capacity (ORAC) of 11,162.82 TE·:g&minus:1. Aspalathin, hyperoside and orientin were the major flavonoids, with quercetin, luteolin and chrysoeriol detected in trace quantities. Differences (p <: 0.05) between aqueous and &beta:-CD assisted CGRE was only observed for aspalathin reporting the highest content of 172.25 mg·:g&minus:1 of dry matter for extracts produced at optimal extraction conditions. Positive, strong correlations between TPC and antioxidant assays were observed and exhibited regression coefficient (R2) between 0.929&ndash:0.978 at p <: 0.001. These results demonstrated the capacity of &beta:-CD in increasing polyphenol content of green rooibos.
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