Optimising the Polyphenolic Content and Antioxidant Activity of Green Rooibos (Aspalathus linearis) Using Beta-Cyclodextrin Assisted Extraction

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 (0-15 mM), temperature (40-90 degrees C) and time (15-60 min). Optimal extraction conditions were: 15 mM beta-CD: 40 degrees C: 60 min with a desirability of 0.985 yielding TPC of 398.25 mg GAE.g(-1), metal chelation (MTC) of 93%, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging of 1689.7 p.mol TE.g(-1), ferric reducing antioxidant power (FRAP) of 2097.53 p.mol AAE.g(-1) and oxygen radical absorbance capacity (ORAC) of 11,162.82 TE.g(-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 13-CD assisted CGRE was only observed for aspalathin reporting the highest content of 172.25 mg.g(-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 (R-2) between 0.929-0.978 at p < 0.001. These results demonstrated the capacity of beta-CD in increasing polyphenol content of green rooibos.

Automated summary

This study optimized the beta-cyclodextrin-assisted extraction of crude green rooibos, finding that the optimal conditions were 15 mM beta-CD: 40 degrees C: 60 min, resulting in high polyphenolic content and antioxidant activity. Aspalathin, hyperoside, and orientin were identified as the major active compounds.