Physicochemical Properties of Betacyclodextrin-Assisted Extracts of Green Rooibos (Aspalathus linearis)

Betacyclodextrin (beta-CD)-assisted extracts of green rooibos displayed elevated polyphenolic content and antioxidant activity compared with aqueous extracts. This study aimed to analyse the physicochemical properties of aqueous green rooibos and 15 Mm beta-CD at 40 degrees C for 60 min. Sorption isotherms and colour (L*a*b*C*) were evaluated. Thermogravimetric analysis and Fourier transform infrared were conducted to verify encapsulation. Sorption isotherm studies revealed that beta-CD reduced water uptake, resulting in a reduction in the monolayer value of GRE (7.90) to 6.40 for beta-GRE. Betacyclodextrin contributed to increased lightness (L*) and decreased redness (a*) of green rooibos. However, storing extracts at varied water activity resulted in a reduction in L* and chroma (C*), with a higher reduction observed for GRE than beta-GRE. Thermogravimetric analysis revealed that GRE degraded at 180 degrees C, followed by beta-GRE at 260 degrees C and beta-CD at 340-375 degrees C. Betacyclodextrin increased the thermal stability of green rooibos; as a result, beta-GRE displayed a superposition of GRE and beta-CD in its thermogram, confirming the formation of inclusion complexes. Fourier transform infrared spectra indicated the disappearance or shifting of characteristic peaks, with the formation of hydrogen bonds between GRE and beta-CD at the 1255 cm-1 band depicting C-O stretching of carboxylic acid.