Effect of Heat on Aspalathin, Iso-orientin, and Orientin Contents and Color of Fermented Rooibos (Aspalathus linearis) Iced Tea

Abstract

The phenolic quality of commercial South African fermented rooibos iced teas in terms of aspalathin, iso-orientin, and orientin contents in comparison to a "cup of tea" was shown to be inferior. The role of the different manufacturing stages of powdered extract used in iced tea formulation and, more specifically, the impact of pasteurization and sterilization on the color and phenolic content of the beverage, were assessed as potential causes of its inferior phenolic quality. Aspalathin and its corresponding flavones, iso-orientin and orientin, were found to be present at all stages of the powdered extract production process. Spray-drying did not significantly (P ≥ 0.05) alter the aspalathin, iso-orientin, or orientin content of concentrates. Simulated normal-temperature sterilization (NTS at 121 °C/15 min) and high-temperature sterilization (HTS at 135 °C/4 min), but not necessarily pasteurization (93 °C/30 min), significantly (P < 0.05) reduced the aspalathin, iso-orientin, and orientin contents of different iced tea formulations. Heat-induced losses of iso-orientin and orientin were lower than those for aspalathin. Conversion of aspalathin to the flavones is implicated. The addition of ascorbic acid and/or citric acid to the base iced tea formulation containing only rooibos extract and sugar proved to be beneficial, especially for the retention of aspalathin. Browning, that is, absorbance at 420 nm, was significantly (P < 0.05) increased in the base formulation. In the case of the formulations also containing ascorbic acid and/or citric acid, absorbance remained unchanged or decreased when subjected to NTS and HTS treatments. This was attributed to removal of brown polymers from solution as the pH values of these formulations were lower than that of the base formulation.

Anti-Oxidative Effects of Rooibos Tea (Aspalathus linearis) on Immobilization-Induced Oxidative Stress in Rat Brain

“…Rooibos has been shown to prevent chemically induced liver damage [77], inflammation [78], lipid oxidation [79], hyperglycemia [80], and oxidative stress [81]. These antioxidant effects of Rooibos tea may be related to the presence of antioxidant polyphenol compounds, including aspalathin (dihydrochalcone C-glucoside aspalathin), nothofagin (C–C linked dihydrochalcone glucoside), and other flavonoids (isoorientin and orientin, which are both oxidation products of aspalathin that are characterized by higher stability at high temperatures and under varying pH conditions) [82]. While we have confirmed that drinking Rooibos tea protects against oxidative effects induced by immobilization stress in rats, the exact mechanism of action of Rooibos is still largely unknown.…”

Phenolic content and antioxidant activity of rooibos food ingredient extracts

“…Quantification of aspalathin, nothofagin, isoorientin and orientin was performed in duplicate by HPLC with diode-array detection as previously described by Joubert et al (2009) on an Agilent 1200 system (Agilent, Santa Clara, CA, USA). Calibration curves were prepared using five concentrations of aspalathin, nothofagin, isoorientin and orientin from 0.01 to 2 mg per injection.…”

Comprehensive two‐dimensional liquid chromatographic analysis of rooibos (Aspalathus linearis) phenolics

“…The monomeric flavonoid composition of rooibos is unique in that it contains the novel dihydrochalcone C ‐glycoside, aspalathin , as well as the cyclic dihydrochalcone, aspalalinin . Rooibos tea furthermore represents an important dietary source of the C ‐glycosyl flavones, such as orientin and isoorientin , both major phenolic constituents of fermented rooibos infusions and extracts . In order to exploit the full potential of rooibos as phytopharmaceutical and to realise authentication of rooibos extracts, comprehensive data regarding its phenolic composition are required.…”