Shelf-Life Stability of Ready-to-Use Green Rooibos Iced Tea Powder—Assessment of Physical, Chemical, and Sensory Properties

Abstract

Green rooibos extract (GRE), shown to improve hyperglycemia and HDL/LDL blood cholesterol, has potential as a nutraceutical beverage ingredient. The main bioactive compound of the extract is aspalathin, a C-glucosyl dihydrochalcone. The study aimed to determine the effect of common iced tea ingredients (citric acid, ascorbic acid, and xylitol) on the stability of GRE, microencapsulated with inulin for production of a powdered beverage. The stability of the powder mixtures stored in semi-permeable (5 months) and impermeable (12 months) single-serve packaging at 30 °C and 40 °C/65% relative humidity was assessed. More pronounced clumping and darkening of the powders, in combination with higher first order reaction rate constants for dihydrochalcone degradation, indicated the negative effect of higher storage temperature and an increase in moisture content when stored in the semi-permeable packaging. These changes were further increased by the addition of crystalline ingredients, especially citric acid monohydrate. The sensory profile of the powders (reconstituted to beverage strength iced tea solutions) changed with storage from a predominant green-vegetal aroma to a fruity-sweet aroma, especially when stored at 40 °C/65% RH in the semi-permeable packaging. The change in the sensory profile of the powder mixtures could be attributed to a decrease in volatile compounds such as 2-hexenal, (Z)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, (E,Z)-2,6-nonadienal and (E)-2-decenal associated with “green-like” aromas, rather than an increase in fruity and sweet aroma-impact compounds. Green rooibos extract powders would require storage at temperatures ≤ 30 °C and protection against moisture uptake to be chemically and physically shelf-stable and maintain their sensory profiles.

Stability of labile xanthones and dihydrochalcones in a ready‐to‐drink honeybush beverage during storage

“…Headspace solid‐phase microextraction (HS‐SPME) was performed as previously reported 18 . The tea solution (10 mL) was placed in a 20‐mL headspace vial containing 2 g of NaCl and the internal standard (10 μL of β ‐phenylethyl butyrate at 100 mg L −1 in ethanol).…”

“…Headspace solid-phase microextraction (HS-SPME) was performed as previously reported. 18 The tea solution (10 mL) was placed in a 20-mL headspace vial containing 2 g of NaCl and the internal standard (10 μL of ⊎-phenylethyl butyrate at 100 mg L −1 in ethanol). Extraction of volatiles from the sample headspace was performed using an SPME fibre (50/30 μm PDMS/CAR/DVB; Supelco, Bellefonte, PA, USA), conditioned in accordance with the manufacturer's instructions.…”

New Insights into the Efficacy of Aspalathin and Other Related Phytochemicals in Type 2 Diabetes—A Review

“…Spray-drying of green rooibos extract for production of powdered extract, an ingredient for such convenience products, has little effect on aspalathin degradation as more than 95% was retained in the powder [ 35 ]. Factors playing a role in aspalathin stability are the specific formulation of the convenience product, in particular the presence of citric acid and/or ascorbic acid, pH, heating and storage temperature, packaging materials (semi-permeable to moisture and oxygen vs impermeable), and the carrier/ bulking agent [ 13 , 36 ]. Heat processing and storage of RTD rooibos iced tea also reduced the isoorientin content, and to a lesser extent, the orientin content of the beverage with temperature and presence of other food ingredients playing a role [ 13 ].…”