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.
Highlights
Rising global obesity and type 2 diabetes, which can be curbed only by addressing unhealthy diet and lifestyle as a long-term strategy [1], underpin initiatives, such as sugar tax on food and beverages to reduce sugar intake
The main objective of the current study was to determine the effect of ingredients, packaging, and storage conditions on the physical, chemical and sensory shelf-life stability of a single-serve green rooibos iced tea powder containing inulin-microencapsulated green rooibos extract (GRE) (IN50) as nutraceutical ingredient
A prebiotic dietary fibre with a low kilojoule content [18], was used as an alternative microencapsulating agent to maltodextrin, the common carrier and bulking agent used by industry
Summary
Rising global obesity and type 2 diabetes, which can be curbed only by addressing unhealthy diet and lifestyle as a long-term strategy [1], underpin initiatives, such as sugar tax on food and beverages to reduce sugar intake. Functional ready-to-drink (RTD) beverages, in particular, offer an excellent means of delivering nutrients and bioactive compounds in a convenient format to the consumer [3]. Challenges of this approach include degradation of bioactive/volatile compounds during food processing and storage [4] and a negative impact on taste [5]. Aspalathin delivery in a RTD green rooibos iced tea presents a challenge as its stability is poor in solution, as shown by De Beer et al [8]. The effect of citric acid, was ambiguous as it improved the stability of aspalathin in the RTD iced tea containing ‘fermented’ (oxidised) rooibos extract, while the opposite effect was observed when a green rooibos extract was used. No information is available on its stability in solution or extract powder
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