Phenolic and physicochemical stability of a functional beverage powder mixture during storage: effect of the microencapsulant inulin and food ingredients

ABSTRACT BACKGROUND The need for a convenience herbal iced tea product with reduced kilojoules merited investigation of the shelf‐life of powder mixtures containing a green Cyclopia subternata Vogel (honeybush) extract with proven blood glucose‐lowering activity and alternative sweetener mixture. RESULTS Prior to long‐term storage testing, the wettability of powder mixtures containing food ingredients and the compatibility of their components were confirmed using the static sessile drop method and isothermal microcalorimetry, respectively. The powders packed in semi‐sealed containers remained stable during storage at 25 °C/60% relative humidity (RH) for 6 months, except for small losses of specific phenolic compounds, namely mangiferin, isomangiferin, 3‐β‐ d ‐glucopyranosyliriflophenone, vicenin‐2 and 3′,5′‐di‐β‐ d ‐glucopyranosylphloretin, especially when both citric acid and ascorbic acid were present. These acids drastically increased the degradation of phenolic compounds under accelerated storage conditions (40 °C/75% RH). Accelerated storage also caused changes in the appearance of powders and the colour of the reconstituted beverage solutions. Increased moisture content and a w of the powders, as well as moisture released due to dehydration of citric acid monohydrate, contributed to these changes. CONCLUSION A low‐kilojoule honeybush iced tea powder mixture will retain its functional phenolic compounds and physicochemical properties during shelf‐life storage at 25 °C for 6 months. © 2017 Society of Chemical Industry