Impact of Thermal Processing on Aqueous Stability of 3-Deoxyanthocyanin-Polysaccharide Complexes in a Model Beverage System

Abstract

Consumer demand for “clean label” ingredients has continued to grow, which has increased the need in the market for more natural food color options. Sorghum 3-deoxyanthocyanins (3DXA) are natural pigments that have higher structural stability under food processing conditions relative to anthocyanins (ACN), but they are relatively hydrophobic and require amphiphilic polysaccharides to improve their aqueous stability. The goal of this work was to determine the impact of thermal processing, ascorbic acid, and storage temperature on the stability of 3DXA-polysaccharide complexes in a beverage model. The effect of thermal processing on the colloidal stability of 3DXA-polysaccharide complexes was investigated by heat treating samples that contained pectin with various degrees of esterification (DE, 32, 54, 70) at pH 3 or 5. Thermally treated samples at pH 5 with DE 54 pectin had a smaller particle size (412-739 d.nm) and better colloidal stability (52-88% after 10 weeks) relative to the samples that were not heated (521-1635 d.nm particle size, 18-66% colloidal stability after 10 weeks), suggesting hydrophobic interactions play a major role in the stabilization of the complexes. In addition, the presence of low molecular weight condensed tannins generally improved the stability of the samples and suggests that tannins may enhance the hydrophobic interactions between pectin and 3DXA. To determine the impact of ascorbic acid on the stability of 3DXA-polysaccharide complexes, a beverage model was prepared with 3DXA extract from non-tannin or tannin sorghum, pectin or gum arabic, sugar, and ascorbic acid. The model was stored at 4, 25, and 40°C for 10 weeks and measured on the UV-vis throughout storage. Hue angle (H°) was measured to determine the impact of ascorbic acid on pigment color properties. The samples with 100 mg/L polysaccharide had high pigment stability in the temperature range of 4-40°C. There was a significant increase in H° in the samples that contained condensed tannins and ascorbic acid, which may be indicative of polymeric or xanthylium pigment formation. Overall, 3DXA-polysaccharide complexes had relatively high stability under thermal processing and in the presence of ascorbic acid, which indicates high functionality as a natural food colorant.