Preparation of acylated blueberry anthocyanins through an enzymatic method in an aqueous/organic phase: effects on their colour stability and pH-response characteristics.

To explore the potential of anthocyanins in pH-colour responsive intelligent packaging and improve the stability of the pigments, 3,4,5-trimethoxybenzoic acid and gallic acid were grafted onto blueberry anthocyanins via enzyme-catalysed grafting. The structural analysis based on UV-vis and IR spectroscopy showed that the two acids were successfully grafted onto the blueberry anthocyanins. The acylation degrees of the 3,4,5-trimethoxybenzoic acid-acylated anthocyanin (Tr-An) and gallic acid-acylated anthocyanin (Ga-An) were 6.38% and 6.51%, respectively. The results from the DPPH radical scavenging assay and ferric reducing antioxidant power assay implied that the antioxidant capacity of Tr-An was worse than that of natural anthocyanin (Na-An), but the antioxidant capacity of Ga-An was stronger than that of Na-An. The grafting of the two acids enhanced the stability of the blueberry anthocyanins and had little effect on the pH-colour response characteristics of the blueberry pigments.

Preparation of Lipid-Soluble Bilberry Anthocyanins through Acylation with Cinnamic Acids and their Antioxidation Activities.

To enable the use of anthocyanins in food with high oil content, bilberry anthocyanins were acylated with cinnamic acids to address their poor lipid solubility. Structural analyses based on Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and 1H nuclear magnetic resonance analyses indicated that cinnamic acids were efficiently grafted onto 6-OH of glucoside and galactoside and 5-OH of arabinose through an esterification reaction. The higher the dose of the acylating agent, the higher the acylation degree (AD) and the lower the total anthocyanidin content (TAC) of bilberry anthocyanins. An-Ci4 presented the highest AD value (6.61%), and An-Ci3 exhibited the lowest TAC value (50.16 mg/g). After acylating with lipophilic cinnamic acids, the lipid solubility of acylated bilberry anthocyanins significantly improved. The color of the native bilberry anthocyanin solution dissolved in ethyl acetate and dioxane was transparent. By contrast, the acylated anthocyanin solution dissolved in these solvents was unmistakably red. In terms of the antioxidant activity, acylated bilberry anthocyanins demonstrated inferior performance in 2,2-diphenyl-1-picrylhydrazyl (DPPH) clearance but a better inhibition ratio in ß-carotene bleaching assay compared with native bilberry anthocyanins. As AD value increased, the DPPH clearance of acylated anthocyanins decreased and their inhibition ratio increased in ß-carotene bleaching assay.