Formation and characteristics of alginate and anthocyanin complexes

Sodium alginates with different mannuronate to guluronate units ratio ALG1 and ALG2 were employed in the formation of insoluble complexes with anthocyanins (ATC) extracted from Vaccinium myrtilus by exploiting the electrostatic interaction between carboxylate groups of sodium alginate (ALG) and flavylium cations of ATC. Monomer composition of ALG1 and ALG2 was determined from the 13C CP-MAS NMR spectra. The amount of ATC incorporated into the complex depended on the type of ALG used, the ALG to ATC weight ratio and the total concentration of the components in the solution. ALG1 having higher amount of G-blocks was favourable in the complex formation with ATC. At ALG to ATC weight ratio being 0.4 to 1 and total concentration of 0.66 g/L, about 1.54 g of ATC per gram of ALG1 and about 1.24 g of ATC per gram of ALG2 was incorporated into the complex. Thermogravimetric analysis showed that the rate of ALG and ATC complex decomposition also depended on the type of ALG used and was 2.5 times higher for ALG2 and ATC complex compared to ALG1 and ATC complex. Furthermore, ALG/ATC complexes showed prolonged antioxidant activity when compared to ATC.