The influence of anthocyanins in pectin-whey protein complexation using a natural pigmented blackcurrant pectin

The influence of bound anthocyanins on pectin-protein complexation was studied by comparing two types of pectin-protein mixtures: (i) the anthocyanin-rich blackcurrant pectin-whey protein (BCP-WP) mixture and (ii) the anthocyanin-free citrus pectin-WP (CP-WP) mixture. The mixtures were prepared at pH 4.5 with (Pectin:Protein Ratio—1:1, 1:5, 1:10) and without (Pectin:Protein Ratio—1:1) heat treatment at 85 °C. Increasing protein ratio upon heating led to the formation of complexes which eventually destabilized the BCP-WP and CP-WP mixtures. However, no direct relationship was observed between the presence of anthocyanins and the destabilization of mixtures. FTIR analyses demonstrated that there were slight perturbations to the bond strengths of BCP, CP and WP functional groups when they were mixed, with or without heating, confirming the occurrence of pectin-protein complexation. Additionally, the spectrum of BCP-WP sedimented fractions showed the emergence of a peak at 800-1200 cm⁻¹, signifying the presence of anthocyanin-protein interactions. This peak, however, was not seen in the spectrum of anthocyanin-free CP-WP sedimented fractions, indicating that the bound anthocyanins of BCP provided WP with additional binding sites. Moreover, the heated BCP-WP mixture at 1:10 ratio had similar net charge as the BCP control (both ca. −20 mV), yet its CP-WP counterpart had a net charge (ca. −19 mV) that was significantly (p < 0.05) lower than the CP control (ca. −33 mV). Considering the findings from FTIR analyses, it was likely that with heat treatment the BCP and WP had interacted mainly via non-electrostatic forces—through hydrophobic interactions and later reinforced by hydrogen bonds upon cooling.