Abstract:
Anthocyanins are natural red–purple–blue pigments of interest as alternatives to synthetic dyes. However, their sensitivity to pH, temperature, dioxygen, light, and matrix composition limits their industrial applications, particularly under near-neutral conditions. In this work, anthocyanin-rich extracts from eggplant peel (EPP), pomegranate juice (PGJ), and blood orange juice (BOJ) were enriched and characterized by HPLC-MS and UV–visible spectroscopy. Their composition, hydration susceptibility (reversible color loss), thermal stability (irreversible degradation), and metal-binding capacity were investigated as key determinants of color diversification and stabilization. BOJ and EPP were more resistant to hydration than PGJ. All extracts formed Al³⁺ complexes at pH 5, reversing hydration equilibria and regenerating color: EPP produced blue complexes, whereas BOJ and PGJ produced purple ones. At 50 °C, BOJ showed the highest stability, while EPP degraded rapidly. To better approximate food-like environments, the extracts were encapsulated in alginate–pectin beads at pH 4 and 5. Encapsulation efficiency ranged from 17.9 to 82.1 %, with the highest values for EPP and PGJ and the lowest for BOJ. Thermal stability was greatest for BOJ, followed by PGJ, with EPP being the least stable. Al³⁺–anthocyanin complexes provided the highest encapsulation efficiency and were especially stable at pH 5, with pectin further improving thermal resistance. BOJ, the most stable extract in both liquid and encapsulated forms, contains flavonoids, particularly flavones, whose planar structures promote strong π-stacking with anthocyanins, enhancing color stability by limiting hydration and the accumulation of thermally sensitive chalcones. Conversely, PGJ experienced greater color loss due to abundant hydration-prone anthocyanidin 3,5-diglucosides, only modestly protected by endogenous ellagitannins. The faster degradation of EPP anthocyanins likely results from their higher sensitivity to autoxidation driven by caffeoyl derivatives, which, although they mitigate hydration-induced color loss, can accelerate thermal breakdown. Finally, incorporation into hard candies confirmed practical relevance: acidified formulations produced vivid red hues, while non-acidified ones yielded purple tones for BOJ and EPP and nearly colorless PGJ. Despite lower color vividness than Allura Red, natural extracts were perceived as more authentic and were thus well appreciated by consumers.
