Anthocyanin stability as influenced by sugar type and water activity in model systems and strawberry-based fruit...

We investigated the influence of bulk composition on the heat stability of black carrot anthocyanins in aqueous model systems. The experimental design comprised aqueous solutions at pH 3 and 5, each with three water activity levels (0.95, 0.90, 0.85) adjusted with sucrose, fructose, or a polyol mixture (erythritol/xylitol, 1:1, w/w) in absence or presence of l-ascorbic acid and 5-(hydroxymethyl)furfural. Anthocyanin retention and color changes after heating at 80 °C for 6 h were monitored by HPLC-DAD-ESI-TIMS-QTOF-HR-MS/MS and colorimetry, respectively, and subjected to quadratic regression analysis. Fructose supplementation was detrimental for anthocyanin stability, with retention dropping below 21% at pH 5. For comparison, polyol supplementation yielded retentions greater than 60% at pH 5, expectedly exhibiting better stability at lower water activity. The detrimental effect of fructose was less pronounced at pH 3. Sucrose similarly exhibited pH-dependent behavior, but provided a superior protection at pH 5 with over 60% of anthocyanins retained, but inferior performance compared to polyols at pH 3. The destabilizing effects of fructose and sucrose was accompanied by the formation of 5-(hydroxymethyl)furfural, reaching concentrations of up to 250 mg/kg in fructose-based systems. The experiments further revealed that anthocyanin degradation was not primarily driven by 5-(hydroxymethyl)furfural itself, but rather by the interplay between water activity, pH, and sugar type, highlighting the multifactorial nature of their instability. The model was validated by heating analogous fruit preparations, demonstrating successful transferability. Overall, these results provide mechanistic guidance for stabilizing anthocyanin color in thermally processed foods and highlight their relevance for the development of sugar-reduced and clean-label formulations. This study is among the first to systematically compare sucrose, fructose, and polyol-based systems at equivalent water activity levels with respect to anthocyanin thermal stability.