Effect of drying temperature on berry press residue anthocyanin stability and profile

Abstract

Berry press residues represent a valuable source of bioactive compounds, particularly anthocyanins and polyphenols, which exhibit strong antioxidant properties. Berry press residues have wide application potential in food systems due to their health benefits as well as colouring capabilities. However, the effects of drying on anthocyanin stability are not fully understood across berry species and drying methods. This study evaluated the effects of conventional hot air and vacuum drying at temperatures ranging from 30 to 90 °C, as well as freeze drying, on the total polyphenolic content (TPC), total anthocyanin content (TAC), antioxidant activity (DPPH assay), and individual anthocyanin profiles in press residues from 10 berry species. Freeze drying preserved the highest levels of both TPC and TAC, while vacuum drying at moderate temperatures (30–60 °C) demonstrated comparable stability and outperformed conventional drying. All thermal methods showed accelerated degradation of anthocyanins above 75 °C, with notable compound losses at 90 °C. Species-specific responses were observed, with chokeberries and honeysuckle berries being particularly susceptible to high-temperature degradation. Chromatographic analysis revealed that rutinoside and glucoside anthocyanins were more thermally stable than sambubioside and diglucoside forms. Strong correlations were found between TPC and antioxidant activity (r = 0.89), whereas the contribution of anthocyanin was more variable (r = 0.66). This study provided a systematic cross-species comparison of 10 berry press residues dried under identical conditions, revealing species-specific degradation thresholds and demonstrating vacuum drying as a method for the substitution of freeze drying. Clear structure-stability relations across 24 individual anthocyanins were demonstrated, offering novel mechanistic insights for optimisation of industrial anthocyanin-rich by-product valorisation. Future research should explore the molecular mechanisms underlying anthocyanin degradation and assess process scalability for industrial applications. Optimising drying protocols may enable sustainable upcycling of berry by-products into high-value functional ingredients.