Polyphenols, known for their antioxidant properties, are plant secondary metabolites whose efficient extraction depends on factors such as solvent type, extraction conditions, and sample matrix. The present study compared different commonly used extraction conditions to recover polyphenols from different dried fruit and vegetable combinations (mainly citrus, berries, and beetroot) to identify a broadly applicable approach suitable for a range of samples. Selected extraction conditions compared cold maceration with a sonication-assisted approach, different temperature conditions (RT and 60°C) and different ethanol (acidified) concentrations (30 and 80%) as extraction solvent. The total polyphenol content (TPC) was determined using the commonly used Folin–Ciocalteu assay as well as Fast Blue assay as an alternative option, which has recently been proposed as a more accurate reflection of the actual polyphenol content.

The results show consistently higher TPC across different samples following extractions with 30% ethanol than 80% as the extraction solvent, indicating better suitability for polyphenol extraction. Furthermore, samples extracted at RT showed higher TPC compared to samples extracted at 60°C. Whilst sonication-assisted extraction slightly improved TPC recovery in some samples, it was generally less favourable due to the prolonged sample processing time. When comparing the Folin–Ciocalteu versus Fast Blue assay, both methods for determining TPCwere highly reproducible, although the Fast Blue assay showed markedly higher values for all samples. The accuracy of the polyphenol assay methods is currently confirmed with HPLC.

In summary, based on the overall best performance of 30% ethanol extraction at RT, this approach could be recommended across a range of different samples. The different performance of the two polyphenol assays requires further attention, and more sensitive approaches such as HPLC should be employed to confirm their accuracy and reliability.