Characterisation of saffron floral bio-residues phenolic compounds under different drying treatments: from agricultural waste to bio-based ingredients

• Comprehensive characterization of phenolic compounds in saffron floral bio-residues. • Thermal stability of acylated anthocyanin derivatives compared to their acylated ones. • Thermal stability of kaempferol, quercetin, caffeic acid, catechins and stilbenes. • Drying (<60 °C) as an economical alternative for conserving saffron bio-residues. Saffron floral bio-residues are generally wasted due to their rapid deterioration. However, they are a source of nutrients and bioactive compounds with important nutraceutical properties. This study aimed to determine the optimal drying temperature to preserve phenolic compounds in saffron bio-residues, providing a low-cost conservation method for small-scale producers. The thermal stability of 37 phenolic compounds including anthocyanins, phenolic acids, flavonols, flavanols, stilbenes, flavanones, chalcones and phenyl-ethanol analogs was analyzed at 40, 60 and 80 °C. Anthocyanins were significantly affected by temperature, while the total concentration of phenolic acids, as well as that of most of the identified flavonols, flavanols and stilbenoids, remained stable at the different drying temperatures. This thermal stability ensured the dried bio-residues maintained similar antioxidant activity, as measured by ORAC assay, at all temperatures. Dehydration at temperatures no higher than 60 °C is suggested as an easy and economical method to preserve saffron floral bio-residues while maintaining the quality of their phenolic compounds.