Valorization of Passiflora caerulea L. seeds via ultrasound-assisted extraction with natural deep eutectic solvents: Phenolics, in vitro bioaccessibility, and antimicrobial properties

Abstract

The extraction of phenolic compounds from Passiflora caerulea L. seeds was studied using eight natural deep eutectic solvents (NADES). Various combinations of choline chloride (ChCl) as a hydrogen bond acceptor (HBA) with organic acids, sugars, and alcohols as hydrogen bond donors (HBD), at a 1:1 M ratio and 20 % water (w/w), were evaluated. The NADES, composed of choline chloride, fructose, and water (ChCl:Fruc:H₂O), was optimized through statistical experimental design to maximize phenolic yield and antioxidant capacity. The optimized extract was characterized in terms of its phenolic profile, in vitro bioaccessibility, and antimicrobial activity, and its structural effects on the seed matrix were investigated using scanning electron microscopy. NADES ChCl:Fruc:H₂O outperformed 60 % ethanol, extracting 26 phenolic compounds versus 13, and achieving an ≈818 % higher total phenolic content, while enhancing bioaccessibility, particularly for gallic and ferulic acids. Regarding bioaccessibility, both the number and concentration of phenolic compounds were higher in the NADES extract, with the greatest relative increase observed in gallic acid (≈350 %). SEM confirmed greater matrix disruption with NADES. Both extracts showed similar inhibition against Salmonella Heidelberg, Staphylococcus aureus, and Bacillus cereus, with slightly lower activity against Staphylococcus epidermidis, Listeria monocytogenes, and Escherichia coli. This first report on P. caerulea L. seed extracts highlights NADES ChCl:Fruc:H₂O as a sustainable method for recovering bioactives, supporting its use in functional foods, nutraceuticals, and cosmetics.