Extraction of apple pomace polyphenols using natural deep eutectic solvents: A sustainable approach

To effectively utilize apple pomace resources, we extracted apple pomace polyphenols using natural deep eutectic solvent (NADES) as the medium, with a solvent-to-solid ratio of 50 mL/g, for a duration of 120 min. Compared to conventional extraction solvents (ethanol and methanol), four NADES significantly enhanced the extraction efficiency of polyphenols from apple pomace. Notably, NADES 1 (betaine: urea = 1:1, 30% water) and NADES 2 (betaine: malic acid = 1:1, 30% water) exhibited superior extraction capabilities, with maximum values reaching 5.245 ± 0.124 mg GAE/g pomace and 5.157 ± 0.164 mg GAE/g pomace, respectively, in Qinguan apple pomace. Both solvents reached their maximum extraction efficiency within 120 min, with NADES 1 achieving a maximum extraction amount of 4.8325 mg GAE/g and NADES 2 achieving 5.3039 mg GAE/g from Fuji apple pomace. NADES 1 and NADES 2 were more efficient in extracting monophenols such as quercetin, rutin, gallic acid, and procyanidin, whereas organic solvents (methanol and ethanol) were more effective for monophenols like methyl gallate and phlorizin. Furthermore, polyphenol extracts obtained using NADES from Fuji apple pomace displayed varying levels of antibacterial effectiveness, with NADES 4 (glucose: lactic acid = 1:5, 60% water) and NADES 2 showing superior efficacy against Escherichia coli and Staphylococcus aureus. This comprehensive study not only demonstrated the potential of NADES in extracting polyphenols from apple pomace but also highlighted their applicability as natural preservatives in the food industry.