Cultivar dependent valorisation of pomegranate peel bioactive compounds through ultrasonic-assisted extraction: Insights from an exploratory full-factorial design

Pomegranate (Punica Granatum) processing generates substantial agricultural by-products, with peels constituting approximately 50% of the fresh fruit mass. While recognized as a rich reservoir of hydrolysable tannins, flavonoids, and phenolic acids, this biomass is often underutilized. Addressing the critical need for sustainable food systems, this study investigates the valorisation of pomegranate peel waste through green Ultrasound-Assisted Extraction (UAE), specifically characterizing the potential of native Maltese cultivars (Bullar and Helu) in comparison to the widely commercially available Wonderful cultivar. By means of an exploratory full-factorial experimental design, this research elucidates the interactive effects of ethanol concentration (10, 40 and 70%), pH (2,7 and 9), and genotype on the recovery of bioactives. While previous literature has extensively covered ethanol concentration, evidence regarding the influence of pH during UAE from pomegranate peels, remains limited. Furthermore, to the authors’ knowledge, the solvent conditions combined interactions with the specific Pomegranate genotypes Bullar, Helu and Wonderful have not been investigated. This study analyzes key responses including Total Phenolic Content (TPC), Total Flavonoid Content (TFC), Orthodiphenolic content, Procyanidins, Monomeric anthocyanins and Antioxidant Activity by means of the CUPRAC assay, complemented by targeted compound determination with High-Performance Liquid Chromatography (HPLC-UV).

Results reveal significant cultivar-dependent variations, with native Maltese cultivars outperforming the Wonderful cultivar in bioactive yield. Bullar and Helu extracts achieved TPC maxima of 170–175 mg GAE/g, significantly higher than the 100–135 mg GAE/g observed for Wonderful. Notably, despite these yield disparities, Bullar and Wonderful exhibited highly similar ethanol-pH interaction profiles for several responses, suggesting potential genotypical similarities between the native and foreign cultivars. The study further identifies critical chemical trade-offs: acidic conditions generally favoured the stability of polyphenols, in turn, maximizing antioxidant activity, while neutral-to-alkaline conditions enhanced flavonoid solubility via ionization of acidic moieties. Crucially, the study demonstrates that optimised extraction cannot be done through a generalised approach. Multi-response desirability analysis indicated distinct optimal conditions for each genotype: Bullar favoured alkaline conditions (pH 9, 68% EtOH), while the polyphenols in Helu were best extracted under slightly acidic conditions (pH 5.4, 60% EtOH). These findings underscore that native Mediterranean cultivars possess suitable bioactive profiles suitable for upcycling into functional food ingredients. By establishing precise, genotype-specific extraction protocols, this research contributes to a smarter circular bioeconomy, transforming agro-industrial waste into high-value pharmaceutical and nutraceutical resources.

"The authors declare that financial support was received for the research and authorship of this abstract and presentation. This work is part of the EXCEL4MED project that has received funding from the European Union’s Horizon Europe research and innovation programme (WIDERA) under grant agreement No. 101087147."