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• Protein recovery from lemon peels has been achieved for the first time by PLE • Optimized PLE required low EtOH (18% v/v) and short extraction time (7 min) • 58 peptides were identified in lemon peel hydrolysates by UHPLC-MS/MS • 19 polyphenols and 2 purine nucleosides were also identified by UHPLC-MS/MS • Thermolysin hydrolysates yielded the most bioactive extracts This study aimed to develop a sustainable and efficient method for protein recovery from lemon peels using Pressurized Liquid Extraction (PLE), optimized through experimental design and response surface methodology. The final protocol, employing 18% (v/v) ethanol, 110 °C, and a 7-min extraction time, demonstrated high extraction efficiency (66%) and environmental compatibility, achieving a greenness score of 0.59 (AGREEprep). The optimized protein extract was subsequently hydrolyzed using alcalase and thermolysin, and the resulting peptide fractions were characterized by spectrophotometric methods and by Ultra High-Performance Liquid Chromatography coupled to Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry (UHPLC-ESI-QTOF-MS/MS). A total of 58 peptides were identified, 39 of which originated from lemon proteins, along with 19 polyphenols, such as vicenin-2, narirutin or subaphylin, and other compounds ( e.g. , organic acids, amino acids, and purine nucleosides), revealing a diverse and multifunctional bioactive profile. Bioactivity assays demonstrated that the thermolysin hydrolysate exhibited the highest antioxidant (97 ± 1% inhibition of hydroxyl radicals), antimicrobial (MIC = 0.75 mg/mL against Staphylococcus aureus ), and antihypertensive activities (49 ± 3 % angiotensin-converting enzyme inhibition), likely due to the presence of peptides enriched in aromatic amino acids such as phenylalanine and tyrosine.
Gómez-Mejía et al. (Wed,) studied this question.