Phenolic Composition and Antioxidant Properties of Lemon-Processing By-Products and Olive Pomace

Agro-industrial residues from lemon and olive processing are relevant by-products of major production chains in northwestern Argentina and represent potential sources of functional compounds. This study compared hydroalcoholic extracts from the solid (SFE) and liquid (LFE) fractions of industrial lemon-processing press effluent, dried lemon peel (DLP), and olive pomace (OP). Phenolic composition was characterized by spectrophotometric methods and HPLC-DAD, while antioxidant properties were evaluated through reducing, reactive-species-scavenging, Fe2+-chelating, and cellular oxidative-stress assays. SFE showed the highest total phenolic (61.11 ± 3.07 mg GAE/g) and flavonoid (120.34 ± 2.58 mg QE/g) contents and the strongest CUPRAC (56.80 ± 1.38 µg GAE/mg) and NO-scavenging (IC50 = 217 ± 7.07 µg/mL) responses, whereas SFE and LFE displayed comparableABTS•+ scavenging and ferric-reducing activity. LFE and OP exhibited greater Fe2+-chelating activity, revealing antioxidant profiles not consistently related to total phenolic content. Only SFE significantly protected Saccharomyces cerevisiae against H2O2-induced oxidative stress. Importantly, physical separation of the lemon-processing effluent generated solid and liquid fractions with distinct phenolic and functional characteristics. These differences suggest potential applications in different food matrices according to physical form and antioxidant profile, supporting differential valorization of a single industrial stream. OP additionally showed distinct functional potential as a complementary solid by-product.