Bioprocessing of Rose Hip Seed By-Products and Its Effects on Phenolic Composition and Antioxidant Activity

Rose hip processing generates seed-rich by-products that remain underexplored beyond oil extraction, despite their potential as a source of phenolic compounds and antioxidant activity. This study investigates the effect of bioprocessing (short-term fermentation) on the phenolic composition and antioxidant activity of rose hip (Rosa spp.) seed by-products, with relevance to cosmetic-oriented applications related to oxidative stress modulation. Rose hip seeds were obtained after juice production and subjected to short-term fermentation (14 days at 21 °C) using Saccharomyces cerevisiae, followed by mechanical separation and drying. Non-fermented and bioprocessed seeds were analyzed for individual phenolic compounds and antioxidant activity (DPPH, ABTS, FRAP), and correlation and multivariate analyses were conducted. Bioprocessing reduced total identified phenolics from 15.79 to 10.72 mg/g DW (≈32%), primarily due to a decrease in epigallocatechin (10.89 to 6.50 mg/g DW). In parallel, the relative contribution of phenolic acids increased, including gallic acid (0.50 to 0.60 mg/g DW) and salicylic acid (0.98 to 1.20 mg/g DW), indicating a selective compositional redistribution accompanied by partial degradation. Antioxidant activity decreased after bioprocessing (DPPH ~340 to ~250 µmol TE/g DW) but remained substantial. Correlation analysis identified epigallocatechin as the main contributor to antioxidant capacity. These findings show that rose hip seeds behave as a process-sensitive phenolic matrix in which bioprocessing alters the balance of individual compounds without complete loss of antioxidant activity. The results indicate that seed-derived by-products retain functional potential for further valorization in cosmetic-oriented applications.