Comparative Assessment of Fermented and Non-Fermented Berry Seeds as Sources of Functional Oils

Berry seeds represent an underexploited byproduct of juice and wine production, and are increasingly valued sources of high-quality cold-pressed oils. In this study, eight berry species, including blackcurrant (<i>Ribes nigrum</i>), red currant (<i>Ribes rubrum</i>), raspberry (<i>Rubus idaeus</i>), strawberry (<i>Fragaria</i>), sea buckthorn (<i>Hippophae rhamnoides</i>), honeysuckle (<i>Lonicera caerulea</i>), viburnum (<i>Viburnum opulus</i>), and rowanberry (<i>Sorbus aucuparia</i>), were investigated to determine the impact of primary fermentation on seed composition and oil quality. Seeds obtained from juice production were compared with those obtained after fermentation. Fermentation consistently reduced seed sugars and carbohydrates by more than 50% while increasing relative protein levels, demonstrating microbial utilization of fermentable substrates. Oil yields showed species-specific responses, with blackcurrant and honeysuckle seeds increasing from ~14 to 15% and ~7 to 8%, respectively, while raspberry decreased from ~9 to 8%, and viburnum decreased from ~6 to 5%. Importantly, fatty acid profiles remained unchanged across all treatments, confirming that fermentation does not alter the natural dominance of linoleic and α-linolenic acids. Tocopherol and total phenolic contents decreased modestly in fermented oils (typically 5-10%), which was reflected in small reductions of DPPH scavenging activity (2-4%) and oxidative stability (0.2-0.5 h). A multivariate heatmap and PCA analyses revealed that berry species identity was the primary driver of biochemical variation, while fermentation introduced only minor within-species shifts. The results indicate that berry pomace remaining after fermentation can still be valorized for cold-pressed oil production with minimal compromise in quality.