Proximate Composition, Antioxidant Activity, and Antimicrobial Properties of Six Cold-Pressed Seed Meals

Cold-pressed seed meals are nutrient-rich agro-industrial by-products with potential food applications, but comparative data under standardized conditions remain limited. This study characterized six cold-pressed seed meals—pumpkin (PSM), grape (GSM), milk thistle (MSM), flax (FSM), hemp (HSM), and sea buckthorn (SSM), procured during a single production run. Proximate composition, water activity, CIELab color, total polyphenol content (TPC), antioxidant activity (DPPH and ABTS), and in vitro antimicrobial activity were evaluated. PSM and HSM had the highest crude protein contents (46.89% and 44.41%), whereas GSM had the highest crude fiber (51.84%), TPC (63.50 mg GAE/g DW), and antioxidant activity in both assays. SSM had the highest ash content (10.19%) and the second-highest antioxidant activity. Water activity was below 0.48 in all samples. SSM was the most active against Staphylococcus aureus (MIC/MBC: 15.63 mg/mL) and Escherichia coli (31.25 mg/mL), whereas HSM was most active against Candida albicans (inhibition zone: 22.30 mm; MIC: 7.81 mg/mL). Exploratory principal component analysis and Pearson correlation described differences among compositional, antioxidant, and color-related profiles. Given the limited number of groups and a single batch per material, findings apply only to these materials. These results provide comparative data to guide further investigation of their potential use as food ingredients within circular bioeconomy strategies.