Cereal by-products (wheat germ, maize bran–germ mixture, rye bran, and wheat bran) from the flour milling industry were characterized for their nutritional value and chemical composition, as well as for antioxidant and antibacterial activities. Carbohydrates (including sucrose) were the major nutritional constituents (56.35–78.12 g/100 g dw), followed by proteins (11.2–30.0 g/100 g dw). The higher energy value (432.3 kcal/100 g dw) was presented by the wheat germ. This by-product also presented the highest citric acid content (0.857 g/100 g dw), the most abundant organic acid detected. Unsaturated fatty acids predominated in all samples given the high content of linoleic (53.9–57.1%) and oleic (13.4–29.0%) acids. Wheat germ had the highest levels of tocopherols (22.8 mg/100 g dw) and phenolic compounds (5.7 mg/g extract, with a high apigenin-C-pentoside-C-hexoside content). In turn, while the wheat bran extract was particularly effective in inhibiting the formation of thiobarbituric acid reactive substances (TBARS), the rye bran extract was the only sample capable of protecting erythrocytes from oxidative hemolysis. Regarding antibacterial properties, in general, the lowest minimum inhibitory concentrations were observed against methicillin-resistant Staphylococcus aureus. These results highlight the characterized by-products as sustainable ingredients for the development of novel bakery and functional food products and contribute to a better bioresource-use efficiency and circularity.
