Towards zero-waste nutrition: unveiling the nutritional and bioactive potential of freeze-dried broccoli stalk powder

Objective: The shift towards sustainable food systems includes valorising agro-industrial by-products like broccoli stalks, rich in nutrients and bioactive compounds. This study assessed the nutritional profile and bioactive properties—phenolic content, antioxidant capacity and potential prebiotic activity—of freezedried broccoli stalk powder. Methods: Broccoli stalks were cleaned, freeze-dried, milled, and analysed for proximate composition (moisture, ash, fat, protein, carbohydrates, dietary fibre) by AOAC methods, with total phenolics and antioxidant capacity measured via Folin–Ciocalteu and ABTS assays, respectively. Potential prebiotic activity was evaluated by monitoring the growth of three probiotic strains (L. rhamnosus GG, L. rhamnosus R11, and L. casei 01) via viable counts, alongside metabolic activity assessed through pH changes and organic acid profiles determined by HPLC. Results: Freeze-dried broccoli stalk powder exhibited high dietary fibre (43.9 g/100 g), substantial protein (21.5 g/100 g), low fat (0.7 g/100 g), and significant total phenolic content (1.721 mg GAE/g) alongside antioxidant capacity (17.240 µmol TE/g). Fermentation with 2% broccoli stalk powder supported the growth of the tested strains, with viable cell numbers often matching or surpassing that achieved with the positive control (FOS) (approximately +0.5 log cycles). HPLC results indicated enhanced carbohydrate utilisation, with significantly higher lactic acid production and comparable acetic acid levels from broccoli stalk powder relative to glucose, both at 2%, after 24 hours of fermentation. These metabolic responses coincided with a decrease in pH. Conclusions: Freeze-dried broccoli stalk powder offers a promising nutritional and functional profile, making it a sustainable and valuable ingredient in functional food development.