Enhancing the Antioxidant Properties of Carrot Wastes Through Lactic Acid Fermentation and Thermophysical Treatments

Carrot wastes contain valuable bioactive compounds, particularly carotenoids, phenolics, and dietary fibre, whose concentration and bioaccessibility can be enhanced through structural and biochemical modifications induced by thermophysical and biological treatments, providing valorization potential. This study evaluated the effects of microwave treatment (1.5 or 3 W/g for 2, 4, and 6 min), ultrasound treatment (100 or 200 g at 40 kHz for 5, 10, or 15 min), and lactic acid fermentation with Lactiplantibacillus plantarum, Ligilactobacillus salivarius, and Limosilactobacillus reuteri for 48 h on the plant cell structure and physicochemical and antioxidant properties of fresh-cut carrot wastes. Among the tested strains, L. salivarius showed the highest growth after 24 h of fermentation (from 8.8 to 9.7 log₁₀ CFU/g), increasing total phenolic content by 1.3-fold. Antioxidant activity improved, with DPPH peaking at 48 h (2.7-fold) and ABTS increasing from early fermentation stages. Ultrasounds enhanced antioxidant properties, so that 100 g-15 min led to maximum increases in total phenols, flavonoids, and ABTS (fold-increase of 1.3, 2.7, and 1.4, respectively), while DPPH values peaked after 5 min (70% increase). Microwave treatment at 3 W/g increased total phenols and flavonoids 1.3-fold, although prolonged exposure reduced antioxidant activity. Overall, selected thermophysical and fermentation treatments may enhance the bioactive potential of carrot wastes.