Combination of dry planetary ball milling and Lactobacillus plantarum fermentation improves nutritional and functional value of okara

• Application of ball milling technology to improve okara's function and nutrition. • Combination of physical and biological modification. • Fermentation capacity is positively correlated with ball milling time. Okara, a soybean by-product, holds significant industrial potential but is currently limited by its unfavorable physicochemical properties. This study innovatively explores the synergistic effects of dry planetary ball milling and Lactobacillus plantarum UFG10 fermentation on enhancing the nutritional and functional properties of okara. As the ball milling time increased (0–10 h), the particle size of okara significantly decreased. UFG10 fermentation significantly reduced the particle size of okara that was un-milled (UO), milled for 2 h (M2), and milled for 5 h (M5), with the particle sizes decreasing from 899 µm, 588 µm, and 251 µm to 367 µm (UF), 360 µm (F2), and 177 µm (F5), respectively. Fermentation had no significant effect on the zeta potential of okara but significantly improved its rheological properties. Furthermore, this dual treatment significantly improved the functional properties of okara such as water holding capacity, water swelling capacity, oil holding capacity, foaming ability and cation exchange capacity. Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) analyses confirmed structural changes in okara, highlighting the effectiveness of the combined treatment in enhancing its physicochemical properties. The fermentation treatment significantly increased the total phenolic content (with an average increase of over 10-fold) and antioxidant activity of okara, which were positively correlated with the ball milling time. Our findings demonstrate that integrating dry planetary ball milling with fermentation represents a novel and effective strategy to transform okara into a high-quality functional food ingredient, offering new insights for its valorization in the food industry.