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To prepare bioactive peptides from rapeseed cake directly, the superfine grinding technology was used，and the resulting rapeseed cake superfine powder was used as the material. Single-factor experiments and response surface analysis were used to optimize the preparation extraction. The active peptides were purified by membrane separation and Sephadex G-15 membrane separation, and their antioxidant activity and structure were evaluated. The results showed that the optimal preparation conditions were as follows: grinding time 30 min, solid-to-liquid ratio 1:20(g/mL), pH2.94, enzyme dosage 6300 U/g, temperature 55 ℃, and enzymatic hydrolysis time 2.25 h. Under these conditions, the yield of peptides could reach 83.28%. The F-2 fraction from hydrolysates with molecular mass less than 1000 Da showed good antioxidant activity, with an ABTS+ free radical eliminating rate of 71.62% at a concentration of 1 mg/mL. Furthermore, five peptides were identified, namely PF, SF, TF, IAIPF, and PLDLL which were predicted to have much higher activity. Overall, the results of this study can provide a theoretical basis for the exploration of bioactive peptides directly from rapeseed cakes.

In order to explore the effects of grinding strength on the physicochemical properties and protein extraction of rapeseed meal powder, cryogenic superfine milling was used to prepare six kinds of rapeseed meal powders according to the grinding time (5, 10, 15, 20, 30, 40, and 60 min), namely SGR-5, SGR-10, SGR-15, SGR-20, SGR-30, SGR-40, SGR-60, and conventional crushing one was used as a control, named GR. The results showed that the structure of the rapeseed meal powder was easily destroyed by a moderate superfine grinding compared with the conventional crushing, which was followed by a reduction in their particle size distribution, insoluble dietary fiber content, and water/oil holding capacity, thereby increasing the protein extraction rate. While the grinding process had almost no effect on their total dietary fiber content. Specially, a minimum particle size of the powder would be gotten when grinding for 40 min, about 16 μm (D50), and further grinding would cause the aggregation of powder particles. Moreover, 30 min of superfine grinding was the optimal condition for the extraction of rapeseed meal protein by alkali-extraction. In addition, the alkali pH was another important parameter for the extraction of rapeseed meal protein.