Effect of Different Particle Sizes on Physical and Functional Properties of Walnut Green Husk Powder

To optimize the resource utilization of walnut green husk and investigate the impact of grinding treatment on walnut green husk powder, this experiment was carried out to investigate the physical characteristics (particle size distribution, filling, flowability, water-holding capacity, oil-holding capacity, swelling capacity, and microstructure) and functional characteristics (active substance content, and antioxidant activity) in walnut green husk powders with varying particle sizes. The results demonstrated that the particle size of walnut green husk powder exhibited a significant difference (P<0.05) following grinding and sieving treatment. The bulk density, water-holding capacity and oil-holding capacity of walnut green husk powder exhibited a continuous decrease with decreasing particle size. Conversely, the angle of repose and sliding angle showed an increasing trend. Additionally, the tap density tended to initially decrease and then increase, while the swelling capacity displayed a pattern of first increasing and then decreasing. Fourier infrared spectroscopy analysis revealed no discernible damage to the molecular structure of the powder during the grinding process. In addition, the extract of the sample with 200 mesh showed significantly higher active substance content and antioxidant capacity than the other samples (P<0.05). Compared with the sample with 100 mesh, the contents of total polyphenols, total flavonoids, terpenoids and quinones were increased by 7.1%, 19.5%, 16.8% and 16.4%, respectively. This experiment provides a theoretical basis for the practical application of micro grinding in walnut green husk processing industry.