Effects of superfine pulverization technology on the morphology, microstructure, and physicochemical properties of Apium graveolens L. root.

In this study, the characteristics of the transverse section of Apium graveolens L. root (AR) were observed. The surface morphology, physicochemical properties, and antioxidant activity of five kinds of powders obtained by superfine pulverization (850-355, 355-180, 180-125, 125-50, and <50 μm) were evaluated. Under the microscope, the transverse section of AR had distinct identification features. Parenchyma cells, cork cells, vessels, fibers, nonglandular hair, and tubing fragments were observed via powder microscopic identification. Scanning electron microscopy (SEM) revealed that superfine pulverization evidently changed the shape and surface morphology of the AR powders. As particle size decreased, the moisture and oil-binding capacity (OBC) of AR powder decreased, whereas its total ash content, water solubility index (WSI), swelling capacity (SC), water-holding capacity (WHC), bulk densities, tapped densities, repose angles, slide angles, and crash angles increased. The AR powder with a particle size of <50 μm had the highest contents of total flavonoids (30.46 mg/g), apiin (15.29 mg/g), and 3'-methoxyapiin (6.78 mg/g). Fourier transform infrared spectroscopy (FTIR) analysis revealed that the chemical composition of the powder and its extracts did not notably change as particle size decreased. Meanwhile, the scavenging ability of DPPH and ABTS radicals increased with the decrease of particle size. Therefore, there are more obvious differences in physicochemical properties and antioxidant activity of AR powders with different particle sizes. This study provides a theoretical basis for the development and application of new AR products. RESEARCH HIGHLIGHTS: Under the microscope, the transverse section of Apium graveolens L. root (AR) had distinct identification features. Scanning electron microscope (SEM) was used to observe the morphology and microstructure of AR after superfine pulverization. The surface morphology and physicochemical properties of the powders obtained by superfine pulverization were evaluated. FTIR analysis revealed no notable differences in the chemical composition of the AR powders with different particle sizes.