Abstract: Taking alfalfa as the research object, the basic components of stems and leaves in different parts and the functional characteristics of alfalfa leaves powder with different particle sizes were determined and analyzed, and the specific surface area, pore size, chemical group and surface ultrastructure of alfalfa leaves powder with different particle sizes were measured and observed. The results showed that the contents of soluble dietary fiber, protein, fat and ash in alfalfa leaves were higher than those in stems, and the highest contents in upper leaves were 12.25%, 28.62%, 6.23% and 11.35%, respectively. When the particle size of alfalfa leaves is in the range of 0.063~0.25 mm, the water-holding capacity and swelling capacity first increase and then decrease with particle size decreasing, When the particle size is 0.125~0.16 mm, the water-holding capacity and swelling capacity reach their maximum values, which are 5.57 g/g and 4.40 mL/g, respectively; oil-holding capacity decreases from 2.83 g/g to 1.84 g/g; cation exchange capacity, cholesterol adsorption capacity and sodium nitrite adsorption capacity gradually increase. The specific surface area, cumulative pore volume and the number of some groups all increased, while the most probable pore diameter decreased. When the particle size of alfalfa leaf is 0.125~0.16 mm, it has better water holding capacity and expansibility, which is suitable for developing food to improve intestinal function and prevent obesity. When the particle size of alfalfa is 0.063~0.08 mm, it has better adsorption capacity for cholesterol, sodium nitrite and cation exchange capacity, and is suitable for developing and preventing hypertension、heart disease and cancer.

Key words: particle size, alfalfa, functional properties, determinate and analysis