## 1 Introduction  
Pulses have been part of the human diet since the earliest domestication of agriculture and plants and are cultivated worldwide [1]. Originally consumed as cooked hulled grains, they are also ground and used as flours or fractionated and used as enriched powders (protein concentrates/isolates). The use of legume flours and powders is often associated with the total or partial replacement of wheat flour. These flours are important levers for growth in the legume crops sector, promoting consumption through their versatile functional food potential. Compared to wheat milling, the milling of legume grains and its underlying mechanisms remain poorly understood [2] There is still little information on the process parameters associated with the production of these powders and their optimization for food applications [3], although legume flours exist for several applications [4; 5; 6; 7]. Ginding is a unit operation that fragments material under mechanical stress. Depending on the type of mill and the desired granulocyte, fragmentation is achieved by applying single or repeated stresses to the grain structure that are greater than the fracture stress of the material, at the grain or at the particle scale. Depending on the type of equipment, various mechanical stresses such as compression, impact, shear, and abrasion/ attrition are promoted and cause material fragmentation and the formation of small particles. Powder properties are determined by the fragmentation mechanisms depending on the grinding equipment and its operating conditions. Some studies have investigated the influence of the milling process on the characteristics of the resulting legume powders, either by comparing the effect of different types of mills or by modulating the milling parameters using the same mill. Most of the legume powders studied were either purchased from commercial flour manufacturers [4,8] or milled on a laboratory or pilot scale using a variety of different milling equipment [9, 10, 11, 12, 13, 14, 15]. Often, a lack of information about the grinding conditions prevented the observation of relationships between process parameters and product properties. [PERSON] et al. (2021) [16] investigated the effect of grinding conditions using a roller mill under different configurations on the powder properties of pea and lentil grains. The grinding scheme based on reduced roll spacing between passes produced more damaged starch. [PERSON] et al. (2019) [4] investigated the effect of parameter settings using a knife mill with different sieve sizes on the properties of legume powders. The sieve size selected had a direct influence on the granulometric characteristics of the flours. They observed differences between the powders produced in the knife mill and commercial flour. Other studies have compared the effects of different mills [9, 11, 15] and their setting parameters [12, 17] in order to understand the mechanisms induced in the separation of constituents during the milling process. These works mainly focused on the optimal separation of cellular components (starch, proteins) to optimize the enrichment of the powder, based on the generation of fractions or streams. There is still a lack of studies in the literature that focus on the effects of the grinding process in order to establish relationships between the parameters of the grinding process, the fragmentation mechanisms, and the properties of the powders produced. The present work aims to contribute to the study of the fragmentation mechanisms of pea grains during grinding under different conditions. Experiments were carried out with yellow split peas ground using two different mills (ball mill and cylinder mill) under different conditions. The powders obtained were characterized in terms of their particle size distribution and their microstructure. The grinding of yellow split peas, using both types of mills, results in powders with a multimodal particle size distribution.