In the context of food and agro-ecological transitions, the development of food applications based on legume flours and plant proteins requires a mastery of grain milling. While wheat grain milling has been extensively studied and is well-mastered, legume grinding and its underlying mechanisms are still poorly understood. The aim of this work is to contribute to the study of the fragmentation mechanisms of pea grains during grinding. Experiments were carried out on hulled yellow pea grains (Kameleon variety) ground under different conditions using a ball mill (MM400, Retsch^®, Haan, Germany) or a micro-cylinder mill. The results showed that the grinding of pea grains, regardless of the type of mill, produced powders characterized by particle size distribution curves with a multimodal shape. The curve analysis was performed according to a simplified deconvolution approach, taking into account different particle populations without diameter overlap. Four particle populations of different sizes were identified and correlated with specific mechanisms governing the grinding of yellow split peas. The physical and biochemical properties of the resulting powders were determined. Taking into account the proportions of the four populations within the powders, the results showed a positive correlation between the volume proportions of very fine (0–10 µm) and fine (10–55 µm) particles within the powders and the starch damage rate and the specific surface area developed, irrespective of the type of mill.

With the increase in the use of plant ingredients in food and the growing demand for pulse protein ingredients, dry fractionation is a sustainable method for producing high-quality protein fractions from pulses. The objective of this work was to assess the morphology of pea fractions obtained by dry fractionation, and their detailed composition with a focus on non-protein components, especially lipids. Pea seeds from a single cultivar were first dehulled, then milled via either stirred ball milling or impact milling, which affected the microstructure of the flours. For instance, scanning electron microscopy revealed that starch granules looked damaged after stirred ball milling, whereas impact milling led to flours with smooth starch granules. Air classification led to a protein-rich fraction (concentrate) with at least 46 g protein /100 g dry matter (d.m.) and to a protein-poor fraction with maximum 18 g protein /100 g (d.m.). The lipids endogenously present in pea seeds (around 3 g/100 g (d.m.) in the starting flour) accumulated in the protein-rich fractions (> 5 g/100 g (d.m.), at the expense of the protein-poor fractions where the lipid content decreased compared to the flour. The same trend was obtained for the ash content. Finally, protein solubility in the flours and protein-rich fractions was investigated in aqueous suspensions at neutral pH, and could be improved by applying a high-pressure homogenization treatment. The microstructure of the suspensions (non-treated, or treated with high-pressure homogenization) was also characterized by confocal laser scanning microscopy. These outcomes expand the current knowledge of dry-fractionated pulse protein concentrates, which is particularly important when targeting their rational use for food applications.

Maize (Zea mays L.) is widely cultivated worldwide for food, feed, and fuel uses. Maize forage has become a valuable feed material, and there is much interest in characterizing its friability, as friability may shape feed value through its effect on ingestibility. The objective of this study was to characterize the friability of maize forage based on its milling behavior within a collection of inbred lines of maize. We proposed two friability indexes—Particle Size Reduction (PSR) and Energy Index—and evaluated their ability to discriminate 24 inbred maize lines differing in digestibility. Both the PSR Index and Energy Index effectively highlighted the variability in friability, which could vary by a factor of two regardless of index. These two friability indexes are based on two different milling technologies and therefore on different mechanical stresses inside the mills that could both inform on friability, but on different scales. In order to interpret the observed differences, we characterized the biomass at different scales, from phenotypic observation of the shoot to physical properties of the chopped maize, down to cell wall amount and composition. The friability assessed through these two indexes was mainly inter-correlated: the lower the milling energy, the more friable the fine particles produced. However, we also identified slight differences between the indexes that could be interpreted in relation to structural scale: while the Energy Index primarily informed friability at the cellular scale, the PSR Index also informed friability at the cell wall scale. This study provided key insight into the friability of maize forage and its relation to physical and fiber properties.