The aim of this work was on one hand to investigate the influence of milling speed and mean particle size of granulometric classes of okra (Abelmoschus esculentus (L.) Moench) seed powders on proximal composition (related to nutritional potential). On the other hand, it was tried to relate flow properties to powder physicochemical characteristics, namely particle size distribution and proximal composition. Then, dry okra seeds were ground with an ultra-centrifugal mill at three rotational speeds, 6 000, 12 000 and 18 000 r.p.m., corresponding to circa 990, 3 958 and 8 906 g, respectively. Each powder was separated into four granulometric classes: ≥500, 315-500, 180-315 and ≤180 µm. Milling speed affected the particle size distribution of dry okra seed powders: on one hand, the higher the milling speed, the lower the mean particle size, mainly because of the higher the proportion of fine particles (<100 µm); on the other hand, at low milling speed, dry okra seed powders were rather monomodal and constituted of large particles, whereas at high milling speed they were bimodal and composed of two populations (fine and large particles). In granulometric classes, fat and protein contents were significantly higher for fine particles, unlike carbohydrate and ash contents that were lower. This differential distribution of macronutrients within granulometric classes was enhanced at higher milling speed. Finally, the ≤180 µm granulometric class, corresponding to the smallest mean particle size, had a low flowability, confirmed by their high cohesion and compressibility, which can be related to its high fat content making it sticky. On the contrary, the ≥500 µm granulometric class was not cohesive, leading to good flow properties.

This study aimed at relating phytochemical properties (total phenolic content and antioxidant activity), reconstitutability (water absorption capacity and water solubility index) and preservation ability (water activity) of okra seed powders to physicochemical properties (particle size distribution and moisture content). Okra seed powders were produced at three different milling frequencies, and then, each obtained sample was sieved with 180, 315 and 500 μm sieves. An increased milling frequency resulted in lower median particle size, water activity and moisture content. The maximal water activity and moisture content were 0.583 AE 0.010 and 12.07 AE 0.05% (w/w), respectively, showing the good preservation ability of okra seed powders. Total phenolic content and antioxidant activity were raised at higher milling frequency. Reconstitutability was significantly enhanced at higher milling frequency and/or for smaller median particle size. Thus, the successive milling and sieving process was successful in improving physicochemical and functional properties of okra seed powders, especially for smaller particles.