Effect Of Milling And Sieving Processes On The Physicochemical Properties Of Okra Seed Powders

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 mu m. 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 mu m); 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 mu m 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 mu m granulometric class was not cohesive, leading to good flow properties.