Dry fractionation of solvent-extracted castor meal

Castor meal is the main by-product from the industrial process of castor oil extraction. It is a nitrogen-rich material with anti-nematode effect, which has been predominantly used as organic fertilizer. Castor meal was dry fractionated by sieving and air classification, and nutritional and physicochemical properties were measured in each fraction. Near Infrared Spectroscopy was tested for accuracy to estimate the nutritional composition of the fractions. Sieving and air classification promoted significant separation of the inputs that compose castor meal. The coarsest fraction (particles > 2.0 mm) was predominantly composed of fruit husk fragments, and it had low crude protein, (16.5–24.7 %), high acid detergent fiber content - ADF (40.3–46.5 %), and high potassium content (13.8–14.2 g/kg). The finest fractions (particles < 0.5 mm) were predominantly composed of seed kernel fragments, and they had high protein content (39.6–49.6 %), low ADF (12.8–25.7 %), and high phosphorus content (14.7–20.2 g/kg). The highest ADF (59.2 %) was found in the fraction predominantly composed of seed coat fragments (light particles, 1.4–2.0 mm). The lowest water holding capacity was found in the fractions with predominance of seed coat fragments, and the highest in the fractions composed of fruit husks or seed kernel. Clay is an input employed in the industrial process that goes into castor meal and influences its composition, especially the ashes content. Near Infrared Spectroscopy was very accurate to estimate the content of protein, lignin, and fibers in the dry fractions of castor meal. • Castor meal can be efficiently fractionated by sieving and air classification. • Fruit husk, seed coat, and seed kernel were isolated in different dry fractions of castor meal. • Fine fractions of castor meal have high protein and low fiber and lignin content. • The clay employed in the industrial process increases the ashes content of castor meal fractions. • Near Infrared Spectroscopy was accurate to estimate the composition of castor meal fractions.