Linseed-sunflower meal co-extrudate as a functional additive for animal feed – extrusion optimization
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The presented study shows a simple way for optimization of extrusion process, which was used for deterioration of cyanogenic glycosides – antinutritive components of linseed, with minimum damage of essential Alpha-Linolenic Acid (ALA) at the same time. Extrusion of the material was done on a laboratory single screw extruder. Content of Hydrogen cyanide (HCN) as a measurement of cyanogenic glycosides in produced coextrudate and fatty acid composition were determined, together with basic chemical analyses, which were done in accordance with AOAC methods. Statistical analysis showed that HCN content in the product was the most dependent (P= 0.0002) on quadratic influence of moisture content of starting material. The highest HCN content (126 mg kg-1) was measured at the lowest moisture content (7%) and the lowest screw speed (240 rpm). Low moisture content caused weak volatilization of HCN along with the evaporating water, which was intensified with higher values of moisture content. However, increase in moisture content from 11.5 to 16% slightly increased the amount of present HCN, due to the lower material viscosity. Extrusion process caused some changes in fatty acid composition, but even the highest degradation of ALA did not exceed 4%. Linear and quadratic influence of moisture content on ALA reduction was significant (P< 0.05), as well as quadratic influence of screw speed. Specific attention has to be paid to selecting appropriate levels of screw speed and moisture content of the material which contains linseed, in order to achieve both detoxification of linseed and preservation of essential fatty acids.