Effect of extrusion cooking on anti-nutritional factor tannin in linseed (Linum usitatissimum) meal

Various oilseeds and their by-products usually constitute a major source of dietary protein as aquafeeds for warmwater herbivorous/omnivorous fish species. The oilseed meals available in India are fairly rich in protein and most of them are traditionally used as valuable feed for farm animals. However, among the factors that limit incorporation of these ingredients in aquafeeds are amino-acid imbalance and presence of anti-nutritional factors. Enhancement of the nutritive value of these ingredients and reduction (or removal) of anti-nutritional factors can be attempted by processing so as to increase the bio-availability of these nutrients. It has been found that various anti-nutritional factors can be destroyed by the process of extrusion cooking. Extrusion is a process whereby raw feed material is exposed to controlled conditions of high temperature, pressure and moisture. In the present experiment, extrusion cooking is used to reduce the anti-nutritional factor tannin in linseed (Linum usitatissimum) meal.

A single-screw cooking extruder, designed and manufactured at the Indian Institute of Technology, Kharagpur, was used for the study. Experiments were carried out following a rotatable central composite design to determine the optimum values of the process variables for which maximum reduction of tannin (Y) occurs. The process variables selected for the study were: barrel temperature (X1) (60-100 degrees C), extruder speed (X2) (60-100 rpm) and oilseed moisture content (X3) (30-50%). Following the design, a second-order response model was fitted.

The optimized values of the process variables were found to be X1 =82.5 degrees C, X2 = 90 rpm and X3 = 41.22%, and the value of the predicted response (i.e. reduction of tannin Y) was found to be 61.25%.