Modeling and optimizing the effect of extrusion processing parameters on nutritional properties of soy white flakes-based extrudates using response surface methodology

Abstract

Thermomechanical effects of extrusion cooking leads to physiochemical changes that may be either beneficial or detrimental. The effects of extrusion processing on the nutritional value of food constituents, specifically protein, as well as the ultimate product are ambiguous. During the extrusion process, peptide bonds are hydrolyzed and molecular structure of protein changes, which can reduce the nutritional value of the protein and amino acids. Our objective was to study the effects of inclusion of soy white flakes (SWF, up to 500 g/kg) and other extrusion processing parameters such as moisture content of feed, barrel temperature and screw speed on the nutritional properties of aquafeed extrudates using a single-screw extruder and to optimize the processing conditions. Response surface regression models were established to correlate the nutritional properties of extrudates to the process variables. Using response surface methodology, extrusion processing was optimized for the maximum values of the analyzed nutritional properties and minimum values of trypsin inhibitor activity (TIA). The proximate composition, lysine content and TIA were significantly (P < 0.05) affected by the process variables. SWF was the most significant variable with quadratic effects on most of the properties. An increase in lysine content, TIA, protein content, ash content and decrease in fat content was observed when SWF was increased from 200 to 500 g/kg in the feed. Increasing temperature resulted in decrease in lysine content and TIA of extrudates. Our study shows that aquafeed with maximum lysine content and minimum trypsin inhibitor activity can be obtained by adding SWF up to 500 g/kg.