Changes in Moisture, Protein, and Fat Content of Fish and Rice Flour Coextrudates during Single-Screw Extrusion Cooking

Abstract

Changes in proximate composition of fish and rice flour coextrudates like moisture, protein, and fat content were studied with respect to extrusion process variables like barrel temperature, x 1 (100–200 °C); screw speed, x 2 (70–110 rpm); fish content of the feed, x 3 (5–45%); and feed moisture content, x 4 (20–60%). Experiments were conducted at five levels of the process variables based on rotatable experimental design. Response surface models (RSM) were developed that adequately described the changes in moisture, protein, and fat content of the extrudates based on the coefficient of determination (R 2) values of 0.95, 0.99, and 0.94. ANOVA analysis indicated that extrudate moisture content was influenced by x 4, protein content by x 1 and x 3, and fat content by x 3 and x 4 at P < 0.001. Trends based on response surface plots indicated that the x 1 of about 200 °C, x 2 of about 90 rpm, x 3 of about 25%, and x 4 of about 20% minimized the moisture in the extrudates. Protein content was maximized at x 1 of 100 °C, x 2 > 80 rpm, x 3 of about 45%, and x 4 > 50%, and fat content was minimized at x 1 of about 200 °C, x 2 of about 85–95 rpm, x 3 < 15%, and x 4 of about >50%. Optimized process variables based on a genetic algorithm (GA) for minimum moisture and fat content and maximum protein content were x 1 = 199.86, x 2 = 109.86, x 3 = 32.45, x 4 = 20.03; x 1 = 199.71, x 2 = 90.09, x 3 = 15.27, x 4 = 58.47; and x 1 = 102.97, x 2 = 107.67, x 3 = 44.56, x 4 = 59.54. The predicted values were 17.52%, 0.57%, and 46.65%. Based on the RSM and GA analysis, extrudate moisture and protein content was influenced by x 1, x 3, and x 4 and fat content by x 2, x 3, and x 4.