Effect of process variables on the extrudate moisture content

Fish and rice flour based coextrudates are gaining importance due to high nutritional value. Extrusion cooking is a versatile technique to develop new products using novel ingredients. The moisture content of the extrudate plays an important role in understanding the pellet physical properties. In the present study extrusion process variables like barrel temperature, x₁ (100-200°C), screw speed, x₂ (70-110 rpm), fish content of the feed, x₃ (5-45 %) and feed moisture content, x₄ (20-60 %) were used to understand the moisture content of the extrudate produced. Experiments were conducted based on rotatable experimental design for the various combinations of process variables and the extrudate moisture content was measured. Second order polynomial regression equation was developed for the extrudate moisture content in terms of the process variables under study. The ANOVA results indicated that x₄ and x₁ had strong effect and were significant at P<0.1 and whereas x₃ and x₂ had a marginal influence on the extrudate moisture content Based on response surface plots the trends of the process variables which can result in minimization of the extrudate moisture content were a x₁ >100°C, x₂ >70 rpm, x₃ in between 25-35 % and x₄ <60. Based on RSM analysis it was observed that barrel temperature and feed moisture content were the two interacting process variables. Further the regression equation was optimized using GA to understand the process variables which can result in maximum and minimum of the extrudate moisture content. The optimized process conditions to obtain maximum and minimum were x₁=106.53, x₂=102.25, x₃=44.87 and x ₄=59.95 and x₁=199.86, x₂=109.86, x ₃=32.45 and x₄=20 and the predicted moisture content values were 41.97 and 17.522. The precisely optimized GA results has corroborated with the trends of the RSM where x₁ has influenced the most followed by x₄ and x₂ and x₃ were found to have a marginal effect.