Scanning Electron Microscope Study of Fish and Rice Flour Coextrudates

Microstructure of fish and rice flour coextrudates was observed using scanning electron microscope (SEM). Experiments were conducted based on rotatable experimental design and microstructure was studied of the products extruded at different combinations of extruder barrel temperature, extruder screw speed, and fish and moisture contents of the feed. SEM photographs revealed that a high extruder barrel temperature of 200° C effected the formation of porous and fibrous product due to starch gelatinization with network of holes whereas the product extruded at 100°C was more compact. A high barrel temperature of 200°C during extrusion cooking resulted in extensive protein denaturation and fiber formation and the fiber strands got cemented with starch material leading to cross-linking. Extruder screw speed of 110 rev/min helped in formation of smooth texture, whereas low extruder screw speed of 70 rev/min resulted in more fragmentations. High protein levels due to maximum fish content of 45 % favored greater fiber formation, better organization and orientation than that with low protein level. Feed moisture content of 60 and 20% induced cracks in the texture, but cracks were more pronounced at lower moisture content indicating less cross linking and binding.