Effect of Starch Source on the Microstructure of Extruded Feed Pellets

Abstract

Scanning Electron Microscopy (SEM) is a powerful tool for analyzing the microstructure of extruded feed pellets. It offers high-resolution imaging to study surface topology, granule morphology, and textural changes, enabling a deeper understanding of how processing conditions affect feed quality. SEM has found extensive application in material sciences and biology, but its adaptation for food science, especially aquafeeds, has provided new insights into structural changes induced during extrusion. This study was conducted to evaluate the effect of different carbohydrate sources on the physical and microstructural characteristics of extruded diets formulated for tilapia. The main objectives were to (i) assess the influence of starch origin on pellet pore size and granule morphology, (ii) analyze the extent of starch gelatinization through extrusion processing, and (iii) examine the structural integrity of pellets using scanning electron microscopy (SEM). Seven experimental diets were prepared using corn flour, wheat flour, rice flour, and their combinations, maintaining uniform protein (25%) and lipid (4%) content across all treatments. The SEM analysis revealed significant differences (P<0.05) in both pore and granule sizes among the various starch-based diets. The highest average pore size (220.63±14.73 μm) was observed in the wheat and rice flour combination (WRF), whereas the smallest pore size (50.60±9.44 μm) was recorded in wheat flour (WF) alone. In terms of granule size, corn flour (CF) exhibited the largest starch granules (7.03±2.37 μm), while the corn and wheat flour combination (CWF) showed the smallest (2.22±0.43 μm). These differences were attributed to the varying botanical origins of starch and their distinct amylose-to-amylopectin ratios, which affect the degree of starch gelatinization and physical expansion during extrusion. The findings underscore the importance of starch selection in aquafeed formulation, as it significantly influences pellet texture, structural stability, water solubility, and digestibility—factors critical to feed efficiency and nutrient utilization in tilapia farming. This research is significant for advancing sustainable aquaculture practices by optimizing carbohydrate use in fish diets, reducing dependency on protein as a primary energy source, and enhancing the overall quality and performance of extruded aquafeeds.