In aquaculture, feed production influences nutrition, performance, water quality, and overall profitability. This study evaluated the effects of three levels of internal fat (IF), resulting from the inclusion of 0%, 2%, or 4% fat in the preconditioner during extrusion, and their interaction with two extruder screw configurations: medium-shear (MS) and high-shear (HS), on kibble physical quality and extrusion parameters. Increasing IF resulted in a quadratic increase in amylose–lipid complexation under the HS configuration (p = 0.030; r2 = 0.9) and a linear reduction (p < 0.001) in specific mechanical energy (SME) with a strong negative Pearson correlation (r −0.9; p = 0.009) in both configurations. Fat inclusion also reduced mass temperature and die pressure (p < 0.05), leading to lower starch gelatinization degree (p < 0.05) from 87.9 ± 0.6% to 83.4 ± 0.3% in MS configuration and 95.6 ± 0.7 to 86.3 ± 0.8% in HS configuration, increased bulk and piece density (p < 0.001), and reduced radial expansion (p < 0.001). These changes decreased floatability (p < 0.05) and water stability, increasing mushiness (p < 0.01). Increased shear partially improved SME transfer, starch cooking, expansion, floatability, and mushiness; however, the negative effects of 4% IF could not be fully mitigated. Overall, higher IF compromised kibble structure, starch gelatinization, and floatability, while screw configuration resulted in only a limited compensatory effect.
Scarpim et al. (Thu,) studied this question.