with an increasing of feed moisture content and after reaching a maximum the ER decreased with further increasing in moisture content. Similar trends were also observed with protein content and barrel temperature.
The regression equation for the relationship between expansion ratio (YER) and independent variables in terms of coded variables is showed in Table 3. The analysis of variance showed that all the quadratic effects from protein content, feed moisture content and barrel temperature were significant with ER. The interaction effect between protein content and barrel temperature, moisture content and barrel temperature were significant with ER. Protein content
was the most significant factor affecting ER. Moisture content was less significant than temperature. This result is some different with
our prior study (Yu et al., 2009) in which feed moisture content
showed more significant effect to ER than barrel temperature. The
difference could be because the protein content was lower and
maintained below 25 g/100 g (dry basis). In this study, protein
content is much higher, and the combination of protein and
moisture content became highly related with the process temperature
and the protein content, so the barrel temperature became
more significant.