Nutritional assessment of Australian canola meals. I. Evaluation of canola oil extraction method and meal processing conditions on the digestible value of canola meals fed to the red seabream (Pagrus auratus, Paulin)

This study assessed the nutrient and energy digestibility of a variety of canola protein products that were produced by processing canola meal under different conditions, using the red seabream, Pagrus auratus. The test canola protein products included solvent-extracted canola meal, expeller-extracted canola meal alone or subjected to one of two different heat treatments (120 or 150°C for 30 min), and expeller meal further processed to produce a canola protein concentrate (CPC). Solvent-extracted soybean meal was also included in the study as a reference ingredient. Daily feed intake and blood thyroid hormone levels over the experimental period were also examined. The total digestible protein content of the expeller- and solvent-extracted canola meals was 356 and 358 g per kg dry matter (g kg DM-1) respectively. The total digestible energy content of the expeller- and solvent-extracted canola meals was 14.23 and 8.60 MJ kg-1 respectively. The organic matter digestibilities of the solvent-extracted canola meal were poorer than noted for the expeller- and solvent-extracted soybean meal. Notably, the two sources of canola meals used in this study (solvent and expeller meals) did not cause problems with declining feed intakes or changes to blood levels of thyroid hormones when included in the diets of the fish at a 30% level, and the diets were fed over a 3-week period. The preparation of a CPC resulted in gains in total digestible energy, but a reduction in the amount of total digestible protein, relative to the expeller canola meal from which it was produced. However, the protein concentrating process marginally reduced the relative digestible value of the protein content. Heating expeller meal at 120 or 150°C for 30 min resulted in progressive reductions of all nutrient and energy digestibilities.