| Summary: | Salmonids (trout, salmon and charr) require high dietary concentrations of protein, and
they utilize protein and lipids as their principle sources of dietary energy. In culture conditions the
protein is mainly supplied by fish meal and other products from the capture fishery. However, the
high cost, and variability in fish meal quality due to processing and storage conditions, dissimilar
raw material quality, as well as fluctuations in the supply of fish meal are major concerns. Feed
accounts for 40% to 60% of the operating costs of salmon fanning. Much of this cost is
associated with the inclusion of fish meal as the predominant protein source. Replacement of at
least some of this fish meal by cheaper plant protein products is one way of reducing these costs.
This study was undertaken to assess the chemical composition and potential nutritive value
(digestibility) of canola protein products developed by processing canola meal by substituting fish
meal in salmonid diets, with rainbow trout (Oncorhynchus mykiss) in fresh water as the test
animal. Sieving, methanol/ammonia treatment and the use of three types of enzyme (Phytase, SP-
249, Alpha-Gal) treatments, singly or in various combinations, were employed in this study. In
addition, a commercially-produced canola protein isolate (CPI) was also evaluated for potential
nutritive value. It was hoped that one of these products would be potentially suitable as a
replacement for fish meal.
The results indicated that sieving canola meal did not have any significant influence on its
chemical composition. Treatment of canola meal with methanol/ammonia however, decreased the
amount of total glucosinolates by over 80%, and lowered the levels of phenolic compounds but this
protocol increased the concentration of phytate. Application of carbohydrases did not result in any
appreciable improvement in the fibre composition of the meals, although it did lead to increases in
the protein content and levels of amino acids, and to decreases in the levels of glucosinolates and
phytate. Low levels of glucosinolates were detected in all the canola protein products that received
the enzyme treatments either singly or in combination. The processing methods used in the production of canola protein isolate (CPI) significantly improved the nutrient composition of the
resultant product. Levels of total glucosinolates, protein, gross energy and phytate of the canola
protein isolate (CPI) were 1.95 umol/g, 90.8% , 24.4 MJ/kg and 4.3 umol/g, respectively
compared to 8.95 umol/g, 36.3%, 19.6 MJ/kg and 45.5 umol/g, of commercial canola meal. In a
three-week digestibility experiment, the effect of processing canola meal on the digestibility of dry
matter, protein and energy by 74 g rainbow trout was assessed using a modified "Guelph system"
of faecal collection. The canola products were included at 30% of the diets (70 % reference: 30%
test canola protein product). Each of the test diet treatment was assigned to triplicate groups of
fish using a completely randomized block design with chromic oxide (0.5%) as an indigestible
marker. The fish were hand fed to satiation twice daily in special designed 150 L fibre glass tanks
supplied with fresh running water (9.9 °C to 11.0 ° C) at a flow rate of 4-5 L/min.
Processing methods had variable effects on the apparent nutrient (dry matter, protein and
energy) digestibility coefficients. All the laboratory processing protocols employed with a view to
enhance the nutritional value of canola meal had significant negative effects on dry matter
digestibility coefficients and generally negligible effects on protein digestibility. There were
however, significant reductions in protein digestibility coefficients in the meals treated with SP-
249 (77.4%) alone or in combination with Alpha-Gal (79.5%) relative to untreated canola meal
(88.1%). Energy digestibility coefficients and the digestible energy contents of the test canola
protein products were the least affected by the processing methods selected for this study.
However, treatment of canola meal with either methanol/ammonia or combination of carbohydratedegrading
enzymes had negative effects on the energy digestibility coefficients and digestible
energy contents. For instance, these two parameters were lowered by about 14 percentage units
and 3 Ml/kg in the ammoniated canola meal and by about 17 percentage units and 2.7 MJ/kg for
the meal treated with the two carbohydrate-degrading enzymes. Digestibility coefficients for dry
matter, protein and energy for the canola protein isolate (CPI) were 77.1%, 97.6%, and 84.7 %,
respectively, and it is noteworthy that all these values were much higher than those values found
for the untreated and treated canola meals.
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