The effects of processing on the nutritional value of canola meal for broiler chickens
Newkirk, Rex Wayne
The effect of commercial prepress-solvent extraction of canola on the nutritional value of canola meal was studied in broiler chicks. In addition, methods of determining the digestible amino acid content of canola meal in vitro, the effects of canola genotype on susceptibility to heat damage during processing, and the feeding value of non-toasted canola meal were determined. Desolventization/toasting reduced the content and digestibility of amino acids in canola meal, especially Lys. In a survey of canola meals from plants across western Canada, non-toasted meal was shown to be of higher and more consistent nutritional value than toasted meals, suggesting that the toasting process should be avoided. Reducing the temperature and duration of desolventization/toasting also resulted in higher quality meals. Desolventization without added moisture resulted in a light-coloured, non-toasted meal with the highest nutritional value. Feeding this non-toasted meal resulted in improved weight gain and feed conversion than did feeding a toasted canola meal, indicating that the non-toasted meal was superior to the toasted product. Toasting reduced the glucosinolate levels in the meal but resulted in larger livers and poorer performance when fed to broiler chickens suggesting the non-toasted meal was less toxic. Lys digestibility of canola meal in broiler chickens was not accurately predicted by in vitro determination of protein solubility in 0.5% KOH, the assay currently used by the canola industry. The neutral detergent insoluble nitrogen (NDIN) content of canola meal was correlated with Lys digestibility, suggesting it could be used as an indicator of the nutritional value of canola meal. Near infrared reflectance spectroscopy was the most accurate predictor of the content and digestibility of the key amino acids in canola meal. Canola genotype affected NDIN content both before and after toasting, suggesting it may be possible to select varieties that are less susceptible to damage during toasting. In conclusion, toasting of canola meal reduces the nutritional value of canola meal and reduces broiler performance and should therefore be eliminated. However, further studies are required to establish methods of producing non-toasted meal commercially and to determine the nutritional value of non-toasted meal for other species.