Temperature and meal quality
During processing, meal must be heated to a minimum temperature to destroy the myrosinase enzyme, which can break down glucosinolates into their toxic metabolites (aglucones) in the animal's digestive tract. However, if temperatures are too high for too long, the protein quality of the meal can decrease.
Damage to crude protein, lysine digestibility and lysine content is most likely to occur in the desolventizing-toasting stage.
In Canada, most crushers have very similar processing conditions and canola meal quality does not vary widely. In some countries, however, there can be considerable variation in temperatures used during canola processing. In these cases, it is important for canola meal users to routinely measure the protein quality of the meal or audit and approve suppliers.
Processors should follow these guidelines:
- Seed moisture content during processing should be 6-10%. Above 10% moisture, glucosinolate hydrolysis will proceed rapidly. Below 6% moisture, the myrosinase enzyme is only slowly inactivated by heat.
- During seed cooking, the temperature must be raised to 80-90°C as rapidly as possible. Myrosinase catalyzed hydrolysis of glucosinolates will proceed with increasing temperature until the enzyme is deactivated so that a slow rate of heating favours glucosinolate hydrolysis.
- The temperature in the desolventizer-toaster should be no more than 100°C. Research shows the commonly used temperature of 107°C causes some protein damage. A maximum temperature of 100°C in the desolventizer-toaster will increase lysine digestibility to levels found in soybean meal.
- Processors should note that traditional toasting causes the meal to become much darker in colour. This is a quality concern for some feed manufacturers, who prefer using light-coloured ingredients due to feed customer preferences.