In a recent ExPress Extrusion Clinic conducted by the Insta-Pro International team here in Des Moines, Iowa, I was asked several good questions after my presentations on the quality of properly extruded soybeans.
One of the questions was “there are claims that, since you rupture the cell walls of an oilseed, the highly unsaturated fat will be prone to rancidity and short shelf life. What would be your answer?”
It was a great question and was something that needed to be asked, my reply was “yes and no, as it all depends on many factors during processing and storage.”
I, then, elaborated on the known advantages an extruder provides that may promote longer shelf life when it is done correctly. The advantages are as listed below:
- Proper extrusion inactive the hydrolytic enzymes such as Lipase, Lipoxidase and Lipoxygenases thus increasing the shelf life of the unsaturated oil.
- Proper extrusion releases the natural Tocopherols, the vitamin E like compounds that are antioxidants that help in preserving the oil.
- Lower moisture content of the extruded soy meal and the lack of significant moisture in the extruded-expelled oil also allows for longer shelf life.
As the fresh extruded meal or the extruded-expelled oil are low in free fatty acids, peroxide value and have no enzyme activities, the quality can deteriorate if they were not managed correctly after extrusion or extrusion-expelling.
Some of the factors that will reduce the shelf life of those extruded products are:
- Lack of immediate cooling of the meal and the oil.
- Exposure to oxygen and direct light
- Come in contact with trace materials that can generate oxidation such as Iron, Zinc, and Manganese.
- Contamination with bacteria that can produce hydrolytic enzymes.
In conclusion, you can find studies to testify to the long shelf life of properly processed soybean or other oilseeds where the above precautions were taken. Otherwise, you can lose those advantages if the process and the storage conditions were not ideal.