Preheating prior to extrusion


Recently, I was in Argentina at an extrusion conference and I was asked for my comments on preheating soybean prior to extrusion.  Apparently, there are people buying preheaters and then extruding in order to reach acceptable urease and trypsin levels to be able to sell their product in the local market.  My response to him was that a preheater is unnecessary in true high-shear dry extrusion from Insta-Pro due to the fact that we can achieve high levels of temperature in a short amount of time, and we have low trypsin levels and urease activity.  Also, in the process of preheating, you are subjecting the soy to heat over an extended period of time, in effect, overcooking it, even if the temperature is lower.  The problem with this is it has been shown by researchers Rutherford and Moughan in the exhibit below that heat treating, even for only a few minutes, reduced the digestibility of the lysine, and of course, lysine is important in commercial diets as it is a crucial factor to animal growth.

My advice to you if a company requires you to use a preheater, ask them for the scientific research that demonstrably shows that the meal quality is the same as high-shear dry extrusion from Insta-Pro.  Always remember, just because someone says a process works, doesn’t mean it is true.  Ask for the proof.  And the proof is in the research.