A protein-sugar complex from condensation resists degradation by rumen microbes because the protein is less soluble and is inaccessible to protein degrading enzymes. However, this complex is highly digestible in the small intestine because acid in the abomasum breaks it up. On the other hand, products of polymerization are largely indigestible in the entire gastrointestinal tract because acid does not affect them. Care should be taken to avoid polymerization when nonenzymatic browning is induced. Soy Pass is produced when sulfite liquor is added to soybean meal and heated.
Sulfite liquor is a by-product of the wood pulping industry and contains the reducing sugar xylose.
Addition of reducing sugar results in more condensation products and increases the UIP concentration of soybean meal. The level of heat is controlled precisely to optimize browning while minimizing polymerization. The TND estimates of this trial indicate the condensation products in Soy Pass are as digestible as commodity soybean meal. SoyPlus is produced by the expeller process of manufacturing soybean meal. Although SoyPlus is higher in UIP and MP than commodity soybean meal, it does not approach the levels of either Soy Pass or AminoPlus.