For soybean meal processors, the goal is to deliver feed ingredients that support animal health and performance. But achieving optimal soybean meal protein quality is a delicate balancing act. Excessive heat treatment during processing can damage the essential amino acids that animals depend on, while insufficient heat can leave harmful anti-nutritional factors in the meal.
To assess soybean meal protein quality, processors have long relied on two relatively accurate lab tests:
- KOH protein solubility measures how much protein dissolves in a diluted solution of potassium hydroxide (KOH). Low levels of KOH protein solubility can signal overheating.
- Trypsin inhibitor activity gauges the presence of anti-nutritional factors that block protein digestion. High TIA levels indicate under-processing or insufficient heat.
The problem is that these two tests were developed using solvent-extracted soybean meal, which is processed much differently from mechanically extracted soybean meal. Much less is known about how these standard protein quality parameters apply to mechanical extraction.
Fortunately, recent research pinpoints practical soybean meal protein quality parameters for mechanically extracted material, helping producers fine-tune their processes to avoid insufficient—or excessive—heating that could impede animal performance.
What the research suggests
Researchers from the Animal Science Lab at the University of Illinois, supported by scientific analysis from labs in Wisconsin and Iowa, set out to define the soybean meal protein quality parameters that correlate with amino acid digestibility. They analyzed samples of mechanically extracted soybean meal by measuring KOH protein solubility and trypsin inhibitor activity, and then examined the corresponding biological (in vivo) performance in roosters.
The study found a strong correlation between KOH protein solubility values and lysine digestibility, an essential amino acid in the diets of monogastric animals, such as poultry. The research indicated that the lower the KOH protein solubility, the lower the digestibility of lysine.
- This data confirms that the KOH protein solubility test can help mechanical processors avoid excessive heat treatment during processing, which may damage the essential amino acid, lysine, that animals need from feed rations.
However, this study found no correlation between trypsin inhibitor activity and lysine digestibility. The research did suggest that TIA inversely correlates to another amino acid, methionine, reflecting previous studies that have reported similar inverse correlations between trypsin inhibitors and certain amino acids in solvent-extracted soybean meal. After all, trypsin inhibitors are the primary anti-nutritional factors in soybeans, and controlling these enzymes is the primary goal of heat treatment during processing.
- This research highlights how inadequate heat treatment can fail to deactivate trypsin inhibitors that may impede the digestibility of certain amino acids. The anti-nutritional factors in underprocessed soybean meal may cause problems such as poor feed conversion, reduced weight gain, and intestinal issues in poultry.
The paradox of soybean meal protein quality
Here’s the catch. Research has demonstrated that trypsin inhibitor activity should be below 10 TUI/mg for optimal poultry performance. But the optimal KOH protein solubility levels for lysine digestibility (82-83% in this study) coincide with elevated TIA levels (11-13 TUI/mg) that are too high for ideal poultry health. Although these levels may deliver a higher value of digestible lysine, the adverse effects of the excess trypsin inhibitor may nullify the advantage, presenting processors with a paradox.
These results suggest that processors must find a practical compromise between these two soybean meal protein quality parameters to minimize anti-nutritional factors while ensuring adequate amino acid availability. Based on these findings, the researchers recommend that soybean meal processors aim for a KOH protein solubility of approximately 77-78% and TIA levels below 10 TUI/mg, adjusting heat treatment processes as necessary to stay within these targets.
By striking a balance between overprocessing (which can damage lysine digestibility) and underprocessing (which leaves too many trypsin inhibitors behind), processors can target optimal soybean meal protein quality parameters to support poultry growth and feed efficiency.
For more details, download the original study, “Quality parameters for mechanically extracted soybean meal.“