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Technical Resources

Assessment of the quality of extruded full fat soybean meal subjected to different processing temperatures

Patino, D. and M. Joseph

Although there are different types of protein used today, soybean meals (SBM) are the most widely used source of high-quality vegetable protein for livestock, aquaculture, and especially for poultry feed. It may be processed in a variety of different ways to increase the protein concentrations and to deactivate anti-nutritional factors, where this feed ingredient is exposed to varying degrees of heating during its processing. However, overheating can damage protein and reduce nutritional value. This study was conducted to determine the quality of full-fat soybean meal (FFSBM) exposed to different processing temperatures. Common lab tests including urease index (UI), crude protein (CP), KOH protein solubility (PS), protein dispersibility index (PDI), and trypsin inhibitor (TI) were measured as an indicator of over-processing and under-processing of FFSBM using the extrusion process. A single screw dry was used to produce 6 experimental FFSBM using die temperatures of 135°C, 145°C, 155°C, 160°C, 165°C, and 170°C in a commercial feed mill. These conditions were selected to achieve both under and overcooking of the soy protein, given the limitations of the equipment. UI, TI, PS, PDI, and CP of the 6 FFSBM produced during the extrusion process plus the raw soybeans were analyzed. Data were analyzed using one-way ANOVA and means were separated using Tukey’s test. The UI in excess of a 0.15 increase in pH units suggests under processing, the content of UI of the raw beans was 2.09. However, after the extrusion process UI decreased less than 0.15 for all the FFSBM produced. The TI levels at 170°C were found to be the least at 0.49 mg/g and were statistically different from the other FFSBMs. The PS and PDI values suggested overprocessing at temperatures of 165°C and 170°C. The PS of the FFSBM produced at these temperatures has less than 65% suggesting overprocessing. However, for the FFSBM produced at temperatures lower than 165°C, there was no statistical difference. The PDI values decreased with an increase in temperature and CP increased from 37.59% in raw beans to 45.23% at 170°C with a consistent increase as the processing temperature was raised.

Overall, the study showed that 160°C was the best operating temperature to get the best extruded FFSBM.