SPECIAL STORY FEED & ADDITIVE MAGAZINE November 2022 71 Additionally, use of FFSBM is useful for feed mills that have not invested in the costly equipment like pumps and tanks that are needed for liquid (oil) addition. Further, the use of full fat soybeans helps lower the energy requirements (by not using pumps to add in the oil externally into the formulation) of producing feeds and thus contributes to lowering the carbon footprint of feed production. However, it is important to understand that proper heat treatment is needed to lower the heat labile anti-nutritional factors like trypsin inhibitor, to extract the maximum benefits of FFSBM. Overzealous operation of extruder at higher temperatures can lead to overheating can damage protein and reduce the nutritional value. Therefore, it is important to understand that the quality of SBM could be affected by the process used, the different amount of nutrients in the beans, and the antinutritional factors. FINDING THE OPTIMAL EXTRUDER PROCESSING TEMPERATURE This study was conducted to find the optimal processing temperature during extruder operation by determining the quality of FFSBM exposed to different processing temperatures. Common lab tests for raw soybeans and extruded FFSBM included crude protein (CP) content analysis and other tests for measuring FFSBM quality. These included official methods (Palic et al., 2008) - urease index (UI) and protein dispersibility index (PDI) and unofficial methods like KOH protein solubility (PS) and trypsin inhibitor (TI) activity. The measurements are an indicator of over processing and under processing of FFSBM when subjected to extrusion process. A single screw dry extruder was used to produce 6 experimental FFSBM using different die temperatures of 135°C, 145°C, 155°C, 160°C, 165°C, and 170°C in a commercial feed mill. The operating conditions were selected to be between the limitations of the equipment and to achieve both under and overcooking of the SBM. Data were analyzed using one-way ANOVA and means were separated using Tukey’s test. RESULTS The UI more than a 0.15 increase in pH units suggest under processing (US Soy in International Buyers’ Guide), the content of UI of the raw beans were 2.09. However, after the extrusion process UI decreased less than 0.15 for all the FFSBM produced (Figure 1). The TI levels at 170°C was found to be the least at 0.60 mg/g and was statistically different from the other FFSBMs. TI values higher than 3.5 mg/g compromised growth performance due to low digestibility and values lower than 1 mg/g could indicate overheating (Woyengo et al. 2017). Therefore, FFSBM produced with temperatures of 135, 145, and 155°C could compromise the growth performance in the animals and FFSBM obtained by 170°C suggests overprocessing (Figure 2). Figure 1. Residual Urease Index (UI) at different extruder die temperatures Figure 2. Trypsin Inhibitors (TI) levels at different extruder die temperatures
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