SPECIAL STORY 72 FEED & ADDITIVE MAGAZINE November 2022 The PDI values decreased with increase in temperature and all values were less than 45% indicating adequate heat treatment (Figure 3). However, the quality standards by US Soy in International Buyers’ Guide recommends a PDI between 20 and 35% to be the best for animal performance. So, temperatures of 155°C and above were in the right PDI range. The PS between 73-88% is considered of acceptable quality and lower values suggest over processing. FFSBM, thus processed at temperatures of 165°C and 170°C are over processed. For the FFSBM produced at temperatures lower than 165°C, there was no statistical difference (Figure 4). Both PS and PDI values suggested overprocessing at temperatures of 165°C and 170°C. The CP increased from 37.59% in raw beans to 45.23% at 170°C with consistent increase as the processing temperature was raised. As the temperature rises more water is evaporated. Therefore, this evaporation decreases the moisture content and leads to an increase in crude protein levels. There were no statistical differences between the different extruder operating temperatures for the Lysine and Methionine content (Figure 5). However, we also calculate the ratio between lysine and crude protein (Lys: CP) as this is an indicator of heat damage. When an ingredient is heat-damaged to an extreme level (final stage of Maillard reaction), the concentration of lysine is reduced, but the concentration of crude protein is not (González-Vega et al., 2011). For SBM, a Lys: CP ratio of 6 and above is generally accepted as an indicator of good protein Figure 3. Protein Dispersibility Index (PDI) at different extruder die temperatures Figure 4. KOH Protein Solubility (PS) at different extruder die temperatures Figure 5. Lysine, Methionine, and Lysine: Crude Protein Ratio at different extruder die temperatures
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