Evaluating the pelleting characteristics of alternative soybean meal protein combinations and soybean meal

The purpose of this experiment was to clarify the effect of different combinations of alternative soybean meal protein on the physicochemical properties and pelleting characteristics of mash feed. A correlation model was also established between physicochemical properties, pelleting efficiency and pellet quality. Seven unconventional protein sources were selected, including clostridia ethanol protein (CAP), cottonseed protein concentrate (CPC), corn gluten meal (CGM), peanut meal (PNM), rapeseed meal (RSM), cottonseed meal (CSM) and distillers dried grains with soluble (DDGS). Six groups were prepared for the alternative soybean meal protein combinations. These feedstuffs were grounded by hammer mill with a 2-mm screen-sized plate sieve, and then mixed with the rest feed raw materials in the same proportion. The pelleting experiment was carried out on the ring die pellet mill. Specifically, the die hole diameter was 3 mm, and the length-diameter ratio of ring die was 10:1. The conditioning temperature and time were 80 ˚C and 135 s respectively. The mash and pellet feed samples were taken to record the processing parameters. The parameters were then measured, including the physicochemical properties of mash feed (apparent density, tap density, angle of repose, angle of friction, water absorption, water solubility, protein dispersibility, and viscosity), and pelleting characteristics (electricity consumption per ton, pelleting rate, pellet durability index, and hardness). Partial least squares regression was utilized to establish the correlation between physicochemical properties and pelleting characteristics. Entropy weight TOPSIS analysis was made to evaluate the pelleting characteristics of different mash feed. The results showed that: 1) There were the significant differences in the physicochemical properties, pelleting efficiency and pellet quality of different groups. The water absorption index varied from 1.79 to 2.20 g/g, the final-viscosity was from 741.50~1 665.00 mPa∙s, the electricity consumption per ton was from 7.46~9.28 kWh/t, and the hardness was from 58.75~84.15 N. 2) The physicochemical properties shared a significant effect on the pelleting efficiency and pellet quality. The compression degree was negatively correlated with the pelleting rate (r=-0.519, P<0.05), positively correlated with the pellet durability index (r=0.545, P<0.05), and significantly and positively correlated with the hardness (r=0.570, P<0.01). The water absorption index and swelling degree were positively correlated with the pellet durability index (r=0.450, 0.548, P<0.05), and significantly and positively correlated with the electricity consumption per ton (r=0.869, 0.903, P<0.01). The viscosity characteristic values were significantly and positively correlated with the electricity consumption per ton (r=0.883, 0.891, 0.860, P<0.01). 3) In terms of pelleting efficiency, the best performance was found in the group with the addition of 38% peanut meal (CGP1 group), whereas, the group with the addition of 100% soybean meal (SBM group) was the worst. In terms of pellet quality, the best quality was observed in the group with the addition of ethanol Clostridium albumenum protein (CAP group), whereas, the worst was in the group with the addition of 32% corn gluten meal (CGP2 group). The finding can provide the basic data and reference for the selection and processing application of non-soybean meal diet protein source. The reduction and substitution of soybean meal can be promoted to alleviate the excessive dependence on the soybean meal import for the national food security.