Model of formula feed specific heat based on different components of feed ingredients

During the processes of conditioning, extrusion and cooling，the consistency and stability of feed products are the most important problems at present. In order to determine the heat and mass transfer properties of formula feed in these processes, the effects of different components of feed ingredients on specific heat were investigated using the continuous differential scanning calorimeter (DSC) method. With the help of a computer program, the apparatus provided different energy fluxes for the active cell containing texting sample and the reference cell containing air, in order to keep the two cells at the same temperature. By analyzing the energy differences between them, the specific heat of a sample could be obtained for the specific heat capacity of raw materials which had a great influence on the feed production. Up to now, there were many research reports on onefold raw material specific heat, however, the studies on formula feed specific heat were very limited. The works in this study took piglet formula feed as an example. The experiments in three factors with five levels were designed by a quadratic orthogonal rotation approach to attempt to determining the specific heat of the mixture of maize (46%-70%), soybean meal (9%-18%) and whey powder (2%-10%). Maize and soybean meal shared a larger proportion in piglet formula feed than other feed ingredients, while whey powder was a type of thermo-sensitive substance that had a great influence on specific heat. The result showed that the specific heat increased with an increase of heating temperature for each onefold raw material, but the whey powder appeared to peak at 58.8℃，which may be the glass transition temperature of whey powder. This situation influenced microstructure and it was harmful to the nutritional quality of whey powder and the palatability of pellet feed. Based on the experiments, a model of specific heat of maize,soybean meal and whey powder mass fraction was established by regression analysis and response surface methodology (RSM).The results showed that the primary and secondary relations that influenced specific heat of formula feed were whey powder>maize>soybean meal，and those of interaction was maize×soybean meal>maize×whey powder>whey powder×soybean meal, and the regression equation was Y=2.63?0.022X1+0.052X2+0.011X3?0.011X1X2+0.026X1X3+5.687×10-3X2X3?0.046X12? 0.017X22?0.054X32 (R2=0.9822). (X1 in mass fraction of maize; X2 in mass fraction of whey powder; X3 in mass fraction of soybean meal). The estimated result by the model revealed that the minimum specific heat of formula feed was 2 536 J/(kg·K) under the mass fractions of maize，soybean meal and whey powder of 66%, 12%, and 6% respectively. The minimum specific heat of the formula feed was a benefit for energy conservation during the feed process and provided useful information for adjusting the machine parameters. The study was the first one to investigate the specific heat of formula feed, and came up with available information for the feed process of conditioning, extrusion, and cooling, which would have a good influence on the consistency and stability of feed products and provides a reference for the thermal processing of different formula feed.