Effects of ingredients and processing conditions on pellet quality

Jenni Lee Briggs, Purdue University

Abstract

Feeding quality pellets enhances animal performance. Therefore, a comprehensive study of steam conditioning and pelleting was undertaken to evaluate factors responsible for the structural properties of pellets. Various rations containing regular corn, high oil corn, soybean meal, and expelled soybean meal were pelleted. The effect of ingredients, steam conditioning pressure, and paddle configuration on pellet quality was evaluated. Increasing raw protein content increased pellet durability. An upper oil limit of 5% (dry basis) could be obtained before detrimental effects on pellet quality were detected. Changing the residence time inside the conditioner by adjusting the paddle pitch increased pellet durability indices by up to 5 points. Mechanical strength in terms of the modulus of elasticity and failure stress of individual pellets was measured via three-point bending. A wide variation in pellet hardness was observed within a treatment. This data is important for future stochastic modeling and for developing quality control programs in feed manufacturing operations. Chemical changes of the primary nutrients due to processing also were evaluated. Differential scanning calorimetry (DSC) studies revealed no starch gelatinization occurred in the conditioning chamber and 36% starch gelatinization was found in pelleted corn rations. The extent of protein thermal denaturation could not be detected using DSC because a representative sample of the original protein could not be obtained. SDS-PAGE was performed to determine possible protein-protein interactions resulting from processing. Small differences in band intensity were observed between processed and unprocessed samples. This suggests that a slight protein network had formed contributing to the cohesive characteristics of pellets. A 3-D finite element model was developed that simulated fluid flow through a steam conditioner. Two paddle configurations and three rotational speeds were evaluated. The mash and steam were assumed to be a continuum and behave as a Newtonian-like fluid. Simulations showed a difference in flow (mixing) patterns due to different blade pitches. The flow patterns changed only slightly when the rotational speeds increased. However, the velocity, which is directly related to the residence time in an actual conditioner, increased significantly. This work may be applied to assessing optimal steam conditioner settings required to produce quality pellets.

Degree

Ph.D.

Advisors

Maier, Purdue University.

Subject Area

Agricultural engineering|Livestock

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