Changes in thermomechanical properties of feed in relation to composition and their effect on pellet manufacturing

Abstract

Due to the growing demand for food, the availability of starch-rich ingredients (e.g. feed grade cereals), whose areal can be used for producing food, is expect to decline. In turn, the use of co-products, from food- and biofuel industry, is expected to increase in livestock feed. However, these co-products are fibre-rich and can negatively affect pellet manufacturing, by reducing pellet quality and increasing energy costs. The thermomechanical properties of feed mashes are considered to be important for agglomeration processes, but its relation to feed composition and its role in pellet manufacturing is poorly understood. The aim of this study was to investigate the effect of fibrous co-product inclusion in feed mashes on their thermomechanical properties and subsequent effects on pellet manufacturing. Treatment mashes were formulated to contain 700 g/kg basic mash, consisting of soybean meal, maize, and soy oil, to which 0–300 g/kg palm kernel expeller, sugar beet pulp, wheat straw and isolated native maize starch were added, according to a four-component mixture design. Treatments were prepared in duplicate, conditioned using a single-shaft conditioner and compacted using a ring-die pelletizer (die hole diameter 6 mm, L/D ratio 12). Pellet quality, production capacity and gross specific mechanical energy consumption per megagram (Mg) were documented. Mash deformability was evaluated by increasing the moisture content of a mash sample to 150 g/kg, followed by compression at 10 MPa and increasing temperature by 4 °C/minute using the Phase Transition Analyzer (PTA; Wenger Manufacturing, Sabetha, KS, US). Inclusion of wheat straw significantly increased mash deformability. Inclusion of isolated native maize starch and fibrous co-products was observed to increase pellet quality in comparison to the basic mash. Mash deformability at compactor temperature was correlated with bulk density (r = −0,83; P < 0.001). Pellet compressive strength was associated with mash deformability (r = 0.78; P < 0.001), but this association was observed to be influenced by wheat straw. Material deformability was correlated with production capacity (r = −0.85; P < 0.001) and energy consumption (r = 0.80; P < 0.001). In conclusion, inclusion of fibrous co-products affects pellet quality in a non-linear relation and increases pellet quality similar to inclusion of isolated native maize starch. Mash deformability could provide an indicator for pellet quality, but the underlying mechanism requires further study. Pelleting of feed mashes with a higher deformability increases energy costs of pellet manufacturing, due to the behaviour during compaction. The thermomechanical properties of feed mashes play a significant role in the pellet manufacturing process.