Effects of screw configuration and interfacial properties on oil incorporation in high moisture extrusion

Routes to include oil in meat alternative products made through high moisture extrusion were investigated. We investigated effects of screw configuration and oil-water interfacial properties of the incorporated emulsion on the behavior of the oil during extrusion, and the characteristics of the extrudate after extrusion. Oil was incorporated in the form of an emulsion, and for comparison also directly added without prior emulsification. For oil addition by emulsion, several plant-based protein sources were compared as emulsifier. The choice of protein emulsifier had a strong effect on wedge length of the extrudate, the maximum linear strain and value of G′ in shear, and the rupture strength of the extrudate. Two screw configurations were used. One with 1 kneading disc section and another with 4 kneading disc sections. It was found that fewer kneading discs in the screw led to less mechanical energy input, leading to less shear on the dough in the extruder. The use of fewer kneading elements resulted in less oil leakage from the product, while the product also was stronger, as demonstrated by the higher rupture strength in the texture analysis, and higher storage modulus G’ in oscillatory shear rheology. Less deformation of the air pockets between protein structures could be seen in the screw with fewer kneading discs in multiphoton microscopy. As a result, both the screw configuration and the interfacial properties of the plant protein emulsifier need to be considered when developing meat alternative products containing oil as a route to control the texture of these products.