Shear-induced fibrous structure formation from a pectin/SPI blend

Well-defined shear flow can be applied to create fibrous, anisotropic samples from biopolymers when present at sufficiently high dry matter contents. Anisotropic biopolymer structures are of high interest especially when made from plant-based polymer blends due to novel food applications, like meat replacers. We investigate shear-induced structuring of a pectin/soy protein isolate (SPI) blend under heating. Scanning Electron Microscope analysis revealed that shear-induced structuring resulted in elongated pectin filaments, oriented in the direction of the shear flow, being entrapped in a continuous protein phase, inducing anisotropy in the blend. The length of the pectin filaments increased upon higher pectin concentrations and shearing temperatures, leading both to higher anisotropy, as measured with the tensile strength analysis. The fibrous appearance of samples became more evident when deforming the product by tearing, which effect was thought to be caused by detachment through or along the long side of the pectin filament. Industrial relevance The efficient preparation of fibrous products based on plant materials is of interest, because these products can be a starting point for the development of meat replacers. Meat replacers made from plant material are a promising, innovative, and sustainable source of protein for human consumption. With an increasing world population, creation of innovative sources of protein are needed to be able to feed everyone (United Nations - Department of Economic and Social Affairs, 2015). Proteins from plant sources, such as soy, are preferred over proteins from animal origin because plant based materials, for example, have lower environmental impact (Day, 2013; Mogensen, Hermansen, Halberg, Dalgaard, R., Vis, & Smith, 2009). In order to replace meat by a plant-based meat replacer, it is important that a similar product in terms of structural properties is developed to improve consumer acceptance (Hoek et al., 2011). Meat replacers are often produced with extrusion cooking, which is a process that has been applied for texturization of plant materials in the application of meat replacers for decades (Campbell, 1981; Harper & Clark, 1978). Previous research showed that a novel technique based on well-defined shear flow can also be used to create fibrous, anisotropic structures from plant-based biopolymers at sufficiently high dry matter contents, with a cone–cone device (Shear Cell) or a concentric cylinder device (Couette Cell) (Grabowska, Tekidou, Boom, & van der Goot, 2014; G. A. Krintiras, Göbel, Bouwman, van der Goot, & Stefanidis, 2014; Manski, van der Goot, & Boom, 2007). This novel technique uses milder conditions for structure formation, due to lower applied shear forces, and has therefore a lower specific mechanical energy input (Grabowska et al., 2016; G.A. Krintiras, Gadea Diaz, van der Goot, Stankiewicz, & Stefanidis, 2015).