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Valorization of rapeseed press cake in directly-expanded products: Analysis of physical, technofunctional and physicochemical properties
von Anna MartinExtrusion is a suitable technology for the valorization of food by-products into expanded products. For this, by-products are often combined with starch, since starch generates a well-expanded product matrix. The formation of an expanded matrix depends on the rheological behaviour of the viscoelastic melt before and after die exit. Whereas the interrelations between the rheological properties and expansion dynamics are well-studied for starch, knowledge on expansion-related properties of by-product enriched blends is scarce.
In an industry-relevant approach, fish feed blends with varying amounts of an exemplary food by-product, rapeseed press cake (RPC), were extruded under several process conditions. It was shown that incresaing by-product levels significantly reduced the sectional expansion and increased the longitudinal expansion of extruded fish feed. Several quality parameters (sinking, hardness, durability, water stability) were negatively affected by the alteration of expansion properties.
When two-component model blends composed of starch and RPC in different ratios were extruded under varying process conditions, it was shown that the RPC content significantly influenced the viscous and elastic properties of blends. The alteration of the rheological properties of the blends could be well-linked to a more pronounced sectional and decreased longitudinal expansion observed during extrusion of the samples. Thermomechanical treatment caused significant physicochemical transformations of some food by-product components, such protein denaturation and aggregation as well as dietary fiber solubilisation. These transformations were associated with the alterations of the rheological properties as well as with the expansion properties of the blends.
The interrelations of material, process and product parameters of extruded by-product enriched blends described in this study enable a better understanding and control of the expansion properties of the products.
In an industry-relevant approach, fish feed blends with varying amounts of an exemplary food by-product, rapeseed press cake (RPC), were extruded under several process conditions. It was shown that incresaing by-product levels significantly reduced the sectional expansion and increased the longitudinal expansion of extruded fish feed. Several quality parameters (sinking, hardness, durability, water stability) were negatively affected by the alteration of expansion properties.
When two-component model blends composed of starch and RPC in different ratios were extruded under varying process conditions, it was shown that the RPC content significantly influenced the viscous and elastic properties of blends. The alteration of the rheological properties of the blends could be well-linked to a more pronounced sectional and decreased longitudinal expansion observed during extrusion of the samples. Thermomechanical treatment caused significant physicochemical transformations of some food by-product components, such protein denaturation and aggregation as well as dietary fiber solubilisation. These transformations were associated with the alterations of the rheological properties as well as with the expansion properties of the blends.
The interrelations of material, process and product parameters of extruded by-product enriched blends described in this study enable a better understanding and control of the expansion properties of the products.