Towards more sustainable meat alternatives: How technical parameters affect the sensory properties of extrusion products derived from soy and algae

High moisture extrusion cooking is a well-established method to develop soy-based meat alternatives. Algae are increasingly researched into as an alternative protein source, particularly the micro-algae spirulina (Arthrospira platensis) is known for its high protein content. However, little is known how spirulina behaves during the extrusion process. This study investigates the sensory properties of spirulina (10%, 30% or 50%) and soy-based meat alternatives (16 samples) produced according to a Design of Experiment (DoE) with different levels of moisture (57%, 67% or 77%), screw speed (600 rpm, 900 rpm or 1200 rpm), temperature (140 °C, 160 °C or 180 °C) and two production days (independent replicates). Conventional profiling by a trained sensory panel (n = 12) based on a product-specific vocabulary was carried out and the samples were also subjected to instrumental texture profile analysis (TPA) and razor shear measurement (MORS). The data revealed that high spirulina content caused a black color, an intense flavor with earthy notes and an algae odor that is rather musty. Additionally, the higher the share of spirulina, the lower were the elasticity, fibrousness and firmness of extruded samples. High moisture content resulted in products evoking a juicy and soft mouthfeel plus a moist appearance. Instrumentally measured texture parameters matched with the sensory profile regarding texture: high moisture induces a decrease in shear force, shear energy, hardness, cohesion, springiness and chewiness. Particularly firmness perceived by the panel correlates with both MORS and TPA measurements while sensory elasticity correlates with springiness. When keeping moisture low, but screw speed and temperature high during extrusion, it is possible to partly substitute soy with spirulina in order to produce firm and fibrous products with a decent algae flavor that will contribute to shape a more sustainable future for food.