Extrusion Processing and Formulation Effects on the Techno-Functional Properties of Melon Peel-Enriched Soy...

The valorisation of agro-industrial by-products through extrusion processing represents a sustainable strategy for developing value-added foods. This study evaluated the effects of barrel temperature (120°C-170°C), feed moisture content (16-25 g/100 g), soy protein concentrate/maize starch ratio (25-40 g/100 g) and melon peel flour content (10-25 g/100 g) on the process parameters and techno-functional properties of extruded snacks. A central composite design and response surface methodology were applied to model residence time (RT), torque (TO), specific mechanical energy (SME), expansion index (EI), apparent density (AD), hardness (HA), water absorption index (WAI), water solubility index (WSI), pH and total colour difference (ΔE). RT, EI, AD, WAI, WSI, pH and ΔE were adequately described by significant models (p < 0.05), with coefficients of determination ranging from 0.72 to 0.98. Feed moisture content was the main factor affecting extrusion performance, reducing SME and expansion while increasing density and HA. In contrast, higher melon peel levels promoted denser and mechanically stronger structures due to the incorporation of dietary fibre. Experimental values ranged from 26.12 to 35.96 s for RT, 1.62 to 2.12 for EI, 0.30 to 0.52 g/cm³ for AD and 18.95 to 36.09 N for HA. The results demonstrate that fibre-protein-starch interactions strongly influence melt rheology and product structure. These findings confirm the technological feasibility of incorporating melon peel flour into extrusion-based snacks and provide new insights into the role of dietary fibre in starch-protein extrusion systems.