Melon Peel Incorporation in Soy Protein-Maize Starch Extrudates: Effects of Formulation and Extrusion Variables on...

The aim of this study was to evaluate the effect of extrusion conditions and formulation on the physicochemical, antioxidant, colour and sensory properties of extruded snacks enriched with melon peel (MP). For this purpose, response surface methodology (RSM) was applied using an experimental design in which the independent variables were barrel temperature (BT: 120°C-170°C), feed moisture content (MC: 16-25 g/100 g), soy protein concentrate/maize starch (SPC/MS: 25-40 g/100 g) ratio and MP (10-25/100 g) content. The response variables included chemical composition (moisture, ash, protein, fat, fibre and carbohydrates), colour parameters (L ^∗, a ^∗ and b ^∗), antioxidant activity (DPPH and ABTS) and sensory attributes (aroma, colour, flavour, texture, appearance and overall acceptability). The results indicated that increasing MP content enhanced dietary fibre levels and antioxidant capacity; however, high levels of this by-product tended to produce denser structures and to reduce the expansion index of the extrudates. Feed MC was identified as the process factor with the greatest influence on the physical and sensory properties, as it regulates melt viscosity and the development of the expanded structure during extrusion. In addition, increasing extrusion temperature promoted browning reactions that altered colour parameters and contributed to the formation of compounds with antioxidant activity. Intermediate levels of MC and MP, combined with moderate-to-high extrusion temperatures, produced extrudates with a better balance between nutritional value, technological properties and sensory acceptability. Therefore, the incorporation of MP represents a viable strategy for the valorisation of agroindustrial by-products and the development of extruded snacks.