Preparation of surfactant-free emulsions using amaranth starch modified by reactive extrusion

The use of emulsions at industrial scale involves simple, efficient and versatile applications. Currently, it is preferred the exploitation of biopolymers such as modified starch that may be used as suitable wall materials, avoiding toxic surfactants during preparation. Therefore, in this work, modified amaranth starch with improved physicochemical and morphological properties was obtained by reactive extrusion from a selected extruder outlet time. Additionally, surfactant-free emulsions based on modified starch were prepared at a registered optimal time. The evolution of particle size distributions was monitored by combining Dynamic Light Scattering (DLS) and light microscopy. For starch modification, results showed that 80 s was the best outlet time from the extruder in order to produce a homogeneous material (particle size: 553 nm; fractal dimension: 2.73). For emulsions, a thoroughly characterisation indicated that DLS and fractal analyses converged at 270 s as optimal preparation time, showing a well-dispersed and stable system (particle size: 342 nm; fractal dimension: 2.85). Thus, this contribution provides a strategy for the obtention of modified amaranth starch having appropriate hydrophobic-hydrophilic balance and T_g values for emulsions stabilisation. On the other hand, the technique applied for emulsions preparation resulted in controllable size and shape of particles. This work proposes a complete sequential process that could be helpful to overcome the challenges faced by a number of industries.