Structural, Rheological, and Physicochemical Properties of Yam Starch Modified by Moderate Electric Fields

Moderate electric fields (MEF) have emerged as a non-thermal technology with the potential to modify the structure of biopolymers. This study aimed to evaluate the effect of MEF (5-15 V/cm) on the structural and techno-functional properties of yam starch. The working hypothesis was that MEF application induces molecular reorganization without inducing starch gelatinization. Scanning electron microscopy revealed slight morphological changes in the shape and surface of yam starch granules treated with MEF, while X-ray diffraction evidenced an increase in relative crystallinity from 25.24% to 26.91% after MEF treatment. Amylose content also increased from 49.8% to 51.8% after treatment at 15 V/cm. MEF also induced changes in short-range molecular order, which were more pronounced at 15 V/cm, as evidenced by increases in the Fourier transform infrared spectroscopy band ratios of 1047/1022 cm⁻¹ (0.724-0.734) and 995/1022 cm⁻¹ (1.272-1.277) compared to native starch. The gelatinization enthalpy remained nearly unchanged after MEF treatment (16.9-19.0 J/g). In addition, MEF modulated viscosity in a field-intensity-dependent manner. The viscosity at 90°C increased from 314.0 mPa·s (native starch) to 366.5 mPa·s at 5 V/cm and decreased to 218.5 mPa·s at 15 V/cm. Principal component analysis indicated that MEF treatment induced structural and functional changes in starch as a function of the applied voltage.