Characterisation of finger millet (Eleusine coracana) starch isolated by conventional and ultrasound-assisted starch isolation methods

Abstract Starch is a versatile biomaterial with a wide range of applications across various industrial sectors. Therefore, starch isolation methods play a crucial role in fulfilling the demand for high-quality starch required for different applications. Waxy maize starch is the most used starch for different food applications. It is isolated using an alkaline extraction method and available in the market at a high price. The traditional process of starch isolation involves labour-intensive and costly downstream processing that leads to exploring cost-effective isolation methods for various food applications. Finger millet (Eleusine coracana) is an underutilised cereal crop composed of 65–70% of starch. In the present study, the starch from finger millet is isolated using conventional and ultrasound-assisted isolation methods to fulfil the current requirement. The isolated finger millet starch was characterised by morphological structure obtained by scanning electron microscopy (SEM), X-ray diffractogram (XRD), infrared spectrum obtained by Fourier transform infrared spectrometer (FT-IR), differential scanning calorimetry (DSC) analysis, and rheological analysis. The SEM images confirmed the reduced particle size and uniform grain size distribution in the starch isolated using ultrasound-assisted isolation. The relative crystallinity of starch isolated using ultrasound-assisted isolation method (69.05 ± 0.57%) was higher compared to other conventional isolation methods (57.18 ± 0.70%, 67.66 ± 1.00%, and 68.34 ± 0.33% for distilled water soaking, alkali soaking, and sodium bisulphite soaking, respectively). The FTIR analysis confirmed no significant changes in the functional group of starch with respect to different isolation methods. Thermal and rheological analysis of isolated starch using ultrasound-assisted isolation indicated the lowest gelatinisation enthalpy (45.38 ± 1.67 J/g) and showed the lowest loss factor indicating the most elastic behaviour, respectively.