Sorghum starch: Extraction, characterization and film development

Abstract

Sorghum starch was extracted from sorghum grain (24.27 % average yield) and had a high carbohydrate content (86.66 %), indicating its high purity. This starch was used for the production of films with different concentrations of sorghum starch (2, 3 and 4 %) and glycerol (20, 30 and 40 g/100 g of starch). Most films were homogeneous and practically amorphous; however, the micrographs revealed the presence of some starch granules. These films also had relevant barrier properties to ultraviolet light, with infrared spectrum characteristic of sorghum starch, high lightness (L* = 87.77–90.19) and a tendency of color for the pink, but with low intensity of hue (h° = 297.06–315.20; chroma = 7.00–9.47). Thickness varied from 0.048 to 0.081 mm and the water solubility from 27 % to 48 %. Thermogravimetric analysis revealed the existence of three thermal events, correspondents to the elimination of water, decomposition of glycerol and starch, respectively. The glass transition temperature decreased with increasing glycerol content, keeping in range of 9–15°C. The film with the best mechanical performance was the one composed of 4 % starch and 30 g/100 g glycerol, as it presented a tensile strength of 3.63 MPa and elongation of 44.10 %. Water vapor permeability varied from 5.504 a 14.234 g.mm.m−2.dia−1.kPa−1, due to the increase in the concentrations of starch and glycerol. The characterization directed the usage of such films to pack vegetables and, therefore, proved that the sorghum starch is a promising source for the production of biodegradable films.