COCOYAM STARCH PROPERTIES AND POTENTIAL APPLICATION IN BIODEGRADABLE FILMS

There is great interest in producing biodegradable films using alternative raw materials to commercial starches. Tropical starchy sources are potential targets in this research. Cocoyam (Xanthosoma sagittifolium) is a plant that contains a considerable amount of starch in its tuberous roots, but it is still little explored scientifically and commercially. This work aimed to evaluate the potential use of cocoyam starch in producing biodegradable films. The structural characteristics of cocoyam starch and its potential for producing biodegradable films were determined for this. The methodology consisted of the extraction process in an aqueous medium of the starch, followed by its characterization concerning the physical-chemical, morphological, structural and thermal properties and subsequent application in formulations of biodegradable films, with substitution of 100 (CY100), 75 (CY75), 50 (CY50), 25 (CY25) and 0 % (CY0) of commercial cassava starch. Cocoyam starch showed 19.93±0.94 % of apparent amylose content, 50.56±1.28 mg of EAG/100 g of total phenolic compounds, 92.02±3.02 % of digestible starch and 5.61±0.27 % resistant starch. The cocoyam starch granules ranged between 2 and 8 μm, with a polyhedral and oval shape characterized as bimodal granules. The starch had a high-brightness white color (93.35) and a gelatinization temperature of 65.81±0.09 °C, with a gelatinization enthalpy of 15.38±0.33 J/g. A type C pattern crystallinity and monohydrated calcium oxalate crystals characterized cocoyam starch. The measured crystalline area was 22.1 % of type A, 2.2 % of type B and 1.4 % of cocoyam, with a total crystallinity of 25.7 %. Calcium oxalate crystals form the raphides identified in the micrographs. Biodegradable films with higher concentrations of cocoyam starch presented greater thickness (0.27 to 0.10 mm) and lower transparency appearance (45.29 to 47.02). Regarding the mechanical properties, biodegradable films with a higher concentration of cocoyam starch showed higher elongation to rupture (102.67 to 17.57 %) and lower tensile strength (0.58 to 3.57 MPa). Young's modulus increased with the replacement from zero to 50 % of cocoyam starch by cassava starch (CY100 = 2.24 MPa, CY75 = 2.90 MPa and CY50 = 3.49 MPa), with a subsequent decrease. The changes in the mechanical properties of the films provided by cocoyam starch occurred due to the interaction of the hydroxyl groups of the amylose and amylopectin chains, resulting in hydrogen bonds inside the starch granules. The use of cocoyam starch allowed greater elongation to rupture and lower tensile strength, being more flexible when compared to the use of cassava starch. However, Young's modulus increased by replacing 50 % of cocoyam starch with cassava starch. Replacements greater than 50 % promoted a sharp decrease in the energy required to deform the angles and bond length between the atoms of the polymeric chains. High levels of cocoyam starch led to films with more translucent characteristics and white color. Cocoyam starch stood out as a promising source for commercial exploitation for application in industry and with potential use as a material for the composition of biodegradable films.