Unfermented cassava starch ("polvilho doce") was subject to annealing treatment at 507C for 24, 48, 96, 120, 168 and 192 h, in 1:5 starch to water ratio. The annealing treatment changed the internal structure of "polvilho doce" at increasing treatment time. Peak viscosities decreased significantly, denoting that there was a decrease in leaching of amylose from the granules. The pasting temperatures were increased, setback and breakdown were reduced while hold and final viscosities increased, showing an improvement of the stability of the paste. Swelling power and solubility were reduced at all temperatures and the solubility at 557C was zero after 120 h of treatment. The DSC data for T o , T p , T c and DH increased and the gelatinization range was narrowed. The X-ray diffractograms changed from C A to A pattern (samples annealed for 48, 96, 120, 168 and 192 h), denoting an increase in organization of double helices of amylopectin. Annealing imparts to the samples some waxy starches characteristics which can be very useful in the food industry.
Natural and synthetic polymers have been widely used for preparation of biodegradable materials. In this work, three different blends containing starch/chitosan/PVA were prepared by varying the contents of cassava starch (MS blend), chitosan (CH blend) and PVA (PVA blend). The films were characterized through tensile/strength tests, infrared spectroscopy and biodegradation tests in soil. The PVA blends showed higher values of extension at break and lower loads, leading to more flexible materials when compared to MS and CH blends. The infrared spectra of all blends showed new bands that can be assigned to the carbonyl group (1716–1732 cm−1). Besides, changes in the intensity of other characteristic bands indicate that there are significant physical/chemical interactions among the components of the blends. All samples were shown to be biodegradable, leading to weight losses above 50% after 18 days of biodegradation in soil.
The effects of annealing on the properties of unfermented (polvilho doce-PD) and fermented (polvilho azedo-PAD) cassava starches were studied. The samples were submitted to annealing treatment for 24, 72, 96, 144, 192 and 240 hours. The annealing treatment changed the main physicochemical (gelatinization, enthalpy and temperature) and rheological properties (swelling power, peak viscosity and pasting temperature) of the both samples. The increase in the gelatinization temperatures and the narrowing of the gelatinization range was attributed to an reinforcement in the packing of the double helices of the amylopectin. The PAD samples seemed to be more affected by this treatment than PD ones. The PAD samples presented some characteristics of a waxy starch, such as increased crystallinity and increased stability of the pastes, which from a technological point of view is very important to diversify further its use in the food industry.
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