One of the most critical challenges for the food packaging industry to overcome is the development of biodegradable coatings from renewable sources. In this work, purple yam starch (PYS), chitosan (CS), and glycerol were blended to obtain biodegradable films for characterization as intended food coatings. The films had a homogeneous surface, and the amount of CS highly influenced the film thickness. Infrared spectroscopy indicated hydrogen bond interactions between PYS and CS in the films. Thermogram data suggested that glycerol contributed to the thermal stability of the films, due to its greater interaction with CS than to the PYS. Finally, the application of a YS/CS film on apples for 4 weeks was able to preserve the fruit quality, as weight loss from the coated apple was significantly lower than the uncoated apple (p ¼ 0.44, Dunnet's posthoc test). YS/CS films have great prospects in the food packaging industry as a new biodegradable coating.

The calcium oxalate content from two Amazonian amilaceous roots, Xanthosoma sagittifolium and Pachyrhizus tuberosus, before and after cooking were studied in the present work. Calcium oxalate raphides were observed by light microscopy in longitudinal sections from fresh tubers. The functional properties and physicochemical characteristics of isolated starches from both species were also investigated. Starches granules were observed with scanning electronic microscopy and presented a typical oval-circular shape, smooth surfaces and size ranging from 3.6 μm to 14 μm. Lower gel clarity, slightly high water-binding capacity, A-type starch structure and low values of crystallinity degree were determined in the isolated starches. High intensity bands related to vibrations of glucosidic bonds of polysaccharides were observed by infrared spectroscopy in both starches. Thermal degradation behavior data of the isolated starches reveled high initial decomposition temperatures. Thus, the studied cooked tubers presented low levels of calcium oxalates and are safe to be consumed as a boiled vegetable. Their isolated starches possess good functional characteristics to be applied as an ingredient to products in food industry.

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