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The objective of this study was to evaluate the effects of acid and oxidation modifications on sorghum starch, as well as the effect of dual modification of starch on the physical, morphological, mechanical, and barrier properties of biodegradable films. The acid modification was performed with 3% lactic acid and the oxidation was performed with 1.5% active chlorine. For dual modification, the acid modification was performed first, followed by oxidation under the same conditions as above. Both films of the oxidized starches, single and dual, had increased stiffness, providing a higher tensile strength and lower elongation when compared to films based on native and single acid modified starches. However, the dual modification increased the water vapor permeability of the films without changing their solubility. The increase in sorghum starch concentration in the filmogenic solution increased the thickness, water vapor permeability, and elongation of the films.

Gelatinization and retrogradation, influenced by amylose and amylopectin ratio, are important characteristics for starch hydrogels elaboration. The objective of this study was to evaluate the influence of amylose content and the gelatinization method on the physicochemical characteristics of native and cross-linked rice starch hydrogels. The native and cross-linked starches were gelatinized with heating or alkaline solution, added polyvinyl alcohol, frozen and then freeze-dried. The cross-linked starch had a low final viscosity (101.38 RVU), which made the heat-induced gelatinized hydrogel readily disintegrated in water. However, modified starch hydrogels obtained by alkaline-induced gelatinization resulted in a more rigid structure than the native starch hydrogels. In addition, the starch sample with high amylose content had lower water absorption (322.2%) due to the greater stiffness of the hydrogel structure that resisted swelling. The alkaline-gelatinization resulted in stiffer hydrogels with lower water absorption (322.2 to 534.8%), while the heat-gelatinized behaved as a superabsorbent (658.7 to 1068.5%). The variability of the hydrogels properties of this study can enable a range of applications due to different amylose contents and gelatinization methods.

Biodegradable films from native or acetylated starches with different amylose levels were prepared. The films were characterized according to the mechanical, water vapor barrier, thermal, and biodegradability properties. The films from acetylated high amylose starches had higher moisture content and water solubility than the native high amylose starch film. However, the acetylation did not affect acid solubility of the films, regardless of the amylose content. Films made from high and medium amylose rice starches were obtained; however low amylose rice starches, whether native or acetylated, did not form films with desirable characteristics. The acetylation decreased the tensile strength and increased the elongation of the films. The acetylated starch-based films had a lower decomposition temperature and higher thermal stability than native starch films. Acetylated starches films exhibited more rapid degradation as compared with the native starches films.

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Starch nanocrystals (SNCs) are insoluble platelet particles with multifunctional properties. SNCs production is mainly based on acid hydrolysis of cornstarch with low yield. This study focuses on investigating the effect of pretreatments (heat‐moisture‐treatment [HMT], annealing [ANN], and sonication [SNT]) on unconventional pinhão starch to produce SNCs by acid hydrolysis to improve the yield and SNCs properties. All starches hydrolysis is described by a first‐order model reaction and shown two phases related at k values. The faster hydrolysis is from SNT (k = 0.61 day−1) and the slower one is at ANN (k = 0.40 day−1). Furthermore, the acid hydrolysis is described by a rapid (0–2 days) phase, followed by a slow phase lasing 3–7 days. The HMT increases the yield of the SNCs (14.7%) but promotes losses in the RC (47.34%) as compared with the native starch (yield 10.23%; RC 52.23%). The ANN improves crystallites perfection, protecting them from acid attack. The pretreatments allow pinhão starch to be used as promising feedstock to produce SNCs with good yield and RC. In addition, ANN can be useful to improve the thermal stability and SNT to speeding up the hydrolysis for SNCs production, while HMT can increase the hydrolysis yield.