Thermal transitions of cassava starch at intermediate water contents

Characterization of acid hydrolysis based nano-converted mung bean (Vigna radiata L.) starch for morphological, rheological and thermal properties

Mung bean starch nanocrystals (SNC) were fabricated using acid hydrolysis. The resulting nanocrystals were studied for their morphological, thermal, and rheological properties. Irregular or round-shaped nano-scale crystals with average hydrodynamic diameter of 179 nm obtained after acid hydrolysis. The mung bean SNC revealed a C_B-type crystalline pattern with enhanced crystallinity as studied by X-ray diffraction (XRD). Lower negative zeta potential was obtained for mung bean SNC as compared to its native starch. Thermal peaks disappeared for nanocrystals, which indicated an increased thermal instability of mung bean SNC. A shear-thinning behavior, even at high concentrations of SNC in the suspension was noticed. The elastic behavior was observed at all studied concentrations and it was independent of the frequency change.

All-natural bio-plastics using starch-betaglucan composites

Grain polysaccharides represent potential valuable raw materials for next-generation advanced and environmentally friendly plastics. Thermoplastic starch (TPS) is processed using conventional plastic technology, such as casting, extrusion, and molding. However, to adapt the starch to specific functionalities chemical modifications or blending with synthetic polymers, such as polycaprolactone are required (e.g. Mater-Bi). As an alternative, all-natural and compostable bio-plastics can be produced by blending starch with other polysaccharides. In this study, we used a maize starch (ST) and an oat β-glucan (BG) composite system to produce bio-plastic prototype films. To optimize performing conditions, we investigated the full range of ST:BG ratios for the casting (100:0, 75:25, 50:50, 25:75 and 0:100 BG). The plasticizer used was glycerol. Electron Paramagnetic Resonance (EPR), using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a spin probe, showed that the composite films with high BG content had a flexible chemical environment. They showed decreased brittleness and improved cohesiveness with high stress and strain values at the break. Wide-angle X-ray diffraction displayed a decrease in crystallinity at high BG content. Our data show that the blending of starch with other natural polysaccharides is a noteworthy path to improve the functionality of all-natural polysaccharide bio-plastics systems.

Thermomechanical characterization of an amylose-free starch extracted from cassava (Manihot esculenta, Crantz)

The aim of this study was to determine and compare the melting (T_m), glass transition (T_g) and mechanical relaxation (T_α) temperatures of a new waxy cassava starch. Thermal transitions measurements were obtained by Differential Scanning Calorimetry (DSC) and Dynamical Mechanical Thermal Analysis (DMTA). The experimental data showed a high correlation between water volume fraction and melting temperature (T_m) indicating that the Flory-Huggins theory can be used to describe the thermal behavior of this starch. The T_m of waxy cassava starch-water mixes were lower than a waxy corn starch-water reference system, but differences were not statistically significant. The mechanical relaxation temperatures taken at tan δ peaks were found 29-38°C larger than T_g. The T_α and T_g measured for waxy cassava starch exhibited similar properties to the ones of waxy corn starch, implying that waxy cassava starch can be used in food and materials industry.

Digestibility prediction of cooked plantain flour as a function of water content and temperature

The effect of temperature (T=55-120°C) and water content (X1=1.4-2.0 kg kg(-1) dry basis) on the gelatinization and digestibility of plantain flour (Dominico Harton genotype) were investigated. The degree of plantain starch gelatinization (α) was measured by DSC and modelled as a function of T and X1, using the Weibull model. Rapidly digestible starch (RDS) and resistant starch (RS) fractions were evaluated for different α values. An appropriate dimensionless variable was introduced to the analyzed and modelled RDS and RS as a function of α. Starch gelatinization begins at a temperature above 59.6 ± 0.5°C and α is strongly dependent on T in non-limiting water conditions. The combined effects of T and X1 on the RDS and RS can be explained by α. We demonstrate that various heat treatments and water contents lead to the same α, with the same RDS and RS values.

Phase transitions in the starch-water system studied by adiabatic scanning calorimetry

We report high-precision measurements of phase transitions in the starch-water system by using for the first time adiabatic scanning calorimetry (ASC). Potato starch and nixtamalized corn flours were studied by this technique as a function of the moisture content. We calculated the percentage of gelatinized starch granules, as a function of the temperature, for both flours. For bi-phasic behavior in potato starch, at intermediate water contents, we propose an explanation based on previous hypotheses and on the experimental behavior as deduced from ASC measurements. ASC results suggest, in the case of nixtamalized corn flour, that uniform moisture is present in corn starch granules for all the considered moistures. A shift to higher temperatures of the peak temperature is observed when comparing the c(p)(T) curves with the classical DSC endotherms as measured for this flour. For both flours we estimated from the ASC results the melting temperatures of the starch granules, at zero moisture content, by using Flory's equation.