Phosphate Positioning and Availability in the Starch Granule Matrix as Studied by EPR

Effect of anion type on enzymatic hydrolysis of starch-(thermostable α-amylase)-calcium system in a low-moisture solid microenvironment of bioextrusion

The effect of six anions (Cl-, OH-, NO₃-, SO₄²-, C₆H₁₀O₆²- and PO₄³-) on a starch (St)-enzyme (thermostable α-amylase, TαA)-calcium (Ca) system was investigated in a low-moisture solid state. Two levels of Ca salts (1 and 10 mmol/100 g St) added to potato starch with and without TαA were analyzed by FT-IR, DSC and SEM. The surface morphologies of the St-Ca complexes were different in the presence of various anions, and the residual Ca salts around the St granules might decrease the enzymatic action. For bioextrusion, TαA (0.5‰ and 1.5‰) were introduced for a relatively low Ca content (1 mmol/100 g). Significant differences in enzyme activity were observed, increasing the activity of TαA by SO₄²- (146.54 %) > C₆H₁₀O₆²- > Cl- > control > NO₃- > OH- ≈ PO₄³- and C₆H₁₀O₆²- (123.20 %) ≈ Cl- ≈ SO₄²- > control > PO₄³ > OH- > NO₃- for the low and high enzyme levels, respectively.

Comparative Assessment of the Bioremedial Potentials of Potato Resistant Starch-Based Microencapsulated and Non-encapsulated Lactobacillus plantarum to Alleviate the Effects of Chronic Lead Toxicity

Lead (Pb) is a well-recognized and potent heavy metal with non-biodegradable nature and can induce the oxidative stress, degenerative damages in tissues, and neural disorders. Certain lactic acid bacterial strains retain the potential to mitigate the lethal effects of Pb. The present work was carried out to assess the Pb bio-sorption and tolerance capabilities of Lactobacillus plantarum spp. Furthermore, potato resistant starch (PRS)-based microencapsulated and non-encapsulated L. plantarum KLDS 1.0344 was utilized for bioremediation against induced chronic Pb toxicity in mice. The experimental mice were divided into two main groups (Pb exposed and non-Pb exposed) and, each group was subsequently divided into three sub groups. The Pb exposed group was exposed to 100 mg/L Pb(NO₃)₂ via drinking water, and non-Pb exposed group was supplied with plain drinking water during 7 weeks prolonged in vivo study. The accumulation of Pb in blood, feces, renal, and hepatic tissues and its pathological damages were analyzed. The effect of Pb toxicity on the antioxidant enzyme capabilities in blood, serum, as well as, on levels of essential elements in tissues was also calculated. Moreover, KLDS 1.0344 displayed remarkable Pb binding capacity 72.34% and Pb tolerance (680 mg/L). Oral administration of both non- and PRS- encapsulated KLDS 1.0344 significantly provided protection against induced chronic Pb toxicity by increasing fecal Pb levels (445.65 ± 22.28 μg/g) and decreasing Pb in the blood up to 137.63 ± 2.43 μg/L, respectively. KLDS 1.0344 microencapsulated with PRS also relieved the renal and hepatic pathological damages and improved the antioxidant index by inhibiting changes in concentrations of glutathione peroxidase, glutathione, superoxide dismutase, malondialdehyde, and activated oxygen species, which were affected by the Pb exposure. Overall, our results suggested that L. plantarum KLDS 1.0344 either in free or encapsulated forms hold the potentiality to deliver a dietetic stratagem against Pb lethality.

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.

Uptake of Cu2+ by starch granules as affected by counterions

Potato and wheat starch granules were soaked in 1% aqueous solutions of copper(II) salts: acetate, chloride, and sulfate. Such treatment caused sorption of Cu(2+) ions at the granule surface and their penetration into the granule interior as was proven, for sectioned granules of investigated starch, by scanning electron microscopy combined with an X-ray microanalysis system (energy dispersive spectroscopy). Copper ions incorporated into the granules influenced the starch thermal stability. Uptake of Cu(2+) by potato, determined by flame atomic absorption spectrometry, was much higher than obtained for the wheat starch. Moreover, it was dependent on copper counteranions present in the solution. In all investigated granules, the most effective sorption occurred in the acetate solution. Starch dehydration or/and freezing and thawing, affecting the water-dependent inner structure of the granules, also influenced the amount of Cu(2+) taken from the solutions. Thus, compared to that in native starch, this value was considerably higher in Cu(CH 3COO)2, almost unchanged in CuSO4, and significantly lower in the case of CuCl2 solution. The influence of chloride and sulfate anions seemed to correlate with their water structure-making and structure-breaking ability, affecting the migration of Cu(2+) in the amorphous parts of the granules. However, high Cu uptake observed for acetate solution could be explained on the basis of acetate anion hydrolysis activating the polysaccharide matrix for cation binding. The obtained results provide new information about interactions of starch granules with salt solution and therefore support our understanding of starch properties.

Electron paramagnetic resonance study of water distribution in starch granules

An electron paramagnetic resonance (EPR) study was performed for potato and wheat starch containing Cu2+ ions as a paramagnetic probe. Distribution of water in the starch granules as well as the interactions between the copper and starch matrix of different crystalline structures were determined. EPR spectra of the native starches consisted of two different centers of Cu2+. One of them, giving at 293 and 77 K an EPR signal of axial symmetry with a well-resolved hyperfine structure (HFS), was assigned to the Cu2+ -starch complex in which Cu2+ ions strongly interacted with oxygen atoms of the starch matrix. Another Cu2+ species, exhibiting an isotropic signal at 293 K and an axial signal with resolved HFS at 77 K, was attributed to a [Cu(H2O)6]2+ complex freely rotating at room temperature and immobilized at low temperatures. Interaction of Cu2+ with the starch matrix and the relative number of the particular copper species depended on the crystallographic type of starch. Dehydration at 393 K resulted in elimination of the rotating complex signal and decrease of the total intensity of the EPR spectrum caused by clustering of the Cu2+ ions. Freezing at 77 K and thawing led to restoring of the spectrum intensity and reappearing of the signal of the [Cu(H2O)6]2+ complex. This effect, related to liberation of water molecules from the granule semicrystalline growth rings on freezing/thawing, was especially visible for wheat starch, indicating differences in the water retention ability of starch granules of different crystallographic structure.