Changes of porcine pancreas α‐amylase in activity and secondary conformations under inhibition of tea polyphenols

To investigate two‐sided functions of tea polyphenols (TP) in antinutrition and energy balance modulation, TP were extracted from Chinese green tea and used to complex porcine pancreas α‐amylase (PPA). Changes of PPA in activity and secondary conformations were analysed. Porcine pancreas α‐amylase was found sensitive to TP treatment. Tea polyphenols exhibited IC₅₀ at 0.41 mg mL^?1 against PPA and maximum inhibitory rate (98.17%) at 3.0 mg mL^?1. Tea polyphenols inhibition was concluded as noncompetitive pattern based on its unchanged Km value (0.98 mg mL^?1) for soluble starch substrate. Tea polyphenols inhibition arose from pH 1.5 to 10.14, covering gastric and intestinal environments inside body. Circular dichroism spectra analysis revealed regular changes of PPA in secondary conformations (increased proportions of α‐helix and β‐sheet) prior to its inactivation at low TP concentrations. Tea polyphenols‐inhibited PPA had distinct double‐negative peaks at 204 nm and 208 nm. Porcine pancreas α‐amylase was inactivated by TP in ways of complexation and modification of secondary conformations.     

Studies of IAA and IBA as fungal α‐amylase inhibitors using enzyme kinetics,molecular modeling and thermodynamics

Simple sugars like glucose and maltose are found to induce the production of aflatoxin. Since the formation of simple sugars is directly linked to α‐amylase function in fungus, it is considered that the inhibition of this enzyme is an effective approach to control the production of aflatoxins. The action of two indole derivatives such as indoleacetic acid (IAA) and indolebutyric acid (IBA) has been investigated by means of enzyme kinetics, isothermal titration calorimetric and molecular docking analysis. The results suggested that both IAA and IBA can inhibit α‐amylase in a competitive manner.     

Granule structural,crystalline, and thermal changes in native Chinese yam starch after hydrolysis with two different enzymes–α‐amylase and gluco‐amylase

Starch extracted from Chinese yam was characterized by scanning electron microscope (SEM), X‐ray powder diffractometer (XRD), and differential scanning calorimeter (DSC) in the process of enzymatic hydrolysis. Yam starch was digested by α‐amylase and gluco‐amylase for different lengths of time, respectively, and two different enzymatic hydrolysis results were compared. The most notable phenomenon revealed by SEM after α‐amylase hydrolysis was the formation of the cavum in the center of the starch granules, while after gluco‐amylase hydrolysis, the outer layer of the granules was peeled off and then some granules even broke into pieces. The XRD of the two enzyme hydrolyzed starches revealed the crystal type of the starch changed from typical C‐type XRD pattern to the representative A‐type pattern in the process of enzymatic hydrolysis. The above results also demonstrated that the partially B‐type polymorph was more easily degraded than A‐type. The thermal result showed that the modified yam starches by both enzymes exhibited increased peak gelatinization temperatures (T_p) and decreased gelatinization enthalpy (ΔH).     

Physicochemical characterisation and α‐amylase inhibitory activity of tea polysaccharides under simulated salivary,gastric and intestinal conditions

Tea polysaccharides (TPS) are one of the main components of tea with various bioactivities. Digestion could result in the changes of the physicochemical properties and bioactivities of polysaccharides. The objective of this study was to determine the changes in physicochemical properties and α‐amylase inhibitory activities of TPS after simulated digestion. The structure of TPS determined by UV, IR and SEM showed that no obvious changes after salivary digestion, but significant changes after gastrointestinal digestion were observed. After intestinal digestion, the contents of reducing sugar were increased from 0.650 ± 0.011 to 1.594 ± 0.078 mm , and the centre molecular weight was decreased from 540.57 to 375.35 KDa. The molar ratio of monosaccharide was changed after digestion. And α‐amylase inhibition rate was significantly increased (P < 0.05). The results could provide information on the digestibility of TPSin vitro and contribute to the development of related functional foods or medicines.     

Enhanced production of α‐amylase from Bacillus subtilis subsp. spizizenii in solid state fermentation by response surface methodology and its evaluation in the hydrolysis of raw potato starch

This is an attempt to lower the cost of starch hydrolysis by the discovery of new generation α‐amylase. A natural isolate of Bacillus subtilis subsp. spizizenii was capable of producing appreciable amounts of raw potato starch digesting α‐amylase in solid state fermentation of wheat bran. The enzyme productivity has been substantially enhanced by supplementing various nutrients and statistically studying their interactions by response surface methodology. A central composite design for amylase production system elucidated a wheat bran‐based medium supplemented with soybean meal, threonine, and B‐complex vitamins predicting a yield of 521 391 U/g dry solids. The enzyme preparation could effectively digest 5–15% suspension of insoluble potato starch in 6 h revealing the dextrose equivalent of 32–44. The supplementation of a glucoamylase preparation, thereafter, brought about complete saccharification. The yield achieved in the statistically optimized amylase system may be one of the best to date and its capability in directly liquefying raw potato starch granules makes this study novel.     

The Variation of β‐amylase Activity and Protein Fractions in Barley Grains as Affected by Genotypes and Post‐anthesis Temperatures

The variation of β‐amylase activity and protein fractions in barley grains was evaluated using 148 barley genotypes grown in the field and two cultivars under in vitro culture with two temperature treatments during grain development. The results showed that there was significant genotypic variation in β‐amylase activity and protein fraction content. Regression analysis indicated that β‐amylase activity was positively correlated with total protein and the level of each of the protein fractions, with the correlation coefficient between β‐amylase activity and hordein content being the highest. Furthermore, higher post‐anthesis temperatures (32/26°C, day/night) significantly enhanced β‐amylase activity and protein fraction content, presumably as a result of reduced starch content. Albumin and glutelin were the least and most affected, respectively, in comparison with the plants under lower temperature (22/16°C). Temperature post‐anthesis also influenced the morphology of the starch A granule and the number of B granules, suggesting the altered starch structure may also be a reason for deteriorated malting quality under high temperatures.