Affinity purification of 4-α-glucanotransferase through formation of complex with insoluble amylose

4-α-Glucanotransferases (αGTases) are useful enzymes to modify starch structure using their unique hydrolysis pattern and transglycosylation activity. In spite of lacking of a carbohydrate binding module, a thermostable aGTase from Thermus thermophilus (TTαGT) bound to insoluble amylose, leading to simple recovery of the enzyme-amylose complex using centrifugation. At a preparative scale, the recovery yield was 40.3% of the subjected free enzyme via collection of the complex twice. The complex exhibited improved thermostability, which shifted the optimum temperature from 70 to 80°C and increased the half-life at 90°C by three-fold compared with the free enzyme. Texture profile analysis of the gels made of modified starch by either free TTαGT or the complex revealed that the complex with double dosage showed the performance similar to free TTαGT in the modification of starch. In conclusion, the purification method described here would be useful due to easy scale-up and simple process without chromatographic process.     

Characterisation of milk samples with various whey protein contents by pyrolysis–mass spectrometry (Py–MS)

Different milk samples and their 2, 5 and 10% mixtures with ‘artificial’ or natural whey protein were analysed by means of pyrolysis–mass spectrometry (Py–MS). Py–MS followed by multivariate analysis of the resulting mass spectra enabled the determination of the whey protein addition in milk samples. Obtained results showed that this determination seems not to be influenced by the fat content and freezing of the samples, as well as a dilution of the samples. ©     

Starch–lipid complex formation during extrusion-cooking of model system (rice starch and oleic acid) and real food (rice starch and pistachio nut flour)

The formation of starch–lipid complexes during extrusion-cooking of model system (rice starch and oleic acid) and real food (rice starch and pistachio nut flour) was evaluated. Both formulas were extruded at the same processing conditions (temperature profiles, screw speed, and water feed content). The obtained data showed that in model system and real food, the formation of starch–lipid complexes occurred under different processing conditions. In particular, the highest formation of starch–lipid complexes, that is, the highest melting enthalpy value (ΔH _m = 1.18 J/g), was obtained at the middle values of barrel temperature (100 °C) and water feed content (19%) in the model system. Yet, the only processing variable that had a significant effect on the formation of starch–lipid complexes in the real food was barrel temperature. In particular, the highest melting enthalpy of starch–lipid complexes (ΔH _m = 9.28 J/g) was obtained at the highest values of barrel temperature (130 °C). These results point out the importance of considering all components present in the raw materials submitted to extrusion-cooking in order to study biopolymer modifications, which occur during processing.     

Preparation of aqueous dispersion of β-carotene nano-composites through complex formation with starch dextrin

Aqueous dispersions of β-carotene nano-composite were prepared through a blending process with a dextrin of high amylose corn starch in immiscible phases of aqueous dextrin and organic β-carotene solutions and water solubility and stability against oxidation of β-carotene were examined. Gradual evaporation of organic solvent during the mechanical stirring allowed the formation of aqueous solutions in which β-carotene was homogeneously dispersed with dextrin. Proper control of the solid concentrations effectively induced the complex formation between dextrin and β-carotene whereas an excess amount of β-carotene (>8 mg) in a dextrin solution (200 mg in 50 mL) induced crystallization and precipitation of β-carotene. The complex particles showed an irreversible endothermic transition of V-amylose (via DSC). X-ray diffraction analysis, however, revealed that the complex had no typical V-type crystalline arrangement. Hydrodynamic size of the complex particles in the aqueous solution could be decreased to nano-scale (16–30 nm) by a mild ultrasonication. The nano-composite contained β-carotene at approximately 30% on a weight, with improved stabilities against oxidation and enzymatic digestion.     

Physicochemical properties and freeze–thaw stability of rice flour blends among rice cultivars with different amylose contents

Food Science and Biotechnology - The effectiveness of the rice flour blends (RFB) for improving the processing suitability of Dodamssal rice flour (DD), a functional rice variety with a relatively...     

The physicochemical characteristics and hydrophobicity of high amylose starch–glycerol films in the presence of three natural waxes

The film forming behaviour and hydrophobicity of high amylose (HA) starch in the presence of three different natural waxes (beeswax, candelilla wax and carnauba wax) were studied in the presence and absence of Tween-80. The HA starch:glycerol (G) ratio was maintained at 80:20 (on dry solid basis) and the concentration of wax was varied from 5% and 10% (w/w). The melted wax samples were homogenized with HAG dispersion with or without Tween-80 and the films were prepared by solution casting. The hydrophobicity and water-barrier properties in these films were determined by using contact angle (CA), water vapour permeability (K_w) tests, and water sorption isotherm at 0.529 RH and 20 °C. The K_w values of the HAG films decreased significantly (p < 0.05) with the addition of 5% concentration of these waxes. Then the addition of Tween-80 to the HAG + wax films increased the K_w values significantly (p < 0.05). The presence of these waxes in the presence and absence of Tween-80 resulted into different sorption isotherms and the water adsorptivity and moisture diffusion coefficient values were also affected. The presence of Tween-80 increased the CA in HAG + carnauba wax films while the CA was found to decrease in the case of other two waxes. The highest hydrophobicity was observed in HAG + carnauba wax + Tween-80 films in which the CA was >80.0° both at 5% and 10% (w/w) wax concentration. These higher CA values in HAG + carnauba wax + Tween-80 films were found to be related to the higher surface roughness in these films.     

Effect of hydroxypropyl β-cyclodextrin on physical properties and transition parameters of amylose–lipid complexes of native and acetylated starches

The effect of hydroxpropyl β-cyclodextrin (HPβ-CD) on physical properties and digestibility of wheat, potato, waxy maize and high-amylose maize starches before and after acetylation was studied. Effect of HPβ-CD on amylose–lipid complexes in native and acetylated potato starches synthesized using α-lysophosphatidylcholine was also studied. Acetylation increased swelling factor, amylose leaching, peak viscosity and susceptibility to α-amylase hydrolysis, but decreased gelatinization temperature and enthalpy and gel hardness in all starches. HPβ-CD markedly increased swelling factor and amylose leaching in native and acetylated wheat starches but had little or no impact on other starches. Wheat starch gelatinization enthalpy decreased in the presence of HPβ-CD but gelatinization temperature of all the starches was slightly increased. HPβ-CD had no influence on enzymatic hydrolysis. Melting enthalpy of amylose–lipid complex in both native and acetylated wheat starches was decreased by HPβ-CD. Acetylation also decreased the melting enthalpy of amylose–lipid complex in wheat starch. Similar trend of thermal transitions was observed in the presence of HPβ-CD for the amylose–lipid complexes synthesized in potato starch. Acetylation reduces the complex formation ability of the amylose polymer. Similar to gelatinization, acetylation widened the melting temperature range of amylose–lipid complexes while shifting it to a lower temperature. Higher swelling and amylose leaching, and decreased gelatinization temperature and enthalpy resulting from acetylation of wheat starch is consistent with its influence on starch hydration. Similar effects resulting from the inclusion of HPβ-CD were consistent with the disruption of amylose–lipid complex by HPβ-CD which promotes granular hydration.     

The impact of coupled acid or pullulanase debranching on the formation of resistant starch from maize starch with autoclaving–cooling cycles

Maize starch was treated by autoclaving–cooling cycles, coupled with acid or pullulanase hydrolysis to prepare resistant starch (RS). Debranching of retrograded or gelatinized maize starch with acid or pullulanase was studied to show the corresponding impact on RS formation. When maize starch was treated with three autoclaving–cooling cycles and retrograded maize starch was hydrolyzed at room temperature, with 0.1 mol L⁻¹ citric acid for 12 h, analysis results showed that debranching of citric acid was helpful in RS formation for RS yield increased from 8.5 to 11%. Debranching of gelatinized or retrograded maize starch at 60 °C with pullulanase at addition level of 3 PUN g⁻¹ starch showed a more favorable effect on RS formation. When gelatinized maize starch was hydrolyzed by pullulanase for 12 h and then treated with two autoclaving–cooling cycles, RS yield increased to 23.5%. If retrograded maize starch subjected to one autoclaving–cooling cycle was hydrolyzed by pullulanase for 10 h and then followed by two autoclaving–cooling cycles, RS yield elevated to 32.4%. The debranching effect of pullulanase on retrograded maize starch to help RS formation is obvious and most effective, indicating this treatment is applicable in RS preparation to increase the RS yield.     

Proton NMR relaxation study of swelling and gelatinisation process in rice starch–water samples

Proton transverse magnetization decay curves of rice flour starch–water samples were measured and analysed for the presence of four components in the relaxation curve. T₂ values were interpreted on the basis of the diffusive and chemical exchange model that provided evidence for extra granular bulk water and three more water populations whose relaxation rate is governed by diffusive and chemical exchange with starch components. The analysis of relaxation data provided information on dynamics of water molecules as well as on the size and dispersion of diffusive domains. Furthermore, by measuring solid to liquid ratio, transverse and longitudinal relaxation curves of starch–water mixtures at increasing temperatures – from 20 to 77 °C – swelling and gelatinisation processes were monitored.     

The effect of freeze–thaw cycles on microstructure and physicochemical properties of four starch gels

The effect of repeated freeze–thaw (FT) cycles (up to seven) on microstructure, thermal and textural properties of four starch gels from various botanical origins (gingko, Chinese water chestnut, potato and rice) was investigated and compared by scanning electronic microscope, differential scanning calorimetry and texture analyzer. The chemical composition and molecular structure of four starches were also examined. The Chinese water chestnut, potato and rice starch gels formed a honey-comb structure after 7 FT cycles, while gingko starch gel exhibited lamellar structure. The 7 FT cycles decreased the transition temperatures and enthalpies of four starches in comparison with each native starch, and the retrogradation percentage followed the order: rice > gingko > Chinese water chestnut > potato. The 7 FT cycles increased the hardness of all the evaluated starch gels and decreased springiness and cohesiveness. Results showed that the molecular structure of starches caused notable differences to the microstructure and textural properties of starch gels. The higher amount of longer branch chain (degree of polymerization (DP) > 18) might benefit the formation of the lamellar structure of gingko starch. The percentage of branch chains (DP 18–23) was negatively related with the springiness and cohesiveness of native starch gels, while the percentage of medium chains (DP 12–17) was positively related to the springiness of starch gels after 7 FT cycles.     

Characterisation of three starch degrading enzymes: thermostable β-amylase, maltotetraogenic and maltogenic α-amylases

White sesame seeds (Sesamum indicum L.) were studied with the purpose to evaluate γ-irradiation effect at 2.5, 5.0 and 10.0 kGy on lipid and fatty acid content, colour and protein allergenicity and to identify whether sesame oil was extracted from irradiated seeds by using High Resolution Nuclear Magnetic Resonance spectroscopy (HR-NMR). The fat decreased significantly, whereas triglyceride and phospholipid content was significantly decreased by the increase of irradiation dose. Monounsaturated and polyunsaturated fatty acids and unsaturated/saturated fatty acids ratio decreased. The presence of radiolytic decomposition products, shown by NMR, formed after a 2.5 kGy dose, confirmed that the lipid content decrease was a result of the irradiation process. The allergenicity of storage seed proteins was not significantly affected by irradiation up to 10.0 kGy. Colour parameter a^* increased after 5.0 kGy, while L^* values decreased significantly after 2.5 kGy. Conclusively, irradiation could be applied at doses <2.5 kGy while sustaining the sesame seed nutritional benefits.     

Characterisation of three starch degrading enzymes: Thermostable β-amylase,maltotetraogenic and maltogenic α-amylases

Maltogenic α-amylase from Bacillus stearothermophilus (BStA) is widely used as bread crumb anti-firming enzyme. A maltotetraose-forming α-amylase from Pseudomonas saccharophila (PSA) was recently proposed as alternative, hence the need to compare both exo-acting enzymes with some endo-action component. A purely exo-acting thermostable β-amylase from Clostridium thermosulfurogenes (CTB) was included for reference purposes. Under the experimental conditions used, temperature optima of the enzymes are rather similar (60–65 °C), but temperature stability decreased in the order BStA, PSA and CTB. The action of the enzymes on different substrates and their impact on the rheological behaviour of maize starch suspensions demonstrated that, while CTB acts exclusively through an exo-action mechanism, BStA displayed limited endo-action which became more pronounced at higher temperatures. PSA has more substantial endo-action than BStA, which is rather temperature independent. This is important for their impact in processes such as breadmaking, where temperature is gradually increased.     

Effects of heat moisture treatment on the structural,physicochemical and digestibility properties of potato starch–soybean peptide complexes

In this study, potato starch (PS) was complexed with soybean peptides (SPTs) with different molecular weights under heat moisture treatment (HMT) at different moisture contents. The results showed that PSSPT complexes formed under HMT were characterised by weaker and fuzzier polarised cross patterns, and more agglomerates. After HMT, higher gelatinisation temperatures and lower enthalpies were observed for PSSPT complexes. In particular, higher gelatinisation temperatures were observed when moisture levels were higher during HMT. Compared with physically mixed counterparts, the PSSPT complexes under HMT displayed higher pasting temperatures and lower swelling power, and peak viscosity. Higher moisture content during HMT led to a less thermodynamically stable B-polymorphic structure converting to a more stable A-type polymorph. Higher SDS content was found in the PSSPT complexes subjected to HMT with lower moisture content, while relatively higher RS content was associated with higher moisture content of HMT. These results could be attributed to restructuring of the amylose/amylopectin chains, the physical barrier of SPT and interactions between the negatively charged groups in PS and the side chains in SPT. This study will advance our understanding of food multicomponent interactions, as well as guidance for the application development of low-glycaemic index foods containing SDS and RS in the field of fine food processing.     

Effect of heating–cooling on rheological properties of tapioca starch paste with and without xanthan gum

The effect of xanthan gum (Xan) on pasting and gelatinization behavior of tapioca starch (TS) was investigated. Rheological measurements of TS/Xan mixtures with 5% w/w total polysaccharide concentration at different mixing ratios (10/0, 9.5/0.5, 9/1 and 8.5/1.5) were performed to understand the pasting and gelatinization behavior of TS with and without Xan on heating–cooling cycle using a Rapid Visco Analyzer (RVA) and conventional rheometers. Xan increased storage modulus (G′) and loss modulus (G″) of TS dispersions during gelatinization process. Pastes of TS/Xan tended to be more solid-like, i.e., G′ larger than G″, with increasing Xan. The G′ of TS/Xan paste increased when kept at 10 °C indicating the network formation. Pasting temperatures, peak viscosity, final viscosity and breakdown values of TS increased with increasing Xan content but the opposite result was observed in setback value from RVA measurement. Temperature dependence of steady shear viscosity became less pronounced with increasing Xan content on both cooling and reheating indicating that Xan made the mixture more thermally stable. All the results suggest that the sample preparation and measuring conditions influence the rheological properties of TS/Xan mixtures, which should be taken into account in food application.     

Rheological and textural studies of fresh and freeze-thawed native sago starch–sugar gels. II. Comparisons with other starch sources and reheating effects

The viscoelastic and textural properties of freshly prepared and freeze-thawed sago starch–sugar gels were studied in comparison with other native starches from corn, wheat, tapioca, and potato. The gelatinisation and retrogradation properties of starches were studied using a DSC while the pasting properties of starch–sugar mixtures during the cooking period were studied using a starch pasting cell. The freeze-thaw stability of gels was evaluated by gravimetric measurements of the water of syneresis. The different starches gave properties which varied following to their botanical sources. High-amylose cereal starches (wheat and corn) produced harder gels, while low-amylose root starch (tapioca) produced softer gels. Sago and potato gels showed close similarities in their viscoelastic and textural characteristics. Although the freeze-thaw cycle greatly increased the viscoelasticity and hardness of these two gels, reheating at high temperature significantly reduced these negative effects and resulted in partial recovery of the gel structures. Sago starch produced gels with very low syneresis and high cohesiveness, implying its potential use as a gelling agent in the frozen food industries.