Flocculation and coalescence of droplets in oil-in-water emulsions formed with highly hydrolysed whey proteins as influenced by starch

The effects of added unmodified amylopectin starch, modified amylopectin starch and amylose starch on the formation and properties of emulsions (4 wt.% corn oil) made with an extensively hydrolysed commercial whey protein (WPH) product under a range of conditions were examined. The rate of coalescence was calculated based on the changes in the droplet size of the emulsions during storage at 20 degrees C. The rates of creaming and coalescence in emulsions containing amylopectin starches were enhanced with increasing concentration of the starches during storage for up to 7 days. At a given starch concentration, the rate of coalescence was higher in the emulsions containing modified amylopectin starch than in those containing unmodified amylopectin starch, whereas it was lowest in the emulsions containing amylose starch. All emulsions containing unmodified and modified amylopectin starches showed flocculation of oil droplets by a depletion mechanism. However, flocculation was not observed in the emulsions containing amylose starch. The extent of flocculation was considered to correlate with the rate of coalescence of oil droplets. The different rates of coalescence could be explained on the basis of the strength of the depletion potential, which was dependent on the molecular weight and the radius of gyration of the starches. At high levels of starch addition (>1.5%), the rate of coalescence decreased gradually, apparently because of the high viscosity of the aqueous phase caused by the starch.     

Construction of Porous Starch-Based Hydrogel via Regulating the Ratio of Amylopectin/Amylose for Enhanced Water-Retention

The performance of hydrogels prepared with traditional natural starch as raw materials is considerable; the fixed ratio of amylose/amylopectin significantly limits the improvement of hydrogel structure and performance. In this paper, starch hydrogels were prepared by physical blending and chemical grafting, with the aid of ultrasonic heating. The effects of different amylose/amylopectin ratios on the microstructure and water retention properties of starch hydrogels were studied. The results show that an increase in amylopectin content is beneficial to improve the grafting ratio of acrylamide (AM). The interaction between the AM grafted on amylopectin and amylose molecules through hydrogen bonding increases the pores of the gel network and thins the pore walls. When the amylopectin content was 70%, the water absorption (swelling 45.25 times) and water retention performance (16 days water retention rate 44.17%) were optimal. This study provides new insights into the preparation of starch-based hydrogels with excellent physical and chemical properties.     

Particularities in the structure of amylopectin,amylose and some of their derivatives in solution

Because of a well defined supramolecular architecture of the native starch granules the preparation of molecularly dispersed starch solutions is achieved only after autoclaving at temperatures of 135 to 160 C. A detailed analysis of static light scattering data allowed the determination of the molecular parameters of both the amylopectin and amylose. The results were confirmed by (1) measurements in the iron sodium tartrate complex FeTNa, (2) by extrapolation of the data obtained with degraded starches to no degradation and (3) by sedimentation field-flow-fractionation sFFF. Above the overlap concentration strong aggregation due to H-bonding commenced and eventually led to gelation. The process is promoted by the amylose content and could be followed by static and dynamic light scattering. Cationic starches and cationic amyloses display remarkably different behavior. The branched amylopectin expanded uniformly when the ionic strength was lowered but the corresponding amylose exhibited an unusual helix-disorder transition.     

Gelatinization Mechanism of Rice Starch

ABSTRACT

The non-Newtonian behavior and dynamic viscoelasticity of rice starch (Nihonbare; amylose content, 15.8%) solutions were measured with a rheogoniometer. A gelatinization of Nihonbare starch occurred above 3.0% after heating at 100 °C for 30 min. The Nihonbare starch showed shear-thinning behavior at a concentration of 2.0%, but plastic behavior above 3.0% at 25 °C. The viscosity of Nihonbare starch at a concentration of 2.0% solution decreased gradually with increase in temperature from 10 to 55 °C, then it stayed at a constant value with further increase in the temperature. However, for 4.0% solution, rapid decrease in the viscosity was observed after the temperature reached 25 °C up to 50 °C, then it stayed at a constant value. The dynamic modulus of Nihonbare starch stayed at a constant value during increase in the temperature at 4%. The tan δ of the starch showed low values, 0.28, at low temperature range and stayed at a constant up to 30 °C, then it increased a little with increasing temperature. A little decrease of dynamic modulus of Nihonbare starch was observed at low temperature range upon addition of urea (4.0 M). The dynamic modulus, however, decreased rapidly when the temperature reached 50 °C, which was estimated to be a transition temperature. The dynamic modulus also decreased rapidly in 0.10 M NaOH solution above 50 °C. A possible mode of intermolecular hydrogen bonding between amylose and amylopectin molecules of Nihonbare starch is proposed. The short chains (A and B1) of the amylopectin molecules may take part in the intermolecular association in aqueous solution.     

Influence of Amylose-Amylopectin Ratio on Properties of Extruded Starch Plastic Sheets

Abstract

Starch plastic sheets were prepared by extrusion processing of mixtures of granular high-amylopectin and high-amylose starches in the presence of glycerol and water as plasticizers. Amylose content varied between 0 and 70% (w/w). Structural characterization and determination of the mechanical properties of the sheets were performed after aging the materials between 40–65% relative humidity for 2 and 35 weeks and at 90% relative humidity for two weeks. The materials were semicrystalline and viscoelastic. The materials were described as complex heterogeneous multiphase materials. They consisted of amorphous and crystalline phases of amylose and amylopectin as well as granular structures and domains of amylose, amylopectin and amylose-amylopectin helices. Single-helical type crystallinity was formed solely by amylose directly after processing while B-type crystallinity was rapidly formed in amylose-rich materials and slowly during aging of amylopectin-rich materials.

The stress-strain and stress-relaxation properties were related to differences in amylose content, degree of crystallization and water content. The amorphous amylopectin rich materials were flexible and soft but showed an increase in stiffness and a decrease in elongation due to crystallization. Amylopectin-rich materials showed unfavorable relaxation, shrinkage and cracking during aging. The materials rich in amylopectin were sensitive to water content while the amylose-rich materials were not sensitive to water in the range of 9–13% (w/w). Stress-strain relaxation behaviors of the materials were dependent on starch structure and on experimental conditions such as strain rate and extension by which the ratio of elastic and viscous response were varied. An increase in relaxation times was found with increasing amylose content and water content for the materials with solely amylose crystallinity.     

Rapid analysis of starch, amylose and amylopectin by high-performance size-exclusion chromatography

Starch components, amylose and amylopectin, were analyzed by high-performance size-exclusion chromatography. These two-components were separated using a two-column system (E-Linear and E-1000) and dimethyl sulphoxide as the mobile phase. The void volume (V0 = 2.22 ml) was measured using tobacco mosaic virus. Column calibration was accomplished with dextrans of known average molecular weight (Mw range = 10,100-2,000,000). The elution volume of amylopectin (Ve = 2.5 ml) indicated that this starch component was fractionated on the column system despite its very large molecular size. Standard curves were prepared from various mixtures of purified corn and wheat amylose and amylopectin. From the linear relationships obtained, the percentages of both components in corn and wheat starches were determined. The method developed proved useful to monitor the purity of amylose and amylopectin preparations, and to estimate rapidly the amylose:amylopectin ratio of starch samples.     

Electrosprayed maize starch and its constituents (amylose and amylopectin) nanoparticles

Starch consists of amylose and amylopectin. Properties such as being natural and highly hygroscopic as well as biodegradability have opened a considerable range of applications for amylose, amylopectin and starch. The performance of particles is highly dependent on their size which in turn determines the specific surface area. This work studies the application of electrospraying to fabricate maize starch and its constituents: amylose and amylopectin nanoparticles. This study showed that electrospraying technique is capable of producing amylose, amylopectin and starch nanopowder with an average particle size around 100 nm. FTIR analysis showed no reaction or interaction occurring in amylose, amylopectin and starch nanoparticle compared with their natural form. Basically, lower concentration, lower viscosity and lower surface tension of the electrospraying solution as well as higher nozzle–collector distance, higher voltage and lower feed rate lead to smaller nanoparticle size. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrolysis of starch or pullulan by glucoamylase or pullulanase immobilized on poly(N-isopropylacrylamide) gel

Starch or pullulan was hydrolyzed using glucoamylase or pullulanase immobilized on N-isopropylacrylamide gel. The gel used is temperature sensitive; its mesh size becomes smaller at higher temperatures (30 °C) and larger at lower temperatures (20 °C). The molecular weight distribution of starch is wide and it consists of high-molecular-weight amylopectin, amylose and glucose. From the change in the chromatograms for the substrate and products, it was found that the hydrolysis rate at 30 °C was faster than that at 20 °C for amylose, though it was the reverse for amylopectin. This finding suggests that the smaller molecular sized amylose can enter the gel phase at both temperature, while the larger molecular sized amylopectin can hardly do so; only the end group, which can partly enter the gel phase at 20 °C (larger mesh size), was hydrolyzed. Further, several molecular weight pullulans (monodisperse) were hydrolyzed and the experimental chromatograms for substrate and products confirm the hydrolysis mechanism estimated. Received: 14 July 1998 Accepted in revised form: 26 August 1998     

Structure of starches extracted from near-isogenic wheat lines

High-sensitivity differential scanning calorimetry (HSDSC) and small-angle X-ray scattering (SAXS) were used to investigate the structural characteristics of starch granules with different amylose content extracted from near-isogenic wheat lines with different combinations of active granule-bound starch synthase (GBSS I) isoforms. Paracrystalline diffraction model, ‘two-state’ model of starch melting and other physico-chemical approaches were used to estimate the sizes of amylopectin clusters, the thicknesses of crystalline lamellae and the structure of amylopectin defects for investigated wheat starches. The joint analysis of SAXS and DSC data has shown that the size of amylopectin cluster, the thickness of crystalline lamellae and the structure of amylopectin defects do not depend on the differences in combinations of active GBSS I isozymes. The data obtained supposed that the amylopectin cluster size and the thickness of crystalline lamellae are, generally, the universal structural parameters for wheat starches. Additionally, the data obtained suggest that increase of amylose content is accompanied by accumulation of both amylose tie-chains, located as defects in crystalline lamellae, and amylose chains oriented transversely to the lamella stack within amorphous lamellae. Disordered ends of amylopectin double helices and/or pre-existing double helices not participating in formation of crystals are considered as amylopectin defects arranged in crystalline lamellae. The relationship between structure of wheat starches extracted from near-isogenic lines and their thermodynamic properties was recognized.     

Branching ratios of starch via proton nuclear magnetic resonance and their use in determining amylose/amylopectin content: Evidence for three types of amylopectin

The branching (α-1,4)/(α-1,6) ratio of starch from a number of sources can be quickly and accurately determined by proton nuclear magnetic resonance (NMR). This NMR ratio, with standard ratios for isolated amylose and amylopectin, can then be used to determine the amylose/amylopectin content of starches. In the course of determining the amylose/amylopectin content of various starches, it was discovered that two different types of amylopectin standards were required to obtain results comparable to those obtained from iodine-binding amylose determinations. These two types were a waxy amylopectin, with a high level of branching, and a potato amylopectin, with a lower level of branching. A third type of amylopectin, with a still lower level of branching, is apparently present in high amylose cornstarches, leading to the conclusion that starches with higher amylose contents generally contain amylopectin with a lower level of branching. The three amylopectin types are referred to as amylopectin I, II and III, with the higher numeral coinciding with higher branching (α-1,4)/(α-1,6) ratio, or less branching.     

Rheological properties of native and hydrolyzed starches in dependence on composition and concentration

The structure formation of starch polysaccharides in aqueous solutions is determined by the ratio of amylose to amylopectin and the molecular properties of these components. Our research is focused on establishing defined correlations between composition, molecular structure in diluted solutions and rheological properties of concentrated aqueous starch polysaccharide solutions. Diluted solutions were investigated by size exclusion chromatography with multi angle laser light scattering detector. Measurements of concentrated aqueous solutions were carried out by a Bohlin cs-rheometer with programmed stress using a cone-plate geometry of 40 mm diameter and a cone angle of 4 degrees. Gels were characterized by oscillatory measurements taking into account the frequency dependence of the storage and loss moduli and the influence of a stress sweep on the moduli. The concentration dependence was investigated with starches of potato, wheat, maize and wrinkled pea. Starches with quite similar amylose content as from potato, wheat and maize, show different behavior in rheological properties. Further differences in structure formation were obtained by enzymatic hydrolysis of potato and wheat starch with bacterial α-amylase. The hydrolyzing conditions were chosen such that the degradation led to molecular weights between 5*10⁵ and 10⁷ g/mol. Detailed information about molecular composition was obtained by fractionation of degraded starches. The amylopectin was found to be degraded more strongly than the contained amylose. In comparison to native starch polysaccharide fractions the amylopectin hinders the gelation process in dependence on its molecular weight distribution and the length of the outer chains.     

Preparation and Characterisation of Thermoplastic Starches from Cassava Starch,Cassava Root and Cassava Bagasse

Summary: Thermoplastic starches (TPS) based on cassava starch have been produced by extrusion at 120 °C, using glycerol as plasticizer. Three forms of cassava starch were employed, viz: cassava root (CR), cassava bagasse (CB) and purified cassava starch (PCS). The main differences between these are the presence of sugars and a few fibres in CR and high fibre concentration in CB. Conditions of processing and characteristics such as amylose and fibre content, crystallinity, water absorption and mechanical behaviour in the tension x deformation test were evaluated. The results demonstrated that the PCS and CR had amylose contents consistent with literature values (14–18%) and that CB is a material constituted mainly by amylopectin. It was found that fibres in high proportions (as in the bagasse) can confer reinforcement properties and are thus able to generate natural composites of TPS with cellulose fibre. The sugars naturally found in the root reduce the elongation of the TPS under tension. The PCS and CR TPS were stable with respect to indices of crystallinity after processing; and during a period of 90 d in a relative humidity of 53%, while the CB TPS tended to vary its crystallinity, probably because its amylose chain had low degree of polymerization.     

Size separations of starch of different botanical origin studied by asymmetrical-flow field-flow fractionation and multiangle light scattering

Asymmetrical-flow field-flow fractionation combined with multiangle light scattering and refractive index detection has been revealed to be a powerful tool for starch characterization. It is based on size separation according to the hydrodynamic diameter of the starch components. Starch from a wide range of different botanical sources were studied, including normal starch and high-amylose and high-amylopectin starch. The starch was dissolved by heat treatment at elevated pressure in a laboratory autoclave. This gave clear solutions with no granular residues. Amylose retrogradation was prevented by using freshly dissolved samples. Programmed cross flow starting at 1.0 mL min(-1) and decreasing exponentially with a half-life of 4 min was utilised. The starches showed two size populations representing mainly amylose and mainly amylopectin with an overlapping region where amylose and amylopectin were possibly co-eluted. Most of the first population had molar masses below 10(6) g mol(-1), and most of the second size population had molar masses above 10(7) g mol(-1). Large differences were found in the relative amounts of the two populations, the molar mass, and hydrodynamic diameters, depending on the plant source and its varieties.     

Structure of starch-bentonite gels

Mixed gels of starch and bentonite are investigated in the interval 0.056–0.089 of total solids/water ratio and 0-100% starch in the solids. The bentonite was a sodium calcium bentonite with a Na/Ca ratio of 1.76. In water it forms gels consisting of a network of band-type structures. Starch forms gels through hydrogen bonds between granules and/or amylose and amylopectin present on the external surfaces of granules and/or in fully stretched form. Mixed gels of bentonite and starch were obtained by adding corn starch granules to the already formed bentonite gels and heating the mixture above the Kofler gelatinization temperature. Amylose and amylopectin were adsorbed on strands of band-type structures of mont-morillonite lamellae. Starch gellation, e.g. diffusion of amylose out of the granule, was facilitated in the presence of bentonite. On the other hand, the presence of starch favored delamination of the montmorillonite particle into thinner lamellae. Maximum gelatinization and polymer adsorption were observed for gels with 20% starch and 80% bentonite. Montmorillonite networks formed the continuous phase for 0-80% starch. At higher starch concentrations, montmorillonite flakes were dispersed within the polymer network. Increase in the water content of the gels caused segregation of the bentonite and starch.     

Characterization of starch polysaccharides by flow field-flow fractionation-multi-angle laser light scattering-differential refractometer index

The coupling between flow field-flow fractionation (FFF), multi-angle laser light scattering and differential refractometer index provides a promising technique for fractionation of starch polysaccharides in aqueous conditions. Native starches with different amylose/amylopectin levels (0-70%) as well as a pure amylose sample were characterized. By applying a sudden drop in the cross-flow-rate, clear separation was achieved between amylose (which elutes first) and amylopectin. Flow FFF produced correct relationships between the molecular mass or the gyration radius versus elution volume for the fractionated amylopectin population. The results are also considered in terms of the macromolecular composition of starches.     

Isothermal microcalorimetric studies on starch retrogradation

In the present study, isothermal microcalorimetry was introduced as a tool to investigate properties of starch retrogradation during the first 24 h. The study was made on purified amylose and amylopectin from corn, as well as on native starches, such as wheat, potato, maize, waxy maize and amylomaize, differing in their amylose content. The results were obtained in the form ofP-t traces (thermal powervs. time), and integration of these traces gave a net exothermic enthalpy of reaction, caused by the crystallization of amylose and amylopectin. TheP-t traces reflected the quantities of amylose and amylopectin in the starch studied. Depending on the amylose content and the botanical source of the starch, the rate of crystallization of amylose was high and predominated over that of amylopectin during the first 5–10 h. The contribution from amylose crystallization to the measured exothermic enthalpy was very substantial during this period. After 10 h, amylose crystallized at a lower constant rate. During the first 24 h, amylopectin crystallized at a low steady rate. The exothermic enthalpies obtained by the isothermal microcalorimetric investigations during the first 24 h of retrogradation were generally low in relation to the endothermic melting enthalpies observed by differential scanning calorimetry (DSC) measurements after 24 h of storage. The discrepancies in enthalpy values between the two methods are discussed in relation to phase separation and the endothermic effects owing to the decrease in polymer-water interactions when polymer-rich regions in the starch gel separate. Besides the exothermic enthalpies obtained, theP-t traces also made it possible to study the initial gelation properties of amylose from different botanical sources. The present study further demonstrated that isothermal microcalorimetry can provide a possible way to investigate the antistaling effect of certain polar lipids, such as sodium dodecylsulphate (SDS) and 1-monolauroyl-rac-glycerol (GML), when added to starches of different botanical origin. The net exothermic heat of reaction for starch retrogradation during the first 24 h was decreased when GML or SDS was added to the starch gels. The recordedP-t traces also showed how the effect of the added lipid influenced different periods during the first 24 h of starch retrogradation, and that the effect depended mainly on the amylose content, the botanical source of the starch, and the type of lipid used. When GML or SDS was added to waxy maize, the isothermal microcalorimetric studies clearly indicated some interaction between amylopectin and the polar lipids. These results concerning the action of anti-staling agents are further discussed in relation to the helical inclusion complexes formed between amylose-polar lipid and amylopectin-polar lipid.The authors thank Eva Qvarnström at the Dept. of Thermochemistry and Eva Tjerneld at the Dept. of Food Technology for valuable practical assistance. Financial support was obtained from the Swedish Council for Forestry and Agricultural Research (SJFR) and the Swedish Farmer's Foundation for Agricultural Research (Stiftelsen Lantbruksforskning).     

Cloning, expression, and characterization of thermostable region of amylopullulanase gene from Thermoanaerobacter ethanolicus 39E

The bifunctional activities of α-amylase and pullulanase are found in the cloned recombinant amylopullulanase. It was encoded in a 2.9-kb DNA fragment that was amplified using polymerase chain reaction from the chromosomal DNA of Thermoanaerobacter ethanolicus 39E. An estimated 109-kDa recombinant protein was obtained from the cloned gene under the prokaryotic expression system. The optimum pH of the recombinant amylopullulanase was 6.0. The most stable pH for the α-amylase and pullulanase activity was 5.5 and 5.0, respectively. The optimum temperature for the α-amylase activity was 90°C, while its most stable temperature was 80°C. Regarding pullulanase activity, the optimum temperature and its most stable temperature were found to be 80 and 75°C, respectively. Pullulan was found to be the best substrate for the enzyme. The enzyme was activated and stabilized by the presence of Ca²⁺, whereas EDTA, N-bromosuccinimide, and α-cyclodextrin inhibited its bifunctional activities. A malto-2–4-oligosac-charide was the major product obtained from the enzymatic reaction on soluble starch, amylose, amylopectin, and glycogen. A single maltotriose product was found in the pullulan hydrolysis reaction using this recombinant amylopullulanase. Kinetic analysis of the enzyme indicated that the K _m values of α-amylase and pullulanase were 1.38 and 3.79 mg/mL, respectively, while the V _max values were 39 and 98 μmol/(min · mg of protein), respectively.     

Profluorescent nitroxides: Thermo-oxidation sensors for stabilised polypropylene

The profluorescent nitroxide, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was investigated as a probe for the radical-mediated degradation of stabilised polypropylene. TMDBIO has been previously shown to be a sensitive probe for free-radical degradation during the thermo-oxidation of unstabilised polypropylene. Here we report on the effect that adding hindered phenol or phosphite stabilisers to polypropylene has on the free-radical sensing ability of TMDBIO during thermo-oxidation. In addition, novel dual-functional, hindered phenol containing profluorescent nitroxides, 5-[2-(4-hydroxy-3,5-di-tert-butylphenyl)ethenyl]-1,1,3,3-tetramethylisoindolin-2-yloxyl (HSTMIO) and its derivatives were investigated as probes for the radical-mediated degradation of polypropylene. These dual-functional probes were shown to be efficient stabilisers for polypropylene during thermo-oxidation at 150 °C in oxygen and sensors of thermo-oxidation during its early stages, in the so-called “induction period”.     

Formation of complexes between alkyl polyglycosides and potato starch

The formation of complexes between soluble potato starch and three commercial alkyl polyglycosides has been studied by means of surface tension measurements at 37 degrees C. All surfactants assayed form complexes with starch, the quantity of bound surfactant being proportional to the amount of starch present in the solution. For all alkyl polyglycoside-starch systems tested, there is a direct proportional relationship between the bound and total surfactant concentrations, so that the formation of the surfactant-starch complex continues until the minimum surface tension is reached without detectable starch saturation prior to the occurrence of surfactant micelles. Binding isotherms and Scatchard plots support the idea that alkyl polyglycosides are bound to amylose by positive cooperative binding and to amylopectin by non-cooperative Langmuir-type binding.     

Transient entanglements and clusters in dilute polymer solutions

A convenient method to monitor polymer dissolution is to measure the pressure drop created by passing a polymer solution through a capillary constriction rheometer. In this work, we studied the dissolution of polyethylene oxide (PEO) and cationic starch (C‐starch). We found that for freshly dissolved and entangled PEO, the main contribution to the overall pressure drop is due to the contraction and expansion of PEO entanglements at the entrance and exit of the capillary, and that the friction in the capillary plays a minor role. On the other hand, for well‐dissolved PEO, because of the absence of PEO entanglements, the loss of pressure is mainly due to friction. At high velocities the contraction and expansion coefficient for freshly dissolved PEO was more than 20 times higher than for well‐dissolved PEO, resulting in a three times higher overall pressure drop. C‐starch consists of amylopectin (～ 85%) and amylose and is known to contain clusters when freshly dissolved, likely formed from the globular amylopectin molecules. For C‐starch, the main contribution to the overall pressure drop is due to friction. Entrance and exit effects contribute only 10% to the overall pressure drop, which might be due to the linear amylose molecules in C‐starch. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 253–262, 2008