Microstructure and elastic modulus of mixed gels of gelatin + oxidized starch: Effect of pH

The microstructure and elastic shear modulus of cold-set gels formed from high-sugar aqueous mixtures of gelatin (7 wt%) + oxidized starch (0-6 wt%) were investigated as a function of pH. Samples prepared at 90 °C, with citric acid added to adjust the pH, were rapidly quenched to ∼1 °C, subjected to a standard thermal treatment (40 °C for 10 min), and then investigated by confocal microscopy and small-deformation rheology at 24 °C. Under ‘natural’ conditions of pH ≈ 5.2 (no citric acid addition), the samples exhibited phase separation with a characteristic spinodal-type morphology. The spatial extent of the structural heterogeneity, expressed by a single length-scale parameter, was found to increase with starch concentration. Gradual acidification led to a reduction in this length-scale parameter, leading to complete inhibition of phase separation below a certain characteristic pH value in the range 4.5-4.9 (depending on starch content). Over the investigated pH range, the effect of starch addition was to reduce the storage modulus of the resulting gel. This reduction was more pronounced for the phase-separated samples. The pH of maximum rigidity was found to decrease from pH_max ≈ 4.6 for 0 wt% starch to pH_max ≈ 4.2 for 6 wt% starch. Taken all together, these observations can be understood in terms of the effects of pH on the cross-linking behaviour of the gelatin and the nature of the gelatin-starch electrostatic interactions. The microscopy results are consistent with a transition in behaviour from thermodynamic incompatibility (segregative interactions) at high pH to soluble complexation (associative interactions) at low pH.     

Isomaltodextrin strengthens model starch gels and moderately promotes starch retrogradation

Isomaltodextrin (IMD) is a novel highly branched α-glucan with emerging applications in foods due to its nutritional functionalities. In this study, the impact of IMD on the viscoelasticity and microstructure of starch gels and starch retrogradation were investigated. IMD solutions displayed typical Newtonian behaviour. Their viscosities had a positive correlation with concentration and a negative correlation with temperature. When maintained at relative humidity of 95%, IMD absorbed 40% water of its original weight. The addition of IMD to normal corn starch increased strength of gels as indicated by higher storage moduli (G′) and resulted in a denser and smaller pore structure, but there were no changes in elasticity. Upon storage for 7 days, addition of IMD at high concentration (starch: IMD = 2:1) significantly increased the degree of starch retrogradation. This study provided perspectives underlying applications of IMD in starchy foods as a novel ingredient with textural functionality.     

磷酸化醋酸酯淀粉流变学特性的研究

采用流变仪研究了低取代度醋酸酯淀粉及其不同磷酸化程度产物的糊的流变特性。结果表明：所有的样品糊均呈现假塑性流体特征。在相同的温度下，剪切应力随剪切速率的增加而增大；在同一剪切速率下，样品糊的剪切应力随温度的上升而降低，剪切应力随取代度的增加而升高，表观黏度随着取代度的增加而上升。当DS〉0．0416时，随着取代度的提高，剪切稀化也增强。     

Preparation of oxidized corn starch in a screw extruder under alkali‐free conditions

To promote water solubility of oxidized starch prepared by the dry process, a twin screw extruder was used as a reactor in the present study. Through single‐factor experiments and orthogonal experiment, the effects of barrel temperature, moisture content, addition amount of NaOCl, and screw speed on the carboxyl content (CC) and water solubility index (WSI) of oxidized corn starch were investigated. The results indicated that high screw speed, medium barrel temperature, and low moisture content could lead to high WSI of oxidized corn starch produced by extrusion. The reaction efficiency and solubility of oxidized starch prepared by reactive extrusion under the optimal condition were all improved greatly, especially the WSI was very high (99.56%). Preparation of oxidized starch by reactive extrusion under alkali‐free conditions could be described as a rapid (only several minutes), continuous, reduced addition amount of NaOCl, eco‐friendly new dry technology.     

微波有机相法制备辛烯基琥珀酸淀粉的表征和流变学研究

研究了在微波条件下,以乙醇为介质制备辛烯基琥珀酸淀粉酯。通过红外、电镜、X衍射等测定,对产品的结构进行了表征,并讨论了淀粉糊的流变学性能。研究表明,利用微波有机相法制备的辛烯基琥珀酸淀粉酯,可作为性能优良的新型增稠剂。     

马铃薯氧化淀粉性质及表征

采用马铃薯淀粉为原料,FeSO4为催化剂,H2O2为氧化剂干法制备氧化淀粉,对氧化淀粉溶解度及其糊的表观粘度、透明度、冻融稳定性、凝沉性等性质进行研究。结果表明,与原淀粉相比,马铃薯氧化淀粉溶解度、透明度增大,表观粘度降低,冻融稳定性增强,凝沉性减弱;并对氧化淀粉结构进行表征。     

Production and characterization of oxidized cassava starch (Manihot esculenta Crantz) biodegradable films

Plastic is one of the most common pollutants in the environment. Therefore, the number of studies on the use of biodegradable packaging is increasing. Starch is the primary material used in the production of biodegradable plastics due to its natural abundance and high biodegradability. Yet, the strong hydrophilic character of starch presents a challenge. Therefore, the modification of its structure through oxidation may yield interesting results as the viscosity reduction. The objectives of this work were to obtain cassava (Manihot esculenta Crantz) starch oxidized with 0.8 and 2.0% active chlorine, to develop biodegradable films and characterize their mechanical properties, solubility in water, permeability to water vapor, degree of swelling, and sorption isotherms. Biodegradable films were produced with starch concentrations of 2, 3, 4, and 5% w/w and 25% glycerol (g/100 g starch) added as a plasticizer. Images of the films were obtained with an atomic force microscope and allow to observe a smooth surface and the absence of starch granules in the film produced with oxidized starches. The tensile strength of the biodegradable film produced with oxidized starch (0.8% active chlorine) was 80 MPa. The value of permeability to water vapor was 1.613 × 10⁻⁹ kg/day/m/Pa, and the average solubility was 41%. The sorption isotherms showed that biodegradable films made with oxidized starches cannot be used in environments with relative humidity below 35% or above 90%.     

Evolutions of rheology,microstructure and starch hydrolysis of pumpkin-enriched bread during simulated gastrointestinal digestion

In this study, the influences of pumpkin flour additions to breadmaking on evolutions of microstructure, rheology and starch hydrolysis during simulated gastrointestinal digestion were investigated. Compared to white bread (PB₀), the bread supplemented with 20% pumpkin flour (PB₂₀) showed more continuous and fibrous gel network structure with most starch granules encapsulated in the network throughout the in vitro digestion. Due to the dilution of digestive fluids and enzymatic hydrolysis, the digesta moduli and viscosity remarkably decreased as time progressed, but PB₂₀ presented significantly higher rheology compared to PB₀ in each digestion phase. At the end of intestinal phase, the in vitro starch digestibility was 69.9% for PB₀, significantly higher than that for PB₂₀ (55.4%). This is presumably attributed to the abundant dietary fibre in pumpkin flour, contributing to the increased digesta viscosity and the formation of more compact and stable gel networks that would hinder the contact of starch granules with α-amylase. In addition, the pumpkin-added breads gave satisfactory results in terms of sensory acceptability. This study has suggested promising potential of incorporating pumpkin flour in the production of functional bakery products with reduced starch digestibility while maintaining good sensory characteristics.     

Gel texture and rheological properties of normal amylose and waxy potato starch blends with rice starches differing in amylose content

This study characterised the textural and rheological behaviour of blends of rice (waxy, low- and high-amylose) and potato (waxy and normal) starch. Blends of potato starch with rice starch in the ratios of 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100 were tested. Addition of rice starch (except high-amylose rice starch) greatly increased the swelling of rice–potato starch mixtures. Addition of rice starch decreased gel firmness for most starch mixtures and increased gel adhesiveness for blends containing waxy potato starch. For rheological measurements, storage modulus was much higher than loss modulus of blends, indicating solid-like behaviour. Starch blends with 20%/40% proportion of rice starch showed a greater thickening effect, whereas with further increase in rice starch proportion, a pseudoplastic, shear-thinning behaviour was observed. This study may provide a basis to develop blends of potato and rice starch for potato noodle production without use of chemical additives.     

Improving gel formation of rice starch added with cross‐linked resistant starch prepared from rice starch

The gel formation properties of non‐waxy rice starch with cross‐linked resistant starch with phosphate (RS4, 10, 20, and 30% based on rice starch) prepared from three rice varieties with different amylose (AM) content were investigated to increase dietary fiber content, improve gel structure, and reduce the glycemic index of rice products. The AM contents of rice starches were 1.71% in Hanganchal1, 22.47% in Nampyeong, and 33.39% in Goamy. All RS4 showed A‐type crystallinity and their RS levels were 46.91, 54.54, and 66.01%, respectively. The initial pasting temperatures of RS4 added rice starches increased as RS4 contents increased, but peak and breakdown viscosities and enthalpy change (△H) reduced. The RS4 addition improved gel shape and texture properties including hardness, cohesiveness, and gumminess, except the 30% Goamy RS4 added gel. The 20% RS4 addition was appropriate to form rice starch gels. The network structure of RS4 added gel formed more regular and firmer than that of control, because RS4 granules were entrapped within the gel matrix like observed by light microscope and scanning electron microscopy. It is suggested that RS4 not only assist in forming a rigid network structure but also increasing a dietary fiber content.

     

Molecular structure,rheological and thermal characteristics of ozone-oxidized starch

The effects of oxidation by ozone gas on the molecular structure, rheological and thermal properties of starch (corn, sago and tapioca) were investigated. Starch, in dry powder form, was exposed to ozone for 10 min at different ozone generation times (OGTs). Average molecular weight decreased in oxidized corn and sago starches but increased in oxidized tapioca starch. All oxidized starches exhibited non-Newtonian shear-thinning behaviour. Starch viscosity decreased drastically with increasing OGT. Young’s modulus for all oxidized corn and sago starch gels stored for 1 and 7 days at 4 °C increased significantly compared to unmodified starch. No differences were noted in gelatinization temperatures and gelatinization enthalpies of all oxidized starches compared to unmodified starch. Retrogradation enthalpy increased markedly in corn starch after 1 min OGT. These results show that the extent of starch oxidation varies among starches of different botanical origins under similar ozone treatment conditions.     

Thermal and rheological properties of breadfruit starch

The thermal and rheological properties of breadfruit starch were studied using DSC and 2 different rheometers. It was found that the gelatinization temperature of starch with excess moisture content (>70%) was at approximately 75 °C. A new endotherm was detected at about 173 °C when the moisture content was lower than required for full gelatinization of the starch. A detailed examination revealed that this endotherm represented the melting of amylose-lipid complexes. Breadfruit starch paste exhibited shear-thinning fluid characteristics, and good thermal and pH stability. The setback viscosity of the breadfruit starch was lower than that of potato and corn starches. The rheological properties of the breadfruit starch paste was well described by the Herschel-Bulkley model at a shear rate of 0 to 100 s(-1), where R(2) is greater than 0.95, and it behaved like a yield-pseudoplastic fluid. Both the storage modulus and loss modulus of the paste initially increased sharply, then dropped after reaching the gelatinization peak. Breadfruit starch gel showed both flexibility and viscosity. Suspension with 6% starch content exhibited very weak gel rigidity; however, this increased significantly at starch contents above 20%.     

Effect of heating temperature,pH, concentration and starch/whey protein ratio on the viscoelastic properties of corn starch/whey protein mixed gels

The viscoelastic properties of corn starch (CS) gels were more dependent on heating temperature, while the properties of whey protein isolate (WPI) gels were more dependent on pH. Thus heating temperature (75, 85, 95 °C) and pH (5, 7, 9) were varied to obtain a series of mixed gels with interesting viscoelastic properties. WPI gels showed extensive stress relaxation (SR) indicative of a highly transient network structure, while CS gels relaxed very little in 2000 s. Based on SR results, it appeared that CS/WPI mixed gels with 25 and 50% CS formed compatible network structures at 15% total solids only at pH 9. This supposition was supported by SEM microstructures obtained for dehydrated gels and a synergistic increase in the large‐strain fracture stress for these gels. Some synergy was also found for mixed gels at 30% total solids at pH 9, while at pH 7 the mixed gels seemed to contain separate additive WPI and CS networks unlike the case for pH 7 at 15% total solids. In both cases (15 and 30% total solids) the degree of elasticity of the mixed gels decreased as the WPI content increased. Mixed gels (CS:WPI = 0.5) at pH 9 showed increased fracture stress and fracture strain relative to the same gels at pH 7. This suggests that a unique chemical compatibility exists at pH 9 and results in gels that combine the elasticity of CS and the internal stress dissipation of WPI. © 2001 Society of Chemical Industry     

Rheological,thermal and microstructural properties of whey protein isolate‐modified cassava starch mixed gels at different pH values

The objective of this study was to investigate the rheological, thermal and microstructural properties of whey protein isolate (WPI)‐hydroxypropylated cassava starch (HPCS) gels and WPI‐cross‐linked cassava starch (CLCS) gels at different pH values (5.75, 7.00 and 9.00). The rheological results showed that the WPI‐modified starch gels had greater storage modulus (G?) values than the WPI‐native cassava starch gels at pH 5.75 and 7.00. Differential scanning calorimetry curves suggested that the phase transition order of the WPI and modified starch changed as the pH increased. Scanning electron microscopy images showed that the addition of HPCS and CLCS contributed to the formation of a compact microstructure at pH 5.75 and 7.00. A comprehensive analysis showed that the gelling properties of the WPI‐modified starch were affected by the difference between the WPI denaturation temperature and modified starch gelatinisation temperature and by the granular properties of the modified starch during gelatinisation. These results may contribute to the application of WPI‐modified starch mixtures in food preparation.     

Techno‐functional properties of wheat flour‐resistant starch mixtures applied to breadmaking

Resistant starch can be used to reduce the availability of carbohydrates in baked products. In this study, the effect of type 4 resistant wheat starch (RS₄) on wheat flour dough and breads was evaluated. Wheat flour was substituted by RS₄ at 10%, 20% and 30% w/w (RS10, RS20 and RS30, respectively). Rheological and thermal behaviours of dough were evaluated. Besides, bread quality, starch digestibility and bread staling were analysed. All substituted dough exhibited viscoelastic behaviour but lower elastic and viscous moduli. Regarding to bread quality, specific volume and crumb texture were negatively affected in samples with RS₄. However, all samples were technologically acceptable. During storage, crumb hardening was observed in breads without and with RS₄ but amylopectin retrogradation was not particularly affected. The in vitro digestibility of bread with RS showed a lower release of reducing sugars and a lower estimated glycaemic index, suggesting a healthier profile for these breads.     

The effect of pH and calcium ion on rheological behaviour of β‐lactoglobulin‐basil seed gum mixed gels

Effect of pH (4.5–7.5) and Ca²⁺ (0.01–0.5 m ) on gelation of single and mixed systems of 10% β‐lactoglobulin (BLG) and 1% basil seed gum (BSG) was investigated. The gelling point of BLG and BSG gels was strongly pH‐dependent, and stiffer gels formed at higher pH. The BLG gels were formed upon heating to 90 °C and reinforced on cooling to 20 °C; however, the gelation of BSG occurred at temperatures below 70 °C. By increasing Ca²⁺ concentration, storage modulus of BLG and BSG gels were increased, although pH had a greater effect than Ca²⁺. In contrast, mixed systems showed two distinct types of behaviour: BLG gel formation and BSG network, suggesting that phase‐separated gels were formed. In addition, higher strength was obtained for BLG‐BSG mixture at higher Ca²⁺ concentration.     

酸解氧化小麦淀粉的制备及性能

以小麦淀粉为原料,盐酸为酸解剂,次氯酸钠为氧化剂,对酸解小麦淀粉的制备及性能进行了研究.考察了反应时间、反应温度、pH、次氯酸钠用量、酸解氧化顺序对酸解氧化小麦淀粉羧基含量的影响,采用糊滴定法测定羧基含量.比较了小麦淀粉、酸解小麦淀粉、氧化小麦淀粉及酸解氧化小麦淀粉性能.结果表明,制备酸解氧化小麦淀粉的较佳工艺条件为:反应温度40℃,反应时间2h,pH9.0,先酸解后氧化顺序优于先氧化后酸解顺序.小麦淀粉经酸解氧化后,其抗酸性、抗碱性、冻融稳定性均得到改善,蓝值增加,膨胀能力降低.小麦淀粉经酸解、氧化后,热稳定性变差;酸解提高了小麦淀粉的熔融焓,而氧化使其熔融焓降低.     

聚乳酸接枝马来酸酐/淀粉共混物对涂料流变性及纸张性能的影响

将聚乳酸接枝马来酸酐与淀粉共混物作为胶黏剂用于造纸涂料中,研究了改性聚乳酸不同用量对涂料流变性以及对涂布纸白度、表面强度、油墨吸收性能的影响;同时与涂料中常用的合成胶乳丁苯胶乳作比较。结果发现:改性聚乳酸用量的增加可以显著降低涂料低剪切黏度和高剪切黏度,改善涂料流变性;同时,随着改性聚乳酸用量增加,涂布纸白度、表面强度和油墨吸收性提高;另外,改性聚乳酸/淀粉共混物作为胶黏剂使用与丁苯胶乳对涂布纸性能影响相差不大,可替代丁苯胶乳或与之配合使用,获得更好的涂布纸性能。