高甲氧基果胶对酸性大豆蛋白体系的稳定机理

为揭示高甲氧基果胶对酸性豆乳体系稳定的作用机理,通过添加不同质量浓度果胶,研究在pH值由7.0～3.0降低过程中大豆蛋白的粒径、ζ-电位以及微观结构变化。结果表明：当体系pH＜6.0时,果胶通过静电作用吸附在大豆蛋白胶粒上,阻止了大豆蛋白颗粒在酸性状态的聚集。果胶质量浓度≤0.2 g/100 mL,质量浓度1.5 g/100 mL的大豆蛋白聚集,体系失稳;果胶质量浓度≥0.4 g/100 mL,质量浓度1.5 g/100 mL的大豆蛋白体系在一定pH值内稳定,果胶质量浓度越大,稳定性越好。酸性大豆蛋白体系的稳定性与大豆蛋白和果胶之间的静电吸附作用以及果胶质量浓度有关。     

Structure and physical properties of pectins with block-wise distribution of carboxylic acid groups

The physical and the interfacial properties of pectins de-esterified by a specific block-wise enzymatic procedure were investigated. Two major types of block-wise de-esterified pectins with different internal distribution of carboxylic acid on the pectin chains were explored. Type C and type U pectins with the same degree of methylesterification are different and a more block-wise intramolecular distribution in comparison to commercial native apple pectin. The most ordered pectin (U63 pectin, 63% methylesterified pectin) has the highest electrophoretic mobility (ζ-potential). It reveals more pronounced intermolecular interactions since it exhibited, at low pH, the lowest circular dichroism intensity at shorter wavelength. U63 pectin (at acidic pH, without calcium addition) has a higher viscosity and formed a stronger gel compared to the less ordered C63 pectin and/or native apple pectin. X-ray patterns show that powdered U63 pectin is more crystalline than C63 pectin, while apple pectin is mostly amorphous. The modified pectin also, most effectively, reduced the surface tension (55 mN/m) and the interfacial tension (5.6 mN/m), probably due to the preferred surface orientation of the carboxylic groups at the water/air or water/oil interfaces.     

Extraction and characterisation of pectin polysaccharide from soybean dreg and its dispersion stability in acidified milk drink

In this study, pectin polysaccharide (SDPP) was obtained from soybean dreg (26.2% yield), and characteristics of SDPP were compared with those of soybean soluble polysaccharides (SSPS) and citrus pectin (HMP). The galacturonic acid and molecular weight of SSPS, SDPP or HMP were 11.8%, 40.6% or 70.2% and 112, 446, or 440 kDa. SDPP had similar viscosity and protein content to SSPS, and functional groups and linear structure to HMP. SSPS, SDPP or HMP differed in particle size of 260, 467 or 1195 nm and ζ–potential of −5.8, −14.6 or −23.5 mV at pH 4.0. The precipitation of acidified milk drink (AMD) was 6.31% without stabiliser or below 1.75% with 0.4% SDPP at pH 3.6–4.6. These results suggested that SDPP combines the structure and characteristic of HMP and SSPS, and AMD with SDPP had great stabilising behaviour at wider pH range (pH 3.6–4.6).     

Rheological and high gelling properties of mango (Mangifera indica) and ambarella (Spondias cytherea) peel pectins

Ambarella and mango peels are good sources of pectins (15–20%), with high degree of methylation (60–78%) and high molar masses. Ambarella and mango ( Améliorée and Mango varieties) peel pectins were extracted using HCl or oxalic acid/ammonium oxalate (OAAO). Purified pectins were analysed for their flow behaviour and phase diagrams were established at pH 3 as sucrose vs. pectin concentration. The gelation kinetics and mechanical spectra of these pectin gels were studied and compared to those of commercial citrus (lime) pectins. At a concentration of 1% (w/v), all pectic solutions had a shear thinning behaviour but at 0.6% (w/v), only OAAO-extracted pectins exhibited such behaviour. Phase diagrams showed that at pH 3, gelation of OAAO mango extracted pectins was possible at low polymer concentration (0.2%; w/w) for a sucrose concentration of 60% (w/w). OAAO-extracted pectins exhibited a higher gelling ability than HCl-extracted ones. Sucrose (45–50%) and pectin (0.2–0.6%) concentration had a deep impact on the gel strength. Our results enable to conclude that the OAAO extraction from mango and ambarella peels allowed the recovery of pectins that exhibit high gelling properties.     

A ≥ 100000-MW Soybean Protein Fraction that Inhibits the Formation of Methanethiol and Hydrogen Sulfide in Aqueous Slurries of Isolated Soy Proteins with Added L-Cysteine

ABSTRACT: The addition of L-cysteine to aqueous slurries of commercial isolated soy proteins (ISP) increased methanethiol headspace levels by 17- to 36-fold over the control. Corresponding levels of hydrogen sulfide were about 10 to 19 times greater than methanethiol. Neither methanethiol nor hydrogen sulfide were detected when L-cysteine was added to aqueous slurries of hexane-defatted soy flour. The production of hydrogen sulfide and methanethiol in aqueous slurries of commercial ISP was inhibited by the addition of a component(s) recovered from the pH 4.6 supernatant obtained during laboratory preparation of ISP by isoelectric precipitation. The inhibitory component had a molecular weight (MW) of ≥ 100000 and an isoelectric point of about 5.9. This component was not serine acetyl transferase. Its inhibitory properties were inactivated at 70°C and diminished with elevated levels of methionine. Adding the ≥ 100000-MW soluble-proteins (from the isoelectric precipitation step) back to a nonheat-treated laboratory ISP during processing reduced the methanethiol level by 88%.     

Preparation and optimization of soy protein isolate–high methoxy pectin microcapsules loaded with Lactobacillus delbrueckii

This study was aimed to use soy protein isolate (SPI) and high methoxy pectin (HMP) as encapsulating materials for probiotic bacterial (Lactobacillus delbrueckii) delivery systems. The encapsulation conditions were optimised, and scanning electron microscopy (SEM) was used to characterise the microstructural changes of the microcapsule. The results showed that the optimal conditions for microcapsule preparation were 90 mg mL^?1 SPI and 1 mg mL^?1 HMP, with a SPI/HMP ratio of 7:1 (v/v), and a L. delbrueckii suspension to SPI–HMP complex ratio of 1:1 (v/v). The viability of the probiotics in the microcapsules reaching the small intestine was 3 log CFU mL^?1 higher than that of naked bacteria. SEM showed that the surface of the SPI–HMP compound microcapsules was smooth and that a large number of L. delbrueckii could be seen in cross‐sections of the microcapsules.     

Pectins as Breadmaking Additives: Effect on Dough Rheology and Bread Quality

The effect of two types of pectins with different degrees of esterification on dough and bread characteristics was analysed. A high methoxyl pectin (HMP) and a low methoxyl pectin (LMP) were assayed in dough without or with salt (2%) at levels ranging from 0.25% to 2.0%. Farinographic water absorption increased when pectins were incorporated in dough with salt, whereas this effect was not observed in dough without salt. Pectin addition diminished the stability of dough in all cases. Texture profile analysis showed that pectins softened the dough, particularly when salt was added. Cohesiveness was also higher in doughs with salt at the maximum level of hydrocolloid addition. In dough with salt, HMP decreased the elastic and viscous moduli, while the values for tan (δ) were increased with respect to control. SEM micrographs showed that dough with pectin has a filamentous structure. In the breadmaking process, dough with HMP showed a better performance, leading to higher specific volumes and softer crumbs both in fresh and stored bread.     

Interfacial rheology of soy proteins – High methoxyl pectin films

Surface aggregating soy protein-pectin solutions are used in the production of biodegradable films intended for food packaging applications. Structural properties of the surface biopolymer network influence the engineering properties of the films, such as permeability and mechanical strength. Soy protein isolates (SPI) – high methoxyl pectin (HMP) films that develop at the air–water interface were therefore investigated by a combined interface rheological and ellipsometric approach. The behavior of pure SPI interfacial layer is that of a light cross-linked polymer network with a small regime of linear viscoelasticity response. Since SPI progressively accumulate at the air–water interface, higher protein concentration in the solution does not lead automatically to higher surface coverage but due to restricted unfolding of the proteins to weaker and fluid-like films. The rheological behavior of composite SPI–HMP solutions at the air–water interface shows that the HMP addition increases the elastic interfacial modulus. The stabilizing effect in presence of the polysaccharide is attributed to a protein–polysaccharide complex formation at the interface.     

酰胺化果胶的特性、应用及研究现状

本文将酰胺化果胶与普通低酯果胶以及高酯果胶进行了多方面的比较，重点介绍酰胺化果胶的特性。结合国内外对酰胺化果胶生产和研究的状况，及其在食品工业和医疗方面的应用现状，对酰胺化果胶生产的开发前景进行了分析。     

Characterization of low-phytate soy protein isolates produced by membrane technologies

Soy protein isolates (SPI) produced by combining electro-acidification and tangential ultrafiltration/diafiltration (UF/DF) (pH 6), were compared in terms of composition and proteins solubility with isolates produced by UF/DF (pH 9) and isoelectric precipitation (pH 4.5). Mineral and phosphorus (phytic acid) removal was enhanced for the SPI pH 6. Whey-like proteins (M.W. < 66 kDa) were also found in higher concentration for the SPI produced by membrane technologies. This difference in composition resulted in improved solubility characteristics for the SPI pH 6 by as high as 25% and 60%, when compared to the SPI pH 4.5 and SPI pH 9, respectively. Improvement in solubility was most important between pH 2 and 4.5. The quantity of H⁺ ions added to the soy protein extract (SPE) and SPI to reduce the pH from 9 to 4.5, during solubility measurement, was related to the degree of proteins aggregation, as determined by size-exclusion high-performance liquid chromatography, and at a lesser extent to their phytic acid content. For the pH range of 4.5 to 2, the degree of proteins aggregation alone determines the quantity of H⁺ ions added.Industrial relevanceSoy protein production is one of the major agricultural sectors of significant importance to North America and soy proteins represent 69% of global plant protein consumption in the world. Soy protein concentrates and isolates are produced at the industrial scale by isoelectric precipitation. This process has a high productivity, however, it also generates large volumes of effluent. The final products also have significant contents of minerals and of phytic acid, the latter of which is well known to decrease the proteins and minerals adsorption in the intestine.We were the first group to combine bipolar membrane electrodialysis (BMED) and ultrafiltration (UF) (dead-end) for the production of soy protein concentrates (Mondor, Ippersiel, Lamarche & Boye, 2004). The new approach resulted in a significant decrease of the volumes of effluent due to the use of BMED to adjust the pH of the extract prior to UF and by improving the protein washing step using diafiltration (DF). It was also shown that for the pH range 6–9, minerals and phytic acid removal was improved with a decrease in pH. In this work, we present the characteristics of a soy protein isolate with a low phytic acid/protein ratio (SPI pH 6) produced by BMED and tangential flow UF/DF applying an optimal VCR5, re-VCR 5 sequence at pH 6. The SPI pH 6 shows an improved solubility by as high as 25% and 60%, when compared to an isolate produced by isoelectric precipitation at pH 4.5 and to one produced by UF/DF at pH 9, respectively. Improvement in solubility was most important between pH 2 and 4.5 indicating that this isolate could be considered as a valuable ingredient for the formulation of fruit juice beverages or power juices, considering that the pH of these liquid food products is around 3.5.     

Effect of pH on the properties of soy protein–pectin complexes

The interactions of a commercial soy protein isolate (SPI) and a 2:1 SPI:high methoxy pectin (PEC) complex were evaluated over a range of pH values (3-7). The SPI formed very large (> 50 ??m) and largely insoluble aggregates (< 10%) close to its isoelectric point (IEP, pH 4 and 5) and smaller, more soluble (> 80%) particles at higher and lower pH values. The addition of PEC increased the solubility of SPI close to its IEP (pH 4 and 5) and prevented the formation of very large aggregates. However, PEC reduced the solubility of SPI at higher and lower pH values presumably via a depletion mechanism. The ??-potential of diluted SPI dispersions decreased from positive to negative with increasing pH, passing through zero at pH 4.6, the isoelectric point (IEP) of the protein. At pH < 6, the addition of PEC reduced the charge of the protein suggesting the formation of a complex while at pH 6 or 7 there was no evidence of complex formation. The increased SPI solubility in the IEP in the presence of PEC is probably due to the formation of charged complex which do not aggregate while the decreased solubility of protein in the presence at high and low PEC is probably due to the formation of insoluble complexes and a depletion interaction respectively. Thermal treatment (30 min, 90 °C) enhanced the solubility of the SPI:PEC complexes close to the IEP (pH 4 and 5), but reduces it at low pH (pH 3). The SPI:PEC complexes could be manufactured in the form of a beverage at pilot scale where their solubility was enhanced by homogenization.     

Effect of Sequestering Intrinsic Iron on the Electron Paramagnetic Resonance Signals in Powdered Soy Proteins

This investigation examined iron in powdered soy protein products using electron paramagnetic resonance (EPR) spectroscopy, and the effect that selectively binding free iron in isolated soy protein (ISP) had on the occurrence of metastable radicals in powdered soy proteins. EPR analyses of soybean defatted flour, commercial ISP and laboratory ISP samples revealed a peak at g = 4.3 characteristic of high‐spin ferric iron in a rhombic‐coordinated environment. Commercial ISP samples examined contained higher levels of the rhombic ferric iron than laboratory‐prepared ISP samples. During the first 6 wk of storage the primary singlet EPR signal at g = 2.0049 in the commercial ISP samples approximately doubled, and the laboratory prepared samples increased by about 9‐fold. The EPR signal was initially about 4‐times higher in the freshly prepared commercial samples compared to the corresponding laboratory ISP. Laboratory ISP samples prepared with added deferoxamine to sequester endogenous iron exhibited a large increase in the high‐spin ferric iron EPR signal at g = 4.3. ISP treated with deferoxamine also exhibited a multiple‐line EPR signal at about g = 2.007, instead of the typical singlet signal at g = 2.0049. The power at which the signal amplitude was half‐saturated also changed from about 1 mW in the control ISP to about 20 mW in the deferoxamine treated ISP. The multiple‐line EPR spectrum from the ISP treated with deferoxamine increased during storage over a 6‐wk period by about 6‐fold. The observed changes in EPR line‐shape, g‐value, and power saturation with the deferoxamine treatment indicate that the primary free‐radical signal in powdered ISP samples may be from stabilized tyrosine radicals with spin densities distributed over the aromatic ring.     

New method for the purification of electrically charged polysaccharides

A new technique for the purification of pectins using protein (sodium caseinate) was developed and that could replace the process of ethanol which is currently used in industries. Commercial pectins were used as a model to verify the feasibility of the process and to define some important parameters. The results indicated that this purification technique is based primarily on the electrostatic interactions between these two polymers. The electrostatic interactions were strongly dependent on pH and salt concentration. The maximum pectin precipitation was obtained at pH 3.5. At this pH, the pectin acquires a negative charge while the protein is positively charged, promoting thus their attractions. Furthermore, the dissociation of the pectin–caseinates complex and the precipitation of caseinate at pH 4.6 were observed in the presence of salt. This method is very specific, suggesting that it could be used to purify some electrically charged polysaccharides.     

In vitro digestibility of rare sugar (D-allulose) added pectin–soy protein gels

Confectionery gels are known to be high-caloric products due their high sugar content. Changing their formulations by substituting the sugar with alternative natural sweeteners and functionalising them, the addition of proteins has gained attention. Understanding the rate of digestion of these products is also important for selecting the appropriate formulation. In this study, in vitro gastric digestion behaviour of the gels formulated with D-allulose, a low-calorie rare sugar, soy protein isolate (SPI) (1%, 2.5%) and pectin (4%) were examined. Digestion decreased the hardness of the gels (P < 0.05), but, at 2.5% SPI concentration. Moisture content of the samples increased after digestion and presence of SPI induced higher water uptake. At the end of 2 h of digestion, 1% soy protein isolate containing gels had the highest brix values showing that after a certain concentration, soy protein isolate governed the system due to improved soy protein–pectin interaction or due to improved gelation with Maillard reaction. NMR relaxometry experiments further confirmed the changes in the gels with the increase in T₂ values. Power law model was fitted for the dissolution behaviour using the ^oBrix values of the digestion medium. Dissolution of sugar and the contribution of SPI to the gel network were clearly observed in SEM images. Results showed that these gels had the potential to slow down the emptying rate of stomach thus could lead to ‘fullness’ for a longer time.     

Investigation of the composite system of β-lactoglobulin and pectin in aqueous solutions

The compatibility in aqueous systems of β-lactoglobulin (β-lg) with low and high esterified-sodium polypectates (LMP and HMP) was investigated. The mixture did not separate into two co-existing liquid phases in any case studied. At pH above the isoelectric point (IP) of β-lg, the behavior of LMP and HMP was similar when mixing with β-lg. Pectins and β-lg were co-soluble was around a particular ionic strength (μ) (0.07 M for HMP and 0.3 M for LMP). In these circumstances, the flow behavior of pectin was hardly affected by the addition of β-1g . At all other μ, the mixture formed a liquid phase containing both β-lg and pectin and a small amount of β-lg precipitates. Here, the viscosity of the liquid phase was slightly higher than the viscosity of a solution containing the same concentration of pectin. At pH 3.5, i.e. pH⩽IP of β-lg, the behavior of LMP and HMP was different when mixing with β-lg. LMP formed insoluble complexes with β-lg at low μ (⩽0.25 M), but precipitation was suppressed at high μ (0.5 M). The composite system of β-lg/HMP formed a white, homogeneous and stable dispersion at low μ (0.07 M). The viscosity of this dispersion was much higher than the additive viscosity of individual solutions would be. Probably, the oppositely charged β-lg and HMP formed soluble complexes, which further associated into large aggregates. This complexation was also suppressed at high μ (0.5 M).     

Carbon-centered radicals in isolated soy proteins

ABSTRACT:  Solid-state electron paramagnetic resonance (EPR) spectroscopy of commercial samples of isolated soy proteins (ISP) revealed a symmetrical free-radical signal typical of carbon-centered radicals ( g = 2.005) ranging from 2.96 × 10¹⁴ to 6.42 × 10¹⁴ spins/g. The level of free radicals in ISP was 14 times greater than similar radicals in sodium caseinate, 29 times greater than egg albumin, and about 100 times greater levels than casein. Nine soy protein powdered drink mixes contained similar types of free radicals up to 4.10 × 10¹⁵ spins/g of drink mix, or up to 6.4 times greater than the highest free-radical content found in commercial ISP. ISP samples prepared in the laboratory contained trapped radicals similar to the levels in commercial ISP samples. When ISP was hydrated in 2.3 mM sodium erythorbate or 8.3 mM L-cysteine, frozen and dried, the level of trapped free radicals increased by about 17- and 19-fold, respectively. The ESR spectrum of defatted soybean flakes contained overlapping signals from the primary free-radical peak ( g = 2.005) and a sextet pattern typical of manganese-II. The manganese signal was reduced in the laboratory ISP and very weak in the commercial ISP.     

Beverage cloud stability with isolated soy protein

The purpose of this study was to optimise the use of isolated soy protein (ISP) as a clouding agent for beverages. ISP was fractionated by hydrophobic interaction chromatography (HIC) using 2 M KCl in a step gradient manner. A hydrophilic and a hydrophobic fraction were collected. The proteins therein were separated by SDS-PAGe. Each fraction was combined with citrus pectin in nine different ratios at pH 3·7 and subjected to cloud stability and turbidity studies for 28 days at 4°C. The molecular weight patterns of the two fractions were different, indicating separation in the HIC column. Analysis of variance with repeated measures found no significant difference in cloud stability between the two fractions (P<0·05). Empirically, the hydrophilic fraction acted as a better clouding agent. Significant differences in cloud stability and cloud turbidity were found between different ratios of pectin: protein (P<0·05). No correlation was found between the initial cloud composition and cloud stability. Hydrophilic fraction in pectin: protein ratios 1: 2 and 4:1 gave optimum cloud stability. This study reiterated the usefulness of ISP as a clouding agent. © 1998 Society of Chemical Industry.     

Physicochemical and textural properties of heat-induced pea protein isolate gels

Chemical and thermal properties of pea protein isolates (laboratory prepared or native; PPIn and commercial; PPIc) and textural properties of heat-set gels obtained from pea protein isolates were compared with homologous soy protein isolates (laboratory prepared, or native; SPIn and commercial; SPIc). The protein banding pattern resulting from electrophoresis separation confirmed the presence of predominant storage proteins of pea and soy seeds in the respective protein products. PPIc and SPIc had lower nitrogen solubility than their native counterparts, likely due to their denaturated state which was further confirmed by the absence of distinct endotherms in these commercial materials compared to the laboratory prepared ones. Addition of NaCl at 1.0–2.0% (w/w) to PPIn and SPIn slurries increased thermal transition temperatures for both proteins.     

Characterization of pectin extracted from banana peels of different varieties

Pectins were extracted from banana peels of five different varieties using citric acid solution. The chemical characteristics of banana peel pectins were investigated and compared with citrus peel and apple pomace pectins which were extracted under the same extraction conditions to assess the potential of banana peels as an alternative source of commercial pectin. The yield of banana peel pectins ranged from 15.89 to 24.08%. The extracted banana peel pectins were categorized as high methoxyl pectin with the degree of esterification between 63.15 and 72.03% comparable to those of conventional pectin sources from citrus peel (62.83%) and apple pomace (58.44%). The anhydrouronic acid (AUA) content of banana peel pectins varied from 34.56 to 66.67%. Among various banana varieties being studied, pectin from Kluai Nam Wa variety had the highest AUA content (66.67%) which met the criteria for food additive pectin indicating its commercial significance as an alternative pectin source.     

The stabilizing behaviour of soybean soluble polysaccharide and pectin in acidified milk beverages

The mechanisms of stabilization of soybean soluble polysaccharide (SSPS) and high methoxyl pectin (HMP) in acidified milk drinks were studied focusing on the differences in behaviour between the two polysaccharides. The changes in casein micelles size during acidification with glucono-δ-lactone or by direct acidification were measured using light scattering. When HMP was added to skim milk before acidification, pectin adsorbed on the surface of the casein micelles via electrostatic interactions and prevented casein aggregation. Results suggested that adsorption of pectin occurred from the beginning of acidification and somewhat affected the rearrangement of casein micelles in the pH range between 5.8 and 5.0. On the other hand, SSPS, at concentrations up to 2% (w/w), did not interact with caseins at pH >4.6. At pH <4.2 SSPS showed better stabilizing properties than HMP. In addition, between pH 4.2 and 3.2, SSPS-stabilized acid dispersions were not affected by pH, while dispersions homogenized with pectin showed a size distribution that depended on pH. The differences in structure between SSPS and HMP account for the unique functionalities of the two polysaccharides in acid milk systems.