Effects of heat treatment and pectin addition on beta-lactoglobulin allergenicity

The specific effects of heat treatment and/or addition of low/high-methylated pectin (LMP/HMP) on the allergenicity of beta-lactoglobulin (beta-Lg) and its hydrolysis products were investigated through a two-step in vitro digestion approach. beta-Lg was first hydrolyzed by pepsin and then by a trypsin/chymotrypsin (T/C) mixture done in a dialysis bag with a molecular weight cutoff of 1000. The protein digestion was followed by SDS-PAGE electrophoresis performed on each digestion product, and their in vitro allergenicity was analyzed by immunoblotting. Such procedure was applied on beta-Lg samples mixed with the two kinds of pectin before or after heating (80 degrees C, 25 min) to determine the respective impact of heat treatment and pectin addition. Heat denaturation improved significantly the susceptibility of beta-Lg against the pepsin and the T/C. This effect, which was coupled to a reduction in immunoreactivity of the digested beta-Lg, appeared to be distinctively modulated by LMP and HMP. Through nonspecific interaction with the beta-Lg, pectin could reduce the accessibility of cleavage sites and/or epitope sequences. This mechanism of action is discussed in relation to the intra- and intermolecular interactions between beta-Lg and pectin initiated under the experimental conditions.     

Kinetics of formation and functional properties of conjugates prepared by dry-state incubation of beta-lactoglobulin/acacia gum electrostatic complexes

The formation of conjugates between beta-lactoglobulin and acacia gum based on electrostatic complexes formed at pH 4.2 was investigated upon dry-state incubation for up to 14 days at 60 degrees C and 79% relative humidity (RH). By means of SEC-HPLC and RP-HPLC, it was shown that the beta-lactoglobulin incubated alone was able to form polymers with molecular masses higher than 200 kDa until 50% of the initial monomeric protein disappeared after 14 days. In the presence of acacia gum at initial protein to polysaccharide weight mixing ratios of 2:1 and 1:2, only 35% of the initial beta-lactoglobulin monomers disappeared after 14 days. Using RP-HPLC, an apparent reaction order of 2 was found for the disappearance of monomeric beta-lactoglobulin both in the presence or absence of acacia gum. However, the reaction rate was faster in the absence of acacia gum. SDS-PAGE electrophoresis with silver staining confirmed the formation of beta-lactoglobulin/acacia gum conjugates. The solubility curves of the incubated beta-lactoglobulin showed a minimum around pH 4-5. By contrast, the minimum of solubility of the beta-lactoglobulin/acacia gum incubated mixtures shifted to lower pH values compared to initial mixtures. The conjugates exhibited higher foam capacity than the incubated protein as well as lower equilibrium air/water surface tension. Conjugation at ratio 1:2 led to increased interfacial viscosity (300 mN s m(-1) at 0.01 Hz) compared to beta-lactoglobulin alone (100 mN s m(-1) at 0.01 Hz), but similar interfacial elasticity (30-40 mN m(-1)). The foam capacity of the conjugates was significantly higher than that of the incubated beta-lactoglobulin as well as foam expansion and drainage time, especially at pH 5.3, i.e., higher than the pH of formation of the conjugates.     

Quantification of the interactions between beta-lactoglobulin and pectin through capillary electrophoresis analysis

Biopolymer interactions have many potential applications in pharmaceutical, cosmetic, nutraceutical, and functional food industries. Attractive interactions between proteins and polysaccharides can lead to the formation of complexes. Binding parameters of beta-lactoglobulin (beta-lg)/pectin complexes were determined using frontal analysis continuous capillary electrophoresis and the overlapping binding site model. At pH 4, approximately 23 beta-lg molecules were cooperatively complexed on low-methoxyl pectin, where each beta-lg molecule covered an average of 12 galacturonic acid residues. The calculated binding constant was 1431 M(-1). The interactions between pectin and four selected peptides located on the outer surface of the beta-lg were investigated in order to identify which part of the protein was likely to interact with the pectin. The peptide beta-lg 132-148, which corresponds to the alpha-helix zone, and the peptides beta-lg 76-83, 41-60, and 1-14 would be involved in the interaction with the pectin.     

Physical and oxidative stability of fish oil-in-water emulsions stabilized with beta-lactoglobulin and pectin

The oxidation of fatty acids can be inhibited by engineering the surface of oil-in-water emulsion droplets to decrease interactions between aqueous phase prooxidants and lipids. The objective of this research was to evaluate whether emulsions stabilized by a multilayer emulsifier systems consisting of beta-lactoglobulin and citrus or sugar beet pectin could produce fish oil-in-water emulsions that had good physical and oxidative stability. Sugar beet pectin was compared to citrus pectin because the sugar beet pectin contains the known antioxidant, ferulic acid. A primary Menhaden oil-in-water emulsion was prepared with beta-lactoglobulin upon which the pectins were electrostatically deposited at pH 3.5. Emulsions prepared with 1% oil, 0.05% beta-lactoglobulin, and 0.06% pectins were physically stable for up to 16 days. As determined by monitoring lipid hydroperoxide and headspace propanal formation, emulsions prepared with the multilayer system of beta-lactoglobulin and citrus pectin were more stable than emulsions stabilized with beta-lactoglobulin alone. Emulsions prepared with the multilayer system of beta-lactoglobulin and sugar beet pectin were less stable than emulsions stabilized with beta-lactoglobulin alone despite the presence of ferulic acid in the sugar beet pectin. The lower oxidative stability of the emulsions with the sugar beet pectin could be due to its higher iron and copper concentrations which would produce oxidative stress that would overcome the antioxidant capacity of ferulic acid. These data suggest that the oxidative stability of oil-in-water emulsions containing omega-3 fatty acids could be improved by the use of multilayer emulsion systems containing pectins with low metal concentrations.     

Effect of milk concentration on the irreversible thermal denaturation and disulfide aggregation of beta-lactoglobulin

The kinetics of beta-lactoglobulin (beta-LG) denaturation in reconstituted skim milk samples of various concentrations (9.6-38.4% total solids) over a wide temperature range (75-100 degrees C) was studied. The thermal denaturation of beta-LG had a reaction order of 1.5 at all milk solids concentrations and at all temperatures. The rate of denaturation of beta-LG was markedly dependent on the milk solids concentration and the heating temperature. At 75 degrees C, the thermal denaturation of beta-LG was retarded at higher milk solids concentrations. However, this retardation was less pronounced at higher temperatures so that a similar rate of denaturation was observed at all milk solids concentrations at 100 degrees C. From an examination of the level of disulfide-aggregated beta-LG, it was evident that most, but not all, of the denatured beta-LG was involved in disulfide-aggregated complexes, either with other denatured whey proteins or with the casein micelles. As with beta-LG denaturation, the rate of disulfide aggregation of beta-LG was markedly dependent on the milk solids concentration.     

Effects of caseins on thermal stability of bovine beta-lactoglobulin

Casein fractions have been shown to act as molecular chaperones and inhibit aggregation of whey proteins in dilute solutions (< or =1% w/v). We evaluated if this approach would stabilize protein solutions at higher concentration and thermal processing temperatures desired for beverage applications. Mixtures of beta-lactoglobulin (BLG) (6% w/v) with either beta-casein (BCN) (0.01-2% w/v) or alpha s-casein (ACN) (2% w/v) were adjusted to pH 6.0 and heated (70-90 degrees C) for 20 min, cooled, and then analyzed to determine the degree of aggregation. Aggregation was determined by solution turbidity as optical density (OD) at 400 or 600 nm. The addition of 0.05% (w/v) BCN or greater caused a drop in turbidity for solutions heated at 70-90 degrees C. In contrast, inhibition was observed in BLG-ACN mixtures at 70 degrees C but not at > or =75 degrees C. Moreover, prolonged heating (90 min) of BLG with 2% (w/v) BCN (pH 6.0) at 90 degrees C produced a clear solution while BLG-ACN solutions formed translucent gels after heating for 15 min. The weight-averaged molar mass and root-mean-square (rms) radius of soluble aggregates were determined by size exclusion chromatography in conjunction with multiangle laser light scattering (SEC-MALS). SEC-MALS confirmed the turbidity results by showing that the BLG-BCN mixture (8% w/v protein) produced aggregates with lower molar mass and smaller rms radius (majority 20-40 nm). These results showed that BCN is a feasible component to stabilize higher concentrations of whey proteins in beverages.     

Multivariate analysis of the influence of pectin,white syrup,and citric acid on aroma concentration in the headspace above pectin gels

Pectin gels consist of polysaccharide networks surrounded by water. The gel networks can prevent release of aroma molecules from the gel to the gas phase above. In this study static headspace measurements were performed to correlate aroma concentration in the gas phase above pectin gels to different amounts of the gel ingredients. As a consequence, aroma concentration in the headspace in relation to gel texture, as characterized by rheology measurements, was also studied. Aroma concentration in the headspace above strong gels was low, due to entrapment of aroma molecules within the gel structure. Viscous solutions generally gave a high aroma concentration in the headspace, but owing to a complex matrix, this was lowered when large amounts of the gel ingredients were added. However, a high correlation between interaction terms and square terms of design variables and rheology parameters with aroma compounds indicated nonlinear and complex relationships.     

Effects of cryostabilizers, low temperature, and freezing on the kinetics of the pectin methylesterase-catalyzed de-esterification of pectin

The kinetics of the pectin methylesterase (PME)-catalyzed de-esterification of pectin was studied at 25 degrees C in the presence of sucrose, fructose, maltodextrin (DE = 16.5-19.5), and carboxymethylcellulose at different concentrations and in the presence of maltodextrin and sucrose at different concentrations in a temperature range between +25 and -4 degrees C in subcooled and frozen states. The objective was to determine whether the reaction is diffusion-controlled, to gain insight about the factors determining the diffusion of the reactants, and to determine the effect of the carbohydrates, low temperature, and freezing on the structural conformation of the enzyme. The results indicate that the PME-catalyzed de-esterification of pectin is diffusion-controlled. Nevertheless, the diffusion is not controlled by the macroviscosity of the reaction medium, but rather by the microviscosity experienced by the diffusants. Low temperature in the temperature range studied does not affect the structural conformation of the enzyme, while freezing seems to have some effect.     

Inhibition of buckwheat starch digestion by the formation of starch/bile salt complexes: possibility of its occurrence in the intestine

During the digestion of starch in foods, starch is mixed with bile in the duodenum. Because fatty acids and some kinds of polyphenols could bind to starch, it was postulated that bile salts might also bind to starch. The purpose of this paper is to study the effects of bile and bile salts on starch/iodine complex formation and pancreatin-induced starch digestion. Bile suppressed starch/iodine complex formation and inhibited pancreatin-induced starch digestion slightly in control buckwheat starch, but did so significantly in buckwheat starch from which fatty acids and polyphenols had been extracted. Such significant suppression and inhibition by bile were also observed in a reagent soluble starch. The effects of cholate and taurocholate on the starch/iodine complex formation and the pancreatin-induced starch digestion were essentially the same as those of bile. Bile, cholate, and taurocholate suppressed amylose/iodine complex formation more significantly than amylopectin/iodine complex formation and inhibited pancreatin-induced amylose digestion more effectively than the digestion of amylopectin. It is concluded from the results that bile salts could bind to starch, especially amylose, the helical structures of which were not occupied by other molecules such as fatty acids and polyphenols, and that the binding resulted in the inhibition of starch digestion by pancreatin. The conclusion suggests that the function of bile salts can be discussed from the point of not only lipid digestion but also starch digestion.     

Effects of salt concentration and cation balance in soils on leaf tipburn and calcium content of strawberry leaves and fruit

Abstract

Strawberry plants cv. Cambridge Favourite were grown in pots of soil in a glasshouse. A relationship was found between the function ^aCa: S^aCations(soil solution) x guttation score, the severity of leaf tipburn and the calcium concentration in the emerging leaf. Slightly less well related but of more practical use was the function ^cCa: S^cCations/electrical conductivity of the soil solution; values below 0.15 mS^‐1 resulted in increased tipburn and reduced calcium concentrations in emerging leaves and in the fruit.     

钠吸附比和盐分浓度对新疆典型砂壤土物理性质的影响

新疆土壤盐碱化问题严重影响农田水盐运移和作物产量。为探究钠吸附比（Sodium Adsorption Ratio,SAR）和盐分浓度对当地典型砂壤土物理性质的影响,该研究测定了4个SAR水平（40,30,20,15,10,5 (mmol/L)1/2）和8个盐分浓度水平（200,150,100,50,20,10,5,2 mmol/L）下土壤团聚体快速湿润过程中的团聚体水稳性;并测定了4个SAR水平（40,30,20,5 (mmol/L)1/2）和3个盐分浓度水平（200,100,20 mmol/L）溶液处理后的土壤水分特征曲线（Soil Water Characteristic Curve,SWCC）,量化了土壤脱水过程中土体压缩量与溶液SAR和盐分浓度的关系。结果表明：1）土壤团聚体水稳性与SAR和盐分浓度均呈显著负相关关系,SAR高于30 (mmol/L)1/2时,土壤团聚体水稳性才会显著下降;2）SAR对新疆典型砂壤土的SWCC有影响,且这种影响与盐分浓度有关;3）盐分浓度和SAR对土壤压缩量的影响存在交互作用。研究结果可为合理选用不同盐分组成和浓度微咸水灌溉以最大程度保护农田土壤结构和土壤水环境提供理论依据。     

盐胁迫下大气CO2浓度升高对黄瓜幼苗生长、光合特性及矿质养分吸收的影响

采用营养液培养和开顶箱法,研究了盐胁迫下CO2浓度升高对黄瓜幼苗生长、光合特性及矿质养分吸收的影响。结果表明,黄瓜生长在80mmol/L NaCl下,其生物量、光合速率、气孔导度、蒸腾速率均显著下降,而胞间CO2浓度明显升高;CO2浓度升高可增加盐胁迫下黄瓜幼苗生物量,使光合速率、气孔导度、蒸腾速率升高。表明CO2浓度升高能减轻盐胁迫对光合功能的不利效应。80mmol/L NaCl可使黄瓜幼苗体内总N和K 的浓度降低,而使Na 浓度增加;CO2浓度升高具有提高盐胁迫下总N和K 浓度,降低Na 浓度的效应,说明CO2浓度升高可减轻盐胁迫的毒害作用,提高黄瓜幼苗生物量。     

棉(Gossypium hirsutum L.)纤维发育相关酶和纤维比强度对棉铃对位叶氮浓度变化的响应研究

于2008～2009年在长江流域下游棉区,选用纤维比强度差异明显的德夏棉1号（平均比强度26.2 cN/tex）、科棉1号（平均比强度35 cN/tex）和美棉33B（平均比强度32 cN/tex）为试验材料,设置不同施氮量以形成不同的棉铃对位叶氮浓度,研究了棉铃对位叶氮浓度对纤维发育过程中关键酶（蔗糖酶、蔗糖合成酶、磷酸蔗糖合成酶、-1, 3-葡聚糖酶）活性及纤维比强度形成的影响。结果表明,棉铃对位叶氮浓度随施氮量的增加而上升,随花后天数的变化符合幂函数方程YN＝t-［YN:棉铃对位叶氮浓度（%）;t:花后天数（d）;、为参数］。在花后同一时期,纤维发育关键酶活性和纤维比强度均随棉铃对位叶氮浓度的上升呈先升后降的趋势,可用抛物线方程Y=ax2+bx+c拟合［Y:酶活性或纤维比强度（cN/tex）;x:叶片氮浓度（%）;a、b、c为参数］。表明在纤维发育过程中,棉铃对位叶氮浓度显著影响纤维中相关酶活性和纤维比强度的形成,各指标所对应的最佳棉铃对位叶氮浓度差异较小;因此,通过调节对位叶氮浓度可调控相关酶活性达到最优以及棉花高强纤维的形成。在本试验条件下,中部棉纤维发育所需的最佳对位叶氮浓度动态变化方程分别为:NDexiamian1=7.2841t-0.2771(R2=0.9860＊＊);NKemian1=7.1807t-0.2989(R2=0.9879＊＊);NNuCOTN33B=7.1467t-0.2819(R2=0.9755＊＊)。     

降雨及隔盐层对滨海盐碱地水盐运动的影响

 为探索不同材料隔盐层对滨海盐碱地水盐运动的影响,在白蜡林地树穴底部布设炉渣和沙子作为隔盐层,比较研究不同深度土壤水分和总盐分的季节性变化规律。结果表明：土壤表层和不同深度处土壤含水量及含盐量变化规律不同,表层主要受降雨和蒸发影响,底层则同时还受地下水位变化的影响;1个雨季中,土壤表层强降雨的淋洗作用极为明显,表层不同隔盐层的差异性不太明显,但离表层30cm处各隔盐层隔盐和抑制返盐的效果非常明显,设置炉渣隔盐层处理的电导率从5月份的591ms/m下降到了10月份的493ms/m,沙子隔盐层处理的电导率从558ms/m下降到501ms/m;离表层60cm处炉渣隔盐层从810ms/m下降到582ms/m,沙子隔盐层从607ms/m下降到560ms/m。从减小电导率的幅度上来看,炉渣的隔盐效果好于沙子。     

Effects of high-pressure processing at low temperature on the molecular structure and surface properties of beta-lactoglobulin

High-pressure processing (HPP) was utilized to induce unfolding of beta-lactoglobulin (beta-LG). beta-Lactoglobulin solutions at concentrations of 0.5 mg/mL, in pH 7.5 phosphate buffer, were pressure treated at 510 MPa for 10 min at either 8 or 24 degrees C. The secondary structure, as determined by circular dichroism (CD), of beta-LG processed at 8 degrees C appeared to be unchanged, whereas beta-LG processed at 24 degrees C lost alpha-helix structure. Tertiary structures for beta-LG, as determined by near-UV CD, intrinsic protein fluorescence spectroscopy, hydrophobic fluorescent probe binding, and thiol group reactivity, were changed following processing at either temperature. The largest changes to tertiary structure were observed for the samples processed at 24 degrees C. Model solutions containing the pressure-treated beta-LG showed significant decreases in surface tension at liquid-air interfaces with values of 54.00 and 51.69 mN/m for the samples treated at 24 and 8 degrees C, respectively. In comparison, the surface tension for model solutions containing the untreated control was 60.60 mN/m. Changes in protein structure during frozen and freeze-dried storage were also monitored, and some renaturation was observed for both storage conditions. Significantly, the sample pressure-treated at 8 degrees C continued to display the lowest surface tension.     

Specificity of disulfide bond formation during thermal aggregation in solutions of beta-lactoglobulin B and kappa-casein A

Heat-induced (90 degrees C, 10 min, pH 6.7) intermolecular disulfide bond formation in 1:1 mixtures of beta-lactoglobulin B (beta-Lg) and kappa-casein A (kappa-CN) was studied by enzymatic digestion with trypsin or glu-C, reverse-phase HPLC, and MALDI-TOF-MS. Observed masses were compared to theoretically calculated masses of disulfide-bonded peptide dimers and trimers, and the number of different masses matching peptide combinations involving each bond was used as a measure of confidence of identification. The beta-Lg cysteine residues 121 or 119 were involved in bonds with both cysteines of kappa-CN and all cysteines of beta-Lg. This agrees with the supposed initiatory role of beta-C121 in heat-induced SH/SS interchange. The largest numbers of matches corresponded to bonds linking beta-C119/C121 with kappa-C11 or with beta-C66. Multiple matches were recorded for beta-C119/C121 bonding with beta-C119/C121, with beta-C160, or with kappa-C88. However, beta-C106 was observed only in bonds with beta-C119/C121 and did not appear to bond to kappa-CN, suggesting it remains buried in the core of the protein.     

Effects of grazing on a salt marsh

Changes in the quantity of plant material in three salt marsh systems: (1) a pristine unaltered marsh, (2) a marsh grazed by ungulates, and (3) a marsh formerly grazed by ungulates, were measured periodically over two years. All three had a mixture of Spartina alterniflora and Salicornia virginica while the latter two also contained Distichlis spicata. The annual production, potential detritus contribution percent dry weight, mineral concentration, plant species composition, and fiddler crab populations were examined for comparative purposes. In addition, the effects of simulated grazing were evaluated at three times of year in a pure stand of S. alterniflora. Finally, an economic assessment and comparison of the three systems was also considered.Living S. alterniflora attained the greatest quantity of standing material in late summer and dead plant material in late winter. Live D. spicata was most plentiful in August and less abundant during February; S. virginica displayed no apparent annual variation in production. Average yearly standing crop increments indicated that the aerial plant production for the ungrazed system (583·4 g/m²/yr) exceeded the production of the formerly grazed marsh (322·3 g/m²/yr). The production of the formerly grazed system exceeded that of the grazed marsh which had an annual production of 221·9 g/m²/yr. Significantly more fiddler crabs were found in the ungrazed area than in the grazed marsh system.     

Effects of foliar spray of two kinds of zinc oxide on the growth and ion concentration of sunflower cultivars under salt stress

This study investigated the effects of foliar application of normal and nano-sized zinc oxide on the response of sunflower cultivars to salinity. Treatments included five cultivars (‘Alstar’, ‘Olsion’, ‘Yourflor’, ‘Hysun36’ and ‘Hysun33’), two salinity levels [0 and 100 mM sodium chloride (NaCl)], and three levels of fertilizer application. Fertilizer treatments were the foliar application of normal and nano-sized zinc oxide (ZnO). Foliar application of ZnO in either forms increased leaf area, shoot dry weight, net carbon dioxide (CO₂) assimilation rate (A), sub-stomatal CO₂ concentration (Ci), chlorophyll content, Fv/Fm, and Zn content and decreased Na content in leaves. The extent of increase in chlorophyll content, Fv/Fm and shoot weight was greater as nano-sized ZnO was applied to the normal form. The results show that the nano-sized particles of ZnO compared to normal form has greater effect on biomass production of sunflower plants.     

盐阳离子类型及浓度对土壤持水及干缩开裂的作用效果

为探索阳性盐离子对土壤持水性能的影响,同时定量分析失水过程所致的土体收缩及裂缝特征,选取陕西粉黏壤土作为供试土壤,分别采用含有K+、Na+、Ca2+和Mg2+4种离子的盐溶液(浓度均为5、30和100 g/L)对土样进行饱和处理,采用离心机法测定土-水曲线,进一步对土壤持水能力进行评价;同时测定土体沉降高度,采用数字图像处理技术获取面积密度和长度密度等裂隙度量指标,对土体收缩和开裂水平进行定量分析。结果发现:1)van Genuchten模型适用于盐溶液浸泡土壤的土-水曲线拟合;2)4种盐离子均基本导致土壤持水能力降低(5 g/L Na+除外),且持水性与离子浓度呈负相关关系;同时使得土壤饱和含水率、残余含水率和进气吸力降低,其中土壤饱和含水率与离子浓度呈负相关关系;3)K+和高浓度Na+有利于减轻土壤轴向收缩度,且土体轴向收缩应变与K+(P0.01)和Na+(P0.05)浓度呈负相关关系;在收缩过程中,不同离子对土壤容重的影响程度表现为Mg2+Ca2+Na+K+;4)4种离子均可减轻土壤开裂程度,且裂缝面积密度和长度密度与K+(P0.01)、Na+(P0.01)和Ca2+(P0.05)浓度呈负相关关系,与Mg2+浓度呈正相关关系(P0.01)。研究可为盐碱土壤持水能力评价、制定灌溉制度提供参考。     

江苏北部滨海盐土盐肥耦合对菊芋生长和产量的影响

在江苏北部滨海盐土进行田间试验,研究了不同盐分含量土壤上盐肥耦合对菊芋生长和产量的影响。结果表明:(1)随着土壤盐分含量的增加,菊芋株高显著下降,菊芋茎粗、块茎产量和地上部生物量随土壤盐分的增加变化趋势与菊芋株高相似。随着氮肥和磷肥施用量增加,菊芋主茎高度显著增加,菊芋茎粗随氮肥施用量增加变化不明显,而块茎产量和地上部生物量随肥料用量增加变化趋势与菊芋株高相似。(2)随着施氮、磷量增加,在各盐分含量土壤上菊芋主茎普遍长高,随着土壤盐分含量的增加,氮和磷效应越明显,菊芋茎粗、块茎产量和地上部生物量在不同土壤盐分含量下,其变化趋势与菊芋主茎高度变化趋势相似。(3)各处理措施均能影响菊芋块茎产量,经方差分析,土壤盐分含量、氮肥施用量、磷肥施用量、盐肥交互作用、氮磷肥交互作用均呈极显著关系,从处理间区别看,影响菊芋块茎产量的主要因素是土壤盐分含量,氮肥和磷肥次之。其中S1N2P3处理所获得的产量最高,此处理土壤盐分含量为0.9～1.5gkg-1,氮肥和磷肥施用量均为60kghm-2。