加工方式对非发酵面团小麦醇溶蛋白致敏性的影响

该研究探究了热加工(水煮、烘烤、微波、高温高压)、冷处理(液氮、速冻机速冻)和非热加工(超高静压、辐照、脉冲强光、臭氧和超声波)处理对非发酵面团小麦醇溶蛋白致敏性的影响。利用SDS-PAGE和双抗体夹心ELISA法研究各种加工处理后非发酵面团小麦醇溶蛋白的分子量和致敏性变化。结果表明:200和300 MPa的超高静压处理后,非发酵面团小麦醇溶蛋白的致敏性显著增加(P0.05),均增至125%左右;水煮、微波、高温高压、烘烤、液氮、速冻机处理、超高静压250MPa、辐照(7、13kGy)、臭氧熏蒸、脉冲强光和超声波处理均能显著降低非发酵面团小麦醇溶蛋白的致敏性(P0.05),其中以水煮、高温高压、液氮、臭氧和脉冲强光(PL-1)处理的脱敏效果最显著(P0.01),均降至60%左右。由此可知,加工方式能够显著影响非发酵面团小麦醇溶蛋白的致敏性,可作为食品中过敏原安全控制的有效手段,为脱敏食品的生产提供有效参考。进一步研究需要结合其他体内试验的评估,特别是小麦易敏人群的临床试验。     

高压均质-冷冻干燥技术制备大豆分离蛋白微粒及其功能特性

为了进一步改善大豆分离蛋白的分散性及功能性质,该研究以大豆分离蛋白为原料,通过对天然大豆分离蛋白进行高压高剪切处理并联合冷冻干燥技术,制备大豆分离蛋白微粒,考察压力(60～100 MPa)对大豆分离蛋白微粒尺寸、功能性质及结构特性的影响,探究其构效关系。结果表明:随着压力逐渐增加,大豆分离蛋白平均粒径大幅度减小,粒径分布曲线向左侧移动,与天然大豆分离蛋白相比,在100 MPa时大豆分离蛋白粒径减小了1 631%,粒径曲线分布较宽。在60～100MPa压力范围内随着压力的增加。与天然大豆分离蛋白相比,大豆分离蛋白微粒的分散性指数(Protein Dispersibility Index, PDI)和功能性质均显著提高(P0.05),其中在100 MPa时大豆蛋白质的溶解性提高了172.98%,乳化活性和乳化稳定性分别增加了约28.71%和77.82%,持油性增加了约123.76%,起泡性随时间的变化其泡沫高度也均有所提高。由扫描电镜图可以观察到,未经过高压均质的大豆分离蛋白粒子呈聚集状态,球状的表面向内凹陷,经过高压均质联合冷冻干燥处理后的大豆分离蛋白微粒呈现网络结构。在高压和高剪切力的作用下,大豆分离蛋白微粒的疏水基团大量暴露,表面疏水性随之增加,静电斥力增加,α-螺旋和β-转角向β-折叠和无规则卷曲结构的转化是蛋白质的溶解性等功能性质提高的主要原因。溶解性等功能性质的提高有利于大豆分离蛋白更好的应用于食品加工行业,进一步为蛋白的理化性质及结构优化提供新思路。     

高压微射流压力对大豆蛋白-大豆多糖体系功能性质的影响

为提升大豆分离蛋白（soy protein isolate,SPI）的功能性质,该文引入大豆可溶性多糖（soybean soluble polysaccharides,SSPS）,构建大豆分离蛋白-大豆可溶性多糖体系（SPI-SSPS）,研究动态高压微射流（dynamic high-pressure microfluidization,DHPM）处理对SPI-SSPS功能特性的影响。分别采用0,60,100,140和180 MPa的 DHPM压力处理SPI-SSPS,探究不同压力对SPI-SSPS起泡特性、乳化特性、溶解性、粒度分布和表面疏水性的影响。结果表明,DHPM处理能提高SPI的溶解性和起泡特性,且SSPS的存在能显著提高DHPM对SPI功能性质的改善效果（P<0.05）。100和60 MPa的DHPM处理能使SPI-SSPS呈现较高的起泡能力和起泡稳定性,分别为未处理样品的1.2和2.4倍。140 MPa的DHPM处理使SPI-SSPS溶解性较强,为未处理样品的1.8倍。然而,DHPM处理会显著降低SPI-SSPS的乳化特性、粒径和表面疏水性（P<0.05）。随着处理压力的增加,SPI-SSPS的粒度和表面疏水性逐渐降低,在180MPa的DHPM处理下SPI-SSPS具有较小的粒径和较低的荧光强度。综上所述,DHPM结合SSPS改性技术可用于改善SPI的功能性质（如溶解性、起泡性）,促进SPI在食品工业的应用。该文的研究结果可为SPI的功能性质改性提供参考。     

葡聚糖分子量对玉米醇溶蛋白接枝物结构和乳化性的影

为了探究葡聚糖接枝作用对玉米醇溶蛋白结构和乳化性的影响,明确蛋白质结构与功能性的关系,本研究以玉米醇溶蛋白(Zein)和不同分子量(6、20、40和70 k Da)葡聚糖(dextran,DX)为原料,采用湿热法制备Zein-DX接枝物,并对接枝物的结构和乳化性进行研究。结果表明,低分子量(6 k Da)DX具有更高的反应活性,赖氨酸和精氨酸是参与Zein与DX接枝反应的主要氨基酸。傅里叶红外光谱(fourier transform infrared,FTIR)证明了DX以共价键与Zein形成了复合物。DX的共价接枝能够导致Zein荧光猝灭的发生,降低Zein的热稳定性,改善Zein的乳化活性(emulsifying activity index,EAI)和乳化稳定性(emulsifying stability index,ESI)。低分子量(6 k Da)DX与Zein形成的接枝物最大发射波长发生显著红移,三级结构变的松散,具有更低的热稳定性,且EAI最高达到(23.28±0.71)m2/g。然而,高分子量(70 k Da)DX与Zein形成的接枝物ESI高达(26.44±0.47)min,高于其他Zein-DX接枝物样品。乳状液粒径和流变性分析表明,随着DX分子量的增加,乳状液粒径降低,黏度增加,这与ESI的研究结果相符。研究结果可为改善玉米蛋白功能性和深入了解玉米蛋白改性机制提供理论依据。     

~(60)Co-γ辐照对花生过敏原Ara h 2蛋白构象及致敏活性的影响

为探讨辐照处理对花生Ara h 2蛋白结构与致敏活性的影响,采用不同剂量~(60)Co-γ辐照处理分离纯化所得到的花生过敏原Ara h 2蛋白,结合紫外扫描光谱、圆二色谱(CD)和聚丙烯酰胺凝胶电泳(SDS-PAGE)评估辐照处理后Ara h 2蛋白的结构变化,并用免疫印迹法和间接酶联免疫吸附法检测辐照处理后Ara h 2的抗原性变化。结果表明,~(60)Co-γ辐照处理可以显著改变花生Ara h 2蛋白的构象,使其降解、发生交联。随着辐照剂量的增大,Ara h 2蛋白与抗体的结合能力呈逐渐下降趋势,且与蛋白紫外吸光度的增强和α-螺旋含量的降低呈现良好的相关性。当辐照剂量为10 kGy时,可基本破坏Ara h 2蛋白的结构和免疫活性。~(60)Co-γ辐照处理可以有效降低花生过敏原Ara h 2蛋白的致敏性,这为花生脱敏技术的研究提供了新思路。     

限制性酶解改性鲢鱼肌原纤维蛋白功能性质的研究

为了提高肌原纤维蛋白的功能,采用不同酶(胰蛋白酶、中性蛋白酶及复合酶)对鲢鱼肌原纤维蛋白进行限制性酶解改性,在酶解过程中,通过对水解度、蛋白分子量大小、肌原纤维形态学变化及功能性质进行测定与观察,探究其功能性质随改性程度的动态变化规律。结果表明,随着酶解的进行,鲢鱼肌原纤维长度逐渐变短,蛋白的溶解性逐渐增加,酶解80 min时,肌原纤维主要以1~3个肌节形式存在,3组蛋白质的溶解性分别达到61.2%、36.9%和58.4%;3组酶解蛋白的乳化性和起泡性随反应时间的增加均呈先增后减的趋势,其中复合蛋白酶酶解40 min时乳化活性及起泡性最大,分别达到65.5m2·g-1和110%,胰蛋白酶改性20min时蛋白乳化稳定性最好,可达46.6 min,远大于未酶解蛋白的14.7 min。分子量分布及SDS-PAGE图谱显示,蛋白平均分子量均为20~30 k Da,水解度均低于5%。综上,酶的选择对溶解性的改善至关重要,而乳化性及起泡性的改善不仅需要对酶进行筛选,还需对水解度进行严格限制,保持酶解后蛋白具有较大的分子量,避免酶解过度。本研究结果为蛋白质乳化性和起泡性的改性研究提供了参考。     

高静压与к-卡拉胶对低脂猪肉凝胶保水和质构的影响

高静压处理与添加水溶性多糖是改善肉制品质构、保水性等品质的重要手段。本研究侧重调查100～300 MPa压力、0～1.0% к-卡拉胶添加水平对猪肉糜凝胶保水、质构的影响。试验结果表明，添加0.5%的к-卡拉胶可显著降低猪肉凝胶的蒸煮损失，提高总持水性及凝胶硬度(P＜0.05)；200 MPa以上的高静压不仅可以显著降低肉糜的蒸煮损失，而且也能够显著提高凝胶的硬度、黏结性与咀嚼性(P＜0.05)；但100～300 MPa的高静压对1.0%卡拉胶水平的凝胶弹性影响不明显(P＞0.05)。此外，对于肉制品保水性的评价，应注意选择合适的评价方法，尤其是蒸煮损失差异较大的肉制品样本，评价方法选择的合理性将直接影响评价的结果。     

超高压处理对低盐牛肉乳化肠品质的影响

为探究超高压(UHP)处理对低盐牛肉乳化肠品质的影响,本试验以低盐牛肉乳化香肠(食盐添加量1.4%)为研究对象,以未经UHP处理的C1组(食盐添加量2.8%)和C2组(食盐添加量1.4%)为对照,比较了不同压力(100、200、300、400 MPa)对低盐牛肉乳化肠感官品质、理化指标和微生物指标的影响。结果表明,UHP处理降低了处理组乳化肠的菌落总数(TVC)和挥发性盐基氮(TVB-N)值,当压力≥200 MPa时,乳化肠的TVC和TVB-N值均显著低于C1和C2组(P<0.05);随着压力的增大,蒸煮损失先减小后增大,100和200 MPa处理组乳化肠蒸煮损失最低,分别为3.00%和3.97%,且均显著低于C2组(P<0.05);与C2组相比,UHP处理使低盐乳化肠的硬度、弹性、咀嚼性、内聚性都有所增加,并提高了产品的咸味分数,对多汁性、总体风味及总体可接受性具有改善作用;UHP处理促进了脂质氧化,当压力为300 MPa时,硫代巴比妥酸反应产物(TBARS)值最高;亚硝酸盐含量不受UHP处理的影响,且符合肉制品亚硝酸盐残留量要求。综上,UHP处理能够改善低盐牛肉乳化香肠的品质特性,这为低盐肉制品的开发提供了技术支持和理论依据。     

超高压下酶解处理对甘薯蛋白乳化特性的影响

为研究在超高压下酶解处理后甘薯蛋白酶解产物乳化特性的变化,选用蛋白酶K(Proreinase.K)、碱性蛋白酶(Alcalase)、中性蛋白酶AS1.398、中性蛋白酶Neutrase和木瓜蛋白酶(Papain)5种酶,在4种压力(100、200、300和400 MPa)及最适酶活温度和pH下处理5种酶与甘薯蛋白的混合液4min后,取上清液并测定其水解度、乳化液的微观结构、乳化活性指数(EAI)、乳化稳定性指数(ESI)。结果表明,与常压下相比,超高压下5种酶解产物的水解度均显著增加,超乳化液颗粒除Alcalse外,其余4种均变得更为细小均一,且4种产物的EAI显著提高,其中Papain在300MPa下处理的酶解产物EAI最佳,为101.59m~2·g~(-1)。而经超高压下酶解处理后5种酶解产物的ESI均比常压下提高,Neutrase在300MPa下处理后的ESI最好,达到75.80min。此外,选用Papain(p H值7,55℃)在300MPa(EAI最佳的条件)下处理6min,酶解产物的EAI和ESI均达到最大值,分别为129.58m2·g-1和21.98min。本研究为甘薯蛋白作为乳化剂在食品工业中的应用提供了基础理论支撑。     

挤压温度对大豆分离蛋白与原花青素复合物结构和功能特性的影响

为了探究不同挤压温度（40、60、80、100和120℃）对大豆分离蛋白（Soy Isolate Protein,SPI）与葡萄籽原花青素（Grape Seed Proanthocyanidin Extract,GSPE）复合物功能性质及结构特性的影响。该研究以溶解度、乳化性、乳化稳定性、ζ-电位、粒度为指标,利用荧光光谱、红外光谱分析该复合体系中大豆分离蛋白功能性质及结构的变化。结果表明：相较于挤压SPI,经过挤压处理的SPI-GSPE复合物的溶解度、乳化活性指数、乳化稳定性指数、ζ-电位绝对值及持水性均显著提高（P<0.05）,其表面疏水性、持油性显著下降（P<0.05）。随着挤压温度的升高,SPI-GSPE复合物的溶解度、持油性及乳化活性均先增大后减小且在80℃达到最大值,而其表面疏水性先减小后增大且最小值在80℃,ζ-电位绝对值、乳化稳定性及持水性均随温度的升高而降低。粒径分析结果表明,挤压处理后SPI与GSPE形成了更加致密的复合物;荧光光谱及红外光谱结果表明,与GSPE的复合及挤压处理使SPI氨基酸残基所处微环境发生变化,蛋白结构发生变化。以上结果表明挤压温度为...     

Effects of high hydrostatic pressure on some functional and nutritional properties of soy protein isolate for infant formula

The effects and mechanism of high hydrostatic pressure (HHP) on some functional and nutritional properties of soy protein isolate (SPI) for infant formula were investigated. Results indicated that solubility, water holding capacity, emulsification activity index, and foaming capacity were improved at lower pressure and time levels, whereas these properties declined at higher levels. However, the emulsification stability index dropped when the pressure increased and the foaming stability decreased with pressure and time levels rising. HHP-treated SPI gave better swallowing properties and in vitro digestibility than control. The hardness, adhesive force, and springiness of SPI gels increased with increaded pressure and elongated time, being lower than those of the control. Near UV circular dichroism spectra confirmed the alteration of tertiary and/or quaternary conformations caused by HHP. Sodiumdoecyl sulfate polyacrylamide gel electrophoresis results indicated that β-conglycinin was more pressure labile than glycinin, and high molecular weight subunits formed via disulfide linkage at higher treatment levels.     

Thermal Behavior of Whey Protein Concentrate Treated by Heat and High Hydrostatic Pressure and Its Functionality in Wheat Dough

Solutions of commercial whey protein concentrate (CWPC, 82% protein) at 5, 10, 20, and 30% were treated with heat at 90°C or with high hydrostatic pressure (HHP) at 85 Kpsi (Kpsi = 6.9 MPa) for 30 min. A CWPC solution at 20% also was treated for 30 min with heat at 60, 70, 80, and 90°C and HHP at 20, 40, 60, and 85 Kpsi. Differential scanning calorimetry (DSC) thermograms of untreated CWPC (82% protein) showed two endothermic peaks: the first had an enthalpy value of 4.72 J/g between 57 and 86°C, and the second had an enthalpy value of 2.36 J/g between 120 and 143°C. The first enthalpy peak disappeared after heat treatment at 90°C for 30 min and HHP treatment at 85 Kpsi for 30 min, whereas the second peak remained, independent of concentration. The results indicate that HHP treatment caused changes in the protein of CWPC, and the changes were comparable to those caused by high-temperature treatment. Differential scanning calorimetric analysis of CWPC, heat treated at 60°C, showed an enthalpy value for the first peak of 3.34 J/g, ≈1.41 J/g lower than for untreated CWPC. A sharp decrease in enthalpy to 0.52 J/g for the first peak was observed at 70°C, with complete disappearance at 80°C. The second enthalpy peak was present at all temperatures studied, with significantly higher enthalpy values at 90°C than at lower temperatures. DSC value for the first enthalpy peak for CWPC decreased significantly as HHP treatment level increased from 20 to 85 Kpsi. CWPC treated with HHP at 20 Kpsi had an enthalpy value for the first peak that was ≈2 J/g higher than for the untreated sample. It can be postulated that low HHP treatment of 20% of CWPC solution for 30 min promotes the formation of covalent or noncovalent cross-links and strong protein-protein interactions, hence the higher enthalpy values. Scanning electron micrographs showed that spray-dried, untreated CWPC was a globular form, whereas heat- and HHP-treated CWPC was a solid glasslike, porous or spongy form. Incorporation of 10% untreated CWPC into wheat flours decreased mixograph water absorption, extended mixing time, and caused rapid breakdown of gluten after optimum dough development. Incorporation of 10% heat- or HHP-treated CWPC significantly increased mixograph water absorption and extended mixing time compared to the control but decreased mixing time compared to dough fortified by untreated CWPC. Mixing tolerance of dough was restored by both heat- and HHP-treated CWPC.     

Protein Digestibility of Selected Legumes Treated with Ultrasound and High Hydrostatic Pressure During Soaking

In vitro protein digestibility (IVPD) of lentils, chickpeas, peas, and soybeans treated with ultrasound or high hydrostatic pressure (HHP) during soaking and then heated for 30 min at 98°C was determined using the three-enzyme method (trypsin, chymotrypsin, and peptidase). The IVPD of raw legumes ranged from 72% for soybeans to 83% for dry green peas. The increase in the IVPD after soaking was observed in lentils but not in other legumes. Heating increased the IVPD of the tested legumes by 2–13%. While the effects of applying ultrasound or HHP on IVPD of legumes were mostly inconsistent or insignificant, soaking under HHP for 1 hr and subsequent heating at 98°C for 30 min increased IVPD of legumes. Compared with raw legumes, the soluble protein concentrates exhibited 2–4% higher IVPD, while insoluble proteins exhibited 0.2–1.5% lower IVPD. SDS-PAGE of legume proteins before enzyme digestion exhibited 8–18 protein bands from 20 kDa to 100 kDa representing isolated soluble proteins and from 20 kDa to 100 kDa representing insoluble proteins. After enzyme digestion, soluble proteins exhibited 2–6 minor protein bands with molecular weights <30 kDa, while insoluble proteins of lentils, chickpeas, and peas exhibited one major protein band at ≈52 kDa and two or three minor protein bands with molecular weights <30 kDa. The major insoluble proteins observed as electrophoresis bands after enzyme digestion may be responsible for the reduced protein digestibility of legume proteins.     

Structural rearrangement of ethanol-denatured soy proteins by high hydrostatic pressure treatment

The effects of high hydrostatic pressure (HHP) treatment (100-500 MPa) on solubility and structural properties of ethanol (EtOH)-denatured soy β-conglycinin and glycinin were investigated using differential scanning calorimetry, Fourier transform infrared and ultraviolet spectroscopy. HHP treatment above 200 MPa, especially at neutral and alkaline pH as well as low ionic strength, significantly improved the solubility of denatured soy proteins. Structural rearrangements of denatured β-conglycinin subjected to high pressure were confirmed, as evidenced by the increase in enthalpy value (ΔH) and the formation of the ordered supramolecular structure with stronger intramolecular hydrogen bond. HHP treatment (200-400 MPa) caused an increase in surface hydrophobicity (F(max)) of β-conglycinin, partially attributable to the exposure of the Tyr and Phe residues, whereas higher pressure (500 MPa) induced the decrease in F(max) due to hydrophobic rearrangements. The Trp residues in β-conglycinin gradually transferred into a hydrophobic environment, which might further support the finding of structural rearrangements. In contrast, increasing pressure induced the progressive unfolding of denatured glycinin, accompanied by the movement of the Tyr and Phe residues to the molecular surface of protein. These results suggested that EtOH-denatured β-conglycinin and glycinin were involved in different pathways of structural changes during HHP treatment.     

Effect of ultrahigh hydrostatic pressure on the activity and structure of mushroom (Agaricus bisporus) polyphenoloxidase

High hydrostatic pressure (HHP, treatment pressure ≤700 MPa) is approved to be the most successful commercial nonthermal processing due to its minimal modifications in nutritional and sensory quality. However, for some pressure stable enzymes such as PPO, this unique technology can hardly inactivate them at treatment pressure below of 700 MPa. This study investigated the effects of ultrahigh hydrostatic pressure (UHHP, treatment pressure >700 MPa) on the activity of Agaricus bisporus mushroom polyphenoloxidase (PPO) both in the phosphate buffer and in the mushroom puree, and on the structure of the enzyme by means of circular dichroism (CD), fluorescence emission spectra, and sulphydryl group detection. The results showed that UHHP treatment at pressure from 800 to 1600 MPa caused significant inactivation on the PPO both in the phosphate buffer and in the mushroom puree. UHHP treatment at 1400 and 1600 MPa for 1 min reduced the enzyme activity by 90.4% and 99.2% in the buffer;, however, higher enzyme activity remained in the puree after UHHP treatment at the same condition. CD and fluorescence spectra analysis showed that the secondary and tertiary structures of UHHP treated mushroom PPO were changed. The sulphydryl group (SH) detection revealed that the SH content on the surface of UHHP treated mushroom PPO was increased. It has been suggested that the inactivation of mushroom PPO by UHHP treatment at pressure higher than 1000 MPa was due to the synergistic effect of the pressure and the heat arising from pressurization, in which heat plays a major role.     

Hydrophobic probe binding of beta-lactoglobulin in the native and molten globule state induced by high pressure as affected by pH,KIO(3) and N-ethylmaleimide

High hydrostatic pressure (HHP) at 500 MPa and 50 degrees C induces beta-LG into the molten globule state. Retinol, cis-parinaric acid (CPA), and 1-anilino-naphthalene-8-sulfonate (ANS) fluorescence from pH 2.5 to 10.5 in the presence of the native and molten globule states of beta-LG indicate that retinol binds to beta-LG in the calyx, CPA at the surface hydrophobic site, and ANS in multiple hydrophobic sites. HHP treatment results in a decrease of beta-LG affinity for retinol and CPA, suggesting conformational changes in the calyx and surface hydrophobic site of beta-LG during HHP treatment. beta-LG treated by HHP in the presence of N-ethylmaleimide (NEM) retains retinol affinity, suggesting that NEM protects the calyx conformation of beta-LG during HHP treatment. HHP treatment of beta-LG in the presence of KIO(3) exhibits a great decrease of CPA affinity compared to HHP-treated beta-LG in the absence of KIO(3), suggesting the formation of non-native disulfide bonding at the CPA binding site.     

超高压处理对绵羊肉嫩化机理的研究

实验研究了超高压处理条件下绵羊肌肉感官特性、显微结构、钙激活酶(Calpains)粗酶活性和剪切力值的变化，并探讨了超高压处理对绵羊肌肉的嫩化机理。超高压处理后绵羊肌肉的感官特性发生变化，随处理压力升高，绵羊肌肉颜色变淡，出现轻微的类似蒸煮的成熟风味。在压力为400 MPa，保压时间为10 min的处理条件下，绵羊肌肉显微组织结构变化明显：肌节收缩，肌原纤维的Z线断裂，M线降解，I带变白。当压力水平在100～400 MPa范围变动时，随压力升高，Calpains粗酶活性显著下降(P＜0.01)；当压力达到400 MPa时，Calpains粗酶活性几乎失活。超高压处理后绵羊肉的剪切力值显著下降(P＜0.05)。实验结果表明，超高压处理促进了绵羊肉的嫩化。     

Beta-lactoglobulin molten globule induced by high pressure.

Beta-lactoglobulin (beta-LG) was treated with high hydrostatic pressure (HHP) at 600 MPa and 50 degrees C for selected times as long as 64 min. The intrinsic tryptophan fluorescence of beta-LG indicated that HHP treatment conditions induced a conformational change. HHP treatment conditions also promote a 3-fold increase in the extrinsic fluorescence of 1-anilinonaphthalene-8-sulfonate and a 2.6-fold decrease for cis-paraneric acid, suggesting an increase in accessible aromatic hydrophobicity and a decrease in aliphatic hydrophobicity. Far-ultraviolet circular dichroism (CD) spectra reveal that the secondary structure of beta-LG converts from native beta-sheets to non-native alpha-helices following HHP treatment, whereas near-ultraviolet CD spectra reveal that the native tertiary structure of beta-LG essentially disappears. Urea titrations reveal that native beta-LG unfolds cooperatively, but the pressure-treated molecule unfolds noncooperatively. The noncooperative state is stable for 3 months at 5 degrees C. The nonaccessible free thiol group of cysteine121 in native beta-LG became reactive to Ellman's reagent after adequate HHP treatment. Gel electrophoresis with and without beta-mercaptoethanol provided evidence that the exposed thiol group was lost concomitant with the formation of S-S-linked beta-LG dimers. Overall, these results suggest that HHP treatments induce beta-LG into hydrophobic molten globule structures that remain stable for at least 3 months.     

Whey Protein Concentrate Treated with Heat or High Hydrostatic Pressure in Wheat-Based Products

Commercial whey protein concentrate (CWPC) treated with heat or with high hydrostatic pressure (HHP) was incorporated by replacement into wheat flour, and its effects on dough rheology and the quality of cookies, noodles, and bread were evaluated. Wheat flour fortified with heat- or HHP-treated CWPC produced smaller cookies than those fortified with untreated CWPC. Increasing the fortification level of heat- or HHP-treated CWPC from 5 to 10% further decreased cookie diameter. The water absorption for noodle dough decreased by 5% with 10% fortification of untreated CWPC. Both heat- and HHP-treated CWPC increased water absorption from 33% in the control to 35.8%. Incorporation of untreated CWPC decreased the lightness (L*) value of Cantonese noodle dough, while dough fortified with heat- or HHP-treated CWPC had higher L* values compared to those of the control. Yellowness (b*) was improved with incorporation of both untreated and treated CWPC. Cooking loss of Cantonese noodles fortified with untreated or heat- or HHP-treated CWPC was comparable to or lower than that of the control. Incorporation of untreated CWPC increased hardness and cohesiveness of Cantonese noodles. Noodles fortified with heat- or HHP-treated CWPC had similar hardness and were softer than the control and the noodles fortified with untreated CWPC. Wheat flour fortified with 10% untreated CWPC produced wet and sticky bread dough and a small loaf (730 mL). Handling properties of dough were improved and bread volume was increased by 50 mL when heat- or HHP-treated CWPC was incorporated. Incorporation of 10% CWPC increased protein content of bread up to 20.2% and also increased the proportion of essential amino acids.     

Purification and thermal and high-pressure inactivation of pectinmethylesterase isoenzymes from tomatoes (Lycopersicon esculentum): a novel pressure labile isoenzyme

Tomato pectinmethylesterase (PME) was successfully purified by a two-step method consisting of affinity chromatography followed by cation exchange chromatography. According to this procedure, four different isoenzymes were identified representing molar masses around 34.5-35.0 kDa. Thermal and high-pressure inactivation kinetics of the two major isoenzymes of tomato PME were studied. A striking difference between their process stability was found. The thermostable isoenzyme was completely inactivated after 5.0 min at 70 degrees C, whereas for the thermolabile isoenzyme, temperatures at around 60 degrees C were sufficient for complete inactivation. The thermostable isoenzyme was also found to be pressure stable since no inactivation was observed after 5.0 min of treatment at 800 MPa and 20 or 40 degrees C. The thermolabile isoenzyme appeared to be pressure labile since it could be completely inactivated after 5.0 min of treatment at 700 MPa and 20 degrees C or 650 MPa and 40 degrees C. Inactivation kinetics at pH 6.0 could be accurately described by a first-order model.