Factors Influencing the Occurrence of Methanethiol in Aqueous Slurries of Soy Protein Concentrates

: Aqueous slurries of 6 commercial soy protein concentrate (SPC) contained from 9.8 to 21.7 ppb methanethiol, which corresponds to odor values (in water) of 49 to 108. Effects of temperature (5.5, 24, and 65°C), pH (4.8,6.6, and 9.0), transition metals (FeCl₃, FeCl₂, and CuCl₂), lipoxygenase, and EDTA on methanethiol levels in SPC slurries were investigated. Higher temperature (65°C), basic pH (9.0), transition metals, lipoxygenase, and EDTA caused significant increases in methanethiol compared with the control. CuCl₂ caused greater increases in methanethiol than FeCl₃ and FeCl₂. In contrast, treatments with lower temperature (5.5°C) or acidic pH (4.8) resulted in lower levels of methanethiol in all commercial SPC samples examined.     

Headspace Evaluation of Methanethiol and Dimethyl Trisulfide in Aqueous Solutions of Soy-protein Isolates

Volatile compounds from 2 samples of aqueous soy‐protein isolates (SPI) (7%) were analyzed using both static and dynamic headspace methods. Based on dynamic headspace analyses, the most powerful odorants were (1) dimethyl trisulfide, (2) methanethiol, (3) hexanal, (4) an unidentified charred, sweaty feet‐like odor, (5) 2‐pentyl furan, (6) 2,3‐butadione, and (7) an unknown burnt‐like odor. The most powerful odorants by static headspace analyses were (1) dimethyl trisulfide, (2) hexanal, (3) methanethiol, and (4) 2‐pentyl furan. Using deuterium labeled DMTS as an internal standard, DMTS was quantified at 60.1 and 45.5 ppb in the SPIs. This corresponds to odor values of 6014 and 4554, respectively. Using a cool, on‐column technique, direct injection of concentrated‐headspace volatiles and solvent‐recovered volatiles with an internal standard of d₆‐DMTS detected both methanethiol and DMTS at similar levels as with the traditional injection methods.     

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%.     

Compounds Contributing to the Odor of Aqueous Slurries of Soy Protein Concentrate

ABSTRACT: Gas chromatography olfactometry/mass spectrometry (GCO/MS) studies on static and concentrated headspace of the aqueous slurries from soy protein concentrate (SPC) revealed acetaldehyde, methanethiol, hexanal, dimethyl trisulfide (DMTS), and 2-pentyl furan as the most odorous volatiles. Further aroma extract dilution analysis (AEDA) of the volatile extracts identified the following as the odorous substances: hexanal, 2-heptanone, octanal, 2-octanone, 1-octen-3-one, DMTS, 3-octen-2-one, 2-decanone, benzaldehyde, 2-pentyl pyridine and trans, trans -2,4- nonadienal, along with several unidentified odorants. Methanethiol and acetaldehyde, which have low boiling points, were not detected by AEDA, however. This is the first time that acetaldehyde, methanethiol, and dimethyl trisulfide have been identified as primary odorants in SPC.     

大豆分离蛋白的凝胶稳定性的研究进展

大豆分离蛋白因其蛋白质含量高,具有凝胶性等多种功能特性,在食品工业中得到广泛应用。但大豆分离蛋白在贮藏过程中,其凝胶的稳定性往往下降,严重地影响了产品的质量。国内外研究发现,在贮藏过程中蛋白组成成分、蛋白浓度、温度、pH 值和离子强度等的变化对凝胶形成具有一定影响,通过各种改性方法可以提高大豆蛋白的凝胶稳定性。     

大豆蛋白11S组分的分离方法研究

采用Nagano法结合电泳图谱ImageMaster 1 D Elite V4.00软件分析法,对大豆分离蛋白的11S组分进行了分离效果研究。确定最佳工艺参数组合为:酸沉pH值6.4、Ca2 浓度40mmol/L和冰浴时间5h。制得的样品中11S组分含量可以达到81.9%。     

大豆分离蛋白对面包品质影响的研究

通过面包的焙烤试验和质地分析,研究了添加大豆分离蛋白对面包品质的影响。结果表明:在本试验条件下,添加2%的大豆分离蛋白既能提高面包的营养价值,又能提高面包的保水能力,延长面包的货架期,改善面包的质地结构。     

HPLC检测火腿肠中大豆分离蛋白的方法研究

利用高效液相色谱(HPLC)法测定火腿肠中大豆分离蛋白的含量。色谱条件为:Xb ridgeBEH300 C4色谱柱;蒸发光散射检测器;梯度洗脱;流动相A:0.05%三氟乙酸-HPLC级水溶液,B:0.05%三氟乙酸四氢呋喃溶液;流速1.0 mL/min;检测波长254 nm;柱温30℃;进样量20μL。大豆分离蛋白在1%～9%含量范围内与特征峰面积呈良好的线性关系,回归方程为Y=2 923.1 X-970.85,相关系数R=0.994 2,平均回收率为99.30%,RSD为2.04%。HPLC法准确度、精密度、稳定性、重现性良好,为火腿肠中大豆分离蛋白的定量检测提供了可选择的方法。     

Interactions between Whey Protein Isolate and Soy Protein Fractions at Oil–Water Interfaces: Effects of Heat and Concentration of Protein in the Aqueous Phase

ABSTRACT:  The 2 main storage proteins of soy—glycinin (11S) and β-conglycinin (7S)—exhibit unique behaviors during processing, such as gelling, emulsifying, or foaming. The objective of this work was to observe the interactions between soy protein isolates enriched in 7S or 11S and whey protein isolate (WPI) in oil–water emulsion systems. Soy oil emulsion droplets were stabilized by either soy proteins (7S or 11S rich fractions) or whey proteins, and then whey proteins or soy proteins were added to the aqueous phase. Although the emulsifying behavior of these proteins has been studied separately, the effect of the presence of mixed protein systems at interfaces on the bulk properties of the emulsions has yet to be characterized. The particle size distribution and viscosity of the emulsions were measured before and after heating at 80 and 90 °C for 10 min. In addition, SDS-PAGE electrophoresis was carried out to determine if protein adsorption or exchanges at the interface occurred after heating. When WPI was added to soy protein emulsions, gelling occurred with heat treatment at WPI concentrations >2.5%. In addition, whey proteins were found adsorbed at the oil–water interface together with 7S or 11S proteins. When 7S or 11S fractions were added to WPI-stabilized emulsions, no gelation occurred at concentrations up to 2.5% soy protein. In this case also, 7S or 11S formed complexes at the interface with whey proteins during heating.     

大豆分离蛋白对羊肉保鲜效果影响研究

以新鲜羊肉为原料,采用涂膜保鲜法分别研究了大豆分离蛋白、食盐对羊肉保鲜效果的影响。以羊肉的感官指标、pH、挥发性盐基氮值和菌落总数为判断标准,探讨了两种保鲜剂对羊肉保鲜效果的影响。结果表明,大豆分离蛋白膜溶液的浓度在5%时,在4℃条件下可以保鲜20 d,肉的品质和感官指标较好。其保鲜效果优于食盐且安全性高。     

大豆分离蛋白的特性及在微胶囊领域的应用进展

由于乳化、成膜、吸脂、保水和抗氧化等理化功能显著,大豆分离蛋白作为微胶囊壁材的应用潜力巨大。已有的研究表明其在提升生物活性物质的氧化稳定性方面发挥了显著的作用。本文综述了大豆分离蛋白微胶囊的常见制备方法和研究进展,并其发展前景进行了展望。     

凝固剂对热改性SPI与猪肌肉盐溶蛋白共凝胶作用的影响

本文研究通过单因素实验和正交实验研究凝固剂葡萄糖酸-δ内酯(GDL)、CaCl2、MgCl2和复合凝固剂对改性大豆分离蛋白(SPI)与猪盐溶蛋白(SSPP)共凝胶的影响。结果表明,GDL对蛋白质共凝胶具有破坏作用,而CaCl2、MgCl2对共凝胶均有促进作用。蛋白质混合凝胶形成的最佳条件为:加热时间20min、CaCl2与MgCl2分别为0.3%、温度95℃、m(SSPP):m(SPI)=7:3。     

谷氨酰胺转氨酶对大豆蛋白游离伯胺含量的影响

利用了在硫基乙醇作用下,邻苯二甲醛(OPA)试剂与伯胺可以发生荧光反应,使用荧光分光光度计快速检测溶液中游离伯胺含量。应用此方法研究了加酶量、反应温度、反应时间、及反应pH对谷氨酰胺转氨酶(TGase)作用于大豆分离蛋白后对其游离伯胺含量的影响,并对主要影响因素利用响应面发进行优化,找出TGase反应条件的最佳组合。实验结果表明:加酶量20 U/g,反应温度为52℃,反应时间60 min,反应pH 7为TGase最佳反应条件,改性后每克大豆分离蛋白伯胺含量由0.059μmol减少为0.028μmol。     

大豆分离蛋白凝胶制备和凝胶质构特性研究

本研究以大豆分离蛋白为原料，考察蛋白质浓度、pH值、加热温度、加热时间对凝胶形成的影响，采用物性仪对不同务件下制备的凝胶的质构特性进行研究，不同评价指标得出的结论不尽相同。通过正交实验得出形成凝胶硬度最大的制备条件为：蛋白浓度12％，pH值6．5，加热温度95℃，加热时间35min；形成凝胶脆性最大的制备凝胶争件为：蛋白浓度12％，pH值7．0，加热温度95℃，加热时间25min；形成凝胶弹性最好的制备凝胶务件为：蛋白浓度12％，pH值7．0，加热温度85℃，加热时间35min；形成凝胶粘附性最大的制备凝胶条件为：蛋白浓度12％，pH值7．0，加热温度95℃，加热时间35min。     

等电点附近大豆分离蛋白乳化稳定性的研究

等电点附近的大豆蛋白由于所带电荷减少、疏水相互作用增强而以聚集体的形式存在且其溶解性较差,故鲜有研究者关注该条件下大豆蛋白的乳化特性。本研究从颗粒稳定乳液的角度出发,分别以等电点附近(p H 5.0)和远离等电点(p H 7.0)两个条件制备了大豆分离蛋白(soy protein isolate,SPI)稳定的乳液,比较了两种条件下SPI的界面性质及所得乳液的储藏稳定性。结果发现,p H 5.0时SPI的溶解度仅为4.70±0.15%,远远低于p H 7.0时的93.28±1.89%;然而SPI浓度为0.50%时,p H 5.0的界面压却高于p H 7.0;以p H 5.0条件制备的SPI乳液,其界面蛋白吸附量高达87.03±1.28%,而p H 7.0制备的乳液仅为36.15±1.48%;p H 5.0的乳液两个月后液滴的平均粒径为63.15±0.30μm,与新鲜制备乳液(62.36±0.41μm)相比基本不变;p H 7.0的乳液经过两个月储藏后其液滴平均粒径从45.78±0.38μm增加至55.19±1.86μm。可见,以等电点附近条件制备的SPI乳液依然具有良好的储藏稳定性。     

大豆分离蛋白O/W型乳液膜的制备及其性质研究

摘要：为提高大豆分离蛋白膜的性质,制备以大豆分离蛋白（SPI）为原料的O/W乳液膜,采取单因素实验法比较O/W乳液膜与SPI膜的差异性,探究不同SPI质量浓度（20、30、40、50和60 mg/mL）对O/W乳液膜性能及结构的影响。结果表明：O/W乳液膜的遮光性、机械性能、耐水性及热稳定性要优于SPI膜。随着SPI质量浓度的增加,O/W乳液膜的拉伸强度随之增加,断裂伸长率降低。蛋白质量浓度为60 mg/mL时,O/W乳液膜的抗拉强度达到最大值为7.19 MPa,比蛋白膜的抗拉强度高出33%。利用扫描电子显微镜（SEM）、傅里叶红外光谱（FTIR）和差式扫描量热仪（DSC）对O/W乳液膜蛋白分子间的相互作用进行分析,乳液膜的Tg为100 ℃,且红外光谱中酰胺Ⅲ带和1630 cm-1峰值发生了变化,表明共混组分之间的作用力增强,蛋白质形成了致密且稳定的网络结构。     

Gelation Enhancement of Soy Protein Isolate using the Maillard Reaction and High Temperatures

Soy protein isolate gels prepared by autoclaving solutions in the presence of xylose of glucono-δ-lactone (GDL), were compared. In both cases, the pH decreased from neutral to pH 5.5 during gel formation. In the xylose systems, this pH decrease was a consequence of the Maillard reaction. The Maillard gels showed less syneresis, had a higher breaking force and were more elastic, as determined by stress relaxation, then the GDL gels. The differences were attributed to formation of additional covalent crosslinks due to the Maillard reaction, as evidenced by greatly reduced solubility in sodium dodecyl sulfate +β-mercaptoethanol.     

应用化学发光法研究大豆分离蛋白水解物的抗氧化活性

本文研究了枯草芽孢杆菌固体中性蛋白酶水解大豆分离蛋白的作用条件，应用化学发光法测定不同水解条件的产物清除超氧阴离子能力的大小，并以此确定水解的工艺条件。结果表明，大豆蛋白水解物清除超氧阴离子的能力并不是与水解度正相关。