Protein Isolates from Bambara Groundnut (Voandzeia Subterranean L.): Chemical Characterization and Functional Properties

The physicochemical, functional, and thermal properties of protein isolates obtained from two varieties of Bambara groundnut were evaluated. Proteins were isolated using alkaline extraction (isoelectric precipitation [IEP]) and micellisation techniques. IEP recorded a higher protein yield (56.3–58.2 g/100 g) than the micellised protein (MP) (14.2 – 15.6 g/100 g). A similar trend was observed for the protein content of the isolates. The isolates contained a high level of lysine, arginine, and glutamic acid compared to soy protein. Minimum solubility of the flours of the two varieties occured at pH 5. MP isolates exhibited higher solubility than the corresponding isoelectric (IEP) isolates over all pH values. The micellised protein recorded superior functional characteristics than the isoelectric isolates. The micellised isolates also showed a significantly higher (P < 0.05) foam capacity and stability, oil and water absorption properties than the isoelectric isolate. The MP of both varieties also recorded significantly higher emulsifying properties-+ than their isoelectric protein isolates. The micellised protein also had better gelation properties than the isoelectric isolate. Micellised and isoelectric isolates did not reveal major differences in the electrophoretic patterns; both isolates had three major bands at 35.0, 43.0, and 112.0 kDa. The bands in the isoelectric protein isolate however, were well defined compared with the micellised isolate. All Bambara isolates were not dissociated by 1,4-Dithiothreitol (DTT) suggesting that they do not contain subunits linked by a disulphide bond. This suggests that 7S vicilin may be the major storage protein in Bambara groundnut isolates. Differential scanning calorimetry studies (DSC) of the two varieties of bambara groundnut proteins indicated that the thermograms of the micellised isolates have a higher denaturation temperature Td (97.9–108.4°C) than their corresponding isoelectric isolates (89.5–90.6°C).     

谷氨酰胺转氨酶对荞麦分离蛋白凝胶特性的影响

以荞麦（Fagopyrum esculentum Moench.）为原料,通过碱溶酸沉法提取荞麦分离蛋白（BPI）,分别采用真空冷冻干燥与喷雾干燥制备蛋白粉,研究谷氨酰胺转氨酶（TGase）及不同干燥方式对荞麦分离蛋白理化性质和凝胶特性的影响。结果表明,冷冻干燥荞麦分离蛋白（FBPI）的蛋白组成与BPI类似,而喷雾干燥荞麦分离蛋白（SBPI）的13S球蛋白发生降解。FBPI和SBPI的α-螺旋含量分别为22.10%和20.00%,β-转角含量为19.40%和19.80%,表明喷雾干燥会使蛋白结构更加无序化。SBPI的表面疏水性指数显著（P<0.05）高于FBPI与BPI。与BPI相比,SBPI具有更高的表面疏水性和更均匀的粒径,但溶解度和持水能力较低,而FBPI具有与BPI相似的物理化学性质。加入TGase后,FBPI和SBPI的平均粒径分别由213.01与192.55 nm增加至2289.01与1439.67 nm,表明发生了交联反应。BPI、FBPI和SBPI的电位分别为?15.93、?29.43、?29.35 mV,表明干燥处理能进一步提高蛋白的溶液稳定性。相比于SBPI,BPI和FBPI在升温过程中G'持续下降,表明热处理会破坏BPI和FBPI的蛋白凝胶结构。经加热处理再进行冷却,FBPI的G'显著（P<0.05）高于SBPI与BPI,具有更好的凝胶性。TGase能显著（P<0.05）提高FBPI的储能模量与热稳定性,但对SBPI作用不明显。化学作用力结果显示,疏水相互作用和二硫键是凝胶主要作用力;TGase能有效促进凝胶结构中疏水相互作用和二硫键形成,但会导致蛋白分子间氢键断裂。由此可见,通过冷冻干燥制备的荞麦蛋白能在TGase的作用下形成凝胶性与稳定性较好的凝胶。本研究的结果为荞麦分离蛋白凝胶特性研究及其凝胶类食品的开发与应用提供理论参考。     

谷氨酰胺转移酶对大豆分离蛋白成膜性能的影响

研究了谷氨酰胺转移酶（TGase）对大豆蛋白膜特性的影响。研究表明：在成膜溶液中加入TGase（4U／g）可以使膜的抗拉强度增加16．79，6，表面疏水性增加39．2％，同时也明显降低了膜的断裂伸长率、水分含量、总可溶性物质量及透光率，但是对水蒸气转移速率几无影响。扫描电镜（SEM）显示，酶法交联膜的表面比对照膜略为粗糙，断面却更为均匀致密。SDS-PAGE分析表明，TGase催化SPI产生了共价交联。     

卡拉胶和肌原纤维蛋白混合凝胶质构特性的研究

研究卡拉胶和肌原纤维蛋白(MP)浓度比、pH、离子强度和[K+]对混合凝胶质构特性的影响.结果表明:影响混合凝胶硬度和黏着性的主次因素依次为:[K+]、离子强度、浓度比、pH;影响混合凝胶弹性的因素依次为:[K+]、浓度比、pH、离子强度;影响混合凝胶黏聚性的因素依次为:离子强度、[K+]、浓度比、pH.     

Textural Properties of Cold-set Gels Induced from Heat-denatured Whey Protein Isolates

A 9% whey protein (WP) isolate solution at pH 7.0 was heat-denatured at 80°C for 30 min. Size-exclusion HPLC showed that native WP formed soluble aggregates after heat-treatment. Additions of CaCl2 (10–40 mM), NaCl (50–400 mM) or glucono-delta-lactone (GDL, 0.4–2.0%, w/v) or hydrolysis by a protease from Bacillus licheniformis caused gelation of the denatured solution at 45°C. Textural parameters, hardness, adhesiveness, and cohesiveness of the gels so formed changed markedly with concentration of added salts or pH by added GDL. Maximum gel hardness occurred at 200 mM NaCl or pH 4.7. Increasing CaCl2 concentration continuously increased gel hardness. Generally, GDL-induced gels were harder than salt-induced gels, and much harder than the protease-induced gel.     

谷氨酰胺转氨酶对大豆与小麦混合蛋白凝胶性质的影响

研究谷氨酰胺转氨酶（transglutaminase,TG）对大豆和小麦混合蛋白凝胶特性的影响,通过游离巯基含量、表面疏水性、热特性、二级结构和微观结构等测定对混合蛋白凝胶的构象进行了表征。结果显示,当大豆蛋白比例低于45%时,随着大豆蛋白所占比例的增加,凝胶强度显著增强。TG交联混合蛋白凝胶后,其游离巯基减少,热稳定性增强,表面疏水性降低。与TG催化小麦蛋白相比,大豆蛋白添加量为45%的混合蛋白凝胶强度提高了62.74%,β-折叠含量增加了5.701%,游离巯基含量减少了47.48%。     

Microbial Transglutaminase Affects Gel Properties of Golden Threadfin-bream and Pollack Surimi

ABSTRACT: The properties of surimi gels from threadfin-bream and pollack surimi set at 30 °C or 45 °C with microbial transglutaminase (MTGase) from Streptoverticillium ladakanum were determined. The optimal amounts of MTGase and setting conditions were: 0.3 unit/g surimi either at 30 °C for 90 min or at 45 °C for 20 min for threadfin-bream, and 0.2 unit/g surimi at 30 °C for 60 min for pollack. The strength of golden threadfin-bream surimi gels with 0.35 unit MTGase set at 30 °C for 90 min or 45 °C for 20 min was 3400 g cm, almost 3-fold of the control. SDS-PAGE analyses indicated that inter- and/or intramolecular cross-linking formed in the myosin heavy chain of MTGase-containing surimi gels.     

Effect of Calcium Salts on the Properties of Proteins from Oil Sardine (Sardinella longiceps) During Frozen Storage

ABSTRACT:  The effect of calcium sulfate and calcium chloride on the enzymatic and structural properties of actomyosin isolated from sardine was investigated. Mince was prepared from sardine and different concentrations of calcium chloride and calcium sulfate were added to the mince and kept in frozen condition at −20 °C. The physico-chemical and functional properties of proteins from mince were analyzed as a function of time. The solubility of proteins decreased during storage. The reduction in solubility was less for samples treated with calcium chloride. However, sardine mince showed better functionality during storage in the presence of calcium compounds. The ATPase enzyme activity of actomyosin increased with increase in concentration of calcium and decreased after reaching the maximum value. ATPase activity of proteins from mince decreased during storage at low temperature. The reduction in ATPase activity did not correlate with the loss of functionality of proteins. SDS-PAGE did not reveal any major changes in the protein profile during storage as well as in the presence of different concentration of calcium compounds. The secondary structural content of actomyosin was not altered in the presence of both calcium chloride and calcium sulfate as evident from circular dichroic measurements.     

焦磷酸钠对氧化猪肉肌原纤维蛋白的谷氨酰胺转移酶交联反应及凝胶性能的影响

以猪肉肌原纤维蛋白为研究对象,考察焦磷酸钠(sodium pyrophosphate,TSPP)对微生物谷氨酰胺转移酶(microbial transglutaminase,MTG)催化天然和氧化肌原纤维蛋白交联的程度及后续蛋白凝胶特性的影响。结果表明,肌原纤维蛋白的氧化程度随着H2O2溶液浓度的升高而增加,但TSPP在一定程度上可抑制羟自由基对蛋白的攻击,且TSPP处理(+TSPP)样品的MTG交联程度明显高于未经TSPP处理(-TSPP)样品。无论是否添加TSPP,随着H2O2溶液浓度的升高,蛋白凝胶的储能模量(G’)和凝胶强度均逐渐降低,加入MTG后均有所回升,且增幅随着H2O2溶液浓度升高逐渐降低。相对于未经TSPP处理样品,TSPP处理条件下未氧化样品的G’和凝胶强度增幅更高,但氧化时增幅降低速度更快。说明虽然TSPP处理有利于MTG交联引起的凝胶性能提高,但当受到氧化胁迫时,TSPP处理反而对其不利。     

谷氨酰胺转氨酶对大豆分离蛋白塑料拉伸性能的影响

研究了微生物谷氨酰氨转胺酶对大豆分离蛋白塑料拉伸性能的影响,发现在50℃时转氨酶对大豆分离蛋白催化聚合反应60 min,形成的高分子聚合物使大豆分离蛋白的抗拉强度和杨氏模量分别由未经处理时的9.2 MPa和265.4 MPa增加到14.7 MPa和390.1 MPa,同时增加了蛋白质的变性温度和热焓值。在酶处理90 min时,由于转氨酶变性失去活性及大豆分离蛋白的部分变性,蛋白质塑料的拉伸性能反而下降。对大豆分离蛋白的预热处理降低了转氨酶的催化聚合反应,且变性后的大豆分离蛋白制备的塑料拉伸性能大大降低。     

谷氨酰胺转胺酶和磷酸盐对鱿鱼鱼糜凝胶性能的影响

研究添加谷氨酰胺转胺酶(TGase)和磷酸盐对鱿鱼鱼糜凝胶硬度和弹性的影响。结果表明:TGase和磷酸盐在鱼糜凝胶化过程中起重要作用,且不同添加量的TGase和磷酸盐均可提高鱿鱼鱼糜的硬度和弹性;单因素试验确定最佳添加量为(以鱼糜质量为基本):TGase(100U/g)0.50%、焦磷酸钠0.30%、六偏磷酸钠0.30%、三聚磷酸钠0.30%;采取二段加热法(60℃保温1h),鱼糜的硬度、弹性达到最大。     

Fractionation and Properties of Sarcoplasmic Proteins from Oil Sardine (Sardinella longiceps): Influence on the Thermal Gelation Behavior of Washed Meat

ABSTRACT: The properties of total sarcoplasmic proteins from oil sardine (Sardinella longiceps) have been assessed. Ammonium sulfate fractionation of total sarcoplasmic proteins yielded 5 different fractions. The UV-ab-sorption spectra of all 5 sarcoplasmic proteins fraction showed a peak in the wavelength range of 275 to 280 nm indicating aromatic amino acid residues in its composition. The SDS-PAGE of different fractions showed components in the molecular weight range of 97 to 29 kD. The thermal stability in the temperature range of 40° to 80 °C of different fractions were varied in nature. The flow profile of different fractions indicated pseudo-plastic behavior and minimum structural impairment for fraction V at 30 and 40 °C, respectively. The gelation profile of washed sardine meat in combination with different sarcoplasmic proteins fraction revealed fraction V could enhance the storage modulus values during heating regime.     

分离大豆蛋白凝胶光学性质的研究

深入地研究了分离大豆蛋白凝胶的透明性与ｐＨ值,加热温度、蛋白质浓度、离子强度（ＮａＣｌ浓度）和葡萄糖酸－δ－内酯（ＧＤＬ）的关系。结果表明：在ｐＨ〈３．５或ｐＨ〉５．５,温度〉８０℃、蛋白质浓度〉２．５％、低离子强度（ＮａＣｌ浓度〈１０ｍｏｌ／Ｌ）和无葡萄糖酸－δ－内酯的条件下,有利于形成透明性分离大豆蛋白凝胶。可为进一步研究大豆蛋白凝胶的光学性质和研制透明的大豆蛋白产品提供理论依据。