乳清蛋白可食用膜抑菌性、溶解性的研究

主要研究了Nisin、纳塔霉素和溶菌酶不同组合添加下乳清蛋白可食用膜的抑菌性和溶解性,结果表明:随着抑菌剂浓度的增加,膜的抑菌效果增强,不同抑菌剂组合下膜的抑菌效果不同,0.35%Nisin和0.08%溶菌酶组合下抑菌效果更好。在酸性环境中,当添加0.03%溶菌酶和0.25%纳塔霉素时,可有效降低膜的溶解性;在中性环境中,各组膜的溶解性几乎相当,在碱性环境中,大部分膜的溶解性要低于其在酸性环境中。     

Incorporated glucosamine adversely affects the emulsifying properties of whey protein isolate polymerized by transglutaminase

Glucosamine (GlcN) and microbial transglutaminase (Tgase) are used separately or together to improve the emulsifying properties of whey protein isolate (WPI). However, little is known about how the emulsifying properties change when GlcN residues are incorporated into WPI cross-linked by Tgase. We used Tgase as a biocatalyst to cross-link WPI in the presence of GlcN in a liquid system for 12 h at a moderate temperature (25°C). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analyses indicated that protein polymerization and GlcN conjugation occurred simultaneously, phenomena also supported by the loss of free amines (9.4–20.5%). Addition of 5 U Tgase/g protein improved the emulsifying properties of moderately cross-linked WPI polymers. The Tgase-treated WPI polymers had a larger particle size (～2.6-fold) than native WPI, which may have reduced coalescence and flocculation in an oil-in-water emulsion system. However, the incorporation of GlcN residues into WPI, predominantly via enzymatic glycation, partly inhibited the cross-links between the WPI molecules catalyzed by Tgase, reducing the size of the WPI polymers 0.81- to 0.86-fold). Consequently, WPI+GlcN conjugates provided less stability to the emulsion. Moreover, high NaCl concentration (0.2 M) decreased the emulsifying properties of the WPI+GlcN conjugates by neutralizing negative electric charges in the glycoconjugates. However, the improved emulsifying properties of WPI cross-linked by Tgase may be useful in food processing at higher NaCl concentrations due to the formation of the thicker steric barrier at the oil-water interface.     

Effect of adding zein,soy protein isolate and whey protein isolate on the physicochemical and in vitro digestion of proso millet starch

Mixtures of proso millet starch with zein (15%, w/v), soy protein isolate (SPI, 15%, w/v) and whey protein isolate (WPI, 10%, w/v) as starch–protein composites were prepared through heat–moisture treatment, and the effects of protein addition on the physicochemical, structural and digestibility properties of starch were investigated. Rapid Visco Analysis showed that the addition of zein, SPI and WPI gave significantly decreased setback values to 240.7cp, 192.0cp and 83.0cp, respectively, and setback values decreased reflected the excellent cold paste properties. Thermal analysis showed that each protein reduced the enthalpy, but especially WPI (reduced by 94.7%), suggesting that the double helices of the starch granules were decreased. X-ray diffraction showed that starch crystallinity was decreased after protein addition. The digestibility studies revealed that the addition of zein, SPI and WPI decreased the content of rapidly digestible starch and increased the resistant starch content to 8.4%, 14.6% and 17.5%, respectively. The whey protein displayed a more obvious impact on the digestibility of proso millet starch. These results will help guide the production and processing of starchy foods with desirable properties.     

Plasma lipid concentrations in preruminant calves fed whole milk with whey protein isolate

The objective was to investigate the acute effects of retinol acetate added to whey protein isolate (WPI) on postprandial changes in plasma retinol (experiment 1) and the acute effects of milk fat added to WPI on triglyceride (TG), chylomicrons and very low density lipoprotein (VLDL), and fatty acid concentrations (experiment 2) in suckling calves at 1 and 6 wk of age. In experiment 1, 16 Holstein male calves were alloted to 2 equal groups. On the days of measurement, the calves were fed at 0900 h whole milk [4% of body weight (BW)] mixed with vitamin A acetate (500,000 IU) with or without WPI (0.04% of BW). At 1 wk of age, significantly higher postfeeding concentrations of plasma retinol were observed in the calves fed milk with WPI. At 6 wk of age, no differences in the plasma retinol concentrations were observed between 2 groups. On the days of measurement in experiment 2, 16 male calves were fed at 0900 h whole milk (4% of BW) with added milk fat prepared by centrifugation from whole milk (2% of BW) with or without WPI (0.04% of BW). The milk supplemented with fat was prepared on the day before the measurement. At 1 wk of age, significant higher postfeeding concentrations of plasma TG concentrations were obtained in the calves fed WPI than in the control calves, immediately after the meal or from 7 h later onward. Plasma chylomicrons and VLDL concentrations at 1 wk of age were significantly higher in the WPI-fed group than in the control group at 8 h postfeeding. In the calves with the WPI diet, plasma concentrations of myristic, palmitic, stearic, oleic, and linoleic acids at 1 wk of age were significantly higher than those in the control calves at 8 h after feeding. However, chylomicrons and VLDL, and fatty acid concentrations did not differ between the 2 groups after feeding at 6 wk of age. Results indicate that WPI increases plasma lipid concentration of preruminant calves only at 1 wk of age. These data are interpreted to indicate that WPI enhances mainly lipid uptake in the intestines of neonatal calves.     

Influence of whey protein isolate on pasting,thermal, and structural characteristics of oat starch

We investigated the effects of different concentrations of whey protein isolate (WPI) on oat starch characteristics in terms of pasting, thermal, and structural properties. The pasting properties of the starch showed that hot paste viscosity increased with the addition of WPI in the system, and relative breakdown decreased. Thermal analysis showed a significant effect of WPI on oat starch by increasing the peak temperature of differential scanning calorimeter endotherms. The X-ray diffraction and Fourier transform infrared spectroscopy studies revealed that WPI increased the ordered structuration of starch paste, as evident by an increase in relative crystallinity; in addition, a decrease in infrared bands at 1,024 cm^?1 and 1,080 cm^?1 suggested decreased gelatinization of oat starch granules. Overall, WPI at different concentrations affected the oat starch gelatinization properties.     

超声辅助处理对乳清分离蛋白糖基化产物的理化特性影响

采用超声辅助技术对乳清分离蛋白(WPI)进行糖基化改性,并与水浴加热法进行比较,探究两种处理方式对糖基化反应产物理化性质的影响。结果表明,与水浴法相比,超声辅助法可以更快地促进糖基化反应的进行,且对糖基化产物的理化性质有较大改善;当超声温度为70℃,功率为300 W,超声时间为40min时,乳清分离蛋白和葡萄糖的接枝度达到48. 10%,且乳清分离蛋白—葡萄糖接枝物的乳化性、在等电点处溶解性均增大。乳化系数由23.67 m~2/g增大到40.84 m~2/g;等电点附近的溶解度由19.09%增大到47.95%。且以接枝物为基质的乳液的粒径更小,储藏稳定性更好。     

乳清蛋白菊粉糖基化复合物的褐变特性与抗氧化活性

以褐变程度及抗氧化活性为检测指标,研究湿热反应条件对乳清蛋白菊粉糖基化复合物的褐变特性与抗氧化活性的影响。研究结果表明:反应物浓度越大,反应温度越高,乳清蛋白菊粉糖基化产物的褐变强度越大,抗氧化活性越强;起始反应pH值越大,乳清蛋白菊粉糖基化产物的褐变强度及还原能力越强,而其DPPH.清除能力呈现先升高后降低的趋势。当反应物浓度为6%,温度为100℃,起始反应pH值为9时,所获得的乳清蛋白糖基化产物抗氧化活性较强。     

乳清蛋白抗菌薄膜中山梨酸钾的扩散性研究

将山梨酸钾添加至乳清分离蛋白成膜液中制成抗菌包装薄膜,通过扩散实验并结合菲克扩散理论,研究了在不同浓度、温度、p H条件下抗菌蛋白薄膜中山梨酸钾的扩散行为。根据幂律模型的扩散指数,发现p H3.8时山梨酸钾的初期释放动力学属于非菲克扩散,而在其他条件下基本符合菲克第一扩散定律。扩散系数研究表明:抗菌膜中山梨酸钾浓度增加,温度升高,p H降低,扩散系数呈非线性增大;模拟液p H3.8时,由于薄膜溶胀性较大,山梨酸钾的扩散系数在35℃条件下高达5.722×10-12m2/s;通过阿伦尼乌斯公式中活化能比较,发现山梨酸钾的扩散系数在p H为3.8的模拟液中最易受温度影响。      

微射流和超声波对长期贮藏大豆分离蛋白溶解性的影响

在常温贮藏条件下,大豆分离蛋白(SPI)的溶解性随贮藏时间的延长而逐渐下降。通过测量贮藏时间0、120、240、360d的SPI,结果显示可溶性蛋白含量从贮藏0d的59.5%±1.2%降低到360d的43.3%±1.6%。粒径和浊度分析显示随贮藏时间的延长,SPI发生聚集,不利于溶解的变化。而经过微射流和超声波的双重处理后,SPI溶液中可溶性蛋白含量上升到88.1%±1.3%。SPI凝胶电泳图谱和凝胶排阻色谱显示蛋白亚基的变化有利于提高溶解性。SPI聚集的粒径减小,分布范围变窄。SPI在不同悬浮液的浊度都明显下降。      

黑木耳多糖与乳清分离蛋白分子间作用力的研究

目的 研究黑木耳多糖与乳清分离蛋白分子间的作用力。方法 本研究利用化学键解离剂处理黑木耳多糖-乳清分离蛋白复合物,通过可见光吸收光谱、傅里叶红外光谱、荧光光谱技术检测其浊度及二级、三级结构变化,分析维系该复合物的主要作用力,并利用离子交换色谱进行单糖组成成分分析,结合分子对接技术预测其结合位点。结果 浊度结果表明,氢键和疏水相互作用是维持复合物稳定的主要作用力;红外光谱、荧光光谱检测发现,尿素、十二烷基硫酸钠的添加改变了复合物的二级和三级结构,再次证明复合物间的主要作用力为氢键和疏水相互作用;黑木耳多糖的单糖成分主要为甘露糖(63.4%);分子对接结果显示,甘露糖主要通过氢键与乳清分离蛋白的组氨酸、谷氨酸、天冬氨酸、色氨酸等氨基酸残基结合。结论 本研究揭示了黑木耳多糖通过氢键及疏水相互作用与乳清分离蛋白结合,并预测结合位点在组氨酸、谷氨酸、天冬氨酸、色氨酸等氨基酸残基处,研究结果为黑木耳多糖-乳清分离蛋白复合物在酸性环境中的应用提供了理论基础。     

Improvement of functional properties of whey protein isolate through glycation and phosphorylation by dry heating

Whey protein isolate (WPI) was glycated with maltopentaose (MP) through the Maillard reaction, and the MP-conjugated WPI (MP-WPI) was then phosphorylated by dry heating in the presence of pyrophosphate. Glycation occurred efficiently, and the sugar content of WPI increased approximately 19.9% through the Maillard reaction. The phosphorylation of MP-WPI was enhanced with an increase in the dry-heating time from 1 to 5 d, and the phosphorus content of WPI increased approximately 1.05% by dry heating at pH 4.0 and 85°C for 5 d in the presence of pyrophosphate. The electrophoretic mobility of WPI increased with an increase in the phosphorylation level. The stability of WPI against heat-induced insolubility at pH 7.0 was improved by conjugation with MP alone, and further improved by phosphorylation. Although the emulsifying activity of WPI was barely affected by glycation and phosphorylation, the emulsifying stability of phosphorylated MP-WPI (5 d), was 2.2 times higher than that of MP-WPI. Gelling properties such as hardness, resiliency, and water-holding capacity of heat-induced WPI gel were markedly improved, and the gel was rendered transparent by phosphorylation. The calcium phosphate-solubilizing ability of WPI was enhanced by phosphorylation. These results suggested that phosphorylation by dry heating in the presence of pyrophosphate after conjugation with MP is a useful method for improving the functional properties of WPI.     

不同来源蛋白酶水解对大豆分离蛋白分散性及溶解性的影响

研究了动物(胰蛋白酶)、植物(木瓜蛋白酶与菠萝蛋白酶)、微生物(碱性蛋白酶和中性蛋白酶)三种来源蛋白酶的低限度水解对大豆分离蛋白(SPI)分散性和溶解性的影响。结果表明,三种来源蛋白酶轻度水解可显著提高SPI的分散性,但却使其溶解性有不同程度的降低。三种来源蛋白酶水解产物的分散度大小依次为:植物来源蛋白酶>微生物来源蛋白酶>动物来源蛋白酶,而其溶解性则相反:动物来源蛋白酶>微生物来源蛋白酶>植物来源蛋白酶。本文对采用酶解的方法制备高分散性与高溶解性SPI具有一定的参考价值。通过对木瓜蛋白酶水解沉淀物进行分析,可以推测酶解使SPI溶解度显著下降的原因可能是SPI被水解后通过疏水作用力和氢键相互聚集形成了不溶性的沉淀。     

大豆分离蛋白溶解性和乳化性影响因素研究

研究了pH、大豆分离蛋白(SPI)质量浓度、NaCl浓度、搅拌时间和温度等因素对SPI溶解性和乳化性的影响.结果表明,0.8%的SPI在pH 6.0的条件下,实验浓度范围内的NaCI均使SPI溶解性和乳化性降低,适当的延长搅拌时间和升高温度可以显著提高SPI溶解性和乳化性.在室温条件下,搅拌50 min时SPI溶解度最...     

Effect of temperature,pH and film thickness on nisin release from antimicrobial whey protein isolate edible films

BACKGROUND: An active packaging film based on whey protein isolate (WPI) was developed by incorporating nisin to promote microbial food safety. The effect of temperature and pH on the release of nisin from edible films of different thickness was investigated. The film mechanical properties and inhibitory effect were also evaluated. RESULTS: Nisin release was significantly favoured by low pH, with the highest release after 24 h (1325 IU), which was not significantly affected by temperature (5 or 10 °C). Thickness significantly affected film elongation, with thicker films showing the highest elongation (54.3 ± 2.7%). Water vapour permeability (0.15 ± 0.4 g mm m^?2 kPa^?1 h^?1) and elastic modulus were not significantly affected by thickness. The highest nisin effective diffusivity (5.88 × 10^?14 m² s^?1) was obtained using a solution at pH 4, 112 µm film thickness and a temperature of 5 °C. More than four log cycles of Brochotrix thermosphacta were reduced from the surface of a ham sample after 8 days of incubation at 4 °C by the active WPI film containing 473 IU cm^?2 nisin. CONCLUSION: Nisin diffusivity from WPI edible films was favoured at lower pH and film thickness. This active packaging film may be used to preserve the quality and safety of meat products. Copyright © 2009 Society of Chemical Industry     

Functionality of spray-dried strawberry powder: effects of whey protein isolate and maltodextrin

The effectiveness of two drying agents, namely whey protein isolate (WPI) and maltodextrin (MD), was evaluated during spray-drying of strawberry puree. With the increase of WPI substitution in the feed material, the surface tension of strawberry puree decreased, and powder recovery increased. Powder recovery (R_p) increased from 39.2 ± 2.3% (S:MD:WPI = 60:40:0) to 56.5 ± 2.8% when MD was replaced by WPI (S:MD:WPI = 60:39:1). Surface morphology of powders showed that the addition of WPI resulted in shrunken particle surface, which gave rise to smaller D_B and particle size. The particles were not spherical, and even with the addition of 0.5% WPI, the particle morphology was altered. The surface shrinkage of strawberry powder increased with increase in WPI from 0.5% to 10%. The production efficiency of strawberry powder could be greatly improved when MD was replaced by 1% WPI.     

谷氨酰胺转氨酶对大豆分离蛋白溶解性和乳化性的影响

以谷氨酰胺转氨酶(Transglutaminase,TG)为交联剂,与大豆分离蛋白(soybean protein isolate,SPI)发生交联反应,通过单因素试验研究热处理温度、TG浓度、交联温度、交联时间、SPI浓度和交联pH值对SPI溶解性和乳化性的影响。结果表明,4%的SPI溶液在70℃下热处理30 min,按照2 U/g SPI的剂量添加TG,在45℃、pH 6.5条件下交联1 h,此时SPI的溶解性、乳化活性和乳化稳定性分别为0.037 g/mL、328.868 cm-1、0.951。与未经处理的4%SPI相比,TG交联SPI的乳化活性和乳化稳定性显著提高,但溶解性显著下降。     

Effects of process variables and addition of polydextrose and whey protein isolate on the properties of barley extrudates

Extrusion cooking is commonly used in the production of snacks. In the present study, extrudates were prepared using barley flour alone and with the addition of either polydextrose (PD) or whey protein isolate (WPI) and both PD and WPI. Independent process variables were water content of the mass (17%, 20% and 23%), screw speed (200, 350 and 500 rpm) and temperature of section 6 and die (110, 130 and 150 °C). Expansion, hardness, water content, porosity and chemical composition of the extrudates were analysed. Highly porous and expanded snack products with high dietary fibre and protein contents were obtained from barley flour and WPI when water content of mass was 17%, screw speed 500 rpm and temperature of section 6 and die 130 °C. Barley flour alone or with PD resulted in hard and non‐expanded extrudates. Expansion of extrudates was statistically significantly increased with decreasing water content of the mass and increasing screw speed in all trials.