Effect of modified whey protein concentrates on empirical and fundamental dynamic mechanical properties of frozen dough

Dairy byproduct proteins are considered natural functional additives having the ability to interact with the starch and gluten network in a dough system and thus behave as dough improvers. Native whey proteins have negative effect in bread making so whey protein concentrates modified to increase viscosity in solution (mWPC) might overcome undesirable weakening of the gluten network which usually occurs in frozen dough products during prolonged times in frozen storage. The objective of this research project was to determine the effect of mWPC on empirical and fundamental dynamic rheological properties of wheat flour dough. The results for empirical rheological studies showed that addition of mWPC had significant effects on mixographic parameters and also increased values of mixing time and peak height percentage. The results for the fundamental mechanical properties of the frozen dough revealed an increase in the values of G′ with the increase in the frequency, along with an upward trend with increasing temperature, but the highest values were obtained after cooling. Addition of mWPC in the dough treatments induced softening in the dough system, as shown by the decrease in the values of the viscoelastic moduli. Rheological and textural changes in the bakery products made from frozen dough could be imparted by the incorporation of modified whey protein concentrates as dough improvers.     

Ultrasound‐induced changes in physical and functional properties of whey proteins

Use of high‐intensity ultrasound to modify certain functional properties of whey proteins is an alternative to traditional method in food industry. Whey protein isolate (WPI) solutions were treated with an ultrasound probe (20 kHz) at different intensities (20% or 30% amplitude) and durations (10 or 20 min). Results showed that ultrasound treatment changed physical and several functional properties of whey proteins including decreased particle size (from 190.4 nm to 138.0 nm), increased surface hydrophobicity (from 5.13 × 10⁵ to 5.77 × 10⁵), free sulphydryl groups (from 52.64 μmol SH g^?1 to 53.64–58.77 μmol SH g^?1), solubility (from 74.95% to 89.70%), emulsion activity index (from 3.18 m² g^?1 to 3.59–5.32 m² g^?1) and emulsion stability index (from 62.26 min to 71.44–104.83 min), and changed viscosity (from 5.51 mPa.s to 4.81–5.64 mPa.s). Therefore, we conclude that high‐intensity ultrasound can be potentially applied to whey proteins to improve its specific functions during food processing.     

Foaming and Emulsifying Properties of Whey Protein Concentrates As Affected by Lipid Composition

Freeze-dried WPC, containing 35 and 75% protein were manufactured by pretreating whey with calcium chloride and heat. These and commercial WPC were subjected to proximate analysis and lipid classes, phospholipid classes, free fatty acids (FFA), and monoacylglycerols (MAG) composition were determined. Solubility, thermal, foaming, and emulsifying properties of the WPC were studied. Pretreatment increased calcium and phosphorus contents and decreased the contents of all other minerals. The pretreatment had no effect on solubility, denaturation enthalpy, and onset temperature of denaturation of WPC. These values were comparable to those of commercial WPC. Foaming capacity and emulsion stability were unaffected, but foam stability increased and emulsifying capacity decreased due to pretreatment. Overall, total lipids and lipid class contents of experimental WPC were too low to affect surface properties of WPC.     

Manufacture of acid gels from skim milk using high-pressure homogenization

The effect of high-pressure homogenization (HPH) alone or in combination with a thermal treatment (TT) was investigated for the manufacture of acid gels from skim milk. Raw skim milk was subjected to HPH (0 to 350 MPa) or a TT (90°C, 5 min), or both, in the following processing combinations: 1) HPH, 2) HPH followed by TT, 3) TT followed by HPH, 4) TT, and 5) raw milk (control). After treatments, L* (lightness) values were measured, and then skim milk was acidified with 3% glucono-δ-lactone and rheological properties (G′ and gelation time), and whey holding capacity was evaluated. Treatments in which HPH and TT were combined showed greater L* values than those in which just HPH was applied. In all treatments, the L* values decreased as the pressure was increased up to 300 MPa with little change afterward. Gelation times were lower when HPH was combined with TT compared with the acid skim milk gels that were just pressure treated. The final G′ in gels obtained from skim milk subjected to the combined process (HPH and TT) was greater and pressure-dependent compared with all other gels. A maximum G′ (∼320 Pa) was observed with skim milk subjected to a combination of thermal processing before or after HPH at 350 MPa. Acid gels obtained from HPH milk at 350 MPa showed a linear decrease in whey holding capacity over time, retaining 20% more whey after centrifugation for 25 min compared with samples treated at lower pressures and all other treatments. Our results suggest that HPH in combination with TT can be used to improve the rheological properties and stability of yogurt, thus decreasing the need for additives.     

高蛋白饮用型长保质期酸奶产品的研究

对高蛋白酸奶的加工方法及稳定体系和工艺进行了研究。通过添加乳清蛋白和膜浓缩2种不同方式提高产品蛋白含量;通过稳定性观察、感官测试和稳定性检测综合评价产品稳定体系。试验结果表明,采用反渗透膜过滤方式提高蛋白含量,杀菌温度118℃,发酵温度43℃;稳定体系琼脂添加量0.05%,果胶添加量0.19%,此条件下产品的感官、持水性和稳定性最佳。     

Effect of heating temperature,pH, concentration and starch/whey protein ratio on the viscoelastic properties of corn starch/whey protein mixed gels

The viscoelastic properties of corn starch (CS) gels were more dependent on heating temperature, while the properties of whey protein isolate (WPI) gels were more dependent on pH. Thus heating temperature (75, 85, 95 °C) and pH (5, 7, 9) were varied to obtain a series of mixed gels with interesting viscoelastic properties. WPI gels showed extensive stress relaxation (SR) indicative of a highly transient network structure, while CS gels relaxed very little in 2000 s. Based on SR results, it appeared that CS/WPI mixed gels with 25 and 50% CS formed compatible network structures at 15% total solids only at pH 9. This supposition was supported by SEM microstructures obtained for dehydrated gels and a synergistic increase in the large‐strain fracture stress for these gels. Some synergy was also found for mixed gels at 30% total solids at pH 9, while at pH 7 the mixed gels seemed to contain separate additive WPI and CS networks unlike the case for pH 7 at 15% total solids. In both cases (15 and 30% total solids) the degree of elasticity of the mixed gels decreased as the WPI content increased. Mixed gels (CS:WPI = 0.5) at pH 9 showed increased fracture stress and fracture strain relative to the same gels at pH 7. This suggests that a unique chemical compatibility exists at pH 9 and results in gels that combine the elasticity of CS and the internal stress dissipation of WPI. © 2001 Society of Chemical Industry     

大豆-牛奶双蛋白益生菌酸奶配方的确定及其营养分析

以大豆蛋白和牛奶蛋白为主要基料,确定双蛋白益生菌酸奶的生产配方并进行营养分析。结果表明,最优配方中,大豆蛋白:乳清蛋白(重量比)=1:2,乳糖添加量为1%。与市售酸奶相比,双蛋白益生菌酸奶蛋白质含量高22.8%,脂肪含量低37.3%,必需氨基酸含量高47.5%,蛋白质消化率修正的氨基酸评分(PDCAAS)高70%以上。双蛋白益生菌酸奶是一种新型营养健康食品,有助于营养改善、提高人体健康水平。     

Hydration of Whey Powders as Determined by Different Methods

Four methods for evaluating water hydration of 15 whey derivative powders were compared, and results are discussed with respect to the chemical composition of the powders. Hydration capacities between 0.21 and 4.64 mL water/g of powder were obtained, depending on the method used. The filtration/centrifugation method gave the highest hydration capacity, whereas the paste-water retention method gave the lowest. The Baumann test and the paste-water retention method were well correlated with protein and lactose content of the powders, enabling differentiation between hydration capacities of whey protein concentrates (35% proteins) and electrodialyzed whey powders (12% proteins). Reliable characterization of hydration required a combination of methods.     

奇亚籽希腊式酸奶的工艺优化研究

目的优化奇亚籽希腊式酸奶的配方和工艺,并考察其抗氧化性。方法以纯牛奶为主要原料,奇亚籽、混合发酵剂、乳清蛋白和白砂糖为辅料制作希腊式酸奶,以感官评分为评价指标,通过单因素试验和正交试验方法研究奇亚籽希腊式酸奶的最佳配方和工艺。结果奇亚籽添加量、混合发酵剂添加量、乳清蛋白添加量、白砂糖添加量、发酵温度和发酵时间因素均对奇亚籽希腊式酸奶的感官品质产生明显影响。其最佳配方和工艺为:以纯牛奶质量为基础,奇亚籽添加量4%、混合发酵剂添加量0.3%、乳清蛋白添加量4%、白砂糖添加量9%、发酵温度42℃、发酵时间6 h。在此条件下,奇亚籽希腊式酸奶的蛋白质含量5.37 g/100 g, pH为4.56, DPPH自由基清除率为44.68%。结论适量添加奇亚籽可改善希腊式酸奶的感官品质,并提高其营养价值,所制奇亚籽希腊式酸奶具有一定的抗氧化效果。     

热处理乳清蛋白对凝固型酸乳凝胶品质的影响

为研究热处理后的乳清蛋白对凝固型酸乳品质的影响,以添加热变前乳清蛋白的凝固型酸乳为对照,采用质构仪对凝固型酸乳的质构特性进行测定,分析筛选出恰当的热变程度的乳清蛋白,应用质构仪与流变仪进一步研究不同热变乳清蛋白添加量、不同糖添加量对凝固型酸乳的质构特性和流变特性的影响,结合电镜扫描,观察其微观结构,选出品质较优的酸奶。结果表明,酸奶中添加0.30%经72 ℃,15 min热处理的变性乳清蛋白和7%白砂糖,制得的凝固型酸乳凝胶的硬度为(263.4±11.85) g,粘附性为(413.2±15.33) g·sec,其微观结构与其他凝固型酸乳凝胶相比,空隙明显更小且分布更均匀,形成的网络结构更为规则、紧密和均一。这说明此热处理条件下的乳清蛋白可作为一种食品添加剂,对生产优质强化型酸奶具有重要的实际意义和借鉴价值。     

乳清蛋白对脱脂发酵乳的流变特性及贮存稳定性的影响

研究了乳清蛋白对脱脂发酵乳流变学特性及贮存稳定性的影响，在VAYC-370为发酵剂的情况下，分别以质量分数为10％，20％，30％和40％的乳清蛋白替代脱脂奶粉进行发酵，结果表明，乳清蛋白会降低发酵乳凝胶的硬度、提高发酵乳的内聚性，同时发现乳清蛋白可提高搅拌型发酵乳的贮存稳定性．表明发酵乳凝胶的内聚性与贮存稳定性呈正相关关系。     

Gelation of Commercial Whey Protein Concentrates: Effect of Removal of Low-Molecular-Weight Components

Low-molecular-weight solutes were removed from reconstituted, commercial whey protein concentrate (WPC) and isolate (WPI) by centrifugal gel filtration. Effects on gelation properties were investigated as a function of pH, protein concentration, and mineral ion addition by least concentration endpoint (LCE) and uniaxial compression testing. Partial removal of low-molecular-weight solutes had little effect on WPC and WPI gelation. Lowest LCE values were obtained at pH 6, 0.2M ion addition, and with KC1 and CaCl₂ addition. Highest gel firmness (shear stress and strain) values were at pH 6 and 7.5, and at 0.1M ion addition. WPI functioned better than WPC by both test procedures.     

转谷氨酰胺酶对乳清浓缩蛋白-纳米微晶纤维素复合膜性能的影响

为了研究转谷氨酰胺酶(TG)对乳清浓缩蛋白(WPC)-纳米微晶纤维素(NCC)复合膜性能和结构的影响,本研究以WPC和NCC为原料,利用TG酶处理对WPC-NCC复合膜的机械性能和屏障性能进行优化,并探究TG酶的交联作用对乳清蛋白分子二级结构和复合膜成膜微观结构的作用情况。结果表明,在TG酶的添加量达到12 U/g_蛋白时,WPC-NCC复合膜的抗拉强度达到2.25 MPa,断裂伸长率达到86.75%,水蒸气透过率为4.40×10^-12 gmPa^-1s^-1m^-2,有效改善了WPC-NCC复合膜的机械性能性和水蒸气屏障性能。经过TG酶的处理,乳清蛋白结构向稳定有序的方向转变,减少了复合膜的孔洞数量和孔径,使成膜表面结构更加致密,促进了复合膜的机械性能和水蒸气屏障性能的提升。