Whey protein concentrate gels with different sucrose content: Instrumental texture measurements and sensory perception

Correlations between instrumental texture, sensory texture and sweetness perception were studied in whey protein concentrate (WPC) gels at different pH (4 and 7), sucrose (0–40%, w/w) and whey protein (10–20% w/w) content. The presence of sucrose modified the structure of WPC gels, mainly at pH 4, making the gel structure more homogeneous and with smaller pores. Sucrose also increased the solid behaviour of gels, their water holding capacity, hardness and adhesiveness. Sweetness perception decreased as protein concentration increased, and was higher in gels at pH 4 than in gels at pH 7. A good correlation was obtained between the instrumental and sensory attributes hardness, cohesiveness and elasticity.     

Properties of gels from whey protein concentrate and honey at different pHs

Structural and functional properties of heat-induced gels from whey protein concentrate (WPC)-honey prepared at pHs 3.75, 4.2 and 7.0 were analyzed. Gel structure was observed by scanning electron microscopy, and the apparent transition temperature for protein denaturation was determined by differential scanning calorimetry. The solubility of the protein components in different extraction media, and the water-holding capacity, firmness, elasticity, relaxation time, adhesivity, cohesiveness and color of gels were determined. Results show that disulfide interchange reactions are important in determining the elasticity, water-holding capacity, relaxation time and cohesiveness of WPC gels. Honey decreases the relaxation time of gels prepared at pHs 7.0 and 4.2, and increases the browning and the water-holding capacity of gels, the apparent transition temperature of WPC dispersions at the three pHs assayed, and the adhesivity of acidic gels. The solubility of the protein constituents of gels in a pH 8.0 buffer increases slightly at honey concentrations of 27.5% or more, which correlates with a decrease in the gel cohesiveness, having these gels a structure with smaller pores. The products obtained could be utilized in the formulation of different desserts, such as flans and cake and tart fillings.     

Biological study on the effect of supplementing wheat flour with fish protein concentrate

The protein quality of 4 Egyptian pastries made from different combinations of flour and fish protein concentrate (0%, 4% and 6%) was measured by rat growth study. Weight gain, feed consumption and PER were determined. Weight gain of rats fed cottage cheese crescents was higher than that fed date bars followed by that fed brouche, then rats fed salty sticks. Feed consumed by rats fed with the corresponding commercial pastries was low except in date bars group. Commercial pastries led to low weight gain and low PER values. Supplementing wheat flour with 6% fish protein concentrate gave the highest weight gain and the highest PER values.     

Biological study on the effect of supplementing wheat flour with fish protein concentrate.

The protein quality of 4 Egyptian pastries made from different combinations of flour and fish protein concentrate (0%, 4% and 6%) was measured by rat growth study. Weight gain, feed consumption and PER were determined. Weight gain of rats fed cottage cheese crescents was higher than that fed date bars followed by that fed brouche, then rats fed salty sticks. Feed consumed by rats fed with the corresponding commercial pastries was low except in date bars group. Commercial pastries led to low weight gain and low PER values. Supplementing wheat flour with 6% fish protein concentrate gave the highest weight gain and the highest PER values.     

Functional properties of biscuits with whey protein concentrate and honey

The effects of honey, lemon juice, and two different whey protein concentrates (WPC) on the structural and functional properties of biscuits, were analysed. Firmness, elasticity, relaxation time, adhesiveness, consistency and cohesiveness of dough and colour, fracture stress and fracture strain of biscuits were also determined. The presence of WPC with a high protein content produced a decrease in the firmness and consistency and an increase in the cohesiveness of dough. Honey increased the adhesiveness of dough, mainly in samples with the WPC of lower protein content and lemon juice, and tended to decrease dough relaxation time. The fracture stress of biscuits decreased with the incorporation of WPC. Also, honey increased the red undertone and yellowness of biscuits and decreased their lightness; however, the addition of lemon juice reduced these effects.     

Effects of wheat flour supplemented with soy protein concentrate on the rheology,microstructure and water mobility of protein-fortified precooked noodles

Wheat flour was supplemented with different levels of soy protein concentrate (SPC) and applied to precooked noodles for protein fortification whose quality attributes were characterised in terms of rheology, microstructure and water mobility. The wheat flours with high levels of SPC showed lower enthalpy values and higher temperatures derived from starch gelatinisation. They also exhibited lower values of the pasting viscosity and dynamic viscoelastic parameters. The mixolab measurements demonstrated that the supplement with SPC was effective in raising the water absorption and dough stability of wheat flour. In addition, the use of SPC-supplemented wheat flours produced precooked noodles with tight and dense structures, which were confirmed by scanning electron microscopic analysis. These microstructural changes were consequently related to higher maximum resistance to extension and lower extensibility of the noodles. However, the SPC-supplemented wheat flours did not significantly affect the cooking loss of the noodles. Furthermore, three water components with different mobility were observed in the precooked noodles whose spin-spin relaxation times were distinctly reduced with increasing levels of SPC. Overall similarities in the sensory noodle attributes were detected as wheat flour was supplemented with SPC at a level of 8% (w/w).     

添加青麦仁粉对小麦粉特性的影响研究

将青麦仁制成全粉添加在小麦粉中,并对它的理化性质、糊化特性及流变学特性进行研究。结果表明:随着青麦仁粉添加量的增大,混合粉的水分、淀粉、湿面筋含量以及面筋指数下降,灰分、蛋白质、膳食纤维、叶绿素、脂肪含量明显升高;粉质特性表现为面团的稳定时间和粉质质量指数下降,吸水率升高,弱化度升高;拉伸特性显示面团的延伸性、能量以及拉伸阻力显著下降;糊化特性呈现出高峰黏度、最终黏度、低谷黏度、回生值以及衰减值整体都呈下降趋势。     

Effect of storage of surfactant gels on the bread making quality of wheat flour

Sodium stearoyl-2-lactylate (SSL), diacetyl tartaric acid esters of monoglyceride (DATEM), glycerol monostearate (GMS) and distilled glycerol monostearate (DGMS) surfactant gels were made with water and varying shortening contents. The SSL, DGMS, GMS and DATEM gels, with and without shortening in them, were stored for 3, 6, 9 and 15 days and their effects on bread-making quality were studied. All the gels improved the bread-making quality, to varying extents depending on the surfactant. On storage of gels, the improving effect was gradually reduced with increasing time, for all the gels made, with or without shortening. The adverse effect of storage on gels with shortening on bread-making quality was greater than that on gels without shortening and it varied from surfactant to surfactant. The results brought to light the adverse effect of storage of gels in improving the quality of bread.     

Effect of denatured whey protein concentrate and its fractions on rennet-induced milk gels

Denatured whey protein concentrate was fractionated by centrifugation to study the effect of its different components (sedimentable aggregates, non-sedimentable component, and diffusible component) on rennet-induced coagulation of milk and gel contraction capacity. Milk coagulation properties were characterized by optical density measurement and dynamic rheometry. The contraction kinetics of the gel during cooking was also characterized. The diffusible component of denatured whey protein concentrate showed no significant effect on coagulation or contraction parameters. Sedimentable aggregates negatively influenced the kinetics of rennet gel formation, as measured by rheology; these aggregates also reduced the contraction capacity of the gel. The non-sedimentable component negatively influenced milk coagulation properties, as measured with both optical and rheological methods, and decreased the contraction capacity of the gel. The results suggest that, beyond the effect of sedimentable whey protein aggregates, soluble proteinaceous complexes (non-sedimentable and non-diffusible) could interact with renneted casein micelles and limit gel formation and contraction.     

Structural and rheological properties of amaranth protein concentrate gels obtained by different processes

The heat-induced gelation of amaranth protein concentrates (APCs) by three processes was studied. The first was the conventional process for isolating protein (standard process-st), the second included an acid washing step prior to protein extraction (acid washing process-aw) and the third included heating (50 °C) during the alkaline extraction step (heat process-ht). The dispersions (12%, w/v) were heated to 55–90 °C and assessed by rheological measurements made under small deformations, whereas the gels obtained by heating at 70, 80 or 90 °C/30 min were subjected to uniaxial compression measurements (TPA and mechanical properties). The rheological parameters associated with the network structure, elasticity modulus (E) and storage modulus (G′), increased with increasing gelation temperature. For the APCst and APCht gels, protein aggregation occurred in two steps, whereas for APCaw, gelation occurred in a single step. The APCht gels showed the highest fracturability, hardness and adhesiveness, followed by the APCst and APCaw gels (p < 0.05). Similar results were obtained for the mechanical properties at fracture. Increasing the heat treatment temperature from 80 to 90 °C resulted in a more structured matrix with greater water-holding capacity as compared to gels obtained at 70 °C, and these properties were influenced by the extraction processes used to obtain the APCs. Heat extraction (APCht) improved the gelation and water-holding properties, whereas the acid treatment had the opposite effect.     

Steady state flow behaviours of extruded blend of rice flour and soy protein concentrate

Rheological properties in terms of steady state flow behaviours of extruded dispersions (rice flour/soy protein concentrate blend), were investigated using dynamic rheometry. The effects of concentration (2%, 5%, 7%, 9% and 11%) and temperature (25–70 °C) on the rheological parameters (yield stress, flow behaviour index) of the non-expanded pellet blend (12.5% protein) were determined using common rheological models. Steady-shear viscosities in a range of shear rate from 0 to 500 s⁻¹ were observed as a function of concentration and temperature. From typical curves showing the dependence of shear stress on shear rate, it could be observed that all suspensions exhibited a non-Newtonian and pseudoplastic behaviour. The model that best fitted the experimental data at all temperatures and concentrations was the Herschel–Bulkley model.     

燕麦粉及其与小麦粉混合后白度的探讨

探讨了16个品种燕麦粉的白度,并将燕麦粉按不同比例与小麦粉混合,对混合粉的白度进行测定分析。结果表明,燕麦粉的白度值为60.00~69.90;不同品种、不同地区的燕麦粉白度有所差异;燕麦粉的白度整体上明显小于小麦粉的白度。分析发现混合粉白度与燕麦粉和小麦粉的比值成显著线性关系,且燕麦粉白度越小,随着小麦粉比例的增大,混合粉的白度上升幅度增大。     

Effects of protein hydrolysis on pasting properties of wheat flour

Protein hydrolysis is used widely in the food industry for the purpose of improvement of food or industrial quality, and the processing exists concurrently or subsequently with starch pasting. The effects of protein hydrolysis using papain, pepsin, trypsin, and dithiothreitol (DTT) on flour pasting properties were here investigated at five set concentrations. There were notable decreases in the peak, the trough viscosity, and the integral area of the viscosity curve as the concentrations of papain, trypsin, and DTT increased. DDT and pepsin concentration did not have any effect on final viscosity. Both breakdown and setback showed significant downtrends as the concentration of papain increased but no change as DDT concentration varied. Low concentrations of papain and pepsin prolonged peak time slightly, but higher concentrations shortened it significantly. For trypsin and DTT, low concentrations increased peak time notably, but high concentrations decreased it significantly. Pasting time and temperature increased in the presence of papain, pepsin, and trypsin, more so at higher concentrations. These results supply a basis for the utilization of hydrolyzed protein in the food industry and for the further studies on the interactions between protein and starch during processing.     

Effect of extrusion cooking on protein modification in wheat flour

Common soft wheat flour was extruded at three different temperatures and two different moistures. To investigate the dependence of the wheat protein modification on processing conditions, their solubilities in sodium dodecyl sulfate (SDS) were compared with those in SDS+(2-mercaptoethanol) ME. Furthermore, free sulfhydryl groups were detected with Ellmans Reagent and SDS-PAGE was performed under reducing and non-reducing conditions. The solubility values in SDS were greatly reduced after extrusion. The solubility values in SDS+ME were not affected. We therefore concluded that intermolecular cross-linking by disulfide bonding through extrusion cooking had occurred. This result was confirmed by SDS-PAGE under reducing and non-reducing conditions. At low and medium temperatures the solubilities were lower at low moisture; however, more free sulfhydryl groups were detected under these conditions, suggesting that moisture content of the flour has an influence on the way and the nature of the protein polymerization. At the highest thermal energy input at low moisture the solubilities increased again. This was accompanied by an increase of detectable free sulfhydryl groups. This led to the conclusion that disulfide bonds were cleaved at high energy input. The solubility development in 70% ethanol was nearly the same as in SDS. This is seen as a proof that gliadins are highly involved in the protein network formed under extrusion conditions. This finding was also confirmed by the results of SDS-PAGE.     

小麦粉面筋蛋白质流变学特性的研究

本试验采用快速黏度仪(RVA)通过面筋蛋白醇溶指数法,研究了不同类型小麦粉的面筋蛋白醇溶指数,探讨了不同小麦粉的粉质特性、拉伸特性及湿面筋、面筋指数及其与醇溶指数、最终黏度的影响.结果表明:不同类型的小麦粉的面筋蛋白RVA曲线存在明显差异,醇溶指数在α=0.05水平上与小麦粉吸水率、延伸性呈负相关,与峰值黏度呈正相关;在α=0.10水平上与小麦粉稳定时间呈负相关,最终黏度在α=0.05水平上与小麦粉面筋指数呈负相关,与峰值黏度呈正相关.因此,麦胶蛋白明显影响小麦粉的吸水率、稳定时间、延伸性及面团的面筋指数,而与拉伸阻力、湿面筋及弱化度无相关性,此与麦胶蛋白的富有延伸性、粘性,但弹性小的性质有关.     

关于大豆浓缩蛋白强化面粉的探讨

通过对我国人民饮食结构的分析认为蛋白营养强化面粉是我国公众营养的发展方向.根据我国大豆和面粉产业的现状,开发大豆浓缩蛋白强化面粉是充分利用我国大豆资源,提高人们的健康水平,企业获取更大经济效益的有效途径.     

全麦粉及小麦粉基本品质及流变学特性对比研究

以郑麦366、普优、加麦2号3种小麦为原料,分别用波通3100磨磨制全麦粉,布勒实验磨磨制小麦粉。研究全麦粉及小麦粉的基本品质及流变学特性。结果表明:全麦粉的营养价值优于小麦粉的营养价值,但是加工品质劣于小麦粉的加工品质。     

小麦粉中蛋白质和淀粉含量对面条品质的影响

对小麦粉中的蛋白质和淀粉组分进行了分离,将淀粉含量不同的混合粉制作成面条,分析其质构特性和食用品质。将面条煮制后,对熟面条进行了质构分析,测定了熟面条的硬拉伸性能、剪切性能和蒸煮损失,并进行了感官品质评价。研究结果表明:随着小麦粉中的淀粉含量的增加(蛋白质含量的降低),面条的质构特性、拉伸性能、剪切性能都呈现显著下降的变化趋势(P<0.05),而面条的蒸煮损失显著增加(P<0.05)。此外,面条的感官评价与质构分析的结果相一致。