膜技术分离脱脂乳中酪蛋白胶束和乳清蛋白工艺的研究

对膜技术分离脱脂乳酪蛋白胶束和乳清蛋白工艺进行了研究,考察了不同筛分膜的分离效果,并研究了不同操作参数对渗透通量的影响。最终确定用切割分子量300kDa的陶瓷膜进行脱脂乳浓缩分离,酪蛋白胶束和乳清蛋白的分离效果较佳,透过液中乳清蛋白占真蛋白的百分比可达98.91%。确定了膜分离的最适操作压力为0.20MPa,最适操作温度为50℃。      

液态乳制品中乳清蛋白和酪蛋白含量分析

随着居民对乳制品消费能力的提升,消费者对乳制品的品质提出了更高的要求,乳中功能蛋白因其重要的生物学功能成为研究热点。该实验采集13种风味发酵乳和风味酸乳以及15种其他液态乳制品,共计28个样品,采用高效液相色谱-串联质谱法测定28种液态乳制品中乳清蛋白和酪蛋白的含量。结果显示,不同来源、不同加工方式液态乳制品中乳清蛋白和酪蛋白的含量存在一定差异,鲜牛奶和纯牛奶中乳清蛋白和酪蛋白的含量普遍高于风味发酵乳和风味酸乳。该文评价了28种液态乳制品中乳清蛋白和酪蛋白的差异性,以期分析不同加工方式对乳品中功能蛋白含量的影响,为消费者购买高品质液态乳制品提供数据支撑。     

酪蛋白水解物替代乳清蛋白的加工性能评价研究

利用复合蛋白酶水解酪蛋白制备适度及深度水解酪蛋白产品,测定酪蛋白水解物的加工性能。结果表明,经过酶解后,适度水解酪蛋白溶解度接近90%,深度水解酪蛋白溶解度接近100%,显著高于酪蛋白和乳清蛋白。此外,适度水解酪蛋白吸油性、起泡性分别约为乳清蛋白的3倍和1.5倍。深度水解酪蛋白在起泡性和乳化性上也显著高于乳清蛋白。可见,两款酪蛋白水解物在起泡性、乳化性、吸油性、溶解性等方面均在一定程度上优于乳清蛋白,可广泛替代乳清蛋白在食品工业中大规模应用。      

酪蛋白磷酸肽钙- 乳清蛋白复合膜物理性质的研究

在乳清分离蛋白(WPI)基础膜中引入酪蛋白磷酸肽钙(CPPs)制备成富钙的单层复配膜和双层复合膜,并对膜的有关物理性质(机械强度、含水量、水蒸气透过系数)进行评价。单层复配膜中CPPs 与WPI 的最大百分比为8%,总钙含量最高为0.59%。CPPs 的添加量对所测膜的物理性质没有显著影响(P ＞ 0.05)。双层复合膜可使总钙含量高达28% 以上,但同时也使膜的机械强度较单层复配膜降低近一半,且含水量显著降低(P ＜ 0.05)。     

乳清分离蛋白成膜工艺的研究

以乳清分离蛋白（WPI）为主料,通过添加甘油（增塑剂）和半胱氨酸（还原剂）,制备乳清分离蛋白膜。同时,对其制备工艺与性能进行了详细分析与测定,从而确定了成膜最佳工艺为:乳清分离蛋白含量为8%,增塑剂添加量为4%,还原剂的添加量为0.6mmol/L。在此工艺条件下测定乳清分离蛋白膜性能:厚度0.101±0.013mm,透明度0.055±0.005,抗拉强度1165.2±20.8g,断裂伸长率70.06%±1.62%,透H₂O性17.13±0.63g/m²·h,透O₂性3.60±0.08g/m²·d,透CO₂性445.56±5.26g/m²·d。      

乳清分离蛋白成膜工艺的研究

以乳清分离蛋白(WPI)为主料,通过添加甘油(增塑剂)和半胱氨酸(还原剂),制备乳清分离蛋白膜.同时,对其制备工艺与性能进行了详细分析与测定,从而确定了成膜最佳工艺为:乳清分离蛋白含量为8%,增塑剂添加量为4%.还原剂的添加量为0.6mmol/L.在此工艺条件下测定乳清分离蛋白膜性能:厚度0.101±0.013mm,透明度0.055±0.005.抗拉强度1165.2±20.8g.断裂伸长率70.06%±1.62%,透H2O性17.13±0.63g/m2·h,透O2性3.60±0.08g/m2·d,透CO2性445.56±5.26g/m2·d.     

高通量快速检测母乳总蛋白、乳清蛋白和酪蛋白含量方法的比较研究

分别利用Lowry、BCA和Bradford三种方法对母乳中总蛋白、乳清蛋白和酪蛋白的含量进行了测定,并以凯氏定氮法为标准,对三种方法的检测结果进行了比较。结果表明Lowry和Bradford法适用于母乳中总蛋白含量的测定,Lowry法适于母乳中乳清蛋白含量的测定,Lowry、BCA和Bradford三种方法均适用于母乳中酪蛋白含量的测定。采用上述方法,只需要4 m L母乳样本,1.5 h内即可完成母乳总蛋白、乳清蛋白和酪蛋白的微量、高通量快速测定。上述方法适用于较大量母婴营养状况的调查研究,可为母乳化婴幼儿配方乳粉的研制以及促进婴幼儿生长发育提供科学依据。      

高通量快速检测母乳总蛋白、乳清蛋白和酪蛋白含量方法的比较研究

分别利用Lowry、BCA和Bradford三种方法对母乳中总蛋白、乳清蛋白和酪蛋白的含量进行了测定,并以凯氏定氮法为标准,对三种方法的检测结果进行了比较。结果表明Lowry和Bradford法适用于母乳中总蛋白含量的测定,Lowry法适于母乳中乳清蛋白含量的测定,Lowry、BCA和Bradford三种方法均适用于母乳中酪蛋白含量的测定。采用上述方法,只需要4 m L母乳样本,1.5 h内即可完成母乳总蛋白、乳清蛋白和酪蛋白的微量、高通量快速测定。上述方法适用于较大量母婴营养状况的调查研究,可为母乳化婴幼儿配方乳粉的研制以及促进婴幼儿生长发育提供科学依据。     

定量分析加热后乳清蛋白与酪蛋白的结合

将复原脱脂乳在 70～ 90℃范围内加热 1 0～ 2 5min后 ,用超速离心分离出酪蛋白微粒 ,并用毛细管电泳法定量分析。结果显示 ,β-乳球蛋白更容易结合到酪蛋白微粒上。当加热条件为 70℃、1 0 min时就有相当多的 β-乳球蛋白发生了这种结合 ,这时酪蛋白微粒中没发现任何 α-乳清蛋白 ,只有当加热温度大于 75℃时才有少量 α-乳清蛋白与酪蛋白微粒结合。复原脱脂乳经 90℃、2 5min加热后几乎所有 β-乳球蛋白都已转入酪蛋白微粒部分 ,而只有近 50 %的α-乳清蛋白转入酪蛋白微粒。     

定量分析加热后乳清蛋白与酪蛋白的结合

将复原脱脂乳在 70～ 90℃范围内加热 1 0～ 2 5min后 ,用超速离心分离出酪蛋白微粒 ,并用毛细管电泳法定量分析。结果显示 ,β-乳球蛋白更容易结合到酪蛋白微粒上。当加热条件为 70℃、1 0 min时就有相当多的 β-乳球蛋白发生了这种结合 ,这时酪蛋白微粒中没发现任何 α-乳清蛋白 ,只有当加热温度大于 75℃时才有少量 α-乳清蛋白与酪蛋白微粒结合。复原脱脂乳经 90℃、2 5min加热后几乎所有 β-乳球蛋白都已转入酪蛋白微粒部分 ,而只有近 50 %的α-乳清蛋白转入酪蛋白微粒。      

Association of denatured whey proteins with casein micelles in heated reconstituted skim milk and its effect on casein micelle size

When skim milk at pH 6.55 was heated (75 to 100 degrees C for up to 60 min), the casein micelle size, as monitored by photon correlation spectroscopy, was found to increase during the initial stages of heating and tended to plateau on prolonged heating. At any particular temperature, the casein micelle size increased with longer holding times, and, at any particular holding time, the casein micelle size increased with increasing temperature. The maximum increase in casein micelle size was about 30-35 nm. The changes in casein micelle size were poorly correlated with the level of whey protein denaturation. However, the changes in casein micelle size were highly correlated with the levels of denatured whey proteins that were associated with the casein micelles. The rate of association of the denatured whey proteins with the casein micelles was considerably slower than the rate of denaturation of the whey proteins. Removal of the whey proteins from the skim milk resulted in only small changes in casein micelle size during heating. Re-addition of beta-lactoglobulin to the whey-protein-depleted milk caused the casein micelle size to increase markedly on heat treatment. The changes in casein micelle size induced by the heat treatment of skim milk may be a consequence of the whey proteins associating with the casein micelles. However, these associated whey proteins would need to occlude a large amount of serum to account for the particle size changes. Separate experiments showed that the viscosity changes of heated milk and the estimated volume fraction changes were consistent with the particle size changes observed. Further studies are needed to determine whether the changes in size are due to the specific association of whey proteins with the micelles or whether a low level of aggregation of the casein micelles accompanies this association behaviour. Preliminary studies indicated lower levels of denatured whey proteins associated with the casein micelles and smaller changes in casein micelle size occurred as the pH of the milk was increased from pH 6.5 to pH 6.7.     

超滤膜分离技术回收乳清蛋白工艺研究

研究利用超滤膜分离技术,从干酪素乳清废弃液中回收乳清蛋白,通过对不同超滤膜性能的比较,选择最佳的超滤膜材料、工艺流程以及运行参数,并测得分离效果。结果表明:采用PW2540型聚醚砜卷式超滤膜较好,其最佳工艺参数为操作温度35℃,操作压力0.5MPa,且超滤膜透液通量较高,运行稳定。乳清蛋白粉中蛋白质含量72.40%,灰分3.85%。经红外光谱检测证明乳清蛋白粉品质得到较大程度的提高。每吨乳清废弃液中可回收乳清蛋白粉5.13kg,具有较好的经济效益及减排环保效益。     

Heat and/or high-pressure treatment of skim milk: changes to the casein micelle size, whey proteins and the acid gelation properties of the milk

Skim milk was subjected to heat, pressure or combined processes. In general, higher levels of whey protein denaturation were observed for milk subjected to combined processes than those heat- or pressure-treated only. Heat treatment caused small changes to the casein micelle size. Pressure treatment decreased the casein micelle size; however, the effect was less marked when heat and pressure treatments were combined. Acidification of the skim milks produced gels with a range of firmness, yield stresses and yield strains depending on the treatments applied. These changes in acid gel properties were not related only to whey protein denaturation levels in the milks.     

Yak milk whey protein denaturation and casein micelle disaggregation/aggregation at different pH and temperature

At the natural pH of yak milk (pH 6.6), a low level (<30%) of κ-casein (κ-CN) was found in the serum phase after heating at 95 °C for 30 min, indicating that as much as 70% of the β-lactoglobulin (β-Lg) and κ-CN complexes is associated with the micelle colloidal particles. The β-Lg and κ-CN levels increased from 13.2% and 2.6% at pH 6.0 to 35.2% and 60.1% at pH 7.0, respectively, when yak milk was heated at 95 °C for 30 min. At pH 6.0–6.4, the denatured whey proteins were associated with the caseins in the colloidal phase, resulting in milk gelation upon heating. The distribution of β-Lg and κ-CN complexes increased in the serum phase, demonstrated by the increasing levels of both β-Lg and κ-CN with increasing pH; at high pH (6.6–7.0), large proportions of β-Lg and α-lactalbumin were lost, presumably forming complexes in the colloidal phase.     

Effect of heat treatment and casein to whey protein ratio of skim milk on graininess and roughness of stirred yoghurt

The aim of this work was to study how heat treatment and casein (CN) to whey protein (WP) ratio of skim milk affect physical characteristics of stirred yoghurt. Different heat treatments (95 °C/256 s, 110 °C/180 s and 130 °C/80 s) were applied to the yoghurt milk with the CN to WP ratios of 1.5:1, 2:1, 3:1 and 4:1. Physical properties, including graininess and roughness, of stirred yoghurt were determined during storage at 4 °C for 15 days. Visual roughness, number of grains, perimeter of grains, storage modulus, and yield stress decreased, when heating temperature or CN to WP ratio increased.     

Effect of preheating and other process parameters on whey protein reactions during skim milk powder manufacture

Skim milk powder was manufactured in a milk powder plant using different preheating temperatures, concentrate heating temperatures and spray drying temperatures. Varying the preheating conditions from 70 °C for 52 s to 120 °C for 52 s had a marked effect on the denaturation of $\beta$-lactoglobulin A, $\beta$-lactoglobulin B, $\alpha$-lactalbumin, bovine serum albumin (BSA), and immunoglobulin G. In contrast, varying concentrate heating temperature (65–74 °C) and inlet/outlet air dryer temperature (200/101 °C–160/89 °C) had a minimal effect on whey protein denaturation. Most of the whey protein denaturation and association with the casein micelle occurred in the preheating section of the powder plant. Aggregation of β-lactoglobulin (β-lg) and BSA predominantly involved disulphide bonds. Although, greater than 90% of the β-lg and BSA was denatured after preheating at 120 °C for 52 s, the extent of association with the casein micelle was lower, 50% for β-lg and 75% for BSA.     

Performance assessment of membrane distillation for skim milk and whey processing

Membrane distillation is an emerging membrane process based on evaporation of a volatile solvent. One of its often stated advantages is the low flux sensitivity toward concentration of the processed fluid, in contrast to reverse osmosis. In the present paper, we looked at 2 high-solids applications of the dairy industry: skim milk and whey. Performance was assessed under various hydrodynamic conditions to investigate the feasibility of fouling mitigation by changing the operating parameters and to compare performance to widespread membrane filtration processes. Whereas filtration processes are hydraulic pressure driven, membrane distillation uses vapor pressure from heat to drive separation and, therefore, operating parameters have a different bearing on the process. Experimental and calculated results identified factors influencing heat and mass transfer under various operating conditions using polytetrafluoroethylene flat-sheet membranes. Linear velocity was found to influence performance during skim milk processing but not during whey processing. Lower feed and higher permeate temperature was found to reduce fouling in the processing of both dairy solutions. Concentration of skim milk and whey by membrane distillation has potential, as it showed high rejection (>99%) of all dairy components and can operate using low electrical energy and pressures (<10 kPa). At higher cross-flow velocities (around 0.141 m/s), fluxes were comparable to those found with reverse osmosis, achieving a sustainable flux of approximately 12 kg/h·m² for skim milk of 20% dry matter concentration and approximately 20 kg/h·m² after 18 h of operation with whey at 20% dry matter concentration.     

Kinetics of heat-induced interactions among whey proteins and casein micelles in sheep skim milk and aggregation of the casein micelles

The interactions among the proteins in sheep skim milk (SSM) during heat treatments (67.5–90°C for 0.5–30 min) were characterized by the kinetics of the denaturation of the whey proteins and of the association of the denatured whey proteins with casein micelles, and changes in the size and structure of casein micelles. The relationship between the size of the casein micelles and the association of whey proteins with the casein micelles is discussed. The level of denaturation and association with the casein micelles for β-lactoglobulin (β-LG) and α-lactalbumin (α-LA) increased with increasing heating temperature and time; the rates of denaturation and association with the casein micelles were markedly higher for β-LG than for α-LA in the temperature range 80 to 90°C; the Arrhenius critical temperature was 80°C for the denaturation of both β-LG and α-LA. The casein micelle size increased by 7 to 120 nm, depending on the heating temperature and the holding time. For instance, the micelle size (about 293 nm) of SSM heated at 90°C for 30 min increased by about 70% compared with that (about 174.6 nm) of unheated SSM. The casein micelle size increased slowly by a maximum of about 65 nm until the level of association of the denatured whey proteins with casein micelles reached 95%, and then increased markedly by a maximum of about 120 nm when the association level was greater than about 95%. The marked increases in casein micelle size in heated SSM were due to aggregation of the casein micelles. Aggregation of the casein micelles and association of whey protein with the micelles occurred simultaneously in SSM during heating.     

Acidification of lactoferrin-casein micelle complexes in skim milk

Lactoferrin electrostatically bound to the casein micelles when added to milk, which caused the absolute zeta potential to decrease and the micelle size to increase. On acidification, the lactoferrin progressively dissociated from the micelles, which, at pH below ∼5.0, caused the zeta potential of the casein micelles to be the same as those in milk without added lactoferrin. Acidification caused increased levels of casein to dissociate from the casein micelles at ∼pH 5.0 as the level of added lactoferrin in the milk increased. Lactoferrin decreased the pH at which the milk gelled and caused the G′ and yield stress of the set gels to increase at low levels of added lactoferrin, decrease at intermediate levels of added lactoferrin and increase again at high levels of added lactoferrin. This unusual effect of lactoferrin on gelation was hypothesised to be due to combined effects of dissociated casein and the lower gelation pH.