不同沉淀方法对牛乳中蛋白质质量分数测定的影响

通过单因素试验和正交试验优化硫酸铜、饱和食盐水、乙醇、乙酸铅、三氯乙酸沉淀牛乳中蛋白氮的最佳沉淀条件,并对分别添加了尿素、硝酸铵、亚硝酸钠、三聚氰胺、三种水解蛋白的牛乳样品进行前处理,采用凯氏定氮法测定各样品蛋白质质量分数,研究不同沉淀剂对含非蛋白氮牛乳中蛋白质质量分数测定的影响。结果表明,三氯乙酸为沉淀牛乳中蛋白质的最佳沉淀剂,沉淀效果优劣顺序为三氯乙酸乙醇饱和食盐水硫酸铜乙酸铅,本研究旨在为进一步提高凯氏定氮法测定牛乳中蛋白质质量分数的准确性提供理论依据。     

加压CO_2在生理盐水中的杀菌效果研究

<正>CO2是一种天然、安全的杀菌剂,它的临界温度和临界压力分别为31.1℃、7.13MPa,加压CO2杀菌技术是利用高于或接近于临界温度和临界压力的CO2对食品进行杀菌。使用这项技术处理生理盐水中的大肠杆菌、枯草芽孢杆菌和金黄色葡萄球菌。选择不同的压力(1MPa、3MPa、5MPa和7.5MPa)、时间(15min、30min、45min和60min)、温度(25℃、35℃、45℃和55℃),研究影响杀菌效果的因素。结果表明随着压力、时间和温度提高,加压CO2的杀菌效果逐渐提高;加压CO2对3种菌的杀菌效果     

牛羊乳蛋白质粒度对其热处理沉淀率的影响

研究牛羊乳蛋白质粒度大小对其热处理沉淀率的影响。采用离心沉淀、原子力显微镜、激光粒度仪和SDS-PAGE分析热处理后(95℃,15 min)牛羊乳蛋白质沉淀率、表面形貌、牛羊鲜乳蛋白质粒度和酪蛋白组成。结果表明:羊乳热处理后沉淀率显著高于牛乳(p0.05);羊乳蛋白质粒子明显大于牛乳,其蛋白质热处理片状凝聚程度(35 858.15 nm~2)大于牛乳(18 215.18 nm~2);鲜牛乳蛋白质粒度大小主要集中在1 nm以下,鲜羊乳蛋白质粒度在1 nm以下相对较少,主要分布在1~1 000 nm之间;牛羊鲜乳酪蛋白主要有β-酪蛋白和αs1-酪蛋白两种,相对分子质量分别为34 000和26 000左右。牛乳的热稳定性高于羊乳;蛋白质粒度大小是影响其热稳定性的直接因素;原子力显微镜结合激光粒度仪是分析乳蛋白粒度的有效手段。     

直读法测牛乳中蛋白质含量

建立了一种直观快速的测定方法以检测牛乳中蛋白质含量.对牛乳进行脱脂、水浴加热后加入一定量的蛋白质沉淀剂,离心分离,根据沉淀体积直接读取蛋白质含量.该法简便易行,在置信度大于90%时,置信区间为(8.72±0.43),RSD为4.75%.该方法快速准确,作为一种快速测量牛乳中蛋白质的方法,结果令人满意.     

超临界CO_2杀灭牛乳中细菌的研究

主要研究超临界CO2对牛乳中细菌的杀菌效果。通过单因素实验来初探压力、杀菌时间和杀菌温度对杀菌率的影响,然后采用正交实验来确定最适的杀菌条件,并对杀菌后牛乳的部分营养成分进行了分析。研究结果表明,当压力为35MPa,杀菌时间为140min,杀菌温度为45℃时,CO2气体对牛乳中细菌的杀菌率为99·8%,且牛乳的营养成分损失较小。实验表明,超临界CO可以有效地杀灭牛乳中的细菌,减小营养成分的损失。     

酪蛋白沉淀测定方法在市售纯牛乳中的应用与验证

为了改进乳品中蛋白质含量的测定方法,在酪蛋白测定方法的前期研究基础上,增加了NaOH溶液碱复溶酪蛋白等电点沉淀物,结合凯氏定氮法对2种市售纯牛乳中的乳蛋白组分进行了测定。实验结果表明,酪蛋白质量分数约为61%,酪蛋白和乳清蛋白相加得到的理论蛋白质含量与实际测定的总蛋白质质量分数误差不超过1.38%,改进后的等电点沉淀分离结合凯氏定氮法高效准确,重现性好,可以用于纯牛乳中酪蛋白的掺假鉴定。     

CO2对乳性质的影响及在乳品杀菌中的研究进展

综述了在不同条件下，在牛乳中充入CO2，同时与未处理的原料乳做对照。通过对牛乳蛋白和脂肪的水解情况、细菌的生长参数、CO2注入温度对牛乳pH值和冰点的影响等方面研究CO2对牛乳的处理效果。结果表明，经CO2处理的牛乳具有很好的抑菌效果，尤其在低温条件下，能够有效抑制乳中细菌的生长，保证乳品的质量，延长乳制品的货架期，具有很好的市场前景。     

应用亚临界CO2综合萃取技术对于干辣椒、木薯、红薯片深加工的可行性研究

本文主要以亚临界CO2萃取工艺的技术原理，以绿色溶剂CO2为萃取溶剂，（乙醇）为夹带剂，在对辣椒、木薯、红薯萃取过程中以不同的压力、温度提取有效成分。亚临界和超临界同属一类工艺技术，而亚临界只是在临界压力之间工作，应用亚临界技术萃取，其萃取压力比超临界的低，生产条件温和、安全，能有选择性地分离辣椒、木薯、红薯的有效成分。     

牛羊乳酪蛋白制备及电泳分析比较

采采用新鲜和复原的牛羊乳为原料,等电点沉淀,通过洗涤、干燥等步骤分别制得牛乳和羊乳酪蛋白,用凯氏定氮法对其进行定量检测,应用十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS—PAGE）分析比较牛羊乳酪蛋白组分差异。结果表明：牛乳酪蛋白得率为86．75％,羊乳酪蛋白得率为90．55％,高含量的酪蛋白主要集中在电泳图谱的中分子量组,可分为ds,CN、as2-CN、β-CN和K—CN,牛羊乳as2-CN分子量羊乳大于牛乳,牛乳a-CN含量比较多,羊乳β—CN含量比较多,鲜乳与复原乳全蛋白主要组分在电泳图谱中除酪蛋白差别外,上端的高分子量组清蛋白区羊乳IgG重链的分子量比牛乳小。应用蛋白质电泳分析技术可以区分羊乳和牛乳的蛋白质组分,等电点沉淀法制备酪蛋白的方法简单,易于操作。     

超临界CO2杀灭牛乳中细菌模型建立

选用超临界CO2对牛乳中细菌进行杀菌处理。采用中心旋转组合试验设计方法,考察了不同的压力、温度和杀菌时间对牛乳中细菌的作用效果,建立了相应的杀菌模型,并利用SPSS对数据进行了相关性分析,得到实测值与预测值的相关系数为0.9980。     

超临界二氧化碳萃取天津冬菜中呈色物质的初步研究

以超临界CO2为溶剂提取天津冬菜中的呈色物质。选用L9(34)正交表,以萃取物A550吸光度平均值为指标,分别考察有无夹带剂存在时,温度、压力、CO2流量对萃取效率的影响。结果表明:压力与温度是萃取的主要影响因素;以水作为夹带剂可有效提高天津冬菜中呈色物质的萃取效率。     

利用超临界技术萃取石榴叶总酚工艺研究

利用超临界CO2 装置对石榴叶中总酚提取工艺进行研究,以期得到高生理活性和高纯度的石榴叶活性物质。通过单因素和正交试验,得到最佳萃取条件为料液比1:2.5(g/ml)、萃取压力25MPa、萃取温度60℃、萃取时间120min。活性物质得率为0.1728%,纯度为42.61%。     

Milk pH as a function of CO2 concentration, temperature, and pressure in a heat exchanger

Raw skim milk, with or without added CO2, was heated, held, and cooled in a small pilot-scale tubular heat exchanger (372 ml/min). The experiment was replicated twice, and, for each replication, milk was first carbonated at 0 to 1 degree C to contain 0 (control), 600, 1200, 1800, and 2400 ppm added CO2 using a continuous carbonation unit. After storage at 0 to 1 degree C, portions of milk at each CO2 concentration were heated to 40, 56, 72, and 80 degrees C, held at the desired temperature for 30 s (except 80 degrees C, holding 20 s) and cooled to 0 to 1 degree C. At each temperature, five pressures were applied: 69, 138, 207, 276, and 345 kPa. Pressure was controlled with a needle valve at the heat exchanger exit. Both the pressure gauge and pH probe were inline at the end of the holding section. Milk pH during heating depended on CO2 concentration, temperature, and pressure. During heating of milk without added CO2, pH decreased linearly as a function of increasing temperature but was independent of pressure. In general, the pH of milk with added CO2 decreased with increasing CO2 concentration and pressure. For milk with added CO2, at a fixed CO2 concentration, the effect of pressure on pH decrease was greater at a higher temperature. At a fixed temperature, the effect of pressure on pH decrease was greater for milk with a higher CO2 concentration. Thermal death of bacteria during pasteurization of milk without added CO2 is probably due not only to temperature but also to the decrease in pH that occurs during the process. Increasing milk CO2 concentration and pressure decreases the milk pH even further during heating and may further enhance the microbial killing power of pasteurization.     

Extraction behaviors of caffeine and chlorophylls in supercritical decaffeination of green tea leaves

The decaffeination of green tea using supercritical carbon dioxide (SC-CO₂) was optimized by response surface methodology (RSM) for the maximal removal of caffeine, and the coextration of chlorophylls was also monitored during decaffeination. The experimental conditions for the SC-CO₂ extraction of caffeine were set up according to the Box-Behnken design of RSM. The relationships between the extraction yield of caffeine and various parameters used for the SC-CO₂ extraction such as pressure, temperature and concentration of ethanol were studied at a fixed CO₂ flow rate. The extraction yields of caffeine and total chlorophyll were significantly influenced by extraction pressure, temperature and concentration of cosolvent, and their extraction yields behaved almost in parallel at different extraction conditions that were obtained by varying pressure, temperature and ethanol cosolvent concentration. At the optimal decaffeination conditions such as 3.0 g of 95% (v/v) ethanol cosolvent per 100 g of CO₂, 23 MPa, 63 °C and an extraction duration of 120 min for 10 g of green tea leaves, the extraction yields for caffeine and catechins were 96.60% (w/w) and 40.61% (w/w), respectively, and the substantial coextraction of total chlorophyll (43.09% of the total amount) was also observed during the decaffeination process.     

Dynamics of precipitation of casein with carbon dioxide

Carbon dioxide is a green alternative for mineral acids (e.g., sulphuric acid) in protein precipitation. The precipitation using a gaseous precipitant differs from the conventional precipitation in the way and the rate at which the precipitant can be applied to the aqueous solution. In this paper, the consequences of using carbon dioxide were investigated for the precipitation of the milk protein casein. Product properties, such as particle size, solids content and calcium release were investigated in a batch system at various mixing conditions and gas addition rates. In addition, mass transfer coefficients were determined from pH response data.The experiments revealed a strong influence of stirring rate and gas flow rate on the particle size. The main effect of varying the gas flow was through the change of acidification rate, much alike precipitation with sulphuric acid. At high acidification rates, the particle size of casein precipitated with carbon dioxide was smaller than with sulphuric acid.     

超临界CO_2法萃取芹菜叶黄酮

在考察超临界CO2萃取温度、萃取压力、萃取时间以及夹带剂用量等单因素对黄酮萃取率影响的基础上,采用Box-Behnken响应曲面设计法,建立影响因素和黄酮得率之间的回归方程。结果表明:萃取温度、萃取压力、萃取时间对超临界CO2萃取芹菜中黄酮工艺影响极显著,夹带剂用量影响显著,最佳提取工艺条件为萃取温度70℃、萃取压力30 MPa、萃取时间2.5 h、夹带剂用量为1 mL/g。该条件下黄酮得率为9.03%,与预测值相近,差异不显著,符合实验要求。     

超临界CO_2萃取大蒜油工艺研究

该文报道影响超临界流体萃取(SFE)技术提取大蒜油的相关因素,包括萃取压力、萃取温度、萃取时间、夹带剂用量等。通过正交试验,确定超临界二氧化碳萃取大蒜油适宜工艺参数组合:即以15％(V／W)无水乙醇为夹带剂,萃取压力为25 MPa,萃取温度为35℃,萃取时间为240 min,在上述提取条件下,SFE提取大蒜油得率达0．446％。结果表明:超临界流体萃取大蒜油呈淡黄褐色,半透明状,略有流动性,呈有新鲜大蒜风味。     

Effects of high‐pressure homogenisation on physicochemical characteristics of partially skimmed milk

The changes in partially skimmed milk (0.5% fat) physicochemical properties and proteins after high‐pressure homogenisation (HPH) at 100, 200 and 300 MPa were investigated. Processing parameters and changes in pH, ethanol precipitation stability, lightness, whey protein denaturation, hydrophobicity and viscosity were evaluated. No significant differences were found between milk pH and nonprotein nitrogen content before and after HPH. Ethanol stability, lightness and hydrophobicity increased when pressure was increased from 100 MPa to 300 MPa. Whey protein denaturation, evaluated through noncasein nitrogen, occurred only at 200 to 300 MPa, and viscosity increased just at 300 MPa. Therefore, HPH changed some milk physicochemical characteristics, mainly those related to protein content. These results highlight that HPH processing is a promising technology to improve partially skimmed milk mouth feel being suitable for dairy products manufacturing.     

油酸-甘油-无水乙醇共混体系与超临界CO2的相平衡

旨在为生物柴油后处理阶段的超临界CO₂提纯工艺提供参考数据,以生物柴油生产过程中后处理阶段体系所含的油酸、无水乙醇及甘油为原料,通过在SYLG-01型超临界流体相平衡实验装置中,观察油酸-甘油-无水乙醇共混体系在温度为308 K下与CO₂达到相平衡状态的过程。结果表明,油酸-甘油-无水乙醇共混体系为液-液两相,与CO₂在相平衡实验装置内最开始是气-液-液态,随着压力的增加,当CO₂达到超临界状态时,不同相之间的流动性和传递性增强,共混体系变成了均一态。因此,改变超临界CO₂的压力,有望将体系中的游离脂肪酸和副产物甘油同时萃取分离。     

常见热杀菌方式对关中羊乳品质的影响

采用5种常用热杀菌方式处理关中羊乳,即低温长时巴氏杀菌(65 ℃/30 min)、高温短时巴氏杀菌(72 ℃/15 s)、超巴氏杀菌(95 ℃/5 min)、高温高压灭菌(121 ℃/20 min)和超高温瞬时灭菌(137 ℃/7 s),在测定蛋白沉淀率、酒精稳定性、pH、红度值、粘度和脂肪球变化基础上,结合内源荧光光谱和聚丙烯酰胺凝胶电泳(SDS-PAGE)分析,探究热杀菌处理对关中羊乳品质的影响。结果表明,高温高压灭菌羊乳蛋白沉淀率最高、酒精稳定性最差、pH明显下降、红度值明显增大,但5种杀菌方式对粘度没有显著影响(p>0.05);羊乳脂肪球经巴氏杀菌和超巴氏杀菌后,表观直径略微增大,而高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则导致其明显变小;荧光光谱表明,高温高压灭菌羊乳蛋白结构改变最大,内源荧光强度剧烈升高;电泳显示,巴氏杀菌(65 ℃/30 min和72 ℃/15 s)对羊乳酪蛋白和乳清蛋白影响较小,超巴氏杀菌(95 ℃/5 min)乳清蛋白开始变性、聚集或部分降解,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则使乳清蛋白明显降解甚至消失,酪蛋白出现聚集和解聚。结果表明,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌对关中羊乳品质影响较大,超巴氏杀菌影响次之,而巴氏杀菌则对其影响较小。