Effects of UV induced photo-oxidation on the physicochemical properties of milk protein concentrate
首发时间:2014-04-01
Abstract:The objective of this study was to investigate the effects of UV induced photo-oxidation on protein modification and corresponding changes in color and solubility of milk protein concentrate powder (MPC70) stored at 25 or 40 C and at 11, 33 or 75% relative humidity (RH), respectively. Protein modifications in the soluble fractions were determined using liquid chromatography-mass spectrometry (LC-MS) and those in insoluble fractions using gel electrophoresis. The results showed that photo-oxidation caused significant decreases in L* value. Moreover, the solubility of photo-oxidized MPC70 decreased significantly, while the MPC70 samples without UV exposure retained their solubility, except at 40 C and 75% RH. For the soluble fractions of photo-oxidized MPC70, the MS spectra showed multiple additional fractions besides the un- and lactosylated intact protein fractions compared to control suggesting that the photo-oxidation induced further modifications of the proteins, which coincided with the formation of carbonyl groups in the protein. The insoluble fractions of photo-oxidized MPC70 were mainly caseins as well as high molecular weight aggregates, resulting mainly from non-disulfide covalent crosslinks induced by photo-oxidation. The results suggested that photo-oxidation could induce modification of protein that eventually contributed to the solubility loss and discoloration of MPC70.?????
keywords: milk protein concentrate photo-oxidation protein modification aggregation solubility color.?????
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UV诱导的光氧化对牛奶浓缩蛋白理化性质的影响
摘要:将牛奶浓缩蛋白(MPC 70)分别储藏在温度为25、40℃,相对湿度为11、33、75%的条件下,并利用紫外光照射蛋白粉(同时设置参照组)以研究紫外光诱导的光氧化对蛋白质修饰的影响以及相应的蛋白质颜色及溶解性的改变。利用液相色谱-质谱联用仪(LC-MS)测定蛋白可溶性部分的修饰,利用凝胶电泳测定蛋白不可溶部分的修饰。实验结果表明,光氧化使蛋白的L*值显著降低。并且,用紫外光照的蛋白其溶解度在储藏过程中显著下降,而未被紫外光照的蛋白保持了其原有的溶解特性(在75%相对湿度、40℃下储存的蛋白除外)。比起对照组,光氧化蛋白可溶性部分的质谱图显示了未糖基化的和糖基化的完整蛋白、以及多个位于这些完整蛋白附近的其它组分,这表明,光氧化诱导了蛋白质的修饰,这与蛋白内羰基的形成相一致。光氧化的MPC 70 不可溶性部分主要是酪蛋白以及大分子量的蛋白聚集体,这可能是由光氧化诱导蛋白质通过二硫键的共价交联而形成。综上所述,光氧化可以诱导MPC 70发生修饰,进而降低其溶解度,同时使颜色发生改变。
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No.4590971965297139****
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