Food Chemistry, Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Nikolaus-Fiebiger-Straße 10, 91058 Erlangen, Germany.
Physical Chemistry I, Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 3, 91058 Erlangen, Germany.
J Proteomics. 2019 Sep 15;207:103444. doi: 10.1016/j.jprot.2019.103444. Epub 2019 Jul 16.
Proteolysis during the storage of UHT milk is associated with major technological problems, particularly bitter off-flavors and age gelation limiting the shelf life of milk. In this study, untargeted peptide profiling by MALDI-TOF-MS identified peptides that were formed by proteolysis and reflected the storage of UHT milk. Analysis of nine different commercial UHT samples recorded peptide profiles during and at the end of their shelf life. Relative quantification and sequencing of the peptides revealed that the concentrations of 22 peptides increased significantly during the storage of UHT milk due to the activity of endogenous milk proteases and microbial proteases as well as other unidentified proteolytic mechanisms. Based on highly discriminative AUC values from receiver operator characteristic (ROC) curve analysis, we selected ten peptides as marker candidates. Among those, the peptide β-casein (m/z 1668.9) was the most suitable marker differentiating expired-UHT from regular-UHT samples with 100% accuracy. Additionally, β-casein (m/z 1782.0) showed 100% specificity and β-casein (m/z 2696.4) 100% sensitivity. Thus, β-casein, either by itself or in combination with β-casein and β-casein, presents a reliable marker to monitor the storage of UHT milk based on proteolytic mechanisms. SIGNIFICANCE: Enzymatic hydrolysis is the main reason why processed milk spoils during storage. The present study recorded peptide profiles to monitor the release or degradation of peptides in stored UHT milk. Among the detected peptides, statistical analysis revealed that the relative concentration of β-casein reflected those proteolytic processes most precisely. Food authorities can now refer to β-casein as a reliable marker to differentiate between freshly processed milk and products at the end of their shelf life. Furthermore, the food industry can use this marker peptide to improve production processes by monitoring the proteolysis during storage. The recorded peptide profile helps to explain the basic mechanisms leading to storage-induced proteolysis.
UHT 牛奶储存过程中的蛋白水解与主要技术问题有关，特别是苦味和陈化凝胶会限制牛奶的保质期。在这项研究中，基质辅助激光解吸电离飞行时间质谱（MALDI-TOF-MS）的非靶向肽谱分析鉴定出了由蛋白水解形成的肽，这些肽反映了 UHT 牛奶的储存情况。对 9 种不同商业 UHT 样品的分析记录了其货架寿命期间和结束时的肽谱。对肽的相对定量和测序表明，由于内源性乳蛋白酶和微生物蛋白酶以及其他未识别的蛋白水解机制的活性，22 种肽的浓度在 UHT 牛奶储存过程中显著增加。基于接收者操作特征（ROC）曲线分析的高判别 AUC 值，我们选择了 10 种肽作为候选标记物。其中，β-酪蛋白（m/z 1668.9）是区分过期-UHT 和常规-UHT 样品的最适合标记物，准确率为 100%。此外，β-酪蛋白（m/z 1782.0）具有 100%的特异性，β-酪蛋白（m/z 2696.4）具有 100%的灵敏度。因此，β-酪蛋白本身或与β-酪蛋白和β-酪蛋白联合使用，是一种基于蛋白水解机制监测 UHT 牛奶储存的可靠标记物。意义：酶水解是加工牛奶在储存过程中变质的主要原因。本研究记录了肽谱，以监测储存 UHT 牛奶中肽的释放或降解。在所检测到的肽中，统计分析表明，β-酪蛋白的相对浓度最能准确反映这些蛋白水解过程。食品当局现在可以将β-酪蛋白作为区分新鲜加工牛奶和货架期结束产品的可靠标记物。此外，食品行业可以通过监测储存过程中的蛋白水解来使用这种标记肽来改进生产工艺。记录的肽谱有助于解释导致储存诱导蛋白水解的基本机制。
