Venkatachalam N, McMahon D J, Savello P A
Department of Nutrition and Food Sciences, Utah State University, Logan 84322-8700.
J Dairy Sci. 1993 Jul;76(7):1882-94. doi: 10.3168/jds.S0022-0302(93)77521-9.
Skim milk was pasteurized, diafiltered, and concentrated three times by UF. Lactose or sucrose was then added at 3 or 6%. The five samples containing < .05% lactose, 3 and 6% lactose, and 3 and 6% sucrose were UHT processed at 140 degrees C for 4 s using indirect heating, collected aseptically in presterilized containers, and stored at 4, 20, and 35 degrees C. All samples stored at 4 and 20 degrees C gelled after 21 wk of storage. Samples stored at 35 degrees C did not gel. Browning occurred only in samples containing lactose stored at 35 degrees C. Proteolysis in gelled samples was shown by SDS-PAGE. Bands were due to proteolysis, protein crosslinking, and a streaking pattern in ungelled samples. Electron micrographs of gelled samples showed that various casein particles were connected by hairlike protrusions, but the micelles in ungelled samples were not connected and had few protrusions. The Maillard reaction neither promoted nor deferred age gelation. Protein modifications prevented gelation in samples stored at 35 degrees C. Age gelation was probably a two-step process in which dissociated proteins from the casein micelles reformed on micelles as hairlike protrusions. This process was followed by aggregation of the protein particles.
脱脂牛奶经过巴氏杀菌、渗滤，并通过超滤浓缩三次。然后分别添加3%或6%的乳糖或蔗糖。五个样品分别含有<0.05%乳糖、3%乳糖、6%乳糖、3%蔗糖和6%蔗糖，采用间接加热在140℃下进行4秒的超高温瞬时处理，无菌收集到预先灭菌的容器中，并分别储存在4℃、20℃和35℃。所有储存在4℃和20℃的样品在储存21周后发生了凝胶化。储存在35℃的样品没有凝胶化。褐变仅发生在储存在35℃的含乳糖样品中。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）显示了凝胶化样品中的蛋白水解情况。条带是由蛋白水解、蛋白质交联以及未凝胶化样品中的条纹状图案引起的。凝胶化样品的电子显微镜照片显示，各种酪蛋白颗粒通过毛发状突起相连，但未凝胶化样品中的胶束没有相连且突起较少。美拉德反应既没有促进也没有延缓老化凝胶化。蛋白质修饰阻止了储存在35℃的样品发生凝胶化。老化凝胶化可能是一个两步过程，其中酪蛋白胶束中解离的蛋白质在胶束上重新形成毛发状突起。这个过程之后是蛋白质颗粒的聚集。
