Ben Amara-Dali Wafa, Lopez Christelle, Lesieur Pierre, Ollivon Michel
Equipe Physico-Chimie des Systèmes Polyphasés, UMR 8612, CNRS, Université Paris XI, 5 rue J. B. Clément, 92296, Châtenay-Malabry, France.
J Agric Food Chem. 2008 Jun 25;56(12):4511-22. doi: 10.1021/jf073491g. Epub 2008 May 22.
The sensorial, functional, and nutritional properties of goat dairy products result from the specific fatty acid composition of goat's milk fat. However, information on the physical and thermal properties of goat's milk fat is scarce. In this study, crystallization of triacylglycerols (TG) in goat's milk fat globules was investigated using polarized light microscopy and the coupling of time-resolved synchrotron radiation X-ray diffraction (XRD) and high-sensitivity differential scanning calorimetry (DSC). The molecular organization of the solid fat phase was characterized for cooling rates between 3 and 0.1 degrees C/min. Quenching of goat's milk fat globules from 50 to -8 degrees C and 4 degrees C was also examined to identify the most unstable polymorphic forms of TG. Then, the melting behavior of fat crystals was studied on subsequent heating at 1 degrees C/min. Triple chain length (3L: 68.6-70 A) and double chain length (2L: 37-45.4 A) structures were characterized and 5 polymorphic forms, alpha, sub-alpha, beta' 1, beta' 2, and beta were identified. Polymorphic transitions were observed within goat's milk fat globules as a function of time after quenching and as a function of temperature on heating. From a technological point of view, this work will contribute to a better understanding of the rheological properties as well as on the flavor evolutions of goat's milk-based products.
山羊乳制品的感官、功能和营养特性源于山羊乳脂肪特定的脂肪酸组成。然而，关于山羊乳脂肪物理和热性质的信息却很匮乏。在本研究中，利用偏光显微镜以及时间分辨同步辐射X射线衍射（XRD）与高灵敏度差示扫描量热法（DSC）联用技术，对山羊乳脂肪球中三酰甘油（TG）的结晶情况进行了研究。针对3至0.1℃/分钟的冷却速率，对固体脂肪相的分子结构进行了表征。还研究了将山羊乳脂肪球从50℃淬冷至-8℃和4℃的情况，以确定TG最不稳定的多晶型物。随后，以1℃/分钟的升温速率研究了脂肪晶体的熔化行为。表征了三链长（3L：68.6 - 70 Å）和双链长（2L：37 - 45.4 Å）结构，并鉴定出5种多晶型物，即α、亚α、β'1、β'2和β。观察到山羊乳脂肪球内多晶型转变是淬冷后时间以及加热时温度的函数。从技术角度来看，这项工作将有助于更好地理解基于山羊奶产品的流变特性以及风味演变。
