Tansman G F, Kindstedt P S, Hughes J M
Department of Nutrition and Food Sciences, University of Vermont, Burlington 05405-0086, USA.
J Dairy Sci. 2014 Dec;97(12):7354-62. doi: 10.3168/jds.2014-8277. Epub 2014 Oct 18.
Powder X-ray diffraction has been used for decades to identify crystals of calcium lactate pentahydrate in Cheddar cheese. According to this method, diffraction patterns are generated from a powdered sample of the crystals and compared with reference cards within a database that contains the diffraction patterns of known crystals. During a preliminary study of crystals harvested from various Cheddar cheese samples, we observed 2 slightly different but distinct diffraction patterns that suggested that calcium lactate pentahydrate may be present in 2 different crystalline forms. We hypothesized that the 2 diffraction patterns corresponded to 2 enantiomeric forms of calcium lactate pentahydrate (L- and DL-) that are believed to occur in Cheddar cheese, based on previous studies involving enzymatic analyses of the lactate enantiomers in crystals obtained from Cheddar cheeses. However, the powder X-ray diffraction database currently contains only one reference diffraction card under the title “calcium lactate pentahydrate.” To resolve this apparent gap in the powder X-ray diffraction database, we generated diffraction patterns from reagent-grade calcium l-lactate pentahydrate and laboratory-synthesized calcium dl-lactate pentahydrate. From the resulting diffraction patterns we determined that the existing reference diffraction card corresponds to calcium dl-lactate pentahydrate and that the other form of calcium lactate pentahydrate observed in cheese crystals corresponds to calcium l-lactate pentahydrate. Therefore, this report presents detailed data from the 2 diffraction patterns, which may be used to prepare 2 reference diffraction cards that differentiate calcium l-lactate pentahydrate from calcium dl-lactate pentahydrate. Furthermore, we collected crystals from the exteriors and interiors of Cheddar cheeses to demonstrate the ability of powder X-ray diffraction to differentiate between the 2 forms of calcium lactate pentahydrate crystals in Cheddar cheeses. Powder X-ray diffraction results were validated using enzymatic assays for lactate enantiomers. These results demonstrated that powder X-ray diffraction can be used as a diagnostic tool to quickly identify different forms of calcium lactate pentahydrate that may occur in Cheddar cheese.
几十年来，粉末X射线衍射一直被用于鉴定切达干酪中五水合乳酸钙晶体。根据这种方法，从晶体的粉末样品中生成衍射图谱，并与数据库中包含已知晶体衍射图谱的参考卡片进行比较。在对从各种切达干酪样品中收获的晶体进行的初步研究中，我们观察到两种略有不同但明显不同的衍射图谱，这表明五水合乳酸钙可能以两种不同的晶体形式存在。基于之前对从切达干酪中获得的晶体中乳酸对映体进行酶分析的研究，我们假设这两种衍射图谱对应于五水合乳酸钙的两种对映体形式（L-和DL-），据信它们存在于切达干酪中。然而，粉末X射线衍射数据库目前仅在“五水合乳酸钙”标题下包含一张参考衍射卡片。为了解决粉末X射线衍射数据库中这一明显的空白，我们从试剂级L-五水合乳酸钙和实验室合成的DL-五水合乳酸钙中生成了衍射图谱。从所得的衍射图谱中我们确定，现有的参考衍射卡片对应于DL-五水合乳酸钙，而在干酪晶体中观察到的另一种五水合乳酸钙形式对应于L-五水合乳酸钙。因此，本报告提供了来自这两种衍射图谱的详细数据，可用于制备两张区分L-五水合乳酸钙和DL-五水合乳酸钙的参考衍射卡片。此外，我们从切达干酪的外部和内部收集了晶体，以证明粉末X射线衍射区分切达干酪中两种五水合乳酸钙晶体形式的能力。使用乳酸对映体的酶促测定法对粉末X射线衍射结果进行了验证。这些结果表明，粉末X射线衍射可作为一种诊断工具，快速识别切达干酪中可能出现的不同形式的五水合乳酸钙。
