Lao Ying W, Mackenzie Kim, Vincent William, Krokhin Oleg V
Department of Chemistry, University of Manitoba, Winnipeg, Canada.
J Sep Sci. 2014 Jul;37(14):1788-96. doi: 10.1002/jssc.201400193.
Organoleptic properties of flaxseed oil deteriorate during storage due to methionine oxidation in its major cyclolinopeptides. Cyclolinopeptide E was previously identified as being responsible for the manifestation of bitter taste with flaxseed oil ageing. We developed a chromatographic procedure to monitor the oxidation of major cyclic peptides in flaxseed oil. We also used liquid chromatography with mass spectrometry and high-efficiency core-shell reversed-phase sorbents to study the separation of cyclolinopeptides in detail. The Kinetex(TM) family of stationary phases (C8, C18, phenyl-hexyl) was tested, along with the standard porous Luna(TM) C18(2) media. We found that only the phenyl-hexyl stationary phase allows for complete resolution of major cyclolinopeptides, thus permitting direct UV monitoring of degree of conversion for cyclolinopeptide B into C and L into E. We also report, for the first time, a significant effect of peak splitting for some methionine S-oxide (Mso) containing cyclolinopeptides, which most likely appear due to diastereomerization. This results in poor separation efficiency for cyclolinopeptides F, G, and E, and gives baseline resolution of diastereomeric pairs for cyclolinopeptides I and P. Thus, a single oxidation of cyclolinopeptide N yields three distinct chromatographic peaks corresponding to cyclolinopeptide T (cyclo-MsoLMPFFWV, reported for the first time) and pair of cyclolinopeptide I (cyclo-MLMsoPFFWV) diastereomers.
亚麻籽油在储存过程中，其主要环脂肽中的蛋氨酸发生氧化，导致感官特性变差。环脂肽E先前被确定是亚麻籽油老化产生苦味的原因。我们开发了一种色谱方法来监测亚麻籽油中主要环肽的氧化情况。我们还使用液相色谱-质谱联用技术以及高效核壳反相吸附剂详细研究了环脂肽的分离情况。测试了Kinetex™系列固定相（C8、C18、苯基己基）以及标准的多孔Luna™ C18(2)介质。我们发现只有苯基己基固定相能够完全分离主要的环脂肽，从而可以直接通过紫外监测环脂肽B向C以及L向E的转化程度。我们还首次报道了一些含蛋氨酸S-氧化物（Mso）的环脂肽出现峰分裂的显著现象，这很可能是由于非对映异构化导致的。这导致环脂肽F、G和E的分离效率较差，而环脂肽I和P的非对映异构体对实现了基线分离。因此，环脂肽N的单次氧化会产生三个不同的色谱峰，分别对应环脂肽T（首次报道的环-MsoLMPFFWV）以及环脂肽I（环-MLMsoPFFWV）的非对映异构体对。
