van der Burgt Y E, Bergsma J, Bleeker I P, Mijland P J, van der Kerk-van Hoof A, Kamerling J P, Vliegenthart J F
Bijvoet Center, Department of Bio-Organic Chemistry, Utrecht University, The Netherlands.
Carbohydr Res. 2000 Apr 20;325(3):183-91. doi: 10.1016/s0008-6215(99)00329-8.
Granular potato starches were methylated in aqueous suspension with dimethyl sulfate to molar substitution (MS) values up to 0.29. Fractions containing mainly amylose or amylopectin were obtained after aqueous leaching of the derivatised starch granules. Amylopectin in these fractions was precipitated with Concanavalin A to separate it from amylose. Amylose remained in solution and was enzymatically converted into D-glucose for quantification, thereby taking into account the decreased digestibility due to the presence of methyl substituents. It was found that the MS of amylose was 1.6-1.9 times higher than that of amylopectin in methylated starch granules. The distributions of methyl substituents in trimers and tetramers, prepared from amylose- or amylopectin-enriched fractions, were determined by FAB mass spectrometry and compared with the outcome of a statistically random distribution. It turned out that substituents in amylopectin were distributed heterogeneously, whereas substitution of amylose was almost random. The results are rationalised on the basis of an organised framework that is built up from amylopectin side chains. The crystalline lamellae are less accessible for substitution than amorphous branching points and amylose.
颗粒状马铃薯淀粉在水悬浮液中用硫酸二甲酯进行甲基化反应，直至摩尔取代度（MS）达到0.29。衍生化淀粉颗粒经水浸提后得到主要含有直链淀粉或支链淀粉的级分。这些级分中的支链淀粉用伴刀豆球蛋白A沉淀，以使其与直链淀粉分离。直链淀粉保留在溶液中，并通过酶促转化为D-葡萄糖进行定量，从而考虑到由于甲基取代基的存在而导致的消化率降低。结果发现，甲基化淀粉颗粒中直链淀粉的MS比支链淀粉高1.6 - 1.9倍。通过快原子轰击质谱法测定了由富含直链淀粉或支链淀粉的级分制备的三聚体和四聚体中甲基取代基的分布，并与统计随机分布的结果进行了比较。结果表明，支链淀粉中的取代基分布不均匀，而直链淀粉的取代几乎是随机的。基于由支链淀粉侧链构建的有序框架对结果进行了合理化解释。与无定形分支点和直链淀粉相比，结晶片层较难被取代。
