Structural Microheterogeneity of Kefiran from Kefir Grains

Abstract

The structure of kefiran from kefir grains was reinvestigated, because 6-O-substituted galactose was detected in methylated derivatives of kefiran, which was not expected to occur from the structure proposed by KOOZMAN³⁾. Hydrolysis of kefiran with Trichoderma reesei cellulase released only glucose and a pentasaccharide. By methylation analysis and ¹³C-n. m. r. spectroscopy, the pentasaccharide structure was elucidate (1 as β-D-Glc-(1→2)-β-D-Gal-(1→4)-α-D-Gal-(1 →3)-β-D-Gal-(1→4)-D-Glc, and this coincided with the structure proposed by KOOIMAN³⁾. However, methylation analysis of kefiran itself and ¹³C-n. m. r. spectra suggested the presence of an additional structure including 6-O-substituted galactose. Kefiran is considered to be constructed not only by the structure proposed by KOOIMAN³⁾ but also by another repeating unit including 6-O-substituted galactose.