The present invention provides a method of preparing a high-purity galactooligosaccharide composition by fermentation of a low-purity galactooligosaccharide mixture with a yeast strain, Kluyveromyces lactis ATCC 8585. The high-purity galactooligosaccharide composition includes at least 99% of galactooligosaccharides selected from the group consisting of galactotriose, galactotetrose, galactooligosaccharides with five or more sugar units, and combinations thereof and lower than 1% of monosaccharides and disaccharides. The present invention also provides a high-purity galactooligosaccharide composition and use thereof in manufacturing compositions for regulation of blood glucose level and improvement of gut microbiota. For example, the high-purity galactooligosaccharide composition may be employed in manufacture of foods, beverages, health foods, nutritional supplements, and pharmaceutical compositions for patients or pets afflicted with diabetes mellitus or lactose intolerance.本發明提供一種製備高純度半乳寡糖組合物的方法，係利用乳酸克魯維酵母菌ATCC 8585對一低純度半乳寡糖混合物進行發酵反應。該高純度半乳寡糖組合物包含至少99%選自於由半乳三糖、半乳四糖、五糖以上之半乳寡糖、及其任意組合所組成的群組，及低於1%之單糖及雙糖。本發明亦提供一種高純度半乳寡糖組合物，及其用於製備可調節血糖或改善腸道菌相之組合物之用途。例如，本發明高純度半乳寡糖組合物可用於製備適合糖尿病或乳糖不耐症病人或寵物使用之食品、飲品、保健食品、營養補充品、及醫藥組合物。
