Trisaccharides of the Onion (Allium cepa)

The purpose of this work was the characterization of a portion of the carbohydrate material extracted from onions. The portion under study is the third band on a paper chromatogram counting upward from sucrose as band one when the chromatogram is developed with n-butyl alcohol: water (7:1:2, v/v). This band is non-reducing carbohydrate material which yields on acid hydrolysis only fructose and glucose in a 2:1 ratio. Neo- and 1-kestose were isolated from mature onions of the Yellow-Globe Danvers variety. These substances were tentatively identified by the fact that they had an RS value of 0.62 in isopropyl alcohol: n-butyl alcohol: water (7:1:2, v/v). The known compounds, neo- and 1-kestose, were prepared by the action of invertase on sucrose under acid conditions. They were separated on a Whistler-Durso column. The reference compounds and the compounds of Band III from onions were examined by paper chromatography in water-saturated phenol. The RS values of the neo-kestose (IIIc) and 1-kestose (IIIa) are 0.93 and 0.75, respectively. The acetates of the components of Band III and the reference compounds were prepared according to the procedure of Pazur and Gordon. Their mixed melting point were as follows: 1-kestose acetate, 42-43.5° C., and neo-kestose acetate, 56-58° C