基于多孔石墨化碳柱-四极杆-飞行时间质谱解析甜菜果胶精细结构

Combined PGC-Triple-Tof-MS Enables the Separation,Identification of Sugar Beet Pectin Derived Oligomers

采用高温酸法提取甜菜果胶(SBP),经强阴离子交换柱层析分离,获得甜菜果胶水洗脱组分(SBPW)和盐洗脱组分(SBP3).单糖组成分析和分子量表征结果表明,SBPW主要由半乳糖(Gal)、阿拉伯糖(Ara)和半乳糖醛酸(GalA)组成,分子量为1100;SBP3则以GalA为主,分子量为41450.通过顺序酶法降解,应用多孔石墨化碳柱-四极杆-飞行时间质谱(PGC-Triple-Tof MS)联用技术分析鉴定了SBPW和SBP3寡糖的精细结构.结果表明,SPBW的主链为[→4)-α-GalA-(1→2)-α-Rha-(1→]重复单元构成的Ⅰ型聚鼠李半乳糖醛酸(RG-Ⅰ果胶),鼠李糖O-4位被中性糖侧链[α-(1→5)阿拉伯聚糖和β-(1→4)半乳聚糖]所取代.SBP3由α-1,4链接的聚半乳糖醛酸(HG)和RG-Ⅰ构成,HG和RG-Ⅰ通过α-1,4糖苷键直接相连,并发现了α-GalA(1→2)α-Rha(1→4)α-Rha(1→4)α-GalA(1→2)α-Rha的新特征结构.

Sugar beet pectin(SBP)was extracted by high-temperature acid method,the water-eluted components(SBPW)and salt-eluted components(SBP3)were obtained by strong anion exchange chromatography.The results of monosaccharide composition and molecular weight analysis showed that SBPW was mainly composed of galactose(Gal),arabinose(Ara)and galacturonic acid(GalA),with a molecular weight of 1100,while SBP3 was dominated by GalA and weighted 41450.Combined sequential enzymatic degradation and porous graphitized carbon column-quadrupole-time-of-flight mass spectrometry(PGC-Triple-Tof MS),the fine structure of SPPW and SPP3 oligosaccha⁃rides was analyzed.The results showed that the main chain of SPBW was[→4)-α-GalA-(1→2)-α-Rha-(1→]repeti⁃tive units composed of RG-Ⅰpectin,and neutral sugar side chain[α-(1→5)arabinan andβ-(1→4)galactan]were substituted for Rha at the O-4 position.SBP3 consisted of HG and RGⅠwith a molar of 3:2,HG was a linear structure ofα-1,4-linked GalA,HG and RG-Ⅰdomains were connected directly byα-1,4 glycoside bonds.New characteristic structures of oligosaccharide have also been found,similar toα-GalA(1→2)α-Rha(1→4)α-Rha(1→4)α-GalA(1→2)α-Rha.