Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
Carbohydr Polym. 2014 Jan 30;101:256-64. doi: 10.1016/j.carbpol.2013.09.042. Epub 2013 Sep 21.
In order to better understand the thermal stability of spent coffee grounds (SCG) galactomannans and arabinogalactans and the reactions that can occur upon roasting, long term isothermal exposures, up to 3h, were performed at 160, 180, 200, 220, and 240 °C. The resultant products were analysed according to the sugars and linkage composition and also by electrospray mass spectrometry. Galactomannans did not loss mass at T ≤ 200 °C during exposures up to 3h whereas the arabinogalactans showed that thermal stability only for T ≤ 180 °C. This was in accordance with the estimated activation energies of their thermal decomposition of 138 kJ/mol and 94 kJ/mol, respectively. The roasting of galactomannans promoted the formation of new glycosidic linkages, with occurrence of 2-, 6-, 2,3-, 2,6-, 3,6-, 2,3,6-, 3,4,6-linked mannose residues, 3,4,6-linked galactose residues, and terminally-linked glucose residues, observed by methylation analysis. Depolymerisation and formation of anhydrohexose residues at the reducing end and mannose-glucose isomerisation were also observed. The roasting of galactomannans at 200 °C promoted their solubility in water upon alkali extraction and neutralisation.
为了更好地理解废咖啡渣（SCG）半乳甘露聚糖和阿拉伯半乳聚糖的热稳定性以及在烘焙过程中可能发生的反应，在 160、180、200、220 和 240°C 下进行了长达 3 小时的长期等温暴露。根据糖和键合组成以及电喷雾质谱对所得产物进行了分析。半乳甘露聚糖在 3 小时的暴露时间内，T ≤ 200°C 时不会损失质量，而阿拉伯半乳聚糖则表明 T ≤ 180°C 时才具有热稳定性。这与它们的热分解估计活化能分别为 138 kJ/mol 和 94 kJ/mol 相符。半乳甘露聚糖的烘焙促进了新糖苷键的形成，通过甲基化分析观察到 2-、6-、2,3-、2,6-、3,6-、2,3,6-、3,4,6-连接的甘露糖残基、3,4,6-连接的半乳糖残基和末端连接的葡萄糖残基。还观察到末端还原端的去聚合和脱水己糖残基的形成以及甘露糖-葡萄糖异构化。半乳甘露聚糖在 200°C 下烘焙后，经碱提取和中和后在水中的溶解度增加。
