木糖/脯氨酸共裂解过程挥发性化合物形成规律

Studies on formation of volatiles produced in the process of co-pyrolysis of xylose/proline mixtures

采用木糖与脯氨酸的混合体系,研究二者共同裂解形成的挥发性化合物形成规律。首先对木糖和脯氨酸进行单独裂解,木糖裂解的主要产物为糠醛,糠醛占裂解形成的挥发性化合物的45%,这与葡萄糖、果糖和蔗糖裂解时所形成的主要产物5-羟甲基糠醛(分别为28.9%、38.4%和37.4%)和糠醛(18.4%、35.4%和27.5%)有所不同,对木糖、葡萄糖、果糖和蔗糖裂解形成糠醛以及5-羟甲基糠醛的路径进行推测,认为木糖单独裂解时是通过脱水直接变成糠醛。同时,对不同比例的木糖和脯氨酸混合物进行共裂解,木糖和脯氨酸之间的比例对挥发性产物的形成比例具有明显的影响,脯氨酸的存在改变了木糖形成糠醛的路径,木糖主要经形成A-madori产物降解路线形成糠醛,脯氨酸在木糖降解路径中开始只是起到催化剂的作用,然后脯氨酸才与木糖裂解形成的碎片反应而开始被消耗。木糖和氨基酸共裂解形成的挥发性产物的含量要低于木糖单独裂解时所形成的挥发性产物含量,这可能是木糖与脯氨酸结合形成了大分子物质,而这些大分子物质在裂解过程中主要是被碳化。共裂解形成的苯酚含量也比单独裂解时形成的苯酚含量有明显下降,共裂解形成的苯酚含量约为单独裂解时的33%左右。

The neat xylose and proline were pyrolysed at first, respec- tively, and it was shown that the main product of pymlysates was fur- fural, up to 45%, different from the pyrolysates of glucose, fructose and sucrose with higher 5-hydromethyl furfural （28.9% ,38.4% and 37.4% respectively） and furfural （18.4% ,35.4% and 27.5% respectively）. The formation mechanisms of furfural and 5-hydromethyl furfural were elu- cidated of four sugars. And it suggested that furfural was formed in the pyrolysis process of xylose via mainly dehydration. Additionally, the co- pyrolysis of different ratio of xylose to proline mixtures were also inves- tigated and found that the ratio of xylose to proline had obvious influ- ence on the relative proportion of pyrolysates and the present proline changed the furfural formation path when xylose was thermally degrad- ed. The furfural was produced via Amadori products degradation path and proline only played a catalyst role in the degradation of xylose. It vanished only after the reaction with some degradation fragments. The content of total volatile compounds formed in the co-pyrolysis process of xylose was lower than that of xylose alone. Maybe due to some bigger molecules formed when xylose combined with proline, while those molecules were mainly charred. As well, the content of phenol was also decreased greatly, about 33 percent of that of xylose pyrolysed alone.