Maillard反应前体物质参与木质素微生物转化产物的FTIR光谱特性

FTIR Spectral Characteristics of Lignin Microbial Transformation Products Involved with Maillard Reaction Precursors

腐殖质(HS)是由各类前体物质缩聚而成,前体物质是调控HS形成的关键。Maillard反应前体物质能否对木质素转化、HS形成有促进作用有待验证。鉴于此,采用液体摇瓶培养法,以木质素培养液为研究对象,通过添加邻苯二酚、葡萄糖和甘氨酸的单一及组合溶液,启动120 d的液体摇瓶培养,采用离心法收集上清液(细胞代谢产物)和沉淀(菌体残留物),分析两者性质并深入研究菌体残留物FTIR的光谱特性,系统评价各前体物质对木质素向HS转化的贡献。结果表明:(1)在木质素培养液中添加甘氨酸,历经液体摇瓶培养更有利于细胞代谢产物有机分子的缩合,使其结构趋于复杂,而邻苯二酚参与的4个处理及单独添加葡萄糖更易促进细胞代谢产物的降解,使其分子结构更加简单。与作为空白对照(CK)的无菌去离子水相比,外源添加Maillard反应前体物质能够促进细胞代谢产物矿化,使总有机碳(total organic carbon,TOC)含量下降,单一添加邻苯二酚能够使细胞代谢产物TOC含量始终高于其他处理;(2)添加Maillard反应前体物质可显著提升木质素微生物转化形成菌体残留物的回收率,单一添加邻苯二酚的菌体残留物回收率提升幅度最大,而邻苯二酚、葡萄糖和甘氨酸三者组合溶液对菌体残留物回收率的提升幅度最小,葡萄糖和甘氨酸的组合溶液使菌体残留物回收率在整个培养期间始终处于最高水平。添加Maillard反应前体物质使菌体残留物TOC含量的增加幅度小于CK,尽管如此,培养结束时,邻苯二酚参与的4个处理、葡萄糖和甘氨酸组合溶液的添加使菌体残留物TOC含量显著高于CK;(3)木质素经微生物转化形成的菌体残留物拥有羟基O—H、不对称脂族—CH_(3)、对称脂族—CH_(2)—、芳香碳C C及多糖类物质,与土壤胡敏酸有着相似的FTIR特征,但其分子缩合度尚无法达到土壤胡敏酸的复杂程度。各处理在完成培养后,菌体残留物中的羟基含量有着不同程度增加,而多糖含量有所下降,单一甘氨酸以及葡萄糖和甘氨酸组合溶液的添加使菌体残留物的脂族化程度提高,而邻苯二酚参与的4个处理及单独添加葡萄糖可使菌体残留物中的芳香碳比例进一步提高。综上,添加Maillard反应前体物质可促进细胞代谢产物矿化,使TOC含量下降、提高菌体残留物回收率,同时使其羟基含量增加、多糖含量降低,不同前体物质对菌体残留物脂族化和芳香化的影响规律不同,邻苯二酚参与的4个处理及单一添加葡萄糖可使菌体残留物中的芳香碳比例提高。

Humic substances(HS)are formed by the polycondensation of various precursors,and the precursors are the key to regulating the formation of HS.Whether the Maillard reaction precursors can promote the microbial transformation of lignin and the formation of HS remains to be verified.Given this,the method of liquid shake flask culture was adopted,the lignin culture medium serving as the research object,and the liquid shake flask culture of 120 d was started by adding single and combined solutions of catechol,glucose and glycine,and collected the supernatant(cell metabolites)and precipitate(microbial residues)by the centrifugation method.The properties of the cell metabolites and microbial residues were analyzed,and an in-depth study of the FTIR spectral characteristics of bacterial residues was necessary,which was used to evaluate the contribution of each precursor to the microbial transformation of lignin to HS more systematically.The results showed that:(1)Adding glycine into the lignin culture medium after the liquid shake flask culture was more conducive to the condensation of cell metabolites organic molecules,making their structures more complex,while the treatments involving catechol and the addition of glucose alone could promote the degradation of cell metabolites and make their molecular structures simpler.Compared with CK,exogenous addition of Maillard reaction precursors could promote the TOC content loss of cellular metabolites,and single catechol could make the TOC content of cellular metabolites always higher than other treatments;(2)The addition of Maillard reaction precursors could significantly increase the recovery rate of microbial residues formed from the microbial transformation of lignin,in which the recovery rate of microbial residues formed from the treatment of single catechol was the largest.In contrast,the combined solution of catechol,glucose and glycine had the smallest effect on the improvement of the recovery rate of microbial residues.The combined solution of glucose and glycine could keep the recovery rate of microbial residue at the highest level throughout the culture period.Adding Maillard reaction precursors could result in a smaller increase in the TOC content of microbial residues than CK.However,at the end of the culture,the four treatments involving catechol and the addition of a combination solution of glucose and glycine could enhance the TOC content of microbial residues significantly higher than CK;(3)The microbial residues formed from the microbial transformation of lignin had hydroxyl O—H,asymmetric aliphatic—CH_(3),symmetrical aliphatic—CH_(2)—,aromatic C C and polysaccharides,which had similar FTIR characteristics to soil humic acid,but its molecular condensation degree could not reach the complexity of soil humic acid.After the completion of the culture,the hydroxyl content in the microbial residues was increased to different degrees,while the polysaccharide content decreased.The addition of a single glycine and the combined solution of glucose and glycine could increase the aliphatic degree of the microbial residues while the content of polysaccharides decreased.The four treatments involving catechol and a single addition of glucose could further increase the proportion of aromatic C in the microbial residues.In conclusion,the addition of Maillard reaction precursors could reduce the TOC content of cell metabolites,improve the recovery rate of microbial residues,and,at the same time,increase the content of hydroxyl groups and reduce the content of polysaccharides.Different precursors had different effects on the aliphatic and aromatization of microbial residues.The effects of aromatization were different.Four treatments involving catechol and a single addition of glucose could increase the proportion of aromatic C in microbial residues.