Yang Ning, Yang Shucheng, Yang Luxiong, Song Qingsi, Zheng Xing
Department of Environmental Engineering, Xi'an Jiaotong University, Xi'an, 710049, China.
Department of Environmental Engineering, Xi'an Jiaotong University, Xi'an, 710049, China.
Environ Res. 2023 Jan 15;217:114814. doi: 10.1016/j.envres.2022.114814. Epub 2022 Nov 18.
The browning reaction produces melanoidins, 5-hydroxymethylfurfural (HMF) and humic acids which influence subsequent anaerobic digestion and protein recovery. This paper systematically evaluates the variation of organics that make sludge browning with heating temperature and reaction time, the effect of browning organics on protein recovery and anaerobic digestion, and finally proposes a pathway for the occurrence of the Maillard reaction (MR) in the sludge environment. The results show that the browning of sludge hydrolysate is related to the comprehensive influence of the MR, caramelization and humic acid desorption. The increase of temperature (80 °C-150 °C) and pH (9-13) will promote the extent of browning of sludge hydrolysate, and the sludge browning reaction basically stabilizes at the reaction time of 1 h. Humic acid and melanoidin could co-precipitate with the protein, thereby reducing the purity of the recovered protein. The inhibition of anaerobic digestion starts when the melanoidin concentration is 8.01 mmol/L. The three-dimensional fluorescence, GC-MS and FT-IR analysis show that melanoidins have the same functional groups and fluorescence properties as humic acid does, and the humic acid in the supernatant of the sludge treated with ATH was not only converted at its adsorbed state, but also possibly generated by the reaction of the dissolved proteins with polysaccharides. Finally, LC-MS/MS was used to identify the intermediate products of the MR and the possible structural formula of melanoidin. This study further clarifies the browning reaction in hydrothermal sludge treatment and provides help for the accuracy of subsequent studies.
褐变反应会产生类黑素、5-羟甲基糠醛（HMF）和腐殖酸，这些物质会影响后续的厌氧消化和蛋白质回收。本文系统评估了使污泥褐变的有机物随加热温度和反应时间的变化、褐变有机物对蛋白质回收和厌氧消化的影响，最终提出了污泥环境中美拉德反应（MR）的发生途径。结果表明，污泥水解产物的褐变与美拉德反应、焦糖化和腐殖酸解吸的综合影响有关。温度（80℃-150℃）和pH值（9-13）的升高会促进污泥水解产物的褐变程度，且污泥褐变反应在反应1小时时基本稳定。腐殖酸和类黑素会与蛋白质共沉淀，从而降低回收蛋白质的纯度。当类黑素浓度为8.01 mmol/L时开始抑制厌氧消化。三维荧光、气相色谱-质谱联用仪（GC-MS）和傅里叶变换红外光谱仪（FT-IR）分析表明，类黑素与腐殖酸具有相同的官能团和荧光特性，经ATH处理的污泥上清液中的腐殖酸不仅在其吸附状态下发生了转化，还可能是溶解的蛋白质与多糖反应生成的。最后，采用液相色谱-串联质谱仪（LC-MS/MS）鉴定了美拉德反应的中间产物和类黑素可能的结构式。本研究进一步阐明了水热污泥处理中的褐变反应，为后续研究的准确性提供了帮助。
