Mechanism and biodegradability of melanoidins formed in hydrothermal process: From model compounds to food waste.

Hydrothermal pretreatment (HTP) is used to increase the biochemical methane potential (BMP) of food waste (FW). The formation of melanoidins will seriously affect the microbial activity and methane production during anaerobic digestion (AD). Based on spectroscopic methods, similarities and heterogeneity of melanoidins from different sources were investigated, and the wide peak band (260-350 nm) in the ultraviolet region and the differences of amide groups of fructose-amino acid system, fructose-casein system and FW system were revealed. Aqueous phase analysis showed that aldehydes, dicarbonyl compounds and diketopiperazine derivatives were the key intermediates in the formation of melanoidins, and the formation of pyrazines reflected additional competitive pathways in the system. Aqueous phase analysis of the fructose-casein system demonstrated that high protein content hindered the formation of pyrazines. Finally, the fluorescence spectra of the fermentation broth before and after AD proved that melanoidins were difficult to be consumed during AD process.