Researchers have identified a key chemical obstacle in turning food waste into renewable methane: melanoidins, dark-colored Maillard reaction products formed when food waste is heated during hydrothermal pretreatment. The study, published in Energy & Environment Nexus, provides a new semi-quantitative way to track these complex compounds and shows that higher doses can severely damage the microbial system responsible for methane production.
Food waste is rich in organic matter and widely viewed as a promising feedstock for anaerobic digestion, a process in which microorganisms break down organic material to produce biogas. Hydrothermal pretreatment is often used to speed up this process by breaking apart large food molecules before digestion begins. However, high-temperature treatment can also trigger Maillard reactions, the same browning chemistry familiar from cooked foods, producing melanoidins that may interfere with downstream digestion.
"Hydrothermal pretreatment is a useful tool, but our results show that temperature control is critical," said corresponding author Lu Ding. "When melanoidins accumulate, they can shift the digestion system away from efficient methane production and toward microbial imbalance."
Because melanoidins are chemically diverse and lack standard reference compounds, they are difficult to measure directly. The research team combined ultraviolet-visible spectroscopy with three-dimensional excitation-emission matrix fluorescence spectroscopy and parallel factor analysis. This approach allowed them to distinguish melanoidin-like fluorescent components from other humic-like substances and to estimate their relative abundance.
The results showed that melanoidin formation increased continuously as hydrothermal temperature rose from 120 to 200 °C. A sharp rise was observed once the temperature exceeded 140 °C. At 200 °C, the maximum fluorescence intensity of the melanoidin component reached 374.14 arbitrary units, far above the 9.35 arbitrary units measured in untreated samples.
The team then tested how different melanoidin doses affected food waste anaerobic digestion. Low doses, 2.08 and 4.16 mg mL−1, reduced digestion efficiency and lowered methane content, although the overall system did not collapse. High doses, 6.24 and 8.32 mg mL−1, caused methane production to fall by 98.15% and 99.24%, respectively, compared with the control group. In these high-dose treatments, methane generation nearly stopped in the early stage of digestion.
"The most important finding is the dose-dependent effect," said corresponding author Guangsuo Yu. "A small amount of melanoidins can weaken methane performance, while a high amount can push the entire anaerobic digestion system into failure."
Microbial analysis revealed why this happened. Melanoidins changed bacterial and archaeal community structures, but their most damaging effect appeared to be on methanogenic archaea, the microorganisms that produce methane. Acid-producing bacteria remained active, while methanogens were suppressed. This imbalance led to acid accumulation, lower pH and poor methane formation. In high-dose groups, the final pH dropped below the range preferred by methanogens, further accelerating system collapse.
The study offers practical guidance for food waste treatment plants seeking to combine hydrothermal pretreatment with anaerobic digestion. Keeping pretreatment temperatures below the range that strongly promotes melanoidin formation may help preserve methane yield and improve energy recovery.
By clarifying how melanoidins form and how they affect digestion microbes, the work provides a new framework for optimizing food waste resource utilization and improving renewable bioenergy production.
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Journal reference: Niu X, Yang M, Ding L, Hungwe D, Gong Y, et al. 2026. Semi-quantitative characterization of melanoidins during hydrothermal treatment of food waste and their impact on anaerobic digestion. Energy & Environment Nexus 2: e013 doi: 10.48130/een-0026-0008
https://www.maxapress.com/article/doi/10.48130/een-0026-0008
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About Energy & Environment Nexus :
Energy & Environment Nexus (e-ISSN 3070-0582) is an open-access journal publishing high-quality research on the interplay between energy systems and environmental sustainability, including renewable energy, carbon mitigation, and green technologies.
