Key Takeaways & Executive Findings
- •• • Optimal Mg2+ dosage of 750 mg/L increased lactic acid yield to (37.4±0.5) g COD/L (1.2× Blank) and L-lactic acid optical activity to (96.3±0.9)%, directly improving product purity for polymer-grade applications. • • Mg2+ addition significantly enhanced key hydrolytic enzyme activities (α-glucosidase, amylase, protease) and L-lactic acid producing enzymes, while reducing lactate-consuming enzyme activity, accelerating hydrolysis and production rates while slowing lactate degradation—critical for process efficiency. • • At 750 mg/L Mg2+, the relative abundance of Enterococcus and Streptococcus reached 65.0% and 18.7% respectively (total 83.7%), reshaping the microbial community to favor L-lactic acid producers, which is essential for high optical purity. • • Metabolic pathway prediction and functional gene analysis confirmed that Mg2+ upregulated carbohydrate metabolism pathways and lactate dehydrogenase encoding genes, providing a mechanistic basis for enhanced fermentation performance and guiding reactor design.
Abstract
The utilization of food waste as a fermentation substrate can effectively reduce the substrate cost of lactic acid production industrialization, and synergistic fermentation with leachate could promote lactic acid production. However, the effect of magnesium ions in leachate on lactic acid production, metabolic processes, and key functional bacterial communities remains unclear. This study investigated the effect of adding magnesium ions on lactic acid fermentation using food waste as substrate. Results showed that the optimal magnesium ion dosage was 750 mg/L, achieving a lactic acid yield of (37.4±0.5) g COD/L and L-lactic acid optical activity of (96.3±0.9)%. Mechanistic studies revealed that magnesium ions accelerated substrate dissolution, significantly enhanced the activities of key hydrolytic enzymes (α-glucosidase, amylase, protease) and L-lactic acid producing enzymes, thereby increasing hydrolysis and lactate production rates. Simultaneously, the relative activity of lactate-consuming enzymes decreased, slowing lactate consumption. At 750 mg/L Mg2+, the relative abundances of Enterococcus and Streptococcus were 65.0% (2.2 times the Blank) and 18.7% (37.8% of the Blank), respectively, with a total of 83.7%, enhancing lactic acid yield and L-lactic acid optical activity. Metabolic pathway prediction and functional gene analysis further indicated that magnesium ions increased the relative abundance of carbohydrate metabolism pathways and genes encoding lactate dehydrogenase. This study provides technical support for food waste resource utilization.
1. Introduction
Industrial lactic acid production predominantly relies on pure sugar feedstocks (e.g., corn, sugarcane) using lactic acid bacteria or fungi, incurring high substrate and maintenance costs. Global lactic acid demand is projected to reach 1.96 million tons by 2025 with a CAGR of 8.1%, yet conventional processes remain economically and environmentally unsustainable. Food waste, with organic content exceeding 80% dry weight, offers a low-cost alternative substrate, but its complex composition and mixed microbial consortia often result in suboptimal yields and low optical purity of L-lactic acid, a critical parameter for polylactic acid (PLA) production.
This study addresses the bottleneck by investigating the regulatory role of magnesium ions—a common component in landfill leachate—during food waste fermentation. While leachate co-fermentation has been shown to promote lactic acid production, the specific influence of Mg2+ on metabolic pathways and microbial community structure was previously unclear. By systematically evaluating Mg2+ dosages, the authors identified an optimal concentration of 750 mg/L that enhances hydrolytic enzyme activities, enriches L-lactic acid-producing bacteria (Enterococcus and Streptococcus), and upregulates key metabolic genes. These findings offer a cost-effective strategy to improve both yield and optical purity, directly supporting the industrialization of food waste-based lactic acid production.
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LI Yue, ZHANG Wenjuan, DU Zonghai, LI Yuan, CHEN Yueji, GUO Yi, XU Xianbao (2026). Efficacy and Mechanism of Lactic Acid Production from Food Waste Fermentation Regulated by Magnesium Ions. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202605019
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Frequently Asked Questions
What is the optimal Mg2+ concentration for maximizing lactic acid yield and optical purity, and how does it compare to the control?
The optimal Mg2+ concentration is 750 mg/L, achieving a lactic acid yield of (37.4±0.5) g COD/L, which is 1.2 times that of the Blank group, and an L-lactic acid optical activity of (96.3±0.9)%. This dosage balances enhanced production with reduced lactate consumption.
How does Mg2+ addition affect the key enzyme activities involved in hydrolysis and lactic acid production?
Mg2+ addition significantly enhances the activities of α-glucosidase, amylase, and protease, accelerating substrate hydrolysis. It also increases the relative activity of L-lactic acid producing enzymes while decreasing the relative activity of lactate-consuming enzymes, thereby increasing net lactate production.
What is the impact of Mg2+ on the microbial community structure, particularly the abundance of lactic acid bacteria?
At 750 mg/L Mg2+, the relative abundance of Enterococcus and Streptococcus reaches 65.0% and 18.7%, respectively, totaling 83.7%. This enrichment of L-lactic acid producers is 2.2 times and 37.8% of the Blank group for Enterococcus and Streptococcus, respectively, directly correlating with enhanced yield and optical purity.
What metabolic pathways and functional genes are upregulated by Mg2+ addition, and how do they contribute to fermentation efficiency?
Metabolic pathway prediction and functional gene analysis indicate that Mg2+ addition increases the relative abundance of carbohydrate metabolism pathways and genes encoding lactate dehydrogenase. This upregulation facilitates more efficient conversion of carbohydrates to lactic acid, supporting higher yields.
What are the practical implications of these findings for scaling up food waste fermentation to industrial lactic acid production?
The study demonstrates that Mg2+ supplementation at 750 mg/L can significantly improve lactic acid yield and optical purity from food waste, offering a low-cost strategy to enhance process economics. The mechanistic insights into enzyme activities and microbial community shifts provide a basis for optimizing reactor conditions and microbial management in large-scale operations.
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