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Ammonium Enhances Food Waste Fermentation to High-Value Optically Active l‑Lactic acid
journal contribution
posted on 2019-12-13, 20:03 authored by Wenjuan Zhang, Xianbao Xu, Pingfeng Yu, Pengxiao Zuo, Ya He, Hong Chen, Yanan Liu, Gang Xue, Xiang Li, Pedro J. J. AlvarezFermentation of food waste to l-lactic acid
(l-LA), a high value-added platform molecule, is a green
approach for
resource recovery. However, low yield and optical activity (OA) of l-LA are key limiting factors for such efforts. Here, we report
that ammonium addition (300 mg of NH4+-N/L)
can double the yield of LA and increase OA of l-LA by fivefold
during repeated batch fermentation of food waste. This coincided with
a threefold increase in the glycolysis activity and an increase in
the relative abundance of key lactic acid bacteria (LAB) genera and
the ldhL gene associated with l-LA production.
Ammonium addition provided essential nitrogen for LAB growth (47%
of 15NH4+-N underwent assimilation
versus 15% oxidized to 15NO3–-N and 31% to 29N2 and 30N2) and resulted in a stable reducing environment (the oxidation–reduction
potential, ORP, ranged from −470 to −320 mV) that favors
the reduction of pyruvate to l-lactate. Specifically, the
added ammonium promoted beneficial population and metabolic shifts,
including an increase in intracellular NADH levels (0.46 ± 0.02
vs 0.26 ± 0.01 mM for unamended controls) that significantly
increased the l-LA yield. Overall, this study provides a
practical way to enhance l-LA production with high OA during
food waste fermentation and highlights ammonium as an overlooked biostimulator
for food waste biorefinery.