초록
<P>Fermentation of food waste to <SMALL>L</SMALL>-lactic acid (<SMALL>L</SMALL>-LA), a high value-added platform molecule, is a green approach for resource recovery. However, low yield and optical activity (OA) of <SMALL>L</SMALL>-LA are key limiting factors for such efforts. Here, we report that ammonium addition (300 mg of NH<SUB>4</SUB><SUP>+</SUP>-N/L) can double the yield of LA and increase OA of <SMALL>L</SMALL>-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 <I>ldhL</I> gene associated with <SMALL>L</SMALL>-LA production. Ammonium addition provided essential nitrogen for LAB growth (47% of <SUP>15</SUP>NH<SUB>4</SUB><SUP>+</SUP>-N underwent assimilation versus 15% oxidized to <SUP>15</SUP>NO<SUB>3</SUB><SUP>-</SUP>-N and 31% to <SUP>29</SUP>N<SUB>2</SUB> and <SUP>30</SUP>N<SUB>2</SUB>) 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 <SMALL>L</SMALL>-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 <SMALL>L</SMALL>-LA yield. Overall, this study provides a practical way to enhance <SMALL>L</SMALL>-LA production with high OA during food waste fermentation and highlights ammonium as an overlooked biostimulator for food waste biorefinery.</P><P>Ammonium stimulates sustainable food waste valorization using a biological green approach for simultaneous resource recovery of a valuable chiral platform molecule and nutrient removal.</P><BR>[FIG OMISSION]</BR>