Efficient downstream processing of second-generation lactic acid from lignocellulosic waste using aqueous two-phase extraction

The utilization of low-cost, waste-derived lignocellulosic biomass for biotechnological lactic acid production is an area of significant interest. Although numerous attempts have been made to develop novel processes using second-generation feedstocks, the downstream recovery processes for second-generation lactic acid are still relatively uncharted. In this context, this study explores a two-step method for retrieving second-generation lactic acid from a fermented olive leaves medium. The initial step involves an aqueous two-phase extraction using an ethanol/ammonium sulfate system, a method first applied here to lactic acid derived from second-generation raw materials. This is followed by a purification step using activated carbon. The process succeeded in extracting second-generation lactic acid with a yield of 70.02 ± 2.29% in the first extraction stage, followed by a yield of 88.91 ± 0.49% in the second purification step. The lactic acid purity level at the end of the downstream process was 90.17 ± 1.55%, as confirmed by the HPLC data. Furthermore, the study examined the feasibility of direct lactic acid extraction from unfiltered, fermented olive leaves medium, revealing that up to 95.23 ± 0.42% of bacterial cells could be eliminated. The purified lactic acid underwent qualitative identification through FT-IR and 1 H-NMR analysis, with the spectra showing a high degree of similarity to a standard reference substance, thus demonstrating the use of low-cost waste lignocellulosic biomass for the biotechnological production of lactic acid is a topic of great interest. Graphical Abstract