Improving lactic acid production via bio-augmentation with acid-tolerant isolates from source-sorted organic household waste

Abstract

Biotransformation of source-sorted organic household waste (SSOHW) into lactic acid (LA) could be an attractive waste management approach, converting residual resources to the useful platform chemical and at the same time minimizing pollution. However, nutritional content is not always optimal for the inoculated lactic acid bacteria (LAB) due to the complex composition of SSOHW. In the present study, autochthonous acid-tolerant LA strains were isolated from SSOHW. The isolated strains were used as bio-augmentation inoculum for improving LA production from SSOHW. More specifically, four isolates were identified by sequencing to be Lactobacillus panis DTUAT 01, Lactobacillus pontis DTUAT 02, Lactobacillus oris DTUAT 03, and Lactobacillus reuteri DTUAT 04, which could efficiently convert glucose to LA at pH 4. Kinetic modeling was applied to predict performances and characteristics of the four isolates, and multi-response nonlinear regression analysis was performed on the experimental data to determine the kinetic parameters. The estimated kinetic parameters indicated that strain L. reuteri had the highest maximum growth rate (µmax) and LA yield among the four isolates along with relatively high substrate and product tolerance. Finally, bio-augmentation with strain L. reuteri boosted the LA concentration by 29% compared to abiotic augmentation (i.e., control test). Likewise, autochthonous L. reuteri could quickly adapt to SSOHW as shown by the elimination of its growth lag phase. The findings of this work can contribute to the improvement of fermentative LA production from wastes at acidic conditions.