Biorefining and bioprocessing of synthetic food waste for homofermentative production of L-lactic acid using Lactobacillus rhamnosus

Fossil fuels have long served as precursor materials to produce petroleum-based plastics. This study aims to utilize a biorefinery approach to convert synthetic food waste (SFW) into a feedstock to produce L-lactic acid (L-LA). The Taguchi experimental design was employed to screen the process parameters involved in the enzymatic hydrolysis of SFW, resulting in a maximum glucose yield of 37.23 ± 1.91% w /w. Utilizing the hydrolysed glucose obtained from SFW, screening experiments were conducted, revealing that Lactobacillus rhamnosus outperformed other strains with higher biomass and lactic acid concentration. Batch fermentation was carried out with increasing glucose concentrations ranging from 25 g/L to 104 g/L. The lactic acid-to-glucose yield increased from 0.66 ± 0.03 g/g to 0.88 ± 0.06 g/g as the initial glucose concentration rose. A batch bio-kinetic study demonstrated that the Haldane model fit well, achieving an R 2 value of 0.98. To evaluate the necessity of mineral supplementation in the medium, a Plackett-Burman design was employed, revealing the criticality of yeast extract with a p -value of 0.04 and with a t-value of 3.13. In the downstream processing phase, decolourisation with activated carbon showed a slight decrease from 96.8 ± 0.16% to 91.8 ± 0.36% as glucose concentrations increased from 25 g/L to 104 g/L. However, the recovery efficiency of L-lactic acid improved from 57.98 ± 2.6% to 69.21 ± 0.9% during liquid-liquid extraction of L-lactic acid obtained from decolourised fermentation batches at varying glucose concentrations. Thus, this study demonstrates the feasibility of using concentrated glucose derived from SFW as a primary carbon source, with minor supplementation from fermentation media components, for high L-LA production.