Post-extraction cascading valorization of corn steep liquor as a fermentation supplement for lactic acid bacteria

Corn steep liquor (CSL), a major by-product of the corn wet-milling industry, is a nutrient-rich feedstock for industrial bioprocessing. Previous studies have demonstrated its potential for producing value-added metabolites such as biosurfactants and Gramicidin S through spontaneous microbial growth. This work evaluates the potential for further valorization of CSL streams after metabolite recovery through cascading reuse as a nutritional supplement in lactic acid bacteria (LAB) fermentations. Raw CSL and CSL previously subjected to spontaneous or controlled fermentation by Aneurinibacillus aneurinilyticus were extracted using ethanol or phosphate-buffered saline (PBS). The resulting exhausted CSL fractions were chemically characterized. Despite minor variations in selected components such as sugars and minerals, the overall nutritional composition remained largely preserved after extraction, with high Pearson correlation coefficients (r p = 0.961–0.999) between raw and post-extraction CSL formulations. Based on that, a selected subset of non-fermented and post-extraction formulations was assessed as a nutrient source for Lactobacillus pentosus and Lactobacillus rhamnosus . Fermentation assays showed no significant differences in growth kinetics, substrate consumption patterns, and final cell counts compared to untreated CSL. These results support the potential feasibility of reusing chosen post-extraction CSL streams as fermentation supplements within cascading biorefinery schemes. After the proposed extractive processes, the preserved composition of CSL also suggests possibilities for other conventional CSL applications, including animal feed, pending dedicated safety and regulatory evaluation.