Strain-Dependent Lactic Acid Fermentation of Capsosiphon fulvescens Hydrolysate by Lactobacillus spp.

Seaweeds are promising third-generation biomass for biobased chemicals, yet their use for lactic acid (LA) production remains underexplored. We evaluated LA production from the dilute-acid hydrolysate of the aquacultured green alga <i>Capsosiphon fulvescens</i> (C.Agardh) Setchell & N.L. Gardner. The dried biomass contained 53.4% carbohydrate (dry-weight basis). HPLC showed a monosaccharide profile enriched in L-rhamnose and D-xylose, with lower levels of D-mannose, D-glucose, D-glucuronolactone, and D-glucuronic acid. Batch fermentations with three <i>Lactobacillus</i> strains revealed clear strain-dependent kinetics and carbon partitioning. Maximum LA titers/yields (time at maximum) were 2.0 g L^-1/0.49 g g^-1 at 9 h for <i>L. rhamnosus</i>, 2.3 g L^-1/0.30 g g^-1 at 36 h for <i>L. casei</i>, and 2.8 g L^-1/0.23 g g^-1 at 48 h for <i>L. brevis; L. rhamnosus</i> achieved the highest yield on sugars consumed, whereas <i>L. brevis</i> reached the highest titer by utilizing a broader sugar spectrum, notably xylose; <i>L. casei</i> showed intermediate performance with limited xylose use. Co-products included acetic and succinic acids (major) and trace 1,2-propanediol and acetaldehyde, consistent with flux through Embden-Meyerhof-Parnas versus phosphoketolase pathways. These results demonstrate that <i>C. fulvescens</i> hydrolysate is a viable marine feedstock for LA production and highlight practical levers-expanding pentose/uronic-acid catabolism in high-yield strains and tuning pretreatment severity-to further improve both yield and titer.