Lactic Acid Production from Renewable Feedstocks Using Poly(vinyl alcohol)-Immobilized Lactobacillus plantarum 23

Microbial fermentation is the source of commercial lactic acid (LA), and the price of fermentation-derived LA is heavily challenged by the feedstock price. This study evaluated four different categories of renewable feedstock for the future production of LA: sugar cane bagasse (lignocellulosic biomass, second generation feedstock), cheese whey (nutrient rich wastewater), and microalgal biomass of Chlorella vulgaris (third generation feedstock), and macroalgal biomass of Ulva sp. (potential feedstock). Poly(vinyl alcohol)-immobilized Lactobacillus plantarum was used as the fermentative bacterium, and LA titer, yield, and productivity from glucose in continuous fermentation were 29.6 g/L, 0.98 g/g, and 7.39 g/(1, h), respectively. Microalgal hydrolysate served as the best carbon source with very high productivity (12.56 g/(L h) in continuous fermentation) with LA titer and yield of 37.9 g/L and 0.91 g/g sugars, respectively. Sugar cane bagasse attained the maximal LA titer and yield of 41-42 g/L and 0.98-1.0 g/g, due to the low levels of fermentation inhibitors and high glucose utilization efficiency. Cheese whey attained an LA titer and productivity of 33.8 g/L and 11.3 g/(L h), respectively. The yield of LA from whey lactose was the lowest at 0.88 g/g. Macroalgal biomass also showed the best LA fermentation performance compared to previous reports, with LA titer, yield, and productivity of 36.8 g/L, 0.91 g/g, and 12.3 g/(L h), respectively. Restated, this study reported for the first time very high LA titer and productivity from macroalgal biomass. The renewable feedstock with appropriate pretreatment and hydrolysis can be successfully used for the future production of LA via fermentation.