| dc.description.abstract | Lactic acid (LA) is a valuable, widely used platform chemical with diverse applications in industries such as pharmaceuticals, food storage and textiles. LA has antimicrobial and preservative properties and can also be used a precursor to Poly-Lactic Acid, a biodegradable plastic. Sustainable production of LA is increasingly important and is possible from bacterial fermentation of sugars. The Biodomain business unit at Shell are particularly interested in providing new, sustainable routes to LA production at scale and use a commercial starter culture, MidWestern BioAg Lactic Acid Bacteria (LAB) in pilot fermentation of plant-derived feedstock, which resulted in a range of products, including LA, acetic acid and ethanol, with varying and often unpredictable yields. This project aimed to understand the basis of that variability by analysing and influencing the microbial content of the fermentation. Metagenomic analysis of fermenting sweet sorghum (Sorghum bicolor) biomass showed the LAB inoculum did not dominate the fermentation systems as expected, leading to inefficient processes and unpredictable results. New inocula were investigated, including the use of squeezed liquids from post-ensiled sweet sorghum material, termed “sorghum pressate”. The sorghum pressate proved to be a successful inoculum when added with a carbonate-based pH buffer, with high LA yields (average 102 %) and low variability (± 11 %). Sequencing analysis showed the microbial community of the sorghum pressate was dominated by Weissella paramesenteroides, which was subsequently isolated. The W. paramesenteroides isolate from post-ensiled sweet sorghum, grows best anaerobically, at 30 °C and pH 6. W. paramesenteroides can metabolise glucose, fructose, and sucrose, which are the three main soluble sugars in sweet sorghum, for growth and efficient LA production. However, when used as a pure strain inoculum for sweet sorghum fermentation, the isolated W. paramesenteroides strain was unproductive, suggesting that a microbial consortium is required for robust fermentation of the biomass. | en_GB |
