Palm oil waste put to work

Southeast Asia produces over 80% of the world’s palm oil. Extraction of this oil generates copious amounts of the lignocellulose-rich by-product known as empty fruit bunch (EFB). This precious resource is largely wasted at present, being either burned or left to mulch on the ground. Jin Chuan Wu at the A*STAR Institute of Chemical and Engineering Sciences and co‐workers in Singapore have now identified bacteria that turn EFB into the industrially important chemical L-lactic acid.

“Optically pure L-lactic acid is currently produced from starchy materials such as cornstarch,” says Wu. As such, the process uses a food resource and the production cost is high.

Wu believes that the lack of cost-effective processes has also prevented the commercial production of lactic acid from agricultural waste. Most microbes struggle to digest all of the different sugars in EFB, which must be utilized for the process to be cost effective, he explains.

To find the bacterial strain, Wu and co-workers collected soil samples from natural parklands, wetlands and gardens across Singapore. They then grew colonies of the bacteria found in the samples and cultivated them in the presence of the two main sugars found in EFB: xylose and glucose. Next, the researchers selected the strain that produced the most L-lactic acid from both sugar types. “We obtained the most effective strain from the soil samples collected at Jurong Island,” says Wu, referring to the Bacillus coagulans JI12 strain (see image).

Wu’s team found that 50 °C was the optimal temperature for producing lactic acid from xylose and glucose using B. coagulans JI12, whereas the Lactobacillus species normally used for this purpose requires lower temperatures. The higher temperature eliminated some contamination issues, Wu notes, as contaminant microbes do not grow well at this elevated temperature.

Wu and co-workers showed that B. coagulans JI12 could convert EFB — which was hydrolyzed using a procedure they developed in 20122 — to lactic acid with yields of up to 97%. “The excellent performance of B. coagulans JI12 makes it a very promising strain for industrial production of L-lactic acid from lignocellulosic biomass,” says Wu.

The team is now planning to use genetic engineering to improve the acid tolerance of the newly identified bacterial strain. The potential improvement should allow the fermentation to be conducted at a pH lower than 6.0, thus reducing the amount of downstream processing required and further cutting costs. Wu and his team also recently improved the acid tolerance of another strain of lactic-acid-producing bacteria, Lactobacillus pentosus3.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Chemical and Engineering Sciences