Pickle waste used to grow omega-3-producing microbes without sterilization

Researchers at Hiroshima University have shown that liquid waste from traditional Japanese pickle production can serve as a growth medium for a marine microorganism that produces omega-3 fatty acids. The study, published July 21 in LWT – Food Science and Technology, focused on Aurantiochytrium sp. strain L3W, a thraustochytrid isolated and characterized by the same research group in 2021.

The team tested waste liquids from three types of tsukemono: Hiroshimana (HN), sakura radish (SR), and umeboshi (UB). All three wastes are rich in dissolved organic carbon and nitrogen, which the microbe uses as nutrients, but they also contain lactic acid that inhibits growth and fatty-acid production.

Undiluted Hiroshimana waste yielded the highest results under nonsterile conditions, producing 60.6 milligrams of docosahexaenoic acid (DHA) and 2.5 milligrams of eicosapentaenoic acid (EPA) per gram of biomass. These yields were lower than those achieved with a standard laboratory control medium.

The researchers then reused the spent Hiroshimana medium for a second cultivation cycle. The microbe grew again, but DHA and EPA content decreased further, and lactic acid concentration rose to 2.7 grams per liter, confirming lactic acid as a limiting factor for repeated use.

An average Hiroshimana pickle factory generates roughly 100 metric tons of liquid waste annually. The authors estimate this volume could theoretically yield about 26 kilograms of DHA and 810 grams of EPA if fully utilized.

Professor Satoshi Nakai, corresponding author of the study, said the work demonstrates the feasibility of carbon recycling from regional food waste into functional nutrients. The group is now exploring whether the microbial biomass could be fed to hens to produce DHA-enriched eggs or used in aquaculture hatchery feed.

The study is the first to report repeated use of a food-processing liquid waste for thraustochytrid cultivation and the first to identify lactic acid accumulation as a constraint on the number of reuse cycles.

Omega-3 fatty acids such as DHA and EPA are primarily sourced from fish oil for human supplements and animal feed; microbial production from waste streams offers a potential alternative that reduces reliance on marine harvests.