The seasoning liquid used in pickle production has traditionally been discarded because its high salt content makes it difficult to reuse. A research group led by Professor Satoshi Nakai of the Graduate School of Advanced Science and Engineering at Hiroshima University demonstrated that DHA and EPA can be produced using waste seasoning liquid generated during the production of pickles such as Hiroshimana. Effective utilization of pickle seasoning waste, which has been difficult to recycle, could lead to applications such as the production of eggs and farmed fish enriched with DHA and EPA. The findings were published online in LWT.
Provided by Hiroshima University
Demand is increasing for functional foods containing DHA and EPA, including DHA and EPA supplements and DHA- and EPA-enriched eggs. DHA and EPA are also essential for the growth of marine fish and are used in feed for aquaculture.
The research group focused on thraustochytrids, microorganisms that produce DHA and EPA. These microorganisms prefer saline environments and grow by decomposing organic matter. Meanwhile, pickle seasoning waste contains abundant organic matter but is highly saline, making it difficult to recycle.
The researchers therefore began investigating a carbon-recycling scenario in which pickle food waste is used as a substrate (feed) for thraustochytrids, while the resulting biomass is used as a source of DHA and EPA for chickens and marine fish. Although pickle seasoning waste is originally acidic, the researchers adjusted it to neutral pH 7 to temporarily suppress the growth of contaminating microorganisms adapted to acidic conditions, then inoculated it with Aurantiochytrium sp. L3W (L3W), a species of thraustochytrid, and cultured it.
As a result, although the yield did not match that obtained with artificial media, they successfully produced biomass containing DHA and EPA. Biomass obtained from seasoning waste generated during the production of Hiroshimana and umeboshi reached a level suitable for enhancing the DHA content of eggs. The biomass measurements included contaminating microorganisms such as yeast, which is thought to be one reason why the DHA and EPA contents were lower than those obtained with artificial media.
When seasoning waste from sakura radishes was used, both biomass production and DHA and EPA contents were lower. One possible reason is the stronger influence of contaminating microorganisms. Analysis of fatty-acid composition showed that, unlike the other samples, the contribution of oleic acid was higher in the sakura-radish culture.
The researchers then separated the biomass from the Hiroshimana seasoning waste used to culture the L3W strain by centrifugation and adjusted the pH of the supernatant to 7 before reusing it repeatedly for L3W cultivation. Even after repeated reuse, growth of the L3W strain and production of DHA and EPA were confirmed. However, both gradually declined with repeated reuse, and by the second reuse the culture had fallen below a practical level for use as a DHA and EPA source. During this process, lactic acid concentrations increased from 0.75 to 2.4 and 2.7 mg/L.
To investigate the cause of the decline in growth, the researchers added lactic acid to artificial media and examined its inhibitory effects. They found that L3W growth remained at 92% when the lactic acid concentration was 0.75 mg/L but declined to 40% and 36% when concentrations increased to 2.4 and 2.7 mg/L, respectively. These results confirmed that the accumulation of lactic acid can inhibit the growth of the L3W strain during reuse of the seasoning waste. However, the decline in growth observed between the first and second reuse cycles could not be fully explained by the increase in lactic acid concentration. By the second reuse, the depletion of substrates readily utilized by the L3W strain appears to have become a major limiting factor. This is also the first study to demonstrate that lactic acid suppresses the growth of thraustochytrids.
Journal Information
Publication: LWT
Title: Repeated use of liquid pickle seasoning waste for the cultivation of Aurantiochytrium sp. in sustainable production of polyunsaturated fatty acids
DOI: 10.1016/j.lwt.2026.119753
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.