Effects of C18 long chain fatty acids on glucose, butyrate and hydrogen degradation

The effects of linoleic (C18:2), oleic (C18:1), and stearic (C18:0) acids on glucose, butyrate and hydrogen degradation were investigated at 21°C using a culture unacclimated to long-chain fatty acids (LCFAs). Diethyl ether was used to facilitate precise addition of LCFAs and provide adequate dispersion in cultures. Butyrate degradation was affected by diethyl ether but minimal effects were observed on hydrogen and glucose consumption. In the presence of oleic and stearic acids, the glucose consumption rate was similar but was 50% lower in the presence of linoleic acid. The effect of a mixture of 100 mg l−1 of each individual LCFA (300 mg l−1 total LCFA) was approximately the same as 100 mg l−1 linoleic acid alone, suggesting no synergistic inhibition of glucose degradation. Butyric acid degradation was more severely inhibited by the LCFAs with inhibition becoming more severe with the addition of double bonds to the LCFA. Furthermore, mixtures of LCFAs synergistically inhibited butyric acid degradation compared to the results with individual LCFAs. In contrast, although lower hydrogen consumption rates were observed in cultures receiving oleic and linoleic acids compared to cultures receiving stearic acid, inhibition by all three acids individually or in mixture was limited. The introduction of LCFAs into a system may severly inhibit intermediate acid degradation while having little effect on acid production.