In vitro degradation of 10 mono‐ and sesquiterpenes of plant origin by caprine rumen micro‐organisms

The extent of disappearance of 10 mono‐ and sesquiterpenes in presence of mixed rumen micro‐organisms has been measured in 24‐h batch cultures. The molecules that were tested are frequently found in the plants consumed by ruminants in highland pastures (limonene, β‐myrcene, β‐ocimene, α‐pinene, sabinene, γ‐terpinene and thymol) or are potential markers of the diet (camphene, β‐caryophyllene and α‐copaene). All terpenes were tested at 2 µL mL−1, except α‐copaene and thymol, which were tested at 0.9 µL mL−1 and 2 mg mL−1, respectively. Camphene and thymol were not degraded to a significant extent. The disappearance of part of β‐caryophyllene, (−)‐limonene and γ‐terpinene could not be attributed to the direct action of rumen micro‐organisms but rather than to an effect of the extracellular medium. In contrast, a third group of one sesquiterpene (α‐copaene) and four monoterpenes (myrcene, β‐ocimene, α‐pinene and sabinene) was extensively degraded by rumen micro‐organisms, at rates of 1.6, 4.5, 3.5, 4.8 and 5.4 µmol mL−1 inoculum day−1, respectively. The preliminary exposure of rumen micro‐organisms to a specific blend of essential oils compounds, containing mainly thymol, guajacol and limonene, increased the extent of disappearance of γ‐terpinene only.