Effect of Essential Oils Dissolved in Different Solvents on the In vitro Methane Production

The study was taken up to assess the effect of the essential oils (EOs) like cinamaldehyde (CIN), carvone (CAR) and limonene (LIM), dissolved in different solvents like water, 50% methanol, 80% ethanol, petroleum ether (PE), propylene glycol (PG) on in vitro digestibility of nutrients, methane and volatile fatty acids (VFAs) production from wheat straw in a 4x5 factorial experiment. The EOs were supplemented @ 3% of the substrate. Irrespective of the solvent used, the net gas production (NGP) was depressed (P<0.01) in CAR and LIM supplemented groups as compared to control. The digestibility of NDF and true OM was depressed (P<0.01) in all the EO supplemented groups as compared to control. Amongst the EOs, the highest digestibility was observed in wheat straw supplemented with CIN. The CH₄ production was lowest (P<0.01) when wheat straw was supplemented with CAR. The ME availability was also highest in CIN supplemented group, which was comparable to control but higher (P<0.01) than CAR supplemented group. Irrespective of EO, the NGP was high (P<0.01) when ethanol was used as a solvent as compared to methanol. The digestibility of NDF and that of true OM was comparable between water and methanol, but higher (P<0.01) than other solvents.The EOs dissolved in PE and PG showed lowest (P<0.01) CH₄ production. The total VFA production was highest (P<0.01) in PG followed by ethanol and methanol. The propionate and isovalerate were highest in PG supplemented groups. Keeping in view the NGP, digestibility of nutrients, methane and VFA production and correlations worked out for all possible combinations in different parameters, the best combination was cinamaldehyde or carvon dissolved in 50% methanol. The use of petroleum ether and propylene glycol as solvent in such studies should be avoided.