The Effect of Boiled Oil (Olive Oil Produced using Boiled Olive Fruits) on Gut Microbiota in the Rat

To investigate the common belief amongst locals that boiled oil (BO) is more beneficial than virgin olive oil (VOO).

The effect of olive oil on gut microbiota varies according to the species of the microbe. It was reported to promote the growth of some beneficial bacteria and inhibit the growth of others, in addition to its inhibitory effect on pathogenic bacteria. In certain villages in Northern Jordan, a portion of the harvest of olive fruits is boiled before oil extraction. This product is known locally as “boiled oil,” and locals believe that it is more beneficial than VOO.

This study aims to investigate the effect of oil extracted from boiled olive fruits on gut microbiota in comparison with virgin olive oil.

Forty-seven Wistar Albino rats were divided into six groups of 7 rats per group in addition to the reference group. The rats were fed 10 ml/Kg body weight/ day of corn oil, VOO, or boiled oil for the duration of the experiment. The reference group was slaughtered before ingesting any oil. Then, after 3 and 6 weeks, a group from each treatment was slaughtered, and faeces samples were collected from the cecum and the adjacent part of the colon. The collected faeces samples were diluted for bacterial enumeration

After 3 weeks, the groups that were fed boiled oil showed a significant increase in Bifidobacteria in comparison with the control and the VOO group by a mean growth of 8.54 log10 CFU/g, 7.75 log10 CFU/g, and 6.85 log10 CFU/g, respectively. Boiled oil showed a significant increase in Lactobacilli count in comparison with the control and the olive oil group with a mean growth of 9.57 log10 CFU/g, 9.21 log10 CFU/g, and 9.38 log10 CFU/g, respectively. Moreover, for the Escherichia coli count, boiled oil showed a significant increase at 5.84 log10 CFU/g in comparison with the VOO group at 5.24 log10 CFU/g, but boiled oil showed a non-significant increase in comparison with the control group. Moreover, boiled oil showed a significant decrease of total aerobic bacteria at a mean growth of 8.50 log10 CFU/g, whereas the VOO group counted 8.89 log10 CFU/g but showed a non-significant decrease with the control group. After 6 weeks, there was a non-significant increase in Bifidobacteria and lactobacilli for boiled oil in comparison with the control group. In addition, boiled oil showed a significant increase in Bifidobacteria and lactobacilli in comparison with the olive oil group at a mean growth of 6.68 log10 CFU/g and 8.79 log10 CFU/g, respectively. For Escherichia coli, it shows a significant increase at 5.97 log10 CFU/g for boiled oil in comparison with 5.36 log10 CFU/g for the control group and a significant increase compared with the VOO group with a mean growth of 4.94 log10 CFU/g. Moreover, the boiled oil group caused a significant increase in total aerobic bacteria at 8.75 log10 CFU/g, in comparison with the VOO group at 8.37 log10 CFU/g. In addition, boiled oil caused a non-significant increase in total aerobic bacteria in comparison with a control group. Boiled oil did not have a significant effect on total anaerobic bacteria.

Boiled oil exhibited less antimicrobial activity in comparison with virgin olive oil, probably because of the loss of total phenolic compounds.