Rosemary vs oxidizing cooking oil

Sorry there was no post yesterday.  My internet connection, even though I'm on cable internet, is severely affected by weather and Mother Nature decided to bring us some more of those lovely storms and heavy winds.

Jaswir, Che Man, and Hassan (2005) conducted a study using rosemary to reduce the oxidation of the lipids (fats) in palm oil when used for frying, in this case, potato chips.  There was a difference between all three antioxidants (sage, rosemary and citric acid) and control on day one of the 5-day trial. All three were significantly effective at reducing the oxidation of the lipids, though rosemary was the most efficient, citric acid being the least.

In looking for synergistic effects between the herbs, the most effective was the rosemary and sage combination. They did mention the oils will still break down do to heat and the water from the chips but these treatment methods helped reduce the oxidation, extending the length of time they were able to use the oil.  The cooking period for the whole experiment was 25 hours. For the rosemary and the sage, they used the oleoresin constituent specifically.

Changes in color were harder to pin-point.  The treated samples were all darker than control due to the color of the antioxidant but at the end, the control sample was darker. The factors to include are the introduction of the chips to the oil (they did it by weight, not by number so the number of chips could vary) as well as the effect of the heat on the oils.

The viscosity was decreased in the treated samples but not by much.  The viscosity increased throughout the experiment as the heat caused the increase in thickness of the oil.  The viscosity of the oil has a direct relation to the oxidation, the thicker the oil is, the more oxidation. Interestingly, the chips fried for the control significantly absorbed more of the oil than those fried in the rosemary- or sage-infused oils, with the citric acid chips absorbing less than control as well. 

The levels of the treatments needed for optimal effect varied based on which constituent in the oil was to be treated.  Citric acid had the least amount, sage had the most. For those interested, the effects on flavor were not tested.

Have a Great Day!

Jaswir, I., Che Man, Y. B., and Hassan, T. H. (2005). Performance of phytochemical antioxidant systems in refined-bleached-deodorized palm olein during frying. Asian Pacific Journal for Clinical Nutrition, 14(4); 402-413.