Development for effective oxidation inhibition technique of edible oils at frying temperature

To reduce food loss, it is desirable to use fried oil repeatedly. However, oxidation progresses during frying cooking, resulting in off-odors and the formation of harmful substances. Therefore, it is necessary to develop a technology to effectively inhibit the oxidation of frying oil. Currently, there are few studies on methods to prevent oxidation in the presence of some antioxidants at frying temperatures of around 170-180℃. In this study, we conducted oxidation experiments at frying temperatures in the presence of an antioxidant and discussed its effectiveness in inhibiting oxidation.

Soybean oil, commonly used for frying, was selected for this study. The induction period (IP), determined using the Rancimat method, was used to evaluate the oxidation progress of the oil. Typically, antioxidants for edible oils are required to dissolve in oil, so oil-soluble materials are generally used. First, α-tocopherol, an oil-soluble vitamin E, was dissolved in the oil for oxidation experiments. Surprisingly, it was found that oxidation accelerated at frying temperatures. Next, the addition of ascorbic acid (vitamin C), a common antioxidant, was considered. However, because ascorbic acid is water-soluble, we conducted the oxidation experiments using its oil-soluble derivative, ascorbic acid palmitate. Unfortunately, this did not extend IP, and no inhibitory effect on oxidation was obtained.

On the other hand, in our previous study, we discovered that tocopherols were efficiently regenerated and oxidation was effectively inhibited by adding insoluble antioxidants directly to the oil at a low temperature of 120°C. Based on this finding, we conducted experiments by adding ascorbic acid powder directly to the oil without dissolving it. Remarkably, the results showed that this insoluble form of ascorbic acid nearly doubled IP even at the frying temperatures. This breakthrough discovery challenges the conventional wisdom that dissolution is essential for the effectiveness of antioxidants.