Study of the acidic compounds derived from triacylglycerol that contribute to acid value increment

Study of the acidic compounds derived from triacylglycerol that contribute to acid value increment

Ryosuke Aoki

J-OIL MILLS, INC, 7-41 Daikoku-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0053, Japan

Tel.: +81 45 503 2431; Fax: +81 45 504 5315

E-mail: ryosuke.aoki@j-oil.com

Acid value (AV) is a recognized method for measuring free fatty acids (FFA) derived from the hydrolysis of triglycerides, but several studies have reported unexplained increases in AV in frying oils despite no-water addition conditions. In this study, we hypothesized that this elevated AV might be due to the formation of acidic compounds that are not FFA during cooking, and the following experiments were conducted.

Canola oil was heated at 180℃ for 6 hours under no-water addition condition, and FFA and AV were determined by LC and titration methods, respectively. As a result, the AV calculated from the FFA concentration was only 10% of the titrated AV. When we analyzed the oil by LC-MS analysis, we found dioleoyl-(9-carboxy-nonanoyl)-triacylglycerol and oleoyl-linoleoyl-(9-carboxy-nonanoyl)-triacylglycerol as unique acidic compounds. Since these acidic compounds have carboxyl groups, they are speculated to be calculated as AV as well as FFA. In fact, when the French fries were cooked and analyzed with various instruments, the contribution of these acidic compounds to the increase in AV was found to be higher than that of FFA.

This study successfully identified for the first time the acidic compounds that are preferentially formed when canola oil is thermally oxidized under no-water addition condition, or when canola oil is used to fry French fries. Therefore, AV should be considered as an indicator to evaluate not only triglyceride hydrolysis (i.e., FFA) but also thermal oxidation (i.e., the two acidic compounds found in this study). In this presentation we will introduce these studies of ours and share our thoughts from the SDGs perspective as well.