A Quick Method for Determining Total Polar Compounds of Frying Oils Using Electric Conductivity
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A Quick Method for Determining Total Polar Compounds of Frying Oils Using Electric Conductivity Jinwei Li 1 & Wenci Cai 1 & Dewei Sun 1 & Yuanfa Liu 1
Received: 29 June 2015 / Accepted: 21 September 2015 # Springer Science+Business Media New York 2015
Abstract Oil qualities during 40 h unconsecutive frying process were analyzed by combined tradition chemical indexes and electric conductivity (EC), and the correlation between quality index of frying oil and total polar compounds (TPC) was also studied. The result shows that frying oil’s quality trends to deterioration with the extension of frying time. TPC was positively related to EC, acid value (AV), carbonyl value (CV), peroxide value (POV), and p-anisidine value (PAV) of frying oil. The correlation coefficient between TPC and other quality index decrease in the order of EC, AV, CV, POV, and PAV and were 0.9583, 0.9303, 0.9152, 0.7949, and 0.7082, respectively. EC has the highest correlation with TPC. Furthermore, repeated experiment showed that relative standard deviation ranged from 1.08 to 2.17 %, and there are no significant differences in TPC value by between traditional TPC method and EC method (P>0.05). EC method could be a good selection to predict the TPC and discard point of frying oil. Keywords Frying oil . Polar compounds . Quality index
Introduction Frying is one of the most popular food preparation technologies currently, which is widely used at home, restaurants, and * Yuanfa Liu [email protected] 1
State Key Laboratory of Food Science and Technology, Synergetic Innovation Center of Food Safety and Nutrition, School of Food Science and Technology, Jiangnan University, Wuxi 214122, People’s Republic of China
various parts of the food manufacturing (Saguy and Dana 2003). The oil maintained at a temperature of about 150– 200 °C causes desired sensory characteristics, golden brown color, and crispiness of the fried food product. However, it is well known that frying oils used continuously at high temperatures in the presence of oxygen and water from the food being fried are subject to thermal oxidation, polymerization, and hydrolysis. Hydrolysis of triglycerides caused by the steam resulted in the formation of free fatty acids, glycerol, mono- and diglycerides, while a chain of oxidation reactions involving the formation of hydroperoxides is initiated by the air released into the frying system (Houhoula et al. 2003). As a result, some decomposition products with high molecular weights such as polar compounds and polymeric triacylglycerides arise (Farhoosh and Moosavi 2008; Rossi et al. 2007; Sanchez-Gimeno et al. 2008; Xu 2000). These polar compounds limit the reuse of cooking oil due to negative effects on the quality of frying oil and flavor and nutritional value of the fried food (Clarck and Serbia 1991; White 1991; Tyagi, and Vasishtha 1996). In addition, undesirable constituents produced from degraded frying oils may even be harmful to health (Innawong et al. 2004). Various criteria are being used to judge when the frying oils need to be di
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