Determination of Frying Quality of Vegetable Oils used for Preparing Falafel using Infrared Spectroscopy and Multivariate Calibration Yahya Salem Al-Degs & Mohammed Al-Ghouti & Nidaa Salem Received: 18 November 2010 / Accepted: 18 January 2011 / Published online: 1 February 2011 # Springer Science+Business Media, LLC 2011 Abstract The frying qualities of palm and soybean oils are determined using infrared spectroscopy and multivar- iate calibration. Compare to soybean oil, palm oil is more resistive to the chemical and physical changes and this is attributed to the high degree of unsaturation of soybean oil (61.9%) compare to palm oil (13.8%). After 48 h in service, the oil samples were effectively clustered into two groups using principal component analysis which indicated that both oils still maintain their chemical identities. Partial least squares regression (PLS1 and PLS2) a long with mid-FTIR data are used for predicting free fatty acid, viscosity, and total polar compounds of the used oils without running expensive standard procedures. PLS1 and PLS2 outperformed PCR and MLR for predicting the quality indicators of the frying oils. For palm oil and at the optimum calibration conditions, the obtained accuracies (SD) are 105.6% (0.05), 99.8% (1.10), and 103.9% (0.16) for free fatty acid, viscosity, and total polar compounds, respectively. The proposed method is simple, less-expensive, and has comparable accuracy/precision with standard procedures that often used for monitoring frying oils. Keywords Vegetable oils . Free fatty acid . Total polar compounds . Viscosity . Mid-FTIR spectroscopy . Multivariate calibration Introduction The frying power of frying oils is highly dependent on the service time of the oil. Frying food with heat-abuse oil will affect the quality of the final product with bad influence on the consumer ’s health (Fritsch 1981). The chemical reactions that affect the frying oil quality are hydrolysis, oxidation, and polymerization of triglycerol molecules (Benedito et al. 2002). Chemically, all oils and fats are made up of triglycerides which resulted from the reaction between three, two, or one fatty acid chains with glycerol molecule (Fritsch 1981). The main fatty acids composing fats and oils consist of 14–22 carbon atoms and may contain one or more double bonds (Gunstone 2000). Oleic acid (C 18:1 ) is the most abundant monounsaturated fatty acid and found in the majority of vegetable oils (Codex Standards 1999) and this molecule is stable against oxidation at storage and frying temperatures (Abdulkarim et al. 2007). Based on that, high-oleate oils are more stable and more resistive to oxidative frying environment (Su and White 2004). A special oil containing 74.5% oleic acid and very low levels of linoleic (C 18:2 ) and linolenic acids (C 18:3 ) was extracted from Moringa oleifera seeds and found more resistive for frying conditions compared to palm and soybean oils (Abdulkarim et al. 2007, Tsaknis and Lalas 2002). In most investigations, the influence of temperature on oil frying power was assessed in the absence of food and this may be attributed to the experimental difficulties associated with oil monitoring in the presence of food. In Y. S. Al-Degs (*) Department of Chemistry, College of Science, Hashemite University, 30001, Zarka 13133, Jordan e-mail: yahya@hu.edu.jo M. Al-Ghouti Director of Arts and Sciences Unit Fahad Bin Sultan University, 15700, Tabuk, Kingdom of Saudi Arabia M. Al-Ghouti : N. Salem Royal Scientific Society, Industrial Chemistry Center, Amman, Jordan Food Anal. Methods (2011) 4:540–549 DOI 10.1007/s12161-011-9201-9