Abstract
Commercial frying practices and frying conditions at 62 restaurants or fast‐food outlets were investigated and the quality of their discarded frying oils was evaluated by several standard laboratory methods: total polar components (TPC), free fatty acids (%FFA), p‐anisidine and peroxide values, color, viscosity, C18:2/C16:0, absorbance at 232 and 268 nm, and five quick test methods (Foodoil sensor, Oxifrit (RAU‐Test), Fritest, Veri‐Fry‐TAM 150, and Veri‐Fry‐FFA 500). Frying techniques varied from primitive traditional practice at traditional shops to modern sophisticated frying procedures at some franchise restaurants. Discarded oils appeared to be heat‐damaged to a varying extent according to the degree of quality control applied by the corresponding restaurants. Test methods were shown to possess different statistical correlations. Highly significant correlations were found between TPC and Foodoil sensor (c.f=0.93) and between Oxifrit and Fritest (c.f=0.94), each of which were also correlated relatively well to the TPC. Peroxide value followed by %FFA did not significantly (p<0.05) correlate with the TPC. Significant linear relationships (p⊕0.05) were found between the TPC and each of the other indicators but %FFA and peroxide value.