Used food oils: physical-chemical indicators of quality degradation

Abstract

Used food oil (UFO), designated as frying oil, is a residue. Degradation by reuse or during storage, may occur by contacting, chemical, enzymatic and microbiological pathways, but oxidation is a major concern of the industry, as it affects sensory and nutritional quality of edible oils, with potentially toxic compounds formation. In Portugal, UFO's main destination still is the sewerage system, an environmental problem and waste of raw material, which can be re-qualified for non-food uses. However, quality control applied to UFO's, often results into expensive analysis inappropriate for small laboratories and catering industry. This project, developed with the Musketeers Group Portugal co-promotion (2012)(2013)(2014)(2015)(2016), aimed to identify low-cost physicochemical parameters for further implementation as UFO´s Quality Degradation Indicators (QDI) indicating defects quickly and accurately. UFO´s analysis was tested on the use, for industrial frying, and by degradation induced in the laboratory (frying and heat stability tests) by applying following parameters: moisture, water activity (aw), total acidity, peroxide index, iodine index, colour (CIE, CIE Lab), UV absorbency, total polar compounds and microbiological indicators. Internal procedures (ESAS) were validated, redefining working ranges and test conditions, as standards procedures did not provide reliable results for the entire life cycle of oils, whose profile changes with time and reuse. Results demonstrate significant differences with quick response parameters as Total Acidity, Peroxide Index and CIE Lab colour, outlined as QDI's. Moisture, aw and CIE Lab colour proved to be inadequate for this purpose. Iodine Index and UV Absorbency are more complex and time-consuming and were profiled as reference methods.

Effects of Repeated Frying on Physical Properties of Cooking Oil obtained from Local Markets in Makurdi Metropolis, Benue State, Nigeria.

“…This is to say that: frying of food may bring out the aroma, enhance the flavor and texture combination which is very desirable for consumption, making fried foods one of the most popular food products [17]. Conversely, when cooking oils are stored for a long time, excessive recycling or exposed to excessive heat, oil degradation occurs [18][19], and by-products are produced [20]. Elevated temperatures, especially temperature above the smoking point of the oil, will cause significant change in its quality due to the chemical and physical reactions [21].…”