Acrylamide was supplied by Sigma-Aldrich (Taufkirchen, Germany) deuterium-labeled acrylamide-d3 by Promochem (Düren, Germany), Clara-Diastase was supplied by Fluka (Taufkirchen, Germany).Working standard solutions, for spiking samples as well as for the standard, were obtained by dilutions in water. All other solvents and chemicals were of analytical grade. SamplesSolid food samples were homogenized and analyzed fresh, or stored at about 5 °C under refrigeration until analysis. ProcedureA portion of food (10 g) was placed into a 100 ml Erlenmeyer flask. 1.0 ml aqueous solution of deuterium labeled acrylamide (20 µg/ml), 50 ml 0.5% aqueous acetic acid solution and 1 g Clara diastase were added successively. The pH of the mixture was adjusted to 4.5 with glacial acetic acid. The suspension in the stoppered flask was allowed to incubate for 18 h in a water bath at 37 °C with A reliable and sensitive gas chromatography-mass spectrometry method was developed for the determination of acrylamide, a toxic compound recently discovered in baked, fried or grilled food. Satisfactory results for repeatability and recoveries were obtained by this method. The limit of detection for acrylamide was 15 µg/kg food and recoveries were between 95 to 103%.The improved method was then employed to study the influence of heat, heating time and type of frying oil on the formation of acrylamide during the deep frying of French fries. In this matrix acrylamide formation was promoted by heating in a time-dependent manner. It appeared that acrylamide arose, when reducing sugars, dimethylpolysiloxane or partial glycerides were present. Three mechanisms of formation are discussed in this context. Although the mechanistic complexity increases dramatically in the presence of various food components, some recommendations can be given to minimize acrylamide levels in deep fried products.

There are many methods available in the literature to test the physical properties and chemical changes of frying fats. Physical methods include density, viscosity, smoke point, colour, refractive index, ultraviolet (UV) absorption, infra‐red spectroscopy, and dielectric constant. Chemical tests are the determination of free fatty acids (acid value), iodine value, anisidine index, saponification value, non‐oxidised monomer fatty acids, polymerised triglycerides, fatty acids insoluble in petrol ether, and total polar compounds. Quality control in the production of fried food, whether the analyst is a quality control inspector or a member of the health food inspection service, demands a simple, easy procedure, using no chemicals. The results should correspond to official methods such as polar compounds. Among all physical and chemical methods, the determination of polar materials, polymerised triglycerides by size exclusion chromatography (HPSEC), and acid value were selected to be compared with the results of the measurements of the dielectricity constant (Food Oil Sensor) and the relative viscosity and density (Fri‐Check®,respectively. More than 150 samples, taken in commerce by the food inspection, were analysed and statistically evaluated.

A new method has been developed to estimate the stabilising activity of synthetic and natural food additives at frying. Non‐refined and refined vegetable fats and oils were heated at a temperature of 170°C after adding water‐conditioned silica gel for two hours. The degraded products were measured to assess the oil stability at frying temperature. The determination of polymeric triglycerides by size exclusion high‐pressure liquid chromatography (HPLC) was carried out for the estimation of the oxidative heat stability of vegetable fats and oils. Tocopherols, various tocopherol esters and phytosterol fractions, phenolic compounds, like quercetin, oryzanol, ferulic acid, squalene, butyl hydroxytoluol (BHT), butyl hydroxyanisol (BHA), and other compounds, like ascorbic acid 6‐palmitate and gallates, are added to refined sunflower and rapeseed oil and their efficacy determined. Both linoleic and oleic rich oils gave comparable results for the activity of the various compounds. α‐tocopherol, tocopherol esters, and BHA have low effects at frying temperature. Ascorbic acid 6‐palmitate and some phytosterol fractions were found to have the greatest antioxidant activity. Corn oil was more stable than soybean oil and rapeseed oil better than olive oil. It was also observed that non‐refined oils proved to have a better stability at elevated temperature than refined oils. The results show that the stability of the vegetable oils at frying temperature is a function of more than just the fatty acid composition. There is evidence which supports a co‐relationship between the unsaponifiable matter content and oxidative stability. It is believed that a radical peroxidation mechanism predominates at lower temperatures. When a large volume of oil is heated in a fryer and the oxygen supply is poor, non‐radical reactions such as elimination (acid catalysed dehydration) or nucleophilic substitution take place.

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Considerable interest has been developed over the years in optimizing the frying process. This approach has resulted in a better understanding of the process as a system: oil, food, fryer, and the operation in general. The frying‐process is a complex system depending on the extent of chemical reactions like oxidation, polymerisation, and hydrolysis where the physical and chemical properties of the heated fat are altering. It is difficult to estimate the extent of influence of each factor and to keep the frying conditions at an optimum level. The practical and theoretical aspects of deep‐frying such as oil‐uptake, mechanism of heat and mass‐transfer, and some analytical aspects to monitor the fat degradation are discussed. Practical applications: Deep‐frying involves close contact between the oil used and the food to be fried. The used oil becomes part of the food and contributes to the flavor, appearance, texture, shelf life, and nutritional value of the final product. A better understanding of the frying process is needed to produce fried products in a more economical way with an optimum flavor and a better shelf‐life.

Despite slimness mania and acrylamide scare, the market of fried products is still growing. Frying is an extremely effective way to cook food. A fried product tastes good, has a good flavour and is prepared within a few minutes.Every effort has been made to optimise the frying process. With regard to the quality of the fried food, the quality of the frying oil is very important. In the past, important characteristics of industrial frying oils were oxidative stability, high smoke point and low foaming. Nowadays, new frying fats with various additives, with a healthier fatty acid profile and higher heat stability are emerging. Emulsifiers, anti-polymerising agents, and natural and synthetic antioxidants improve the performance during frying. Sesamol, rosemary and other natural extracts display strong stabilising effects during the frying operations. Filtration and the use of heat-stabilising additives help to retard fat degradation and give the producer a larger time-window for optimum frying. The effectiveness of the treatment with filter aids or mineral adsorbents and the stabilising effects of synthetic and natural agents were compared by using the Rancimat test for testing oxidative stability and the OSET (oxidative stability at elevated temperature) test to determine the stability at the frying temperature.

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In the present work a fast and reliable laboratory protocol allowing a holistic statement about thermooxidative structural changes of fats and oils at ambient temperatures, under accelerated conditions using 110°C and under elevated temperature usually used for frying at 170°C is proposed. The results demonstrate that two different routes of degradation may be responsible for fat deterioration at elevated temperatures. Depending on the temperature (at 20, 110, or 170°C) the composition of polar compounds changed. The content of di-and polymerized TAGs increased with time at elevated temperature, e.g., frying whereas the formation of oxidized products dominates at 110°C or lower. These different reaction mechanisms may explain the discrepancy between practical experiences during frying and the estimated oxidative resistance of fats and oils using accelerated tests like Rancimat or OSI.Practical applications: Both the amount of total oxidized monomeric TAGs called total oxidized products (TOP) and the amount of di-and polymerized TAGs (DPTG) can be used to describe the fat degradation at all stages. These parameters are less dependent on the fat composition but proportional to the heating time and applied temperature. A procedure is proposed to compare thermal and oxidative stability of vegetable oils and effectiveness of oxidative stabilizing agents.