Acrylamide (CH2CHCONH2), an industrially produced α,β-unsaturated (conjugated) reactive molecule, is used worldwide to synthesize polyacrylamide. Polyacrylamide has found numerous applications as a soil conditioner, in wastewater treatment, in the cosmetic, paper, and textile industries, and in the laboratory as a solid support for the separation of proteins by electrophoresis. Because of the potential of exposure to acrylamide, effects of acrylamide in cells, tissues, animals, and humans have been extensively studied. Reports that acrylamide is present in foods formed during their processing under conditions that also induce the formation of Maillard browning products heightened interest in the chemistry, biochemistry, and safety of this vinyl compound. Because exposure of humans to acrylamide can come from both external sources and the diet, a need exists to develop a better understanding of its formation and distribution in food and its role in human health. To contribute to this effort, this integrate...

https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=25505&content=PDF

Chemistry, biochemistry, and safety of acrylamide. A review.

Deep-fat frying produces desirable or undesirable flavor compounds and changes the flavor stability and quality of the oil by hydrolysis, oxidation, and polymerization. Tocopherols, essential amino acids, and fatty acids in foods are degraded during deep-fat frying. The reactions in deep-fat frying depend on factors such as replenishment of fresh oil, frying conditions, original quality of frying oil, food materials, type of fryer, antioxidants, and oxygen concentration. High frying temperature, the number of fryings, the contents of free fatty acids, polyvalent metals, and unsaturated fatty acids of oil decrease the oxidative stability and flavor quality of oil. Antioxidant decreases the frying oil oxidation, but the effectiveness of antioxidant decreases with high frying temperature. Lignan compounds in sesame oil are effective antioxidants in deep-fat frying.

https://onlinelibrary.wiley.com:443/doi/pdf/10.1111/j.1750-3841.2007.00352.x

Chemistry of deep-fat frying oils

Preface to the First Edition. Preface to the Second Edition. Contributors. List of Abbreviations. 1 Production and Trade of Vegetable Oils ( Frank D. Gunstone ). 1.1 Extraction, refining and processing. 1.2 Vegetable oils: Production, consumption and trade. 1.3 Some topical issues. 2 Palm Oil ( Siew Wai Lin ). 2.1 Introduction. 2.2 Composition and properties of palm oil and fractions. 2.3 Physical characteristics of palm oil products. 2.4 Minor components of palm oil products. 2.5 Food applications of palm oil products. 2.5.1 Cooking/frying oil. 2.6 Nutritional aspects of palm oil. 2.7 Sustainable palm oil. 2.8 Conclusions. 3 Soybean Oil ( Tong Wang ). 3.1 Introduction. 3.2 Composition of soybean and soybean oil. 3.3 Recovery and refining of soybean oil. 3.4 Oil composition modification by processing and biotechnology. 3.5 Physical properties of soybean oil. 3.6 Oxidation evaluation of soybean oil. 3.7 Nutritional properties of soybean oil. 3.8 Food uses of soybean oil. 4 Canola/Rapeseed Oil ( Roman Przybylski ). 4.1 Introduction. 4.2 Composition. 4.3 Physical and chemical properties. 4.4 Major food uses. 4.5 Conclusion and outlook. 5 Sunflower Oil ( Maria A. Grompone ). 5.1 Introduction. 5.2 Sunflower oil from different types of seed. 5.3 Physical and chemical properties. 5.4 Melting properties and thermal behaviour. 5.5 Extraction and processing of sunflower oil. 5.6 Modified properties of sunflower oil. 5.7 Oxidative stability of commercial sunflower oils. 5.8 Food uses of different sunflower oil types. 5.9 Frying use of commercial sunflower oil types. 6 The Lauric (Coconut and Palm Kernel) Oils ( Ibrahim Nuzul Amri ). 6.1 Introduction. 6.2 Coconut oil. 6.3 Palm kernel oil. 6.4 Processing. 6.5 Food uses. 6.6 Health aspects. 7 Cottonseed Oil ( Michael K. Dowd ). 7.1 Introduction. 7.2 History. 7.3 Seed composition. 7.4 Oil composition. 7.5 Chemical and physical properties of cottonseed oil. 7.6 Processing. 7.7 Cottonseed oil uses. 7.8 Co-product uses. 8 Groundnut (Peanut) Oil ( Lisa L. Dean, Jack P. Davis, and Timothy H. Sanders ). 8.1 Peanut production, history, and oil extraction. 8.2 Oil uses. 8.3 Composition of groundnut oil. 8.4 Chemical and physical characteristics of groundnut oil. 8.5 Health issues. 9 Olive Oil ( Dimitrios Boskou ). 9.1 Introduction. 9.2 Extraction of olive oil from olives. 9.3 Olive oil composition. 9.4 Effect of processing olives on the composition of virgin olive oils. 9.5 Refining and modification. 9.6 Hardening and interesterification. 9.7 Quality, genuineness and regulations. 9.8 Consumption and culinary applications. 10 Corn Oil ( Robert A. Moreau ). 10.1 Composition of corn oil. 10.2 Properties of corn oil. 10.3 Major food uses of corn oil. 10.4 Conclusions. 11 Minor and Speciality Oils ( S. Prakash Kochhar ). 11.1 Introduction. 11.2 Sesame seed oil. 11.3 Rice bran oil. 11.4 Flaxseed (linseed and linola) oil. 11.5 Safflower oil. 11.6 Argan kernel oil. 11.7 Avocado oil. 11.8 Camelina seed oil. 11.9 Grape seed oil. 11.10 Pumpkin seed oil. 11.11 Sea buckthorn oil. 11.12 Cocoa butter and CBE. 11.13 Oils containing a-linolenic acid (GLA) and stearidonic acid (SDA). 11.14 Tree nut oils. Useful Websites. Index.

http://health120years.com/cn/pdf/hd_Vegetable.Oils.pdf

Vegetable Oils in Food Technology: Composition, Properties, and Uses

Over the past 5 years growing demands for reducing fat content of fried foods have greatly stimulated the amount of research spent on the issue of fat uptake during deep-fat frying. The results of these efforts are summarized in this review. Most of the increased understanding of the mechanism of fat uptake has been brought about by improved imaging techniques. It turns out that fat uptake is basically determined by two mechanisms: the condensation effect and the capillary effect. Major reductions claimed in literature and patents are found for coating and batter formulations using various types of biopolymers.

Mechanism and reduction of fat uptake in deep-fat fried foods

Integrated approach to deep fat frying: engineering, nutrition, health and consumer aspects

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.

Testing and comparing oxidative stability of vegetable oils and fats at frying temperature

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.

Analysis of acrylamide and mechanisms of its formation 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.

Chemical and physical parameters as quality indicators of used frying fats

The deep-frying process, normally carried out at 140-200 °C, is a very complex system due to the combination of heat and mass transfer between food and frying medium. The system becomes more complicated as the frying operation proceeds, because the composition of the food being fried and the frying medium is changing continuously due to the progressive deterioration of the frying medium. Apart from a variety of chemical reactions occurring, several changes take place in the frying food, such as gelatinisation of starch, denaturation of protein, and decrease of moisture. These changes bring about swelling of the product, formation of a crusty layer, and the appearance of a golden colour, good texture and taste. The precise control of the fryer enables these physical and chemical changes in the frying of food to convert it into a desirable finished product. This article discusses various types of reactions occurring in the food frying operation, possible mechanisms, a new realistic method - OSET index for measuring heat stability of frying oils - and the protective behaviour of substances that enhance the frying stability of oils.

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New theoretical and practical aspects of the frying process

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.

Christian Gertz

Papers

Testing and comparing oxidative stability of vegetable oils and fats at frying temperature

Analysis of acrylamide and mechanisms of its formation in deep‐fried products

Chemical and physical parameters as quality indicators of used frying fats

New theoretical and practical aspects of the frying process

Fundamentals of the frying process