Deep‐fat frying – An ancient popular process with a lot of open questions

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In 2013 the 7th International Symposium on Deep-Fat Frying took place in San Francisco. During this three-day symposium organized by the European Federation for the Science and Technology of Lipids (Euro Fed Lipid), the newest aspects on deep-fat frying were presented and discussed by more than 90 participants 1. Although deep-fat frying is a well-known and old cooking process dating back to 1600 BC, the symposium showed that still a lot of questions are open and under discussion. One reason for this is that deep-fat frying is a very dynamic process where food is immersed into hot oil resulting in drying and cooking of the food as well as deterioration of the oil with processing time. The complex processes taking place at the surface of the food but also in the oil are still not understood comprehensively. On the other side, since a remarkable part of oil is taken up by food the focus of interest is also on aspects important for maintaining the oil quality. As with the past international symposia on deep-fat frying several recommendations have been given by the participants to improve science and technology of frying as well as safety and quality of the products. The main aspects of these recommendations are risk-based research and analysis of data to identify potentially hazardous oil degradation products, development of more reliable quick tests, clear definition of specifications for frying oils, definition of a baseline for the frying operations as well as research on potential microbiological risks inherent to coated products. The participants of the 7th symposium on deep-fat frying confirmed the recommendations made in 2000 that total polar materials and polymeric triacylglycerols are the best parameters for assessing quality of used frying oil. Additionally, it was stated that peroxide value, anisidine value, and content of free fatty acids should not be used as regulatory indices to monitor and to compare the degree of degradation of frying oils. In practice, these parameters are often still in use although their degree of correlation with oil quality is weak. Also the occurrence of acrylamide in fried food based on asparagine and reducing sugars is still an issue. In 2002 the first announcement on acrylamide in fried food was a shock for the industry 2. Since this time a lot of efforts have been undertaken to minimize the formation of acrylamide while maintaining product quality. Several approaches have been found. This special issue on deep-fat frying takes the most important presentations from the 7th symposium on deep-fat frying, but also includes new aspects in seven Reviews and five Research articles. What are the degradation products of fatty acids during frying and what is their importance for health 3? How do frying conditions influence the oil uptake of food being fried 4, 5? What parameters are relevant for controlling quality of used frying oil 6? Another point coming more and more into the focus of interest is the replacement of synthetic antioxidants by antioxidants from natural sources. Consumers refuse synthetic antioxidants, therefore the search for new and applicable sources is an ongoing story. The most important sources of natural antioxidants are described in a review 7, while another paper discusses the use of antioxidants from herbs for stabilization of rapeseed oil 8. All these points cover the wide area of aspects necessary to understand the frying process better, to improve product quality and to extend service life of frying oil or fat. It was a great pleasure for us to organize and prepare this special issue on deep-fat frying and we thank all the authors for their interesting contributions and their work. We are also grateful to all the reviewers for their time-consuming, but essential, valuable, and important help. In our opinion this special issue gives excellent information on the latest developments and knowledge about deep-fat frying and we are sure that everyone will get new information from this issue of EJLST, available online at http://onlinelibrary.wiley.com/doi/10.1002/ejlt.v116.6/issuetoc. Christian Gertz Maxfry Hagen Felix Aladedunye Max Rubner-Institut Detmold Bertrand Matthäus Max Rubner-Institut Detmold