Behavior of Olive Pomace Oil in frying and comparison with conventional sunflower oil and high-oleic sunflower oil. ·

Study

Research centre: Food and Nutrition Science and Technology Institute – CSIC

Project summary:
Frying is one of the most common culinary techniques and is a widely used practice, both domestically and industrially. It is a very complex process that involves numerous reactions, due to the oxygen in the air, the high temperature and the water coming from the food. The suitability of a frying oil is related, above all, to its resistance to thermal oxidation, and the main variables associated with the oil that influence it are its degree of unsaturation and the nature and content of its minor compounds having protective effects. In addition, there are important differences depending on the type of frying; that is, whether the process is continuous (industrial frying) or discontinuous (domestic frying, in restaurants, fast food establishments, cafeterias, etc.). The behaviour of olive pomace oil in relation to conventional and high oleic sunflower oils has not been evaluated in rigorous and systematic scientific studies. Considering its composition and physiochemical characteristics, this project expects clearly better results for olive pomace oil, due to its high concentrations of oleic acid, than for conventional sunflower oil, even if the latter is rich in antioxidants (tocopherols). With regards to high-oleic sunflower oils whose fatty acid content is similar to that of olive pomace oil, the primary advantage of the latter are its protective frying compounds, such as squalene and phytosterols.

This study aims to provide the necessary scientific basis to demonstrate that olive pomace oil is more suitable for frying than sunflower oils, both conventional and modified “high-oleic sunflower”, in both domestic and industrial frying.

Researchers

Profile of the principal investigator:

Gloria Márquez Ruiz

Profile of the lead researcher:

Gloria Márquez Ruiz is a Scientific Researcher at the Food and Nutrition Science and Technology Institute (ICTAN-CSIC), where he has been working since 1986, and her main research focus is the study of frying oils: quality and stability, development of analysis methods, antioxidant activity, etc. Her research in this field has contributed to the development of new analytical methods for the evaluation of alteration compounds formed in frying and quality control, including the validation of rapid methods for their determination in the hospitality sector, small establishments and cafeterias. She has also extensively studied the influence of numerous variables (temperature, surface area / volume of oil, degree of unsaturation of oil, etc.) on the alteration of different oils, and the effectiveness of different antioxidants (synthetic and natural). The major differences found with regards to the type of frying (continuous and discontinuous) and the interactions between food and oil are also topics addressed by Dr. Márquez in the frying area. She has also carried out research on the digestibility of frying oils and new compounds formed in animal specimens, and on the changes these compounds undergo under gastric and intestinal conditions. Dr. Márquez has published 126 scientific articles and 34 book chapters, directed 6 doctoral theses; and participated in 33 competitive national and international projects, and on 16 contracts with industries and private companies. She has presented the results of her research at 87 scientific congresses and has been awarded the Prize for the Best Oral Communication by the American Oil Chemists’ Society (Indianapolis, 1996), the Prize issued by the Brazilian Society of Fats and Oils for her “Contribution to Analytical Knowledge in the Area of Oils and Fats” (Campinas, 2008), the selection of Lipid Technology (Research Highlights) as one of the best scientific publications in 2003 and 2008, and the Edwin Frankel Award, from the American Oil Chemists’ Society (Salt Lake City, 2016), for the best publication in “Lipid Oxidation and Quality”.

Results

After 7 months of intense lab work at Spain’s Food and Nutrition Science and Technology Institute (ICTAN), attached to the Scientific Research Council (CSIC), it has been shown that Olive Pomace Oil, in comparison to sunflower and high oleic sunflower oils, possesses properties that make it ideal to obtain the healthiest, crunchiest and most golden fried foods. This conclusion was reached after examining three batches of each of these oils, pertaining to different phases of the campaign. All the frying involved potatoes, in every case replicating in the laboratory the continuous (industrial) and discontinuous (domestic) frying modalities. Parameters like the oil’s quality and the modifications that both the oil and the food undergo during frying were analysed.p> Its composition, rich in oleic acid and exclusive bioactive compounds, like squalene and beta-sitosterol, furnishes Olive Pomace Oil with special properties having a protective effect for the oil itself, making it longer lasting and more stable, and for health, with beneficial effects on the body. After the results obtained it was concluded that Olive Pomace Oil performs much better when frying than conventional sunflower oils and other similar ones, and even slightly better than high oleic sunflower oils. All this demonstrates the quality of Olive Pomace Oil and its aptness for use in frying, thanks to its properties, duration and cost-effectiveness.

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Article

Foods (2021): Performance of Olive-Pomace Oils in Discontinuous and Continuous Frying. Comparative Behavior with Sunflower Oils and High-Oleic Sunflower Oils.

Francisca Holgado 1, María Victoria Ruiz-Méndez 2, Joaquín Velasco 2 and Gloria Márquez-Ruiz 1*

Instituto de Ciencia y Tecnología de los Alimentos y Nutrición, Consejo Superior de Investigaciones Científicas, 28040 Madrid, Spain; f.holgado@ictan.csic.es
Instituto de la Grasa, Consejo Superior de Investigaciones Científicas, 41013 Sevilla, Spain; mvruiz@ig.csic.es (M.V.R.-M.); jvelasco@ig.csic.es (J.V.)

* Correspondence: gmarquez@ictan.csic.es

Abstract: Frying performance of olive-pomace oils (OPOs) as compared to sunflower oils (SOs) and high-oleic sunflower oils (HOSOs) was studied in discontinuous frying (DF) and continuous frying (CF) for the first time. DF is used in household, restaurants and frying outlets, while CF is used in the food industry. Oil alteration during frying was determined by measurements of polar compounds (PC) and polymers. Fried potatoes were analyzed for oil absorption and alteration, color, and evaluated in an acceptability test. Results for DF showed that all SOs reached 25% PC at the 9^th frying operation (FO), whereas HOSOs did between the 17–18th FO and variable results were found for OPOs since initial levels of diacylglycerols were different. Rates of formation of PC or polymers were the lowest for OPOs, thus showing the best performance in DF. Specifically for PC, relative rates of formation were 1.00–1.11, 2.46–2.71 and 1.37–1.41 for OPOs, SOs and HOSOs respectively. In CF, OPOs and HOSOs behaved similarly and better than SOs, although none reached 25% PC after 40 FO. The good performance of OPOs can be attributed to the high monounsaturated-to-polyunsaturated ratio, in common with HOSOs, and the additional positive effect of minor compounds, especially β-sitosterol and squalene.

Keywords: frying; high-oleic sunflower oil; olive-pomace oil; polar compounds; polymers; sunflower oil.

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Source: Oriva