Deep-frying – often with palm oil – is one of the classic forms of preparation. Many products such as doughnuts, curd balls and potato and vegetable crisps are made this way. The challenge here, however, is to get a grip on the unwanted oiling out.
By Dr. Jörg Häseler
The use of structured oils, so-called oleogels, for deep-frying combines the advantages of a solid fat with a fatty acid composition of liquid vegetable oils that is beneficial for nutrition. The award-winning work by Sharline Nikolay entitled “Characterization of oleogel-fried foods, demonstrated by the example of French fries” provides the appropriate approaches.
The work shows that the use of oleogels for deep-frying is possible and leads to comparable products as when using conventional deep-frying media. The author not only looked at the production of the oleogels and their behaviour during frying, but also examined the manufactured products in terms of consumer acceptance.
The use of oleogels for deep-frying crisps, potato-based snack items as well as boiled pastries such as doughnuts or curd balls enables an improvement of the oily surface properties and prevents oiling out during storage of these products. The oleogels exhibit the desired properties of a solid fat and at the same time lead to an improvement of the fatty acid profile in terms of nutritional properties.
The topic was structured fat phases in the form of oleogels for use in deep-frying. Particularly high demands are placed on the oil due to the high temperature and the presence of oxygen and water. The oil should be stable under the conditions of deep-frying and not lead to any impairment of the deep-fried food.
The oils used often have a nutritionally favourable fatty acid composition, but oil out during storage of the products. This means that the oil escapes from the product and desired food quality standards may not be met. Alternatively, solid fats are used that are characterized by high proportions of saturated fatty acids that are unfavourable for nutrition. These have the advantage that they solidify again after deep-frying and therefore remain in the product. The resulting dichotomy between nutritional and technological aspects is a major challenge for the industry in the production of deep-fried foods such as snack products.
The use of oleogels for deep-frying combines the advantages of a solid fat in terms of physical and technological properties with the advantageous fatty acid composition of liquid vegetable oils. In this context, the use of domestic rapeseed oil is particularly suitable for the production of corresponding oleogels, as the fatty acid composition with the low content of saturated fatty acids as well as high contents of linoleic acid and α-linolenic acid is positive for nutrition.
The interesting approach of the work is that oleogels based on rapeseed oil were investigated as the solid fat phase. The oleogels are liquid rapeseed oil that is solidified by means of so-called structure formers. This makes it possible to combine the positive nutritional and physiological properties of rapeseed oil with the techno-functional properties of solid fats. The properties can be adapted to the product requirements by the proportion and type of a structuring additive.
In order to investigate the stability of oleogels during frying, experiments were carried out with French fries and different oleogels. Rapeseed oil-based oleogels containing 5 % sunflower wax or 5 % monoglycerides as structure formers were considered. A stress test under frying conditions allowed a comparison between the two oleogels and the use of pure rapeseed oil.
The results of the polar fractions and polymeric triglycerides, as important indicators for the edibility of the frying medium used, were comparable with pure rapeseed oil for the oleogel with 5 % sunflower wax. On the other hand, the oleogel with 5 % monoglycerides – due to the addition of the monoglycerides in the oleogel – already showed an increased proportion of the polar fractions at the beginning of the deep-frying test. This is not a sign that spoilage has already started, but it does make it difficult to comply with the limit value for the polar fractions of 24 %.
The oleogel with 5 % mono-glycerides also had higher levels of polymer triglycerides, a darker colour and a higher level of saturated fatty acids during frying. In addition, the firmness of this oleogel was lower and decreased further during the frying process.
The oleogel with 5 % sunflower wax, on the other hand, showed a higher as well as a more stable firmness. Based on these results, this oleogel proved to be the best variant. The general suitability of oleogels for frying French fries was thus confirmed.
For her Master’s thesis on the use of alternative fat phases for the production of deep-fried foods, Sharline Nikolay recently received the Heinrich Stockmeyer Foundation’s Young Scientist Award, endowed with EUR 2,500. The author completed the thesis in the Life Science Technologies degree programme at the Ostwestfalen-Lippe University of Applied Sciences, with the practical part and technical supervision being provided by the Max Rubner Institute. Due to its practical relevance, the work met with great interest, which in turn led to support from the snack industry for another research project.
