Antonio Rabazas Romero

Trans fatty acid production in deep fat frying of frozen foods with different oils and frying modalities

Abstract Frying process has been considered to be a source of trans fatty acids. However, most trans fatty acids found in foods would come from the oil used and not from the process itself. To test this, the trans fatty acid production was measured frying in extra virgin olive oil (EVOO), high oleic sunflower oil (HOSO) and sunflower oil (SO) various frozen foods 20 times with frequent replenishment (FR) or without replenishment (NR) of the used oil with fresh oil during the frying. Further, the fat extracted from potatoes fried in the EVOO, HOSO and SO from the frying 8 and 20 was also analyzed by gas liquid chromatography to compare it trans fatty acid profile with that of the corresponding fryer oil. Trans fatty acids appear in lower amounts than 5 mg/g oil or fat in both FR and NR. Elaidic acid was the most abundant trans fatty acid in EVOO or in the fat extracted from EVOO fried potatoes while trans linoleic isomers were more abundant in SO. HOSO was in between. Present data suggest that frequent addition of fresh oil through the frying process minimizes the fatty acid changes contributing to obtain fried foods with less amount of trans fatty acids. The consumption of a large standard ratio (∼ 140 g) of these fried potatoes would implied the irrelevant amount of less than 0.13 g of trans fatty acids.

High-performance size-exclusion chromatographic studies on a high-oleic acid sunflower oil during potato frying

The behavior of a high-oleic acid sunflower oil used for 75 repeated deep-fat fryings of potatoes, with a fast turnover of fresh oil during frying, was evaluated by measuring the total polar content isolated by column chromatography. The total polar content increased in the oil from 3.6 ± 0.1 (mean ± SD) mg/100 mg unused oil to 7.6 ± 0.4 mg/100 mg oil after being used in 20 repeated fryings, followed by a tendency to reach a near-steady state throughout the successive fryings. Further, the polar fraction was examined by high-performance size-exclusion chromatography. Triacylglyceride dimers increased continuously from 0.18 ± 0.01 mg/100 mg unused oil to 2.42 ± 0.12 mg/100 mg oil at the 40th frying with no further significant changes. The amount of triacylglyceride polymers increased from 0.03 ± 0.00 mg/100 mg unused oil to 0.70 ± 0.01 mg/100 mg oil at the 60th frying, but did not increase further with continued frying. Oxidized triacylglycerides also significantly increased from 1.13 ± 0.06 mg/100 mg oil to 3.58 ± 0.09 mg/100 mg oil at the 50th frying to reach a near-steady state in successive fryings. Diacylglycerides and free fatty acids levels, related to hydrolytic alteration, did not change from the starting oil after continued fryings. Data from this study indicated that repeated fryings of potatoes in high-oleic sunflower oil with a frequent turnover of fresh oil throughout the frying slightly increased the level of polar material in the fryer oil during the first fryings, followed by minor changes and a tendency to reach a near-steady state in successive fryings.

Fatty Acid Changes in High Oleic Acid Sunflower Oil during Successive Deep-Fat Fryings of Frozen Foods:

High oleic acid sunflower oil (HOSO) is a monounsaturated oil that is being extensively used in frying. The level of total altered fatty acids and the fatty acid pattern of a fryer oil was used to evaluate the alteration of a HOSO used 20 times to fry various frozen foods with frequent replenishment (FR) or without replenishment (NR) with fresh oil during the frying. In addition, the levels of total altered fatty acids and the fatty acid composition of the fat extracted from the fried potatoes after numerous fryings were determined and compared to those of the corresponding fryer oils. Altered fatty acids increased linearly through 20 fryings within FR and NR in the frying oil and also in the fat extracted. Although differences were not quantitatively relevant, changes tended to be higher in the extracted fat, and in the NR modality as a consequence of oil renovation and fat exchange between the frying oil and the potatoes. The decrease in the oleic acid content in the oil was more pronounced (p< 0.001) in NR than in FR method, and more (at least p< 0.01) in the oils than in the corresponding extracted fats. Nevertheless, other fatty acids remained quite stable and similar or increased during frying, by both methods. These results suggest that total fatty acid alteration measure is a useful tool for frying assessments, and that they must be related not only to the degradation of unsaturated fatty acids but also to migrations of some fatty acids from the frozen prefried foods to the fryer oil as revealed by composition of the fat extracted from the fried potatoes.

Deep fat frying of frozen foods in sunflower oil. Fatty acid composition in fryer oil and frozen prefried potatoes

The fatty acid pattern was used to evaluate the alteration of a sunflower oil that had been used 20 times to fry various frozen foods with frequent replenishment (FR) or without replenishment (NR) of the used oil with fresh oil during frying. Furthermore, the fat extracted from potatoes fried in the sunflower oil from fryings 1, 5, 8, 12, 16 and 20 was also analysed by gas–liquid chromatography to compare its fatty acid profile with that of the corresponding fryer oil. The amount of unaltered fatty acids decreased from 96.2 mg per 100 mg oil in the unused sunflower oil to 89.6 mg per 100 mg oil after 20 fryings in the FR oil and to 88.9 mg per 100 mg oil in the NR oil, following a linear adjustment (r > 0.97; p < 0.001). Linoleic acid also decreased while palmitic and oleic acids increased in the bath oil. Fatty acid variations were more pronounced in NR than FR oil for major fatty acids and not only related to the degradation of unsaturated fatty acids but also to the interactions between the bath oil and the fried food fat. Thus the increase in palmitic acid of the fryer oil could be due to migration of this fatty acid from the prefried frozen potatoes as revealed by the composition of the fat extracted from those potatoes. Although the fatty acid variation (eg myristic, palmitic, oleic, trans–cis isomers of linoleic and linoleic acids) was not equivalent in FR or NR fryer oil and in the fat of the potatoes, the changes in total unaltered fatty acids were not significantly different in oil and potatoes. Present data suggest that frequent addition of fresh oil throughout the frying process minimises the fatty acid changes, contributing to the obtainment of fried foods with a healthy fatty acid profile. © 2000 Society of Chemical Industry