ENHANCING FLAVOR QUALITY AND OXIDATIVE STABILITY OF EDIBLE VEGETABLE OILS WITH PHYTOCHEMICAL ANTIOXIDANTS
Location: National Center for Agricultural Utilization Research
Title: Effect of Deep-Fat Frying on Phytosterol Content in Oils with Differing Fatty Acid Composition
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 5, 2007
Publication Date: October 5, 2007
Citation: Winkler, J.K., Warner, K.A., Glynn, M.T. 2007. Effect of deep-fat frying on phytosterol content in oils with differing fatty acid composition. Journal of the American Oil Chemists' Society. 84:1023-1030.
Interpretive Summary: Phytosterols are compounds found naturally in vegetable oils. With a structure very similar to cholesterol, phytosterols, when consumed, actually block cholesterol absorption in the gut and help to lower blood cholesterol. A health claim has been approved by the FDA for phytosterols in certain foods, thus the demand for phytosterols, and their subsequent addition to foods has been on the increase. In addition, some phytosterols have been found to inhibit degradation of oils during heating and frying. However, not much is known about the stability of phytosterols under the processing conditions that occur in foods. This study was undertaken to get a better idea of the stability of phytosterols in oils used for frying. The first experiment looked at the stability of phytosterols in five different oils that were used for the continuous frying of potato chips in a pilot plant scale fryer. In the second experiment, the stability of phytosterols was determined in six oils that were used for intermittent frying of tortilla chips, to mimic the consumer or restaurant-style frying processes. Phytosterols were found to be more stable under the continuous style processing, but were also fairly stable to intermittent frying. The highest amount of phytosterol loss occurred in corn oil, where approximately 15% of the sterols were lost after intermittent frying. Phytosterols were fairly stable in oils that were more easily degraded during the frying process, indicating that the stability of the oil itself was not an important factor in the stability of the phytosterols.
The objective of this study was to determine the fate of phytosterols in vegetable oils with varying fatty acid composition used for frying. High oleic sunflower (HOSun), corn (Corn), hydrogenated soybean (HSBO), expeller pressed soybean (ESBO), and expeller pressed low-linolenic acid soybean oil (ELLSBO) were used for frying potato chips in a pilot plant-scale continuous fryer. The same oils, and regular soybean oil (SBO) were also used in intermittent batch frying of tortilla chips. Phytosterols were measured in oils collected at various times during frying by GC to determine their loss. The formation of polymerized triacylglycerides (PTAGs) and total polar compounds (TPC) were analyzed to determine the extent of oil degradation. In the continuous frying system, phytosterol loss ranged between 4-6% in ESBO, ELLSBO, HOSun, and Corn, with no loss in HSBO. PTAGs and TPC were highest in ESBO and ELLSBO, followed by Corn, HOSun, and HSBO. In the batch frying experiment, phytosterol loss was highest in Corn followed by SBO and HSBO. There was no significant loss of phytosterols in ESBO, ELLSBO, and HOSun. Formation of PTAGs and TPC during batch frying was highest in SBO and ESBO, followed by Corn, ELLSBO, HOSun, and HSBO. In conclusion, phytosterol loss in both the continuous fryer and in the batch frying system appeared to be unrelated either to fatty acid composition, or to the extent of oil degradation.