Frying performance of no-trans, low linolenic acid soybean oils

GERDE JOSE; HARDY CONNIE; FEHR WALTER; PAMELA WHITE

Saint Louis, MO, USA

Conferencia; 97th American Oil Chemists' Society Annual Meeting & Expo; 2006

American Oil Chemists' Society

Soybean cultivars containing oils with ultra-low linolenic acid (ULL, 1.5%) and low-linolenic acid (LL, 2.6%) have been developed by Iowa State University scientists, with an aim to increase the stability of soybean oils during frying without introducing trans fats. To enhance overall stability, expeller pressing was used to extract the oils, a process previously shown to increase oil stability because of antioxidant retention and reduced heat stress during processing. The ULL and LL oils and an expeller-pressed control oil containing 5.2% linolenic acid (Ctrl) were evaluated by frying of French fries in a commercial-like setting for 6 hr/day during 23 consecutive days. Frying treatments were performed in duplicate, and replicate analyses were done. Data were analyzed by using analysis of variance (ANOVA) and mixed models for repeated measures. Total tocopherol isomers in the oils were 1071 ppm for ULL, 1184 ppm for LL, and 1081 ppm for the Ctrl, with LL having a higher level (p=0.05). Color, quantified by using the Hunter Lab spectrometer, decreased in the L (became darker) and b (became less yellow) values for all the oils during frying. The a value tended to increase (more red and less green) for all the treatments over time. Free fatty acid levels (ffa) were not different among the oils until day 14, after which ULL was different than the Ctrl for the remainder of frying. The conjugated dienoic acid values were higher in the Ctrl than in the ULL and LL oils throughout frying. ULL and LL oils had lower percentages of polar compounds than did the Ctrl oil throughout the frying process. The induction values for the oil stability index test were 19.40 hr for ULL, 19.34 hr for LL, and 14.65 hr for the Ctrl oil, with the Ctrl being significantly higher than LL and ULL. A trained sensory panel of 12 individuals evaluated the French fries on days 2, 5, 6, 9, 11, 14, 16, 19, 21, and 23. Positive sensory characteristics of buttery and potato decreased over frying time, and negative sensory characteristics of rancid and painty increased over frying time for all products. The increase in painty flavor in French fries fried in ULL and Ctrl oils was slower than in the fries fried in LL oil.Overall, the ULL and LL oils performed better during frying than did the Ctrl oil. The ULL tended to perform better than the LL oil by some measures, but the small difference in percentage of LL in these two oils (1.5 vs. 2.5%) likely minimized the differences between the two oil types. In some growing conditions, the oil from the ULL cultivar has less than 1.0%, and the oil from the LL cultivar has about 3% LL. Also, the significantly greater tocopherol levels in the LL oil vs. the ULL oil likely enhanced the stability of the LL oil used in this study.