Date of Award
Master of Science
Food Science and Technology
Sharon L. Melton
J.L. Collins, J.R. Mount
The deterioration of palm oil olein (POO) and partially hydrogenated soybean oil (PHSO) during deep-fat frying of fish and potato was compared. Deterioration of the oils during use was assessed by fast analytical tests (dielectric constant, DC, and foam height, FH, measurements) and changes in the fatty acid composition, smoke point (SP), levels of free fatty acids (FFA), dienoic acids (DA) and total polar materials (TPM). The study consisted of four treatments: (1) potatoes fried in POO, (2) fish fried in POO, (3) potatoes fried in PHSO, and (4) fish fried in PHSO. The statistical design of the experiment was a 4 x 4 Latin Square with a split in each square. The design was represented by four replications and four fryers with the split being sampling time from each fryer. The frying oils were used in the following manner. The oil in each fryer was held at 180 C for 8 hours a day for 5 consecutive days with a batch of food being fried every 2 hours starting 1 hour after the fat had reached 180 C. At the end of each day the frying oil was cooled, filtered through cheese cloth and stored covered until the next day. DC and FH were measured on all frying oils every day, and SP, FFA, DA, TPM and fatty acid composition of the frying oils were determined after 1, 3 and 5 days of use. Moisture and fat levels were measured in the last batch of food fried each day at 1, 3 and 5 days of use.
Levels of DA, FH, FFA, and SP were significantly affected by the type of frying oil used and the type of product fried. Across 5 days of frying, PHSO had higher levels of FH, DA and SP and a lower level of FFA than POO. The frying of fish in either oil resulted in a higher DC, FH, DA, FFA and SP than did the frying of potatoes. DC was not affected (P < 0.05) by type of frying oil used. Levels of TPM did not differ (P < 0.05) between types of oil used or types of product fried.
The fatty acid composition of the frying oils was affected by the type of oil used and the type of product fried. Used POO had higher levels of saturated fatty acids (12:0, 14:0, 16:0 and 18:0) and lower concentrations of the unsaturated fatty acids (18:1ω9, 18:1 isomers, 18:2ω6 and 18:2 isomers) than the used PHSO. The frying of fish caused higher concentrations of 18:2ω6. 18:3ω3 and 20:0 than did the frying of potatoes.
All measurements of the frying oils were significantly affected by the amount of time the frying oils were used. Levels of DC, FH, DA, FFA and TPM generally increased in a curvilinear fashion with increasing time of frying oil use while the SP decreased. The level of TPM was 30.7 percent by the third day of use which is higher than the 27 percent recommended as the point at which a frying oil should be discarded. The average percentage of 18:0, an 18:1 isomer, an 18:2 isomer and 20:2ω6 increased significantly across frying time, while the average percentage of 18:2ω6, 18:3ω3, 20:1ω9, 18:2ω7 (diene) and 24:0 decreased.
Results of this study indicate that both oils deteriorated during use; however, compared with PHSO, POO had higher levels of FFA, a lower smoke point and might cause problems in commercial frying operations. Results also indicate that the frying of fish caused a greater deterioration of frying fats than the frying of potatoes. Results also confirm that 27 percent TPM as a level at which a frying fat should be discarded is probably applicable to most frying fats and situations, since the level of TPM was not affected by the type of frying fat used or the type of product fried. Although other measurements such as levels of DC, FH and FFA were highly correlated with levels of TPM, they were affected by one or both of these parameters.
Husain, Norsaadah, "Deterioration of palm oil olein and partially hydrogenated soybean oil during deep-fat frying. " Master's Thesis, University of Tennessee, 1986.