Soybean and palm olein oils : frying performance and characteristics of fried prawn crackers

Four different frying oils: unhydrogenated soybean oil (SO), palm olein (POO) and blends of 80:20 and 60:40 w/w SO:POO were used to fry prawn crackers (PC) intermittently for five days. The degradation of the oils/blends (O/B) were followed by daily measurement by the food oil sensor (FOS), RAU and Fritest, of color (L, a, b and ΔE) and levels of conjugated dienes (DIENES), fatty acid composition, C18:2/C16:0 fatty acid ratio (RATIO), free fatty acids (FFA) and total polar components (TPC). PC fried in each O/B were stored at 25°C for 0 wk (fresh) and 4 wk in the dark (4D) and in the light (4L) and analyzed for flavor volatiles and color, flavor and overall likability scores.

FOS, Fritest and TPC values were not different among frying O/B, and each measurement for each O/B reached maximum value or oil discard point before or by day 5 of frying. The TPC level at discard point (25-27%) was reached by frying day 3 in all O/B mainly because of high TPC (12-14%) in fresh oils. Levels of DIENES and RATIO were higher in SO than in blends or POO and decreased with decreasing SO level in the blends. DIENES and RATIO of each O/B also decreased with increasing frying time. Although FFA content increased with increasing frying time in all 0/B and was higher in POO than in other O/B, after frying day 5, it was still below the level (0.5%) recommended for discard of potato chip frying oil. SO had highest levels of 018:2 and C18:3 fatty acids of all O/B while PO had the highest levels of C16:0 and C18:1. Levels of C18:2 decreased in all O/B during frying while levels of C12:0, C20:2 and C22:4 increased. RAU value, a measure of oxidized products, reached discard point by frying day 4 in the blends compared to day 5 in pure SO and POO. Indicating the pure oils were more stable than the blends during frying. POO had a lower L value (was darker) and higher b value (more yellow) than SO when fresh. All O/B darkened and became more yellow with increasing frying time. After five days frying, POO was still darker than SO or the blends, but SO had similar b values as POO (42.3 versus 43.9) and the greatest color change (ΔE) of all O/B. The darker color of POO could cause early discard in institutions using dark color to judge when a frying oil is fully deteriorated.

The color, flavor and overall likability scores of the fried PC were not different among the O/B and averaged 5.9 ( were liked moderately). However, 4L PC received a lower flavor and overall likability score (4.9) than that (5.8) of fresh or 4D PC. The 4L PC also had much higher levels of 21 of 23 identified flavor volatiles than those present in the fresh or 4D PC. These latter results indicate that for stored fried PC to maintain acceptable flavor, they must be stored in a light barrier package.