Physicochemical and Stability Characteristics of Flaxseed Oils During Pan‐heating

Abstract

Flaxseed oils are used in stir-frying in parts of China. In this study, flaxseed oils were heated at approximately 150°C as a thin film in a frying pan for 3 and 6 min, respectively. Pan-heating caused loss of tocopherols, plastochromanol-8, phenolic acids and chlorophyll pigments. There was a significant decrease in the linolenic acid resulting in a concomitant relative increase in palmitic, stearic, oleic and linoleic acids in the oils after pan heating. Positive CIELAB ''b*'' color value, which indicates yellowness and levels of b-carotene and lutein in these oils showed a 42-56% and 8-53% decrease, respectively. Peroxide values, p-anisidine values, percentage of conjugated dienoic acid, specific extinction at 232 and 270 nm and food oil sensor readings of these oils showed significant increases to levels exceeding good oil quality indices. Acid values only showed one to twofold increase from fresh oil values of 0.65-2.23 mg KOH/g of sample. These results indicate that significant levels of oxidation products would be present in flaxseed oils after pan heating. The flaxseed oil with a lower amount of PUFA appeared to be more degraded suggesting that the major factor affecting the oxidative stability of the flaxseed oils during pan-heating was not the degree of unsaturation but was dependent on the complex interaction between the fatty acids and minor constituents in the oils.

The effect of pan frying on thermooxidative stability of refined rapeseed oil and professional blend

“…In this case, the professional blend (PB) is degraded to a lesser degree than RO. Our results are in agreement with other authors, who also report a linear increase in AV content with frying time in different frying media using different methods of frying (Matthäus 2006;Kiatsrichart et al 2003;Soheili et al 2002a;Choo et al 2007). Kiatsrichart et al (2003) stated that during pan-frying using mid-oleic sunflower oil (NuSunoil) and a commercial rapeseed oil more sensitive for hydrolysis was rapeseed oil, however both oils exhibited low level of free fatty acids.…”

“…At the end of frying AnV of rapeseed oil was 184 while of professional blend almost 3-times lower -65. A rapid increase in AnV was observed by other authors (Choo et al 2007;Soheili et al 2002a). The ratio of AnV increase depended on kind of oil as well as on frying procedure.…”

“…The ratio of AnV increase depended on kind of oil as well as on frying procedure. Choo et al (2007) observed the highest AnV increase for flaxseed cold-pressed oils used for short pan-frying, when after several minutes (3 and 6 min) AnV increased from 0.4-0.7 to 290-588 and 622-876, respectively. In another study by Soheili et al (2002a), after 10 min of heating at 150°C, the AnVof low-linolenic soybean oil was significantly greater (386.5 abs/g oil) than that of partially hydrogenated soybean oil after 14 min of heating (298.5 abs/g oil).…”

Heating effects on physicochemical characteristics and antioxidant activity of flaxseed hull oil (Linum usitatissimum L)

“…The decrease in PUFA in flaxseed hull oil was lower (55.46%). Choo et al (2007) reported that there was a significant decrease in linolenic acid resulting in a concomitant relative increase in palmitic, stearic, oleic and linoleic acids in the oils after pan heating. The data revealed that heating process caused a decrease in the ΣTU/ΣSFA ratio.…”

Characterization of flaxseed oil emulsions

“…The high content of ALA (>50 %) in flaxseed oil, however, renders the oil susceptible to oxidation (Choo et al 2007a). Flaxseed oil is not recommended to be used with heat treatment such as stir frying or pan heating (Choo et al 2007b). …”