Analysis of fatty acid profiles of free fatty acids generated in deep-frying process

Abstract

During the deep fat food frying process, the frying media, oil, continuously degenerates when exposed to high temperature, oxygen and moisture. This leads to physical and chemical changes including the formation of hydrolysis products such as free fatty acids (FFAs) which are associated with undesirable darkening in colour, off-flavouring and a lowering of the smoke point. This study was aiming to develop a method capable of identifying and quantifying individual free fatty acids within oil using a small sample size (100 mg of oil). We used liquid/liquid extraction technique to separate FFAs from the rest of the oil followed by esterification using boron trifluoride (BF) and then gas chromatography analysis. Various extraction conditions were tested. A mixture of 0.02 M phosphate buffer at pH 12 and acetonitrile at solvent: buffer ratio larger than 2:1 showed the highest efficiency in extraction of FFAs. The method was capable of producing accurate fatty acid profiles of FFAs and showed good precision on medium rancidity oil samples. It also captured the differences induced by adding free fatty acids to samples. An interesting discrepancy was found between the new method and the traditional titration method in terms of overall FFA content, which suggests further optimisation and investigation are required.

Shelf-Life Evolution of the Fatty Acid Fingerprint in High-Quality Hazelnuts (Corylus avellana L.) Harvested in Different Geographical Regions

“…By observing results reported in Table 4 for the total amount of FFAs, converted in g/100 g of oleic acid (C18:1 n -9) equivalents, an increase in acidity during the shelf life can be observed. This parameter, correlated but not equivalent to titratable acidity [ 14 ], has no reference values in the available literature [ 38 ].…”

“…However, if researchers are interested in not only the simple hydrolytic activity but also its impact on the glycerolipid fraction, these parameters are not sufficiently accurate to provide information about the quali-quantitative changes in fatty acid (FA) profile/composition. An attempt to go beyond was made by Bazina and He [ 14 ], who developed a method capable of selectively extracting FFAs from small amounts of fat (100 mg) before their esterification with boron trifluoride (BF 3 ). The authors validated the methodology for application to deep-fried fats.…”

Improving oil stability in deep‐fried snack production: A case study

“…The conductivities were set to be recorded every 30 s. The samples were cooled to room temperature before being tested for their TPM contents using a CAPsens 5000 Food‐Oil‐Sensor (C‐CIT AG, Switzerland), then flashed with nitrogen and stored in sealed containers in a fridge before being tested for their FFA contents using a Metrohm Titrino 848 autotitrator equipped an optrode (Metrohm UK Ltd). The method is based on photometric titration and was described in Bazina and He (2018). The experiment was triplicated.…”

Developing emulsion gels by incorporating Jerusalem artichoke inulin and investigating their lipid oxidative stability

“…Lipid oxidation can be measured with different methods including spectrophotometry for conjugated dienes (Liégeois et al 2000) and 2-thiobarbituric acid (TBA) value (Zeng et al 2017), Rancimat method for oil stability index (Tavakoli et al 2019), chromatographic analysis for changes in reactants (Bazina & He 2018), Fourier transform infrared (FTIR) method for peroxide value; differential scanning calorimetry (DSC), iodometric titration, and others (Shahidi & Zhong 2005). Conjugated dienes with strong absorption of UV radiation at 234 nm are produced during oxidation of lipid that contains dienes or polyenes, which is a good index for measuring lipid oxidation (Vieira & Regitano-D'arce 1998).…”