Dietary fats are generally fatty acids that may play positive or negative roles in the prevention and treatment of diseases. In nature, fatty acids occur in the form of mixtures of saturated fatty acid (SFA), monounsaturated fatty acid (MUFA), and polyunsaturated fatty acid (PUFA), so their nutritional and/or medicinal values must be determined. Herein, we do not consider the classic indices, such as ∑SFA, ∑MUFA, ∑PUFA, ∑n-6 PUFA, ∑n-3 PUFA, and n-6 PUFA/n-3 PUFA; instead, we summarize and review the definitions, implications, and applications of indices used in recent years, including the PUFA/SFA, index of atherogenicity (IA), the index of thrombogenicity (IT), the hypocholesterolemic/hypercholesterolemic ratio (HH), the health-promoting index (HPI), the unsaturation index (UI), the sum of eicosapentaenoic acid and docosahexaenoic acid (EPA + DHA), fish lipid quality/flesh lipid quality (FLQ), the linoleic acid/α-linolenic acid (LA/ALA) ratio, and trans fatty acid (TFA). Of these nutritional indices, IA and IT are the most commonly used to assess the composition of fatty acids as they outline significant implications and provide clear evidence. EPA + DHA is commonly used to assess the nutritional quality of marine animal products. All indices have their advantages and disadvantages; hence, a rational choice of which to use is critical.

Nutritional Indices for Assessing Fatty Acids: A Mini-Review.

Numerous analytical methods are routinely used for measuring lipid oxidation in foods. However, there is no uniform and standard method for detecting all oxidative changes in all food systems. Therefore, it is necessary to select a proper and adequate method for a particular application. The available methods to monitor lipid oxidation in foods can be classified into five groups based on what they measure: the absorption of oxygen, the loss of initial substrates, the formation of free radicals, and the formation of primary and secondary oxidation products. A number of physical and chemical tests, including instrumental analyses, have been employed in laboratories and the industry for measurement of various lipid oxidation parameters. These include the weight-gain and headspace oxygen uptake method for oxygen absorption: chromatographic analysis for changes in reactants; iodometric titration, ferric ion complexes, and Fourier transform infrared (FTIR) method for peroxide value; spectrometry for conjugated dienes and trienes, 2-thio-barbituric acid (TBA) value, p-anisidine value (p-AnV), and carbonyl value; Rancimat and Oxidative Stability Instrument method for oil stability index; and electron spin resonance (ESR) spectrometric assay for free-radical type and concentration. Other techniques based on different principles, such as differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR), have also been used for measuring lipid oxidation. In addition, sensory tests provide subjective or objective evaluation of oxidative deterioration, depending on certain details.


Keywords:

lipid oxidation;
dietary lipids;
food quality;
differential scanning calorimetry;
nuclear magnetic resonance;
electron spin resonance;
sensory analysis;
Fourier transform infrared method

Lipid Oxidation: Measurement Methods

Camelina uses, genetics, genomics, production, and management

Effect of heating and cooling on rheological parameters of edible vegetable oils

In this research, five different vegetable oils were oxidized at four different temperatures (373, 383, 393, and 403 K) under Rancimat test conditions. An increasing rate of oxidation could be observed as temperature increased. The natural logarithms of the kinetic rate constant (k value) varied linearly with respect to temperature, with the temperature coefficients (TCoeff) ranging from 6.95×10–2 to 7.40× 10–2 K–1 for the vegetable oils. On the basis of the Arrhenius equation and the activated complex theory, frequency factors (A), activation energies (Ea), Q10 numbers, activation enthalpies (ΔH++), and activation entropies (ΔS++) for oxidative stability of the vegetable oils were calculated. The A, Ea, Q10, ΔH++, and ΔS++ values for the vegetable oils ranged from 6.38×103 to 28.03×103 h–1, from 86.86 to 92.42 kJ/mol, from 2.08 to 2.18, from 83.64 to 89.20 kJ/mol, and from –116.66 to –104.35 J/mol K, respectively.

Kinetic parameter determination of vegetable oil oxidation under Rancimat test conditions

Samples of vegetable oils were oxidized at isothermal conditions in the cell of a Pressure Differential Scanning Calorimeter (PDSC) and in the Methrom Rancimat apparatus. The PDSC and Rancimat experiments were carried out at a temperature in the range of 90-160 °C. From resulting PDSC exotherms their times to reach the peak maximum (τ PDSC ) were determined and used for the assessment of the oxidative stability of the samples. Similarly the measured Rancimat induction times (τ Rancimat ) were used. As PDSC and Rancimat results were obtained at different temperatures the equations for temperature extrapolations of the τ PDSC and τ Rancιmat values have been proposed. Using the Arrhenius type correlation between induction times and temperature and activated complex theory the reaction rate constants, activation energies, activation enthalpies and activation entropies for oils oxidation have been calculated.

Determination of the oxidative stability of vegetable oils by Differential Scanning Calorimetry and Rancimat measurements

In this study, 29 cold-pressed camelina (Camelina sativa L.) oils, pressed from seeds grown in Poland and purchased directly from local producers, were analyzed. The degree of change in the tested oils’ characteristic hydrolytic and oxidative lipid values was determined. Oxidative stability was determined using the Rancimat and PDSC methods. Fatty acid and phytosterol contents were determined by GC-FID, and tocopherols by HPLC. The analyzed oils were characterized by good, but variable, quality, and met the requirements specified for cold-pressed edible oils. Highly desirable fatty acid composition, low SFA content (about 6%), high α-linolenic acid content (34.7–37.1%), and optimal PUFA n-3 to PUFA n-6 ratio (1.79–2.17) were shown. The high nutritional value of camelina oils was confirmed on the basis of high contents of tocopherols (55.8–76.1 mg/100 g), phytosterols (331–442 mg/100 g), and carotenoids (103–198 mg of β-carotene/kg). The optimal nutritional quality indices were as follows: 0.05–0.07 for the atherogenicity index (AI), and 0.1–0.2 for the thrombogenicity index (TI). The significant impact of primary (PV) and total oxidation (TOTOX) of camelina oil on oxidative stability was evaluated using Rancimat and PDSC methods. Both methods were also confirmed to be appropriate for the assessment of the oxidative stability of camelina oils.

Bioactive compounds, nutritional quality and oxidative stability of cold-pressed camelina (Camelina sativa L.) oils

Cold-pressed linseed and camelina oils have been available on the global market for many years. They are known for their high contents of polyunsaturated fatty acids (PUFAs), mainly α-linolenic (ALA). This study aimed to evaluate the quality and oxidative stability of linseed and camelina cold-pressed oils purchased in retail outlets in Poland. The fatty acid composition, peroxide value, acid value, anisidine value, chlorophyll pigments, carotenoid pigments, and oxidative stability of these oils were analyzed. It was found that all analyzed oils meet the standards of requirements of the Codex Alimentarius (2009) for cold-pressed oils. The content of chlorophyll and carotenoid pigments of linseed and camelina oils was significantly different. The percentage composition of PUFAs was high in both types of oils, but it was significantly higher in linseed than in camelina oils. The results of Rancimat and PDSC tests show low oxidative stability of all tested oils, although camelina oils were more stable than linseed oils.



1 Practical applications

Based on the study, it can be concluded that linseed and camelina oils should be included in the human diet to provide an optimal ratio of omega-6 to omega-3 fatty acids. The differences between tested oils of the same seed species were significant. This study shows that quick methods of testing an oils oxidative stability (Rancimat and PDSC) may be successfully applied in oil studies.







The study evaluates the quality of cold-pressed linseed and camelina oils purchased in retail outlets in Poland. The research shows a correlation (r = −0.673) between content of polyunsaturated fatty acids and oxidative stability of tested oils. Oxidative stability was determined by Rancimat test and fatty acid composition by GC-FID.

Katarzyna Ratusz

Papers

Determination of the oxidative stability of vegetable oils by Differential Scanning Calorimetry and Rancimat measurements

Bioactive compounds, nutritional quality and oxidative stability of cold-pressed camelina (Camelina sativa L.) oils

Physicochemical quality and oxidative stability of linseed (Linum usitatissimum) and camelina (Camelina sativa) cold-pressed oils from retail outlets.

Monitoring of rapeseed oil autoxidation with a pressure differential scanning calorimeter

Comparison of the oxidative stability of cold‐pressed rapeseed oil using Pressure Differential Scanning Calorimetry and Rancimat methods