A detailed identification study on high-temperature degradation products of oleic and linoleic acid methyl esters by GC–MS and GC–FTIR

This paper proposes the use of easy ambient sonic‐spray ionization mass spectrometry (EASI‐MS) to detect markers of high‐level oxidation in biodiesel via a simple and rapid single‐shot analytical protocol. Soybean biodiesel was oxidized in Rancimat and then analyzed at different time periods by both EASI‐MS and traditional physicochemical methods. Major changes in the EASI(+)‐MS profile as well in the peroxide value, acidity, and kinematic viscosity were observed after the induction period (IP). Fatty acid methyl esters (FAME) and their respective hydroperoxides were primarily identified using EASI‐MS in fresh biodiesel and at the initial stages of oxidation. After the IP, EASI‐MS revealed the formation of dimers and low‐mass non‐volatile molecules, such as aldehydes, due to hydroperoxide breakdown. Both the dimers and aldehydes are attributed to secondary oxidation products. Therefore, EASI‐MS was found to provide a fast, direct, and accurate technique to identify markers in biodiesel with high‐level of oxidation. Practical applications: EASI‐MS is a useful technique to identify primary and secondary oxidation products formed in biodiesel in a single procedure that is rapid and does not require sample preparation. Therefore, EASI‐MS has potential applications in biodiesel routine analysis to screen samples with high‐levels of oxidation. EASI‐MS provides a fast, direct, and accurate technique to identify markers in biodiesel with high‐level of oxidation.

Section: Resultsmentioning

confidence: 99%

Ambient sonic‐spray ionization mass spectrometry for rapid monitoring of secondary oxidation products in biodiesel

Pereira

Alberici

Fernandes

et al. 2014

“…Some of them, like acrolein or other α,β‐unsaturated aldehydes are unwanted because of health concern. For analysis sophisticated techniques like headspace‐GC–MS are used .…”

Section: Quality Indicators For Used Frying Oils (Laboratory Methods)mentioning

confidence: 99%

Quality control of used deep‐frying oils

Weißhaar

2014

Quality of deep-fried food is inseparably attached to the quality of the used deep-frying oil. Taste, flavor, shelf life, consumer acceptance, and safety of fried food essentially depend on frying oil quality. Evaluation of frying oil quality therefore is an important issue for both frying operators and official food control agencies. Organoleptic evaluation is an essential step in the monitoring of frying fat quality. Several official laboratory methods are available to support the sensory evaluation. Total polar materials (TPM) and polymer TAGs (PTG) are the most reliable parameters for this purpose. Recommended and widely accepted limits are 24% for TPM and 12% for PTG. When oxidative alterations strongly predominate over thermal alterations, sensory defects can appear before TPM and PTG reach recommended values. In that case additional parameters like anisidine value, carbonyl value, or epoxy fatty acids should be considered. A number of physical and chemical rapid methods are available. Despite the limited informative value and the possibility of error of rapid tests, they are essential for fryer operators, because they deliver information about fat quality in real-time. Most reliable for most applications are quick tests measuring TPM. A unique and powerful tool for the simultaneous detection of multiple parameters corresponding to thermal and oxidative alterations is near infrared spectroscopy (NIRS), which will become more and more important in future.

“…Thermo‐oxidation was carried out at 180°C for 10 h and increased polar compounds in reasonable amounts up to 25/100 g were detected. Identification of different isomers of epoxy‐, keto‐, and hydroxy fatty acids, which are partially not completely resolved even by modern capillary GC on polar phases, by GC‐MS and GC‐FTIR was elucidated by Berdeaux and coworkers . Mubiru et al determined epoxy fatty acids in 37 fresh oils from the Belgian market in a range of 0.03–2 g/kg.…”

Section: Introductionmentioning

confidence: 99%

Epoxy fatty acids in used frying fats and oils, edible oils and chocolate and their formation in oils during heating

Brühl

Weißhaar

Matthäus

2015

The occurrence of monoepoxy fatty acids in used frying oils and in other common foods has been determined. Monoepoxy fatty acids with trans-9,10-and cis-9,10-epoxystearate and trans-12,13-, trans-9,10-, cis-12,13-and cis-9,10-epoxyoctadecenoate were found at average levels of 3.7 g/kg in used frying fats and oils, but also at about 2 g/kg in the fat fraction of chocolate. They were also detected in pumpkin seed, sweet almond, groundnut, sunflower, and olive oils at average levels of 3.4, 1.7, 1.4, 1.0, and 0.2 g/kg, respectively. Their formation during heating at 175°C was observed for sunflower, rapeseed, soybean, and linseed oil and compared with the increase of polar compounds and polymerized triacylglycerols as other important quality indicators for frying oils. During heating for 16 h, the level of monoepoxy fatty acids increased to about 30, 18, 8, and 4 g/kg for olive, sunflower, linseed, and rapeseed oils, respectively. The influence of the heating temperature was surveyed for refined soybean oil at 160, 170, 180, and 200°C. Heating of two sets of five different refined and virgin rapeseed oils revealed a significant lower formation of monoepoxy fatty acids for refined oils at a median level of 4.6 g/kg compared to 7.7 g/kg for virgin oils.Practical applications: Determination of fatty acid methyl esters is one of the most common analyses for the evaluation of oils and fats. The assessment of the monoepoxy fatty acids as part of these analyses can provide a first indication about used frying fats and oils, which reached the end of their applicability. The formation of monoepoxy fatty acids is affected by the fatty acid composition of the oil, the heating temperature, and the production of the oil. Therefore, frying oils may contain varying amounts of monoepoxy fatty acids at the maximum limit for polar compounds and polymerized triacylglycerols as used in the official food control. However, all used frying oils investigated by the official food control showing more than 7 g/kg of monoepoxy fatty acids had to be rejected due to the limits exceeded for polar compounds and polymerized triacylglycerols. Therefore, this limit of 7 g/kg monoepoxy fatty acids level is proposed as a level for screening the usability of used frying fats and oils.