Thermal stability of plant sterols and formation of their oxidation products in vegetable oils and margarines upon controlled heating.

Fat-based products like vegetable oils and margarines are commonly used for cooking, which may enhance oxidation of plant sterols (PS) present therein, leading to the formation of PS oxidation products (POP). The present study aims to assess the kinetics of POP formation in six different fat-based products. Vegetable oils and margarines without and with added PS (7.5-7.6% w/w) in esterified form were heated in a Petri-dish at temperatures of 150, 180 and 210°C for 8, 12 and 16min. PS and POP were analysed using GC-FID and GC-MS-SIM, respectively. Increasing PS content, temperature and heating time led to higher POP formation in all tested fat-based products. PS (either naturally occurring or added) in margarines were less susceptible to oxidation as compared to PS in vegetable oils. The susceptibility of sitosterol to oxidation was about 20% lower than that of campesterol under all the applied experimental conditions. During heating, the relative abundance of 7-keto-PS (expressed as% of total POP) decreased in all the fat-based products regardless of their PS contents, which was accompanied by an increase in the relative abundance of 7-OH-PS and 5,6-epoxy-PS, while PS-triols were fairly unchanged. In conclusion, heating time, temperature, initial PS content and the matrix of the fat-based products (vegetable oil vs. margarine) showed distinct effects on POP formation and composition of individual POP formed.

An improved method for sn-2 position analysis of triacylglycerols in edible oils and fats based on immobilised lipase D (Rhizopus delemar).

The use of lipase D (Rhizopus delemar) immobilised on microporous polypropylene as a replacement for the standard pancreatic lipases used in the stereospecific sn-2 position analysis of triacylglycerols from edible oils and fats is studied. Excellent hydrolysis characteristics are obtained in hexane/methanol solvents at reaction temperatures up to 60 degrees C with hydrolysis times of only 10-20 min. The favourable conditions for the hydrolysis reaction allow fats with higher melting points to be analysed and facilitate coupling of the hydrolysis reaction to the later steps in the analytical protocol. The performance of the new method is compared to that of the standard method using pancreatic lipase. The novel procedure is faster, manual sample handling is reduced, while the results obtained with both methods are comparable. The influence of alkyl-chain length on hydrolysis rates seems to be negligible for the most common vegetable fatty acids. Acyl migration was found to be absent. The short-term repeatability of the method ranges from 10% for fatty acids present at levels close to the detection limits to less than 1% for the major fatty acids. The detection limit is approximately 0.05%. Although the application of the immobilised enzyme in fully automated sn-2 position analysis seems to be promising, the attempts to do this using a packed bed reactor were not successful due to a rapid loss of enzyme activity.

Biosensor measurements of polar phenolics for the assessment of the bitterness and pungency of virgin olive oil.

Bitterness and pungency, sensory quality attributes of virgin olive oil, are related to the presence of phenolic compounds. Fast and reliable alternatives for the evaluation of sensory attributes and phenolic content are desirable, as sensory and traditional analytical methods are time-consuming and expensive. In this study, two amperometric enzyme-based biosensors (employing tyrosinase or peroxidase) for rapid measurement of polar phenolics of olive oil were tested. The biosensor was constructed using disposable screen-printed carbon electrodes with the enzyme as biorecognition element. The sensor was coupled with a simple extraction procedure and optimized for use in flow injection analysis. The performance of the biosensor was assessed by measuring a set of virgin olive oils and comparing the results with data obtained by the reference HPLC method and sensory scores. The correlations between the tyrosinase- and peroxidase-based biosensors and phenolic content in the samples were high (r = 0.82 and 0.87, respectively), which, together with a good repeatability (rsd = 6%), suggests that these biosensors may represent a promising tool in the analysis of the total content of phenolics in virgin olive oils. The correlation with sensory quality attributes of virgin olive oil was lower, which illustrates the complexity of sensory perception. The two biosensors possessed different specificities toward different groups of phenolics, affecting bitterness and pungency prediction. The peroxidase-based biosensor showed a significant correlation (r = 0.66) with pungency.

Relation between the endogenous antioxidant system and the quality of extra virgin olive oil under accelerated storage conditions.

Three monovarietal extra virgin olive oils (EVOOs) were subjected to accelerated storage conditions (60 degrees C, dark) representative of the autoxidation process during shelf life. Oxidation markers, i.e., the peroxide value, conjugated dienes, the oil stability index, and minor components, were monitored. The changes in minor components, related to the stage of ongoing oxidation and expressed as a percentage of the induction period (IP), followed a similar pattern in all oils: o-diphenols diminished by the highest rate (halved within 15% of the IP), followed by alpha-tocopherol (halved within 35% of the IP). Carotenoids and chlorophylls were also affected by autoxidation, whereas squalene showed high stability (<20% loss within 100% of the IP). Polar phenols (especially o-diphenols) and alpha-tocopherol were deduced to be the most potent antioxidants of EVOO. They efficiently inhibited oxidative lipid deterioration and subsequent development of sensory defects (rancidity, discoloration), which occurred only after substantial depletion of these antioxidants. Therefore, they could also be used as markers for the oxidative status of EVOO particularly in the early stage of oxidation.

Influence of oil composition on the formation of fatty acid esters of 2-chloropropane-1,3-diol (2-MCPD) and 3-chloropropane-1,2-diol (3-MCPD) under conditions simulating oil refining.

The toxicological relevance and widespread occurrence of fatty acid esters of 2-chloropropane-1,3-diol (2-MCPD) and 3-chloropropane-1,2-diol (3-MCPD) in refined oils and fats have recently triggered an interest in the mechanism of formation and decomposition of these contaminants during oil processing. In this work, the effect of the main precursors, namely acylglycerols and chlorinated compounds, on the formation yield of MCPD esters was investigated in model systems simulating oil deodorization. The composition of the oils was modified by enzymatic hydrolysis, silica gel purification and application of various refining steps prior to deodorization (namely degumming, neutralization, bleaching). Partial acylglycerols showed greater ability, than did triacylglycerols, to form MCPD esters. However, no direct correlation was found between these two parameters, since the availability of chloride ions was the main limiting factor in the formation reaction. Polar chlorinated compounds were found to be the main chloride donors, although the presence of reactive non-polar chloride-donating species was also observed.

Study on the thermal degradation of 3-MCPD esters in model systems simulating deodorization of vegetable oils.

The establishment of effective strategies for the mitigation of 3-MCPD esters in refined vegetable oils is restricted by limited knowledge of their mechanisms of formation and decomposition. In order to gain better understanding on the thermal stability of these compounds, a model system for mimicking oil refining conditions was developed. Pure 3-MCPD esters (3-MCPD dipalmitate and 3-MCPD dilaurate) were subjected to thermal treatment (180-260°C) and the degradation products where monitored over time (0-24h). After 24h of treatment, both 3-MCPD esters showed a significant degradation (ranging from 30% to 70%), correlating with the temperature applied. The degradation pathway, similar for both compounds, was found to involve isomerisation (very rapid, equilibrium was reached within 2h at 260°C), dechlorination and deacylation reactions. The higher relative abundance of non-chlorinated compounds, namely acylglycerols, in the first stages of the treatment suggested that dechlorination is preferred over deacylation with the conditions applied in this study.

Development of an analytical method for the simultaneous analysis of MCPD esters and glycidyl esters in oil-based foodstuffs.

Substantial progress has been recently made in the development and optimisation of analytical methods for the quantification of 2-MCPD, 3-MCPD and glycidyl esters in oils and fats, and there are a few methods currently available that allow a reliable quantification of these contaminants in bulk oils and fats. On the other hand, no standard method for the analysis of foodstuffs has yet been established. The aim of this study was the development and validation of a new method for the simultaneous quantification of 2-MCPD, 3-MCPD and glycidyl esters in oil-based food products. The developed protocol includes a first step of liquid-liquid extraction and purification of the lipophilic substances of the sample, followed by the application of a previously developed procedure based on acid transesterification, for the indirect quantification of these contaminants in oils and fats. The method validation was carried out on food products (fat-based spreads, creams, margarine, mayonnaise) manufactured in-house, in order to control the manufacturing process and account for any food matrix-analyte interactions (the sample spiking was carried out on the single components used for the formulations rather than the final products). The method showed good accuracy (the recoveries ranged from 97% to 106% for bound 3-MCPD and 2-MCPD and from 88% to 115% for bound glycidol) and sensitivity (the LOD was 0.04 and 0.05 mg kg(-1) for bound MCPD and glycidol, respectively). Repeatability and reproducibility were satisfactory (RSD below 2% and 5%, respectively) for all analytes. The levels of salts and surface-active compounds in the formulation were found to have no impact on the accuracy and the other parameters of the method.

Direct analysis of intact glycidyl fatty acid esters in edible oils using gas chromatography-mass spectrometry.

Glycidyl esters (GE), fatty acid esters of glycidol, are process contaminants formed during edible oil processing. A novel direct method for the determination of intact GE in oils and fats based on gas chromatography-mass spectrometry (GC-MS) is presented. The method consists of a simple extraction step of GE from the lipid matrix, purification of the extract and isolation of GE by normal phase liquid chromatography (NPLC). Individual GE in the final fraction are separated and quantified by standard GC-MS operated in selected ion monitoring (SIM) mode. The setup and conditions of the GC-MS were optimized in such a way that thermal degradation of GE and artifact formation were prevented. The method exhibits very good performance parameters: the limit of detection was approximately 0.01 mg/kg for the individual GE (corresponding to 0.002-0.003 mg/kg of free glycidol), the repeatability was in the range of 5-12% for individual GE at levels above 0.1mg/kg, and recovery values ranged from 85 to 115% depending on the level and the chain identity of the GE. The comparison of experimental values with spiked levels and with the results obtained by other methods confirmed a good trueness. Over a period of several months of extensive use the method was found to be very reliable and rugged.