Understanding the difference of 4-hydroxyhexenal and 4-hydroxynonenal formation in various vegetable oils during thermal processes by kinetic and thermodynamic study

The formation of two toxic aldehydes, 4-hydroxyhexenal (HHE) and 4-hydroxynonenal (HNE) were monitored in five vegetable oils during thermal processing (100–200 °C) with the results modelled. HHE was only determined in rapeseed and linseed oil, while HNE was determined in all tested oils and the contents varied significantly depending on the oil type. For HHE/HNE-detected oils, the evolution during heating was well described by the pseudo-first-order kinetic model. The equilibrium contents of HHE/HNE increased and the duration until equilibrium decreased as a function of temperature. The calculated reaction rate constants followed the Arrhenius law. The formation rate of HHE/HNE was remarkably oil-dependent, which was also in accordance with the calculated kinetic and thermodynamic parameters. Accordingly, the above results can contribute to a prediction of HHE/HNE formation in different vegetable oils during thermal processing, especially the temperature/time required during frying, which is generally higher than 100 °C and 6 h., respectively.     

基于热重法的植物油氧化动力学研究

采用热重（TG）及微商热重（DTG）法研究了6种市售植物油的氧化特性,探究了不同升温速率对TG及DTG曲线的影响,通过DTG曲线确定了不同植物油在不同升温速率下的起始氧化温度,并利用Ozawa-Flynn-Wall方程及Arrhenius方程对油脂的氧化进行了动力学参数的推导,同时分析了油脂热降解特性与其主要脂肪酸组成间的相关性。研究表明:随着升温速率的升高,氧化分解的温度随之升高,油脂的起始氧化温度、活化能等参数均可用于表征油脂的氧化稳定性,且植物油的热降解特性与其脂肪酸组成间有着不同程度的相关性;其中油脂的起始氧化温度与其饱和脂肪酸、单不饱和脂肪酸及代表脂肪酸含量成正比,与多不饱和脂肪酸含量成反比;油样的活化能及前指数因子同样也与饱和脂肪酸含量成正比且前者相关性显著,而速率常数κ与样品组分相关性与Ton-组分相关性趋势相反。热重分析法采样量少,操作简单快速,精密度高,可为油脂加工及储藏条件的控制、新型抗氧化剂研发等提供实验依据。      

抗氧化剂之间相互作用对食用植物油氧化稳定性影响的研究进展

由于含有丰富的不饱和脂肪酸,食用植物油在储存和热加工过程中会发生氧化变质。添加抗氧化剂是提高食用植物油氧化稳定性的有效措施,复配抗氧化剂可以提升抗氧化效果、降低抗氧化剂的成本等,研究发现,复配的抗氧化剂之间存在相互作用。本文综述了抗氧化剂之间相互作用的类型、机理、研究方法以及在食用植物油中应用的研究进展,为抗氧化剂在食用植物油中的深入研究提供参考。     

Spectrometric determination of iron and copper in vegetable oils after separation with Schiff base impregnated silica gel column: A simple approach for eliminating the high organic matrix

A simple solid‐phase extraction method has been described for the separation of Fe(III) and Cu(II) from liquid vegetable oils using N,N′‐bis(4‐methoxy salicylidene) ethylenediamine impregnated silica gel and the determination of these ions. The experimental parameters that affect the separation/preconcentration of ions were investigated by batch and column methods prior to the determination by flame atomic absorption spectrometry. Fe(III) and Cu(II) ions in 20.0 g portion of oil samples can be quantitatively sorbed and then eluted completely with 5.0 mL of 2.0 mol L^?1 HNO₃. Limits of detection were calculated as 22.8 and 13.9 μg kg^?1 for Fe(III) and Cu(II), respectively. The repetition of the suggested method was checked by finding relative standard deviation for five repeated analyses, which was 1.5% for Fe(III) and 0.1% for Cu(II). Applicability of the method was controlled with spiked and unspiked sunflower, corn, canola, olive, soya and hazelnut oils.     

Comparative evaluation of the composition of vegetable essential and fixed oils obtained by supercritical extraction and conventional techniques: a chemometric approach

We compared by a chemometric approach the composition of essential (EO) and fixed (FO) oils previously obtained from several vegetable matrices by supercritical CO₂ extraction (CO₂-SFE) and conventional techniques (n-hexane in a Soxhlet apparatus and hydrodistillation). A multivariate approach, by determining the principal components analysis (PCA) applied to data of FO fatty acids and EO volatile compounds, generally indicated that the vegetable oils extracted with CO₂-SFE tightly clustered with those obtained by conventional methods. The graphical distances calculated in the PCA plots between the score of each SFE oil and the corresponding conventional oil revealed that the CO₂-SFE FO and EO profiles were quite similar to conventional oils, with the additional benefit of not having unwanted traces of solvent. SFE FO were more similar to conventional oils than SFE EO (mean values of calculated graphical distances were 0.83 and 1.46 for FO and EO, respectively). Our results strongly corroborate the role of CO₂-SFE as a suitable, environmentally safe and efficient method alternative to the traditional ones for the extraction of natural vegetable oils for food and pharmaceutical applications.     

Benzo[a]pyrene and total polycyclic aromatic hydrocarbons (PAHs) levels in vegetable oils and fats do not reflect the occurrence of the eight genotoxic PAHs

Concentrations of polycyclic aromatic hydrocarbons (PAHs) were determined in 115 samples of olive oil (extra virgin olive oil, virgin olive oil, olive oil, pomace olive oil and blended olive oil), cooking oil (corn oil, sunflower oil, sesame oil, palm olein oil, soya oil, canola oil, mustard oil, peanut oil and mixed vegetable oil) and fat (butter and table margarine) collected from retail stores in Kuwait. Carcinogenic benzo[a]pyrene (BaP) was detected in 43% of the samples analyzed. Benz[a]anthracene and chrysene were detected in 37 and 45% of the samples, respectively, that did not contain BaP. Of the individual non-carcinogenic PAHs, naphthalene showed the highest mean concentration (14 µg kg^?1), while for the carcinogenic PAHs, BaP (0.92 µg kg^?1) and chrysene (0.87 µg kg^?1) showed the highest mean values. Approximately 20% of the samples within the olive oil and cooking oil sub-categories exceeded the EU maximum tolerable limit for BaP, with the highest level of 6.77 and 11.1 µg kg^?1, respectively. For the fat sub-category, 9% of the samples exceeded the tolerance limit, with the highest level of 3.67 µg kg^?1. The Kuwaiti general population's dietary exposure to the genotoxic PAHs (PAH8: benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene and benzo[ghi]perylene) was estimated to be 196 ng day^?1 (3.3 ng kg^?1 bw day^?1, assuming an average adult body weight of 60 kg). Results indicated that PAH8 and BaP_eq (total sum benzo[a]pyrene equivalents) are more reliable measures of the concentrations of other carcinogenic PAHs in oil and fat samples, while BaP and PAHs alone are not good indicators of the occurrence or degree of contamination by carcinogenic PAHs in these food products.     

Temperature dependence of the formation and melting of pectin–Ca networks: a rheological study

Small deformation dynamic rheometry was used to characterise the calcium-induced gelation of low-methoxyl pectins, at two different pH values. The gelation kinetics was interpreted with basis on the change of the storage modulus with time, taken as a measure of changes in cross-linking density within the pectin–calcium network. The temperature influence on the rate of gel formation and ageing was evaluated, as well as the temperature sensitivity of the cured gels. The formation and the softening/melting of pectin–calcium networks were also studied under non-isothermal conditions. The structural diversity of the two pectin samples had a great influence on the gelation kinetics and thermal behaviour of these pectin–calcium networks, due to differences in the steric arrangement or environment and/or availability of the chelating groups. An association mechanism is suggested to predominate under conditions of low availability of dissociated carboxylic groups, due to a low pH, higher degree of methylation, or steric constraints introduced by acetylation or neutral side chains, different from the classical ‘egg-box’ model, and where non-ionic hydrogen bonding and hydrophobic interactions may co-exist and cooperate with coordinative binding of calcium-ions.