The distribution of 4-hydroxy-hexenal and 4-hydroxy-nonenal in different vegetable oils and their formation from fatty acid methyl esters

The formation of 4-hydroxy-hexenal (HHE) and 4-hydroxy-nonenal (HNE) in eight vegetable oils was investigated at 180 °C. HHE was only detectable in soybean (SBO), rapeseed (RO) and linseed oils (LO). HNE was measured in all tested oils, but was found mainly in corn (CO), sunflower (SO) and soybean oil (SBO). Oil-dependent formation of HHE/HNE was remarkably observed. Furthermore, different fatty acid methyl esters in tricaprylin, as model oil systems, were constructed to demonstrate their characteristic contribution to HHE/HNE formation. As expected, HHE and HNE originated from the oxidative degradation of methyl linolenate (MLN) and methyl linoleate (ML) respectively. Whereas low concentrations of MLN (<5.0%) and ML (<1.0%) produced no detectable HHE/HNE. The results suggested MLN/ML could induce both HHE/HNE formation and pro-oxidation at higher concentrations. Unexpectedly, methyl stearate and methyl oleate slightly promoted HHE/HNE formation, which might be attributed to free radical transfer mechanisms during thermal oxidation.     

Suppression of the oxidation of methyl linoleate encapsulated with the extract from defatted rice bran by a compressed hot water treatment

Bran extracts prepared by a compressed hot water treatment at 120, 150, and 180 °C for 7.5 min were used in association with maltodextrin for encapsulation of methyl linoleate. Mixtures of the bran extracts at 120 and 150 °C showed a higher emulsion-stabilizing ability than that at 180 °C. The bran extracts prepared at the higher temperature provided a higher oxidative stability as shown by the longer induction period for the oxidation of the encapsulated methyl linoleate. The induction periods of the encapsulated methyl linoleate using the bran extract prepared at 250 °C for 5 min as the aqueous phase were 3–6 times longer than those of the encapsulated methyl linoleate using water.     

A chemiluminescence study of the oxidation of vegetable oils and model compounds and the effects of antioxidants

Chemiluminescence was used to study the course of oxidation of sunflower oil samples at a number of temperatures between 70 and 121°C. The induction time was determined for each sample and used to estimate the shelf life of the oils at 25°C. In addition, Chemiluminescence during oxidation in air on alumina at 80°C was used to study both sunflower oil and, as a model compound, methyl linoleate with and without added artificial antioxidants. By using the method of inhibitors, the reaction rate and level of hydroperoxide were determined. It was also possible to determine the level of naturally occurring antioxidant in the vegetable oil.     

Effects of sesamol, sesamin, and sesamolin extracted from roasted sesame oil on the thermal oxidation of methyl linoleate

This study investigated the effects of lignan compounds extracted from roasted sesame oil, which were sesamol, sesamin, and sesamolin, on oxidation of methyl linoleate (ML) during heating. These compounds were added at 500 or 1000 mg/kg to ML, and α-tocopherol was used as a reference antioxidant. The ML added with lignans or α-tocopherol was heated at 180 °C for 60 min. Thermal oxidation of ML was evaluated by conjugated dienoic acid (CDA) contents, p-anisidine value (PAV), and ML retention. Contents changes of lignan compounds or α-tocopherol in ML during heating were monitored by high-performance liquid chromatography. CDA contents and PAV of samples increased and ML decreased with heating time at 180 °C. Samples added with lignan compounds showed lower CDA contents and PAV but higher ML retention than samples without lignan compounds. The antioxidant activity of sesame oil lignan compounds in ML oxidation during heating tended to be higher than that of α-tocopherol. The contents of lignan compounds in samples decreased with heating time due to their degradation, but the degradation rates were lower than that of α-tocopherol. This study suggested that sesame oil lignan compounds be used as antioxidants in oil at high temperatures for deep-fat frying due to their higher effectiveness and stability than α-tocopherol.     

Degradation of Lycopene, α-Carotene, and β-Carotene During Lipid Peroxidation

The stability and antioxidant effectiveness of lycopene, a-carotene, and b-carotene were compared during oxidation of methyl linoleate at 37 and 60 °C. Two carotene concentrations, 80 or 160 mg/g of methyl linoleate, were used to determine a concentration effect. At 37 °C, the degradation rates were: lycopene > β-carotene > α-carotene. Lycopene and α-carotene inhibited hydroperoxide formation, lycopene being the more effective antioxidant. β-Carotene inhibited hydroperoxide formation at the lower concentration but did not show an antioxidant effect at the higher concentration. At 60 °C, the carotenes degraded 6 to 8 times faster than at 37 °C and did not show an antioxidant effect. BHT or α-tocopherol effectively suppressed the hydroperoxide formation and degradation of the carotenes.     

Compositional Factors that Influence Lipid Peroxidation in Beef Juice and Standard Sausages

In order to identify how different additives influenced lipid peroxidation formation, a sausage only using beef juice as pigment source and a standard beef–pork meat sausage were studied. The effects of different additives, including fish oil, myoglobin, nitrite, clove extract, and calcium sources on oxidation and sensory properties were examined. Both sausage systems were stored in 3 different manners prior to testing: (1) frozen immediately at ?80 °C; (2) chilled stored for 2.5 weeks followed by fluorescent light illumination at 4 °C for another 2 wk; (3) frozen at ?20 °C for 5 mo. The frozen group 3 showed the highest peroxide formation and thiobarbituric acid reactive substances (TBARS) for both sausage systems. Unpolar peroxides dominated in both systems. The clove extract could offset the peroxide formation from myoglobin/beef juice and/or fish oil, but the addition of clove flavor was recognized by the sensory panelists. Calcium addition reduced lipid peroxide formation. Added nitrite and fish oil seemed to interact to stimulate nitroso‐myoglobin formation. Nitrite was identified to interact with clove addition and thereby, relatively speaking, increased TBARS. The 2 sausage systems generally ranked the additives similarly as pro– and antioxidants.     

Original article: Thermal dynamic properties of isoflavones during dry heating

Thermal stabilities of major soya isoflavones at different dry‐heating temperatures were determined in this study. The conversion of glucoside isoflavones to aglycone isoflavones was monitored as well. The thermal degradation of the isoflavones: glucoside form daidzin, glycitin, and genistin and aglycone form daidzein, glycitein, and genistein followed first‐order reaction kinetics at heating temperatures 100, 150, and 200 °C. The degradation rate constants of the six isoflavones were not significantly different at 100 °C. However, the constants increased with increasing heating temperature. The half‐life for the glucoside and aglycone isoflavones was from 144 to 169 min and 139 to 176 min at 100 °C, respectively. They decreased rapidly to 15.7–54.7 and 36.0–90.7 min when temperature increased to 150 °C. When heated at 200 °C, they further decreased to 5.8–6.0 and 15.7–21.2 min, respectively. The order of thermal stability from lowest to highest was glycitin < genistin < daidzin < glycitein < genistein < daidzein at temperature below 150 °C. However, their thermal stabilities were not different at 200 °C. The conjugated glucosides were cleaved from the isoflavones to produce their corresponding aglycones when heated at 150 °C or higher. The production of glycitein increased constantly and was the highest among the three aglycone isoflavones.     

High correlation of methylglyoxal with acrylamide formation in glucose/asparagine Maillard reaction model

α-Dicarbonyl compounds were highly reactive intermediates formed in Maillard reaction (MR), and o-phenylenediamine (OPD) was widely used as a trapping agent for α-dicarbonyl compounds. Both aqueous glucose/asparagine (Glc/Asn) and glucose/asparagine/o-phenylenediamine (Glc/Asn/OPD) model systems were heated at 150 °C for up to 30 min. The α-dicarbonyl compounds formed in MR were identified by HPLC/MS in our particular model system, indicating that 3-deoxy-2-hexosulose, 2,3-butanedione and methylglyoxal (MG) were three main α-dicarbonyl compounds. In this work, MG was chosen as a representative of α-dicarbonyl compound in MR to investigate the influence on the formation of acrylamide (AA). The concentrations of AA, MG and Asn were detected during MR by HPLC method. The results indicated that the formation of AA increased with the heating time, and nearly 80% of AA formed through participation of α-dicarbonyl compounds. These results were consistent with the changes of amounts of MG. The amounts of formation and consumption of MG increased with heating time, and from 9 min of reaction, the consumed amounts of MG accounted for 73–88% on basis of total amounts of MG formed in MR, suggesting that most of MG take part in the next reaction steps. Meanwhile, the Asn concentration decreased with heating time in both models. The formation of AA and consumption of Asn were highly correlated with MG. Indeed, as MG concentration in MG/Asn model system decreased during heating at 150 °C, the concentration of AA significantly increased. The coefficient of correlation between consumed amounts of MG and the formed amounts of AA is 0.931, again demonstrating that MG does play a role in AA formation.     

Kinetics of anthocyanin degradation and polymeric colour formation in black carrot juice concentrates during storage

The changes in anthocyanins (ACNs) and polymeric colour of black carrot juice concentrate (BCJC) samples were monitored during storage at ?23, 5 and 20 °C for 319 days and at 30 °C for 53 days. While ACN degradation was fitted to a first‐order reaction model, polymeric colour formation was fitted to a zero‐order reaction model during the storage. Half‐life periods for ACN degradation in BCJCs were 603, 137 and 29 days at 5, 20 and 30 °C, respectively. The reaction rate constants for polymeric colour formation were 0.0207, 0.1435 and 0.5581%/days at 5, 20 and 30 °C, respectively. HPLC‐MS analyses of BCJC showed that cyanidin‐3‐galactoside‐xyloside‐glucoside‐ferulic acid (56%) was the major ACN, followed by cyanidin‐3‐galactoside‐xyloside (19%) and cyanidin‐3‐galactoside‐xyloside‐glucoside‐sinapic acid (10%). Cyanidin‐3‐galactoside‐xyloside‐glucoside‐ferulic acid was the most stable ACN in BCJC at storage temperatures. BCJCs should be kept at sub‐freezing temperatures to minimise ACN degradation.     

Changes in Bovine Myoglobin Due to Interaction with Methyl Linoleate in a Model System

Changes in myoglobin due to lipid oxidation were studied in a model system, consisting of a mixture of metmyoglobin and methyl linoleate (2:1), which was mechanically emulsified, freeze-dried and stored at 37°C. After storage, samples were reconstituted, centrifuged and lipid fractions were separated and tested for degree of oxidation. The protein was recovered in two fractions: “soluble fraction” (supernatant) and “aggregates” (precipitated proteins). Absorption spectroscopy confirmed protein insolubilization due to formation of aggregates. SDS-PAGE of metmyoglobin recovered from both fractions indicates gradual formation of covalently bound polymers upon storage. Isoelectric focusing (IEF) shows formation of new bands and zones with a drastic acidic shift of isoelectric points. Two-dimensional IEF/SDS-PAGE shows that the newly formed bands on IEF correspond to covalently bound myoglobin polymers.     

Assessment of conventional and microwave heating induced degradation of carotenoids in olive oil by VIS Raman spectroscopy and classical methods

Raman spectroscopy, as a fast non-destructive method, has shown its potential in revealing heat-induced degradation of extra virgin olive oil carotenoids during microwave versus conventional heating processes. A progressive degradation in carotenoids was observed, starting at 180 °C and 140 °C in microwave and conventional heating processes respectively; this was followed by a rapid degradation at 180 °C only with conventional heating. As the main difference, the Raman bands due to carotenoids completely disappeared at 203 °C with conventional heating, while these bands could still be observed even up to 225 °C with microwave heating. Furthermore a loss of cis double bonds and slightly changes in free fatty acid was also observed in both heating processes. A precise calibration model was established using partial least squares regression, which can be used for monitoring carotenoids content degradation during heating. The accuracy of the model was estimated using the root mean square errors and the correlation coefficient.     

Contribution of Lipids to Volatiles Generation in Extruded Corn-Based Model Systems

Volatile compounds generated by model systems of zein, corn amylopectin and corn oil extruded at barrel temperatures of 120°C and 165°C were analyzed by GC and GU/MS. The largest quantities of lipid oxidation products were detected in systems containing all three components. In each system, the quantity of 2,4-decadienal was low relative to the quantities of hexanal, heptanal, and benzaldehyde. Identification of the Maillard reaction products, 2-methyl-3(or 6)-pen-tylpyrazine, 2-methyl-3(or 6)-hexylpyrazine, and 2,5-dimethyl-3-pen-tylpyrazine, suggested that lipid-derived aldehydes might be involved in the formation of substituted pyrazines.     

几种脂肪酸甲酯的热解特性及动力学研究

采用热重分析法研究了硬脂酸甲酯、油酸甲酯和亚油酸甲酯在氮气气氛中的热分解特性,并采用Coats-Redfern积分法对硬脂酸甲酯、油酸甲酯和亚油酸甲酯的热分解过程进行动力学分析,建立热分解模型。结果表明:硬脂酸甲酯和油酸甲酯的热分解过程表现为简单的一步分解,而亚油酸甲酯则呈现出较复杂的两步分解过程;随着升温速率提高,热分解区间向高温区移动,热分解活化能和指前因子呈现出较好的动力学补偿效应,且在不同升温速率下具有不同的热分解反应机理函数;模拟计算的热分解率与实验数据误差基本在10%左右。动力学模型能够很好地预测各脂肪酸甲酯热分解过程,为进一步扩大试验和生物柴油应用中的高温热分解衰变模型提供理论依据。     

Heat Degradation of Heme in Methemoglobin and Metmyoglobin Model Systems Measured by Reversed-Phase Ion-Pair High Performance Liquid Chromatography

The effect of heat treatment on heme degradation in methemoglobin and metmyoglobin model systems was investigated. The extent of heme degradation was found to be different above and below the denaturation temperature of the proteins. Heme degradation as a function of time followed hyperbolic curves at 78°C, 100°C and 120°C. After 1 hr heating the degradation of heme at 78°C and 100°C was similar, being approximately 22% in metmyoglobin solutions and 26% in methemoglobin solutions. Autoclave heating for 2 hr degraded 87.5% and > 95% of the heme in methemoglobin and metmyoglobin solutions, respectively.     

Rate of Deterioration of Freeze-Dried Salmon as a Function of Relative Humidity

SUMMARY— The rates of several deteriorative reactions, including lipid oxidation, astacene pigment loss, carbon dioxide production, and production of non-enzymatic browning pigments, were studied in freeze-dried salmon at 37°C and at several relative humidities. Results previously obtained in cellulosic model systems containing methyl linoleate were confirmed by data on oxygen absorption as a function of moisture content. Both the rate of the initial peroxide mono-molecular decomposition and the peroxide value decreased as the water content was increased. Astacene pigment loss was reduced significantly by the higher moisture contents; non-enzymatic browning was increased. The significance of the reactivity of water at low moisture contents was demonstrated by its effect on the various reactions.     

Relationship between chlorophyll a and β-carotene in a lipid-containing model system during illumination

The relationship between chlorophyll a (Chl a) and β-carotene during illumination in the presence of fatty acid esters, methyl stearate methyl oleate and methyl linoleate was studied. Mixtures of Chl a, β-carotene and fatty acid esters were exposed to a 40 w light for 3 h. Isomerization and degradation reations of Chl a and β-carotene were monitored using HPLC with diode array detection Three isomers of Chl a and four cis isomers of β-carotene were separated and detected. Both the degradations of total amount of Chl a and β-carotene fit the first-order model. The degradation rate of total amount of β-carotene was highest in methyl stearate, followed by in methyl oleate and in methyl linoleate, while a reverse order was observed for the degradation rate of total amount of Chl a. In the presence of three fatty acid esters, Chl a is more susceptible to isomerization and degradation than β-carotene, and the degradation rates for both Chl a and β-carotene are significantly different (p < 0.05).     

Effect of lipid hydroperoxides on pheophytin in the dark

Pheophytin was heated with hydroperoxyoleate in the medium of methyl palmitate, methyl oleate or methyl linoleate to 60°C in inert gas. The rate of pheophytin destruction due mostly to free peroxy radicals generated by hydroperoxide decomposition was proportional to the content of hydroperoxide. Double bonds of fatty acid esters were competitively attacked by free peroxy radicals. In systems containing low levels of oxygen, methyl esters were slowly autoxidized on heating, and pheophytin moderately inhibited their autoxidation. Because of a low concentration of pheophytins the antioxidant activity was more pronounced under conditions of a lower rate of oxidation chain initiation, i.e. in more saturated systems and at a lower content of hydro-peroxides.     

Heat and storage effects on the flavour of peanuts

Two peanut varieties, Giza 4 and Giza 5 were subjected to different heat treatments such as drying in solar drier at air speed 0.5 and 2 m/sec with average temperature 45 and 60°C and heating in oven at 120 and 150°C. The sensory evaluation of the two varieties showed insignificant differences among varieties and heating processes. A correlation between the sensory and instrumental data was found. The high sensory scores of samples heated at 150°C were attributed to the presence of high concentration of pyrazines which were thought to contribute to flavour and aroma of fresh roasted peanut. A comparative study between the main chemical classes retained in peanut samples after storage for 3 months at room temperature showed that the aldehydes derived lipids increased significantly in the solar dried samples. The antioxidative components produced via Maillard reaction resulted in oxidative stability of the samples heated in oven     

Interaction between Maillard reaction products and lipid oxidation in starch‐based model systems

The effect of Maillard reaction products (MRPs) on the kinetics of lipid oxidation in intermediate‐moisture model systems containing pregelatinised starch, glucose, lysine and soybean oil has been studied. The samples, either containing all components or excluding one or more of them, were heated at 100 °C for different times. Lipid oxidation and browning indices were measured and the results confirmed the ability of MRPs to retard peroxide formation. Under the conditions adopted, the rate of the Maillard reaction was increased by the presence of the oil and its oxidation products. The antioxidant action of MRPs was also evaluated using a peroxide‐scavenging test based on crocin bleaching. The results demonstrated that antioxidant activity developed with increased browning of the samples. © 2000 Society of Chemical Industry     

基于气相色谱法的油酸甲酯和亚油酸甲酯热氧化降解特性研究

利用气相色谱法分别测定油酸甲酯和亚油酸甲酯在不同温度下的氧化曲线,同时采用微分法和积分法对热氧化降解反应方程的参数进行了计算,进而确定了反映油酸甲酯和亚油酸甲酯热氧化降解历程的宏观反应动力学方程。微分法动力学分析结果表明:油酸甲酯热氧化降解反应的平均反应级数为1.37,活化能为5.48 k J/mol,反应动力学模型为rA=-dcA/dt=7.06exp(-5.48/RT)c1.37A;亚油酸甲酯热氧化降解反应的平均反应级数为2.49,活化能为392.73 k J/mol,反应动力学模型为rA=-dcA/dt=1.13×1047exp(-392.73/RT)c2.49A。积分法动力学分析结果表明:当反应级数n=1时,油酸甲酯热氧化降解反应的活化能为27.68 k J/mol,反应动力学模型为rA=-dcA/dt=1 690.55exp(-27.68/RT)cA,亚油酸甲酯热氧化降解反应的活化能为107.04 k J/mol,反应动力学模型为rA=-dcA/dt=2.20×1013exp(-107.04/RT)cA;当反应级数n≠1时,油酸甲酯热氧化降解反应的平均反应级数为1.45,活化能为31.29 k J/mol,反应动力学模型为rA=-dcA/dt=369.19exp(-31.29/RT)c1.45A,亚油酸甲酯热氧化降解反应的平均反应级数为1.60,活化能为108.90 k J/mol,反应动力学模型为rA=-dcA/dt=9.27×1013exp(-108.90/RT)c1.60A。积分法得到的活化能数值更为接近,因此更适合研究油酸甲酯和亚油酸甲酯的热氧化降解反应动力学。