The use of DSC and FT-IR spectroscopy for evaluation of oxidative stability of interesterified fats

The aim of this paper was to assess the oxidative stability of structured lipids synthesized by enzymatic interesterification of a blend of lard and rapeseed oil with concentrates of n ? 3 fatty acids. Differential scanning calorimetry was used to evaluate the oxidation induction time of interesterified fats as a parameter assessing resistance of tested fats to their thermal-oxidative decomposition. Moreover, the IR spectra registered in the classic spectral range (4000–400 cm^?1) were used to differentiate the samples of interesterified fats. The results show that the interesterification process decreased the induction time. Increased content polar fraction in the interesterified fatty product can reduce its resistance to oxidation. FT-IR data of selected spectral ranges correlate with the value of induction time at a statistically significant level. This is a proof that chemical changes occurring during different treatments of the starting mixture can be monitored by FT-IR spectroscopy. Moreover, obtained correlations can be used for the evaluation of an induction value of an unknown oil sample.     

Mixed,lipase-catalyzed inter-esterified fats and hemp oil as a fatty base of model emulsion products with different emulsifiers

The aim of the study was to perform modification of fats to obtain new products, which were used as a fatty basis of model emulsions. The second objective was to assess the stability of the prepared emulsions. For this purpose, turkey fat, chicken fat, and mutton tallow were used and enzymatically inter-esterified with hemp oil. Enzymatic interesterification was performed using a selective catalyst – Lipozyme IR RM. The obtained fat mixtures before and after interesterification were assessed by determining their acid value, peroxide value (PV), anisidine value (AV), polar fraction (PF), and slip melting point (SMP). Later, the fats were used as a fatty basis of emulsions. The variable component in the emulsions was the emulsifier. The emulsions were evaluated for droplet size and viscosity and by the Turbiscan test. It was concluded that the dispersion systems containing mutton tallow and the emulsifier formed during the enzymatic reaction, as well as the one containing the same fat and lecithin, showed the best stability. In the case of emulsions with enzymatically modified mutton tallow, the authors are planning to extend the range of usable properties under examination. In the authors’ opinion, the proposed systems can be used in the cosmetic and food industries.     

Oxidative stabilities of enzymatically interesterified goose fat and rapeseed oil blend by rancimat and PDSC

Goose fat (GF) and rapeseed oil (RSO) 2:3 m m^?1 blend was enzymatically interesterified at 60 °C with and without microwaves assistance. As the catalyst, a commercial preparation of the immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) containing 2 % of water was used, and the catalyst load was 8 % in each case. The starting mixture and the interesterified products were separated by column chromatography into pure triacylglycerols fraction (TAG) and a non-triacylglycerol fraction, which contained free fatty acids (FFA), mono- and diacylglycerols (MAG and DAG). The oxidative stabilities of fats studied and TAG derived from them were assessed by Rancimat at 100 °C and by pressure differential scanning calorimetry (PDSC) under oxygen at 110–140 °C. Interesterification reduced the oxidative stability of GF and RSO blend. The main factors influenced on the oxidative stabilities of fats studied were concentrations of tocopherols and the presence of FFA, MAG and DAG. The structures of TAGs were of minor importance. From the resulting PDSC exotherms, their times to reach the onset (τ _on) and peak maximum (τ _max) were measured and used for calculations of parameters of the Arrhenius type kinetics for thermaloxidative decomposition of fats studied.     

Determination of the oxidative stability of hazelnut oils by PDSC and Rancimat methods

The present study was conducted to determine the oxidative stability of hazelnut oil and compare it with more common and previously tested olive oil and rapeseed oil. The oxidative stability was determined by means of two independent methods, pressure differential scanning calorimetry (PDSC), and oxidative stability index (OSI) using TA Instruments DSC and Metrohm Rancimat equipment, respectively. Both the PDSC and Rancimat devices were set at five different isothermal temperatures in the range of 100–140 °C. The times to reach peak maximum (τ _max) obtained from PDSC exotherms were statistically related with the Rancimat induction times (τ _on) to obtain correlation coefficient >0.99 within linear relation. Based on the Arrhenius equation and activated complex theory, activation energies (E _a), pre-exponential factors (Z), and specific rate constants (k) for studied oils oxidations were calculated. To the best of our knowledge, this is the first study dealing with oxidative stability of hazelnut oil using PDSC technique. According to the results obtained, PDSC seems to be useful and quick method for kinetic analysis of lipid oxidation in hazelnut oil.     

Production of Human Milk Fat Replacement Rich of 1,3-dioleoyl-2-palmitoilglycerol From Enzymatic Interesterification Tripalmitin,Ethyl Oleate And Mixture of VCO,Soybean Oil And Fish Oil

Human Milk is naturally the only source of food for infant in their early life. It contains 2-6% lipid which provides about 50% of the total energy needed by the infant. Human milk fat (HMF) mainly as TAG with the specific fatty acid composition, palmitic acid (C16:0) (20-25%), which is primary located at sn-2 of glycerol bonds (70%) and oleic acid (C18:1), located at sn-1,3 (35%). HMF also provide fatty acids such as linoleic acid, linolenic acid, EPA, DHA and lauric acid that are very important for infant. The purposes of this research are to synthesize of 1,3-dioleoyl-2-palmitoilglycerol (OPO) and to determine the best composition of OPO, VCO, soybean oil and fish oil for HMFS production for infant formula. Interesterification of tripalmitin and ethyl oleate using immobilized lipase from Rhizomucor miehei (Lipozym RM IM) were used to synthesize of OPO. Interesterification product of mixed VCO, soybean oil and fish oil that are source of lauric acid, linoleic acid, α-linolenic, EPA and DHA, were formulated in mass ratio (58:20:20:2) and (70:18:10:2) for obtaining HMFS which have fatty acids composition similar or close to HMF. Composition of fatty acids from product were analyzed by GCMS. From this research, were obtained HMFS containing palmitic acid as much as 28.89% where 84.49% of that are located at sn-2 while sn-1,3 position are dominated by oleic acid as much as 55.11% from the total 38.7% and 70:18:10:2 w/w is the best composition of interesterification product, VCO, soybean oil and fish oil to obtain HMFS similar to HMF.     

Comparative studies of oxidative stability of linseed oil

The oxidative stability of linseed oil was studied using classical method based on determination of peroxide value (PV), the Rancimat method based on conductometric measurements and thermoanalytical methods, i.e. the differential scanning calorimetry (DSC) and thermogravimetry (TG) in oxygen atmosphere.

The onset temperatures T_onset,DSC and T_onset,TG were determined from dynamical DSC and TG curves, respectively. From isothermal DSC curves times t_onset were determined.

The effect of two antioxidants was also studied. An antioxidant blend containing -tocopherol, ascorbyl palmitate, citric acid, ascorbic acid, and ethoxylated ethylene glycol proved more effective than butylated hydroxy anisole for protection of linseed oil against process, in good agreement with results obtained by the classical titration and the Rancimat methods.     

Thermal properties of fats extracted from powdered baby formulas

The aim of this research was to analyse composition, fatty acids distribution and oxidative stability of fats extracted from four samples of baby formulas. The fats were oxidized in a differential scanning calorimeter (DSC) under polythermal (dynamic) conditions and at normal pressure. The DSC experiments were carried out in an oxygen flow atmosphere using different, linearly programmed, heating rates in the range of 4?C12.5?°C/min. The extrapolated onset temperatures were determined using DSC exotherms and used for the assessment of the thermal oxidative stabilities of the samples. Activation energies (E _a), pre-exponential factors (Z) and reaction rate constants (k) for oil oxidation under DSC conditions were calculated using the Ozawa?CFlynn?CWall method and the Arrhenius equation. The melting characteristics of the studied fats were obtained. The fats extracted from the agglomerated samples with higher onset temperatures were more stable than the fats extracted from the initial samples of baby formulas.     

Infrared study of aging of edible oils by oxidative spectroscopic index and MCR-ALS chemometric method

One of the most suitable analytical techniques used for edible oil quality control is Fourier transform mid infrared spectroscopy (FT-MIR). FT-MIR spectroscopy was used to continuously characterize the aging of various edible oils thanks to a specific aging cell. There were differences in the spectra of fresh and aged oils from different vegetable sources, which provide the basis of a method to classify them according to the oxidative spectroscopic index value. The use of chemometric treatment such as multivariate curve resolution-alternative least square (MCR-ALS) made it possible to extract the spectra of main formed and degraded species. The concentration profiles gave interesting information about the ability of the various oils to support the oxidative treatment and showed that all oils present the same aging process. Both methods led to concordant results in terms of induction times determined by the oxidative spectroscopic index and the appearance of oxidation products revealed by MCR-ALS.     

Effects of spice extracts on lipid fraction oxidative stability of cookies investigated by DSC

The addition of natural antioxidants to the bakery products containing fats can extend their shelf life, and it may be more attractive to consumers. In this research, the antioxidant effect of spice extracts and synthetic antioxidant on oxidative stability of fat extracted from cookies was evaluated by differential scanning calorimetry (DSC). The results revealed that addition of spice extracts to the cookies in comparison to cookies without additives reduced the oxidation as evidenced by higher the onset oxidation temperature (t _ON) of antioxidant-treated samples. Using the Ozawa–Flynn–Wall method, the activation energies (E _a/kJ mol^?1) and pre-exponential factors (Z/min^?1) and then induction times (τ/min) were calculated and also used for evaluation of antioxidants efficiency. After baking, cookies were also subjected to sensory studies and to instrumental measurements of colour changes. Among the samples studied, cookies with 0.02 % of rosemary or 0.2 % thyme extracts showed good sensorial acceptability. Cookies fortified with spice extracts also characterised greater lightness compared to the control sample.     

Influence of the fat characteristics on the physicochemical behavior of oil-in-water emulsions based on milk proteins-glycerol esters mixtures

Oil-in-water emulsions based on 10% milk protein preparation, 0.3% mono-di-glycerides (MDG) and 8% vegetable oil were prepared for models typifying ice cream formulations. Two MDG (saturated and partially unsaturated) and four fats (oleic oil, hydrogenated and refined coconut oils, refined palm oil) were chosen to investigate the interactions occurring between the oil phase, the MDG and the milk proteins. Influence of temperature (4 °C) and ageing (24 h at 4 °C) was also tested. The emulsions were characterized for protein desorption, particle size distribution and rheological properties. The dynamic surface activity of the milk proteins and the MDG at the oil-water interface was also determined. At 20 °C, emulsions were mostly stabilized by proteins although the protein load at the globule surface strongly depended on the emulsifier and the oil phase natures. A displacement of the proteins adsorbed at the oil droplet interface by the lipid surfactant was a consequence of the temperature decrease and/or ageing step, suggesting a disruption of the interfacial protein interactions. This disruption was more or less marked depending on the physicochemical characteristics of the surfactant and the oil used (amount of crystallized matter, fatty acid chain length and unsaturation degree). In parallel, the variation of the apparent viscosity of the various emulsions upon temperature was well correlated with the solid fat content. On the whole, the results obtained suggested that not only the surfactant molecules, i.e. emulsifiers and proteins, but also the fat used in the emulsion formulation participated in the development of the interface characteristics and rheological properties.     

Melting Properties of Butter Fat and The Consistency of Butter. Effect of modification of cream ripening and fatty acid composition

The cold unspreadable consistency of butter after taking it out of the refrigerator is a rightful objection on behalf of consumers. The possibilities to improve the cold spreadability of butter are: the enrichment with low melting point triglycerides and the application of a good cream-ripening method. In our investigations milk fat fractions of different low melting points and plant oils of low melting points obtained by cold pressing and extraction have been used to change the original fatty acid composition of milk fat. The cream-ripening, the traditional method and the heat-step ripening method, which seemed to be the most effective to our earlier research, have been applied. The consistency of butter was examined by penetration measurements and its thermal characteristics by differential scanning calorimetric (DSC) method. The cold unspreadable consistency of butter can only be improved by the combination of the heat-step cream ripening and enrichment with low melting point triglycerides to get stable consistency at room temperature. The milk fat fraction of melting point below 5°C made the spreadability better but the spreadable consistency of margarine still cannot be attained. Plant oils with melting point below 0°C improved the cold spreadability of butter to a significantly higher degree than the former did. In the case of the same melting point the plant oil obtained by a cold method (pressing) was more effective. There is a close relationship between the consistency of butter and its product characteristics. From DSC curves the cold spreadability and room temperature stability of butter can be directly concluded. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enzymatic Synthesis of Biodiesel via Alcoholysis of Palm Oil

The enzymatic alcoholysis of crude palm oil with methanol and ethanol was investigated using commercial immobilized lipases (Lipozyme RM IM, Lipozyme TL IM). The effect of alcohol (methanol or ethanol), molar ratio of alcohol to crude palm oil, and temperature on biodiesel production was determined. The best ethyl ester yield was about 25 wt.% and was obtained with ethanol/oil molar ratio of 3.0, temperature of 50 °C, enzyme concentration of 3.0 wt.%, and stepwise addition of the alcohol after 4 h of reaction. Experiments with 1 and 3 wt.% of KOH and 3 wt.% of MgO were carried out to compare their catalytic behavior with the enzymatic transesterification results. The commercial immobilized lipase, Lipozyme TL IM, showed the best catalytic performance.     

Evaluating antioxidants efficiency during storage of ethylic and methylic biodiesel by low pressurized DSC and Rancimat methods

Efficiencies of four commercial antioxidants used during the storage of two biodiesel, BS-ethyl and BS-methyl, respectively obtained from soybean oil by ethylic and methylic routes, were evaluated by measuring their oxidative stability using a low pressurized DSC (low P-DSC) method developed by the authors and by Rancimat method, which is specified by the American ASTM D6751 and European EN 14214 standard methods. The operating temperature of the low P-DSC method was the same as that used in the Rancimat procedure (110 °C). The antioxidants, used in 500 mg kg^?1 content, have the following active components: phenol, biphenol, phenol + amine mixture, and a hydroquinone + organic acid mixture. Samples of each biodiesel–antioxidant mixture were evaluated simultaneously by the two methods, right after their preparation and 30, 60, 90, and 120 days of storage at 23 ± 1 °C. A non-dimensional oxidative induction time parameter, defined as the ratio between the oxidation induction time (OIT) or induction time (IT) values at a storage time t and at t = 0, was used to evaluate the antioxidant activity. For the same mixture, changes of this non-dimensional parameter calculated from OIT or IT show a similar trend with storage time, indicating that it can be determined either from low P-DSC or Rancimat method data. As the efficiency of the studied antioxidants depends on their composition, their interaction with each biodiesel, and on the storage time, this parameter can be used to indicate the best storage time for each antioxidant–biodiesel mixture.     

By-products from fruit processing

The oxidative stability of soybean oil added of extracts from by-products generated in the pulp processing of mango (CM), Barbados cherry (CB) and guava (CG), as well as the combination of these extracts with the antioxidants butylated hydroxytoluene (BHT) and tertiary butylhydroquinone (TBHQ), were evaluated by pressurized differential scanning calorimetry (P-DSC) and Rancimat methods. Among the extracts, that obtained from CB showed the highest content of total extractible phenolic. Soybean oil added of CM extract showed greater (p < 0.05) oxidative stability in Rancimat analysis, while by P-DSC method CB was the extract more effective (p < 0.05) to protect soybean oil. Soybean oil added of CB extract showed higher (p < 0.05) OIT values compared to those added of CM, CG and synthetic antioxidants BHT and TBHQ. The combination of CB, CM and CG extracts with TBHQ showed synergistic effects, while CM and CB combined with BHT showed antagonistic effect on oxidative stability in soybean oil. The OIT results obtained from analysis by P-DSC and the OSI results obtained by Rancimat showed Pearson moderate correlation (r = 0.42). These results suggest the CB, CM and CG extracts as good source of antioxidant compounds with potential for combined application with synthetic antioxidants to prevent oxidation in soybean oil.     

Characterization of oil from roasted hemp seeds using the PDSC and FTIR techniques

The purpose of the present work was to characterize oil extracted from roasted hemp seeds using the PDSC and FTIR techniques. Roasting was conducted in a laboratory convective dryer. DSC method was used for the determination of the oxidative stability of oil extracted from hemp seeds. Pressure differential scanning calorimetry experiments were carried out using a DSC Q20, TA Instruments, coupled with a high-pressure cell. The isothermal temperature (393 K) was used for the data collection. The oxidative induction time was obtained from the PDSC curves. Infrared spectra were registered for every sample in the classic range of 4000–400 cm^?1 with 1 cm^?1 resolution, using System 2000 PerkinElmer instrument. The Grams AI 8.0 and TQ Analyst 8 software were used for spectral data processing. The samples of oil were also characterized by standard quality parameters: fatty acids composition (with use of GC technique), free fatty acids content by titration with 0.1 M potassium hydroxide and peroxide value determined by iodometric titration technique. Samples of oil extracted from hemp seeds after roasting in higher temperatures were characterized by lower induction time than oil from hemp seeds roasted in lower temperature. The results confirm that the induction time obtained from PDSC measurements can be used as parameters for the assessment of the resistance of oils from roasted hemp seeds to their thermal–oxidative decomposition.

     

Influence of the storage on the thermo-oxidative stability of methyl and ethyl esters by PDSC

Biodiesel oxidation is a complex process widely influenced by the chemical composition of the biofuel and storage conditions. Several oxidation products can be formed from these processes, depending on type and amount of the unsaturated fatty acid esters. In this work, fatty acid methyl and ethyl esters were obtained by base-catalyzed transesterification of soybean oil and physicochemically characterized according to standards from ASTM, EN, and ABNT. The thermal and oxidative stabilities of biodiesel samples were investigated during the storage process by pressure differential scanning calorimetry (PDSC) and by viscosity measurements. Absolute viscosities of biodiesels after accelerated aging were also determined. The viscosity increased as the aging temperature and time were raised. The results showed that oxidation induction can occur during storage, decreasing the biodiesel stability. PDSC analysis showed that during storage under climate simulation the values of high-pressure oxidative induction times (HPOIT) were reduced for both FAEE and FAME.     

Influence of the purification process on the stability of <Emphasis Type="Italic">Jatropha curcas</Emphasis> biodiesel

The aim of this work was to evaluate the influence of the purification process on the stability of Jatropha curcas biodiesel. The biodiesel was obtained using a variety of purification processes: three wet methods with different drying processes (vacuum oven, conventional oven and anhydrous sodium sulfate) and one dry method (purification with adsorbent magnesium silicate). Biodiesel was characterized through the analysis of carbon residue, acidity index, infrared and gas chromatography. The composition J. curcas oil indicated 56.3 % of unsaturated fatty acids and 43.7 % of saturated fatty acids. Jatropha oil presented high quantity of saturated acids, which are less susceptible at oxidation. The biodiesel sample that was chemically purified (PUsq) presented better purity, indicating be the process more efficient in remove the residues of synthesis. Thermogravimetric curves of purified biodiesel by wet method, PUsq, with chemical drying using anhydrous sodium sulfate, and PUsv, with vacuum drying, showed the highest initial decomposition temperatures, indicating higher thermal stability. The carbon residue and infrared analyses suggested that contamination by catalyst residue is a determining factor in reduction of the oxidative stability of biodiesel. The oxidative stability was evaluated using Rancimat and pressure differential scanning calorimetry. Biodiesel samples showing better oxidative stability were purified using PUsq and PUsv, which obtained stability of 6 h using the Rancimat technique, the minimum limit set by Brazilian legislation, without the addition of antioxidant, suggesting that these methods least influenced the stability of biodiesel.     

Thermal stability evaluation of methylic biodiesel obtained for different oilseeds

Biodiesel is defined as a mixture of mono- or di-alquil esters of vegetable oil or animal fats. During long-term storage, oxidation caused by contact with air (autoxidation) presents a legitimate concern in relation to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise the quality by adversely affecting kinematic viscosity, acid value, or peroxide value. The oxidation susceptibility of biodiesel, due to the presence of triacilglycerides of poly-unsaturated fatty acids, was evaluated in this study. Samples of sunflower, castor, and soybean biodiesels were obtained through the transesterification reaction, with the intention of achieving the thermal stability study through thermogravimetrical analyses and differential scanning calorimetry high pressure. It was furthermore observed through thermogravimetry and pressure differential scanning calorimetry curves that castor biodiesel exhibited the highest thermal and oxidative stability.     

Simultaneous Determination of 2- and 3-Monochloropropan-1,3-diol Esters in Foods by Enzymatic Hydrolysis and GC–MS Detection

A simple, reliable and accurate method for simultaneous determination of 2- and 3-monochloropropan-1,3-diol fatty acid esters (2- and 3-MCPD esters) in food by enzymatic hydrolysis and gas chromatography mass spectrometry was developed and validated. The extraction of lipids in food was conducted by mixed with hexane and homogenized for 2 min. After extraction, the lipids were directly transferred to enzymatic hydrolysis and the content was determined by gas chromatography mass spectrometry. The main advantage of the proposed method is that it can simultaneously analyse both 2- and 3-MCPD esters in foods and preserve their structural integrity. The limits of detection (LODs) of 2- and 3-MCPD esters in edible oil were 40 and 20 μg kg⁻¹ as 2- and 3-MCPD, respectively. For low fat foods containing less than 3 % fat, the LOD of 2- and 3-MCPD esters were lowered to 1.2 and 0.6 μg kg⁻¹ as 2- and 3-MCPD, respectively. Quantitative recoveries of different fatty acid esters of 2- and 3-MCPD esters were obtained after spiked corresponding standards into blank matrices.