Rancid Oil Research Articles

Lipids: Their Role in the Formation of Endogenous Antioxidants during Food Processing

Lipids are important food nutrients and they also carry out other functions such as to be carriers of aromatic substances or to influence food texture, for example. However, polyunsaturated acids are also easily oxidised. In fact, oxidative rancidity of edible oils is a serious problem in the food industry. As an alternative to the use of synthetic antioxidants, the generation of endogenous antioxidants by carbonyl-amine reactions can be employed to increase food stability. These reactions are widely accepted to be produced as a consequence of Maillard reactions between carbohydrates and amino compounds. However, the contribution of lipid-derived carbonyl compounds to these reactions is much lesser known. This review discusses the role of lipid-derived antioxidants by analysing how they are formed and their antioxidative action.

Potato starch edible films to control oxidative rancidity of polyunsaturated lipids: effects of film composition, thickness and water activity

SummaryThe objective of this work was to study the effect of potato starch‐based films acting as oxygen barrier on the oxidative rancidity of vegetable oil, as an example of a food rich in polyunsaturated fatty acids. The effect of glycerol (Gly) content (0%, 10%, 20%, 30%), film thickness (30, 60, 100 μm) as well as environmental relative humidity (RH) (50% or 75%) were analysed. Results obtained confirmed that potato starch films delayed the rancidity in vegetable oil. Films without Gly provided the same protection as films with 10% Gly. Films with higher Gly content were not as effective oxygen barrier. It is likely that the fact that film protective capability diminished with increased RH or Gly content was due to the increasing moisture content of the films. Despite that fact, potato starch films can be considered a very efficient oxygen barrier even at RH as high as 75%.

Products Formed During Thermo‐oxidative Degradation of Phytosterols

AbstractOxidative degradation of cholesterol has been extensively researched, however, not all products formed have been established. When a phytosterols standard was heated at 60, 120 and 180 °C for different period of time the following groups of components were detected: oxidized phytosterols, fragmented phytosterol molecules, volatile compounds and oligomers. Taking into account all the components formed, we were able to balance the amounts of disappearing sterols with components formed. We established that the amount and type of products formed during thermo‐oxidative degradation is affected by temperature and time. The amount of intact phytosterols decreased when temperature and time increase. The amount of oxidized phytosterols was at the highest level when a temperature of 120 °C was applied, whereas the lowest amounts were observed when a temperature of 60 °C was used. At a temperature of 180 °C the amount of oxidized sterols was lower than at 120 °C and it decreased when the heating time was increased. This indicates that oxidized sterols were the main precursors involved in the formation of other components during thermo‐oxidative degradation. The amount and type of volatile compounds formed increased when time and temperature increased. We observed diversified groups of volatile compounds formed and most of them are defined as off‐flavor compounds for rancid oils.

Anti‐Rancidity Effects of Sesame and Rice Bran Oils on Canola Oil During Deep Frying

AbstractIn this study, the effect of sesame oil (SEO) and rice bran oil (RBO) on the rancidity of canola oil (CAO) during the process of frying potato pieces at 180 °C was investigated. The SEO and RBO were added to the CAO at levels of 3 and 6%. Frying stability of the oil samples during the frying process was measured on the basis of total polar compounds (TPC) content, conjugated diene value (CDV), acid value (AV), and carbonyl value (CV). In general, frying stability of the CAO significantly (P < 0.05) improved in the presence of the SEO and RBO. The positive effect of the SEO on the stability of the CAO was more than that of the RBO. Increasing the amounts of SEO and RBO from 3 to 6% led to decreases in the TPC and AV, and increases in the CDV and CV of the CAO during the frying process. The best frying performance for the CAO was obtained by use of 3% of both SEO and RBO together (CAO/SEO/RBO, 94:3:3 w/w/w).

Electrochemical sensor for hydroperoxides determination based on Prussian blue film modified electrode

An electrochemical sensor for hydroperoxides determination was investigated. The sensor was based on the electrocatalytic reduction of hydroperoxides on Prussian blue (PB)-modified glassy carbon electrode. The modified electrode possesses a high electrocatalytic effect towards all studied peroxides with the highest effect obtained with H2O2 followed by tert-butyl hydroperoxide (TBH), cumene hydroperoxide (CH) and linoleic acid hydroperoxide (LAH). In addition, the modified electrode showed a good stability and a fast response time (<20 s). The lower detection limits of H2O2, TBH, CH and LAH were found to be 10−7 mol L−1, 2 × 10−7 mol L−1, 3.5 × 10−7 mol L−1 and 4 × 10−7 mol L−1, respectively. The electrochemical sensor was then applied for amperometric determination of peroxide value (PV) in edible oil at an applied potential of 50 mV (vs. Ag/AgCl (1 M KCl)). A good linearity has been found in the range 0.02–1.0 mequiv. O2/kg, with a detection limit (S/N = 3) of 0.001 mequiv. O2/kg. The precision of the method (R.S.D., n = 9) for within and between-days is better than 1.9% and 2.7%, respectively at 0.1 mequiv. O2/kg. The method was successfully applied to the determination of PV in real edible oil samples with an excellent agreement with results obtained with the official standard procedure. The proposed method is accurate, simple, cheap and could be used to control edible oil rancidity with a high sample throughputs (more than 120 samples/h).

Dual emission of a bis(pyrene)-functionalized, perbenzylated β-cyclodextrin

A bis(pyrene)-functionalized β-cyclodextrin (1) has been prepared in two steps from perbenzylated β-cyclodextrin. This compound shows dual emission properties, which arise from the pyrenyl chromophores. Upon excitation of 1 at 355 nm, monomer blue fluorescence (386, 407 and 428 nm) is observed in DMSO solution, whereas excimer green fluorescence (477 nm) is seen upon addition of ≥20 vol% water in DMSO. This suggests that modified β-cyclodextrin 1 changes its shape in response to the environment. The sensing properties of 1 towards carboxylic acids and alcohols were investigated in H2O–DMSO (80 : 20 v/v). Monomer fluorescence is restored selectively by medium length normal carboxylic acids, such as enanthic acid (C7) found in rancid oils and capric acid (C10), while both monomer and excimer emissions are enhanced by homologous alcohols, such as 1-heptanol, used in cosmetics and 1-decanol. Remarkably, bulkier substrates, such as tert-butyl alcohol or 1-adamantylcarboxylic acid are not detected.

Use of edible films based on whey protein isolate to protect foods rich in polyunsaturated fatty acids

Whey protein isolate (WPI) films acting as oxygen barriers can be used to delay lipid oxidation in foods with high content in polyunsaturated fatty acids (PUFA). The aim of this work was to study as to what extent WPI films are capable of delaying lipid oxidation in vegetable oil, as an example of a food rich in PUFA. The effect of plasticizer type (glycerol or sorbitol) and content (30, 40, 50 and 60%), as well as film thickness (60, 100 and 180 μm) and relative humidity (50 or 75%) were analyzed. In order to evaluate the film protective capability, specially designed methacrylate cells and an accelerated test of oxidative rancidity were used. Results obtained showed that WPI films delayed the rancidity in vegetable oil. Films with sorbitol were more effective than films with glycerol, providing a protection as effective as aluminum foil. Both plasticizer content and film thickness affected its protective capacity significantly. The thickest films with the lowest plasticizer content provided the greatest protection against lipid oxidation. Plasticizer content affected film protection much more intensively than thickness. WPI films presented a more effective protection at 50% RH than at 75% RH.

DETERMINATION OF CARBONYL VALUE IN RANCID OILS: A CRITICAL RECONSIDERATION

ABSTRACT Different grades of 1‐butanol and 2‐propanol (2‐PrOH) with and without purification were reevaluated for preparation of blank solutions in a modified method for the determination of carbonyl value (CV) in rancid oils (soybean oil and a frying oil). Only purified 2‐PrOH with an absorbance lower than 0.35 at 420 nm was considered suitable as a solvent. Good correlations existed between the absorbance at 420 nm, and the molar concentration for 2‐decenal and 2,4‐decadienal solutions in 2‐PrOH reacted with 2,4‐dinitrophenylhydrazine. The sensitivity of the method in terms of 2‐decenal was higher than that of 2,4‐decadienal. The CVs calculated based on 2,4‐decadienal were higher than those of 2‐decenal, although differences between them were not statistically significant at low levels. Accordingly, the sensitivity of the measurement and the estimated CV content were dependent on the type of standard considered. Triphenylphosphine (TP) exerted a statistically significant effect on the CVs of the soybean oil, unless the peroxide content of the oil sample was very low or much higher than the amount of added TP. The addition of TP to the frying oil was not necessary because the conditions of the CV test did not lead to the production of excess carbonyl compounds caused by the degradation of peroxides.

Evaluation of a simple and sensitive sensory method for measuring rancidity in soybean oils

The purpose of this study was to evaluate the efficacy of the 2 Alternative Forced Choice (2-AFC) sensory method in detecting rancidity in soybean oils. Additionally, correlations between the physico-chemical quality and the sensory attributes of edible soybean oils were studied. Soybean oil samples from four different plants were analyzed for their fatty acid profile, Free fatty acid (FFA), Anisidine Value (AV), Peroxide Value (PV), Conjugated Dienes (CD), Colour, Rancimat and TOTOX. The sensory attributes of the oils were measured using The American Oil Chemists Society (AOCS) sensory method and additionally, rancidity was assessed using the 2-AFC sensory method. All oil samples fit the quality control criteria for edible soybean oil. The 2-AFC The purpose of this study was to evaluate the efficacy of the 2 Alternative Forced Choice (2-AFC) sensory method in detecting rancidity in soybean oils. Additionally, correlations between the physico-chemical quality and the sensory attributes of edible soybean oils were studied. Soybean oil samples from four different plants were analyzed for their fatty acid profile, Free fatty acid (FFA), Anisidine Value (AV), Peroxide Value (PV), Conjugated Dienes (CD), Colour, Rancimat and TOTOX. The sensory attributes of the oils were measured using The American Oil Chemists Society (AOCS) sensory method and additionally, rancidity was assessed using the 2-AFC sensory method. All oil samples fit the quality control criteria for edible soybean oil. The 2-AFC method was sensitive to small differences in rancidity. Differences in anisidine value and Rancimat were correlated to the difference in rancidity (d') among oils

Flow-injection methylene blue-based spectrophotometric method for the determination of peroxide values in edible oils

A flow-injection method for measuring the peroxide value (PV, mequiv. O 2 kg −1) in edible oils is described. The technique is based on spectrophotometric monitoring at 660 nm of methylene blue (MB), generated from leucomethylene blue (LMB) oxidation with peroxides present in oil samples. After being optimized, the method was validated in terms of linearity, precision sensitivity and recovery. Linear calibration graph was obtained in the range 0.1–5 mequiv. O 2 kg −1, with a detection limit ( S/ N = 3) of 0.014 mequiv. O 2 kg −1. The precision of the method (R.S.D., n = 9) for within and between-days is better than 1.5% and 2.2%, respectively at 0.4 mequiv. O 2 kg −1. The method was applied successfully to the determination of PV in six edible oil samples, and compared to the classical official method. Using the linear regression test, Student's t-test and variance ratio F-test, there was no significant difference between the compared methods. The proposed method is accurate, simple, cheap and could be used to control edible oil rancidity with a high sample throughputs (30 samples h −1).

Anti‐radical power gives insight into early lipid oxidation events during frying

AbstractThe aim of this research was to use anti‐radical power (ARP) to study early lipid oxidation events during frying. The 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH•) test was used to determine the ARP. As oil does not dissolve completely in methanol, which is generally used for the DPPH• test, butanol was used instead. Changing the solvent did not influence the value of the ARP. The decrease of the ARP highly correlated with the increase of the peroxide value for soybean oil heated at 110 °C (R2 = 0.99). Sensory analysis showed that rancidity of soybean oil and frying oil, heated at 180 °C, was perceived before the ARP decreased. Once the oil was perceived as rancid, the intensity of rancidity did not change significantly upon further heating. The ARP of soybean oil was found to decrease faster at 110 °C than at 180 °C, suggesting different mechanisms of radical formation. The total polar compounds of frying oil in which French fries were fried did not differ significantly from frying oil that was heated alone. However, frying of French fries caused more hydrolysis of the oil, while the ARP decreased faster when the oil was heated alone. Copyright © 2006 Society of Chemical Industry

Compositional and Sensory Comparisons between Normal- and High-Oleic Peanuts

The high-oleic-acid trait improves the oxidative stability of peanuts (Arachis hypogaea L.) and their products. The explicit effect of the trait on sensory quality, particularly on off-flavors associated with oil rancidity, has not been well documented. To assess the effect of the trait on off-flavors, data from two independent databases were analyzed to compare sensory quality and composition in normal- versus high-oleic peanut genotypes. In data collected using a sensory panel in the Department of Food Science at North Carolina State University, there were small differences between near-isogenic lines for intensities of the roasted peanut, astringent, over-roast, and nutty attributes, with the high-oleic lines exhibiting slightly greater intensities of those attributes. There were no differences for off-flavors such as fruity, painty, stale, moldy, or petroleum. In data collected from the multistate Uniform Peanut Performance Test and evaluated by a panel in the USDA-ARS Market Quality and Handling Research Unit (MQHRU) at Raleigh, NC, there were differences in chemical composition associated with the high-oleic trait, including differences in oil content, tocopherols, and carbohydrates in addition to the expected differences in fatty acid contents. There were small decreases in the intensities of the sensory attributes cardboard and painty associated with the high-oleic trait in the MQHRU data when all high-oleic lines were compared with all normal-oleic lines. Comparison of the near-isogenic pair NC 7 and N00090ol showed differences in oil and glucose contents, but not in sensory attributes. The high-oleic trait does not appear to have a major impact on sensory quality on average, although there were individual instances in which the trait was associated with shifts in sensory attribute intensities that may be perceptible to consumers.

Evaluation of Heat-deteriorated Oils. I. TLC-FID Method for Determining Polar Compounds Content

A simple and accurate method for determining polar compound (PC) content in heat-deteriorated oils was developed, since universal standards are necessary for assessing thermal rancidity in frying oil quality control. At present, the means used for standards differ according to countries. For instance, in Japan the upper limit of acid value (AV) is 2.5 and carbonyl value (CV) is 50, in the United States free fatty acid (FFA) content is less than 2.0%, and in EU countries PC content is below about 25% and smoke point is above 170°C. JOCS official method to determine PC content by column chromatography is complicated and time consuming, and thus in this study JOCS method was modified by TLC-FID, using soybean oil samples prepared under various heating conditions. TLC-FID method with hexane / diethyl ether (87/13 v/v) as developing solvent provided excellent linearity of y=1.02x + 0.53 with correlation coefficient (R2) of 0.9960, where y and x express PC content determined by JOCS and TLC-FID methods, respectively. Thermal rancidity of soybean oil samples heated under different air bubbling conditions was measured with PC content by TLC-FID, AV, CV, and anisidine value. PC content was clearly shown to be reflected in rancidity of sample oils with heating time. Correlation between PC content and AV displayed excellent linearity with correlation coefficient (R2) of 0.9310. The present TLC-FID method determining PC content may thus be concluded an effective means for evaluating the quality of heat-deteriorated oils.

Citrus peel extract – A natural source of antioxidant

Citrus peel extract as a natural source of antioxidant was evaluated during 6 months storage of refined corn oil at 25 and 45 °C. Extracts of citrus peel were prepared by refluxing the dried ground peel with ethanol, methanol, acetone, hexane, diethyl ether and dichloromethane. Maximum amount of citrus peel extract was obtained with methanol. Antioxidant activity of methanolic extract was assessed by measuring free fatty acid (FFA) content peroxide value (POV) and iodine value (IV) during 6 months storage of refined corn oil at 25 and 45 °C. After 6 months of storage at 45 °C, corn oil containing 1600 and 2000 ppm citrus peel extract, showed lower FFA contents (1.5% and 1.0%), and POVs (8.38 and 7.0 meq kg −1) and higher iodine values (81, 89) than the control sample (FFA 17.0% POV 101 meq kg −1 IV 47). Refined corn oil containing 200 ppm of butylated hydroxy anisole (BHA) and butylated hydroxy toluene (BHT) showed FFA contents of 2.0% and 1.8%, POVs 17.0 and 12.7 meq kg −1 and IVs 84 and 87, respectively, after 6 months of storage at 45 °C. These results show that methanolic extract of citrus exhibited very strong antioxidant activity, which was almost equal to synthetic antioxidants (BHA and BHA). Therefore, the use of citrus peel extract is recommended as a natural antioxidant to suppress development of rancidity in oils and fats.

NUTRIENTS AND BIOCHEMISTRY OF NUTS IN DIFFERENT CONSUMPTION TYPES IN TURKEY

Nuts have high nutritive value and have different kinds of consumption properties in some food treatments such as salting, roasting, vacuum packaging or under inert gas. The quality of nuts are affected by biochemical changes such as oxidation and rancidity in nut oils, which contain polyunsaturated fatty acids. In this research, the nutrients, proximate composition and minerals, and biochemical changes in nuts were determined according to consumption types: hazelnuts (Corylus avelana L.), peanuts (Arachis hypogaea L.) and pistachio nuts (Pistacia vera L.). In Turkey, the consumption types of nuts depend on some food treatments such as roasting, salting, vacuum packaging and eating habits such as shelled, unshelled, unroasted and even fresh nuts or combinations of them. The storage periods of the samples which were almost 2 weeks in the market were very short. The protein contents of groundnuts were higher than hazelnuts and pistachio nuts. The fat contents of pistachio nuts were higher than hazelnut and groundnut samples. The total carbohydrate levels of hazelnuts and groundnuts were almost same and were higher than pistachio nuts. Moisture content is the highest for hazelnuts and pistachio nuts, respectively. The mean mineral contents of these nuts are (mg/100 g) Na (0.98, 1.30, 9.38), Mg (140.09, 173.47, 116.90), K (514.01, 558.22, 642.07), Ca (106.16, 67.29, 171.69), Cu (0.99, 0.75, 0.75), Zn (2.96, 0.44, 2.77) and Fe (0.56, 0.41, 0.58). The biochemical changes in nuts were examined in nut oils, iodine value, free fatty acids, anisidine value, UV absorption (λ: 233, 262, 268 and 272 nm). The results had shown that important quality changes did not occur as explained in the conditions of the research samples. Also, positive correlation among the nut samples had not been found. It was established that the changes in the biochemical values depend on the polyunsaturated fatty acids composition of nut oil. The results of the analysis of the levels of oxidation had exhibited differences among the nut oil samples because of polyunsaturated fatty acids ratios rather than because of the different kinds of consuming properties.

Natural Antioxidants Preserve the Lipid Oxidative Stability of Minimally Processed Avocado Purée

ABSTRACT: Lipid oxidation is one of the major phenomena that limit the shelf‐life of avocado products. The effects of adding 100 ppma‐tocopherol, 200 ppm ascorbic acid, and 200 ppm ethylenediaminetetraacetic acid (EDTA) on he stability of the lipidic fraction of minimally processed avocado purées were evaluated throughout storage. α tocopherol, followed by ascorbic acid, reduced oil rancidity processes during storage. Peroxide formation was minimal when a‐tocopherol was added to avocado pulp, prolonging the induction stage of oils for at least 12 wk. When preserved in vacuum, iodine and specific extinction coefficient at 270 nm (k270) values were more stable, with changes of 5.87 g I2/100 g oil and 0.237, respectively, during 24 wk. On the other hand, EDTA was not shown to be effective in preserving the stability of the lipid fraction of avocado preserved by combined methods.

Operation planning in the rectification of essential oils

This paper proposes a methodology that uses a recently developed shortcut model to represent each individual separation task, for planning the operation of a batch distillation column. For a given column and recycle policy, optimization of the recoveries of two key components at each separation renders the set of optimal reflux ratios and advances in each separation. The methodology is specially expedite for systems with a large number of components and whose performance can be upgraded by recycling intermediate cuts, as is the case in the rectification of essential oils. We illustrate the methodology by planning the rectification of crude orange oil to produce an oil essence depleted from light terpenes, which are responsible for rancidity of oils.

The effect of applying a pipe-joint lubricant to connect ductile iron pipe on off-flavors in drinking water distribution systems

This study was used to help define the contribution to taste and odor problems caused by the application of a pipe-joint lubricant to connect ductile iron pipe in drinking water distribution systems. Tyton Joint Lubricant (TJL) was studied. The lubricant produced odors that are continually oxidized by chlorine or oxygen. The mechanism of oxidative rancidity, one of the major causes of food spoilage is the apparent mechanism of oxidation. The odors produced by the lubricant were characterized by a Flavor Profile Analysis (FPA) panel as well as GC/MS and Sensory GC analysis. The most common odors perceived in the TJL water samples for the first six days were waxy/oily and soapy odors with a rancid oil, odor note. The waxy/oily and soapy odors decreased with time in the chlorine medium as the rancid oily odor note increased. Numerous aldehydes, ketones, alcohols and borneol compounds, produced from the lubricants, were tentatively identified and linked to the odors perceived by the FPA panel.

Monitoring the storage stability of RBD palm olein using the electronic nose

Storage stability of RBD palm olein was monitored using a surface acoustic wave (SAW) sensor-based electronic nose. Fatty acid composition, iodine value (IV), peroxide value (PV), and free fatty acid content (FFA) analyses were used to determine the quality of the oils and to compliment the electronic nose data. A descriptive test was carried out by sensory analysis with ten trained panellists. The results from the electronic nose showed significant difference between fresh oil and rancid oil. High resolution olfactory imaging, called VaporPrint TM, was shown to be particularly useful for assessing oil quality in its entirety. A high correlation was observed between electronic nose responses and chemical test data, as well as sensory evaluation score, by using Pearson's correlation. It can be concluded that the SAW sensor based electronic nose may be utilized as an analytical tool to follow the progress of oxidation and breakdown of vegetable oil.

Production of high quality castile soap from high rancid olive oil

Non-edible olive oil, characterized by high acid and peroxide values as well as deep in color and unpleasant odor, was used to produce a fine castile soap (soap sample no. 1). Semi-fine virgin olive oil was also used to produce the standard castile soap (soap sample no. 2). The obtained results illustrated that the unpleasant odor was disappeared in soap no. 1 compared to the standard soap (weakly like oil). Also, there were remarkable that no high differences were observed in all physical and chemical properties (appearance, smooth surface, erosion from hand-washing, consistency, moisture content, total fatty acids, free alkali and salt content) in the two fresh soap samples. Whilst, the color in soap sample no. 1 was fuscous green color compared to the standard soap (which was white to pale yellow). Soap samples were stored on a shelf at room temperature for 6 months showed some changes in their chemical properties. On the other hand, physical properties of the above two samples were improved after the storage period (6 months) where their structures became very firm with high lather volume and rates of their erosions from hand-washing were retrenched except, the color in soap sample no. 1 was not improved which was dark green color. Therefore, the present study recommend to use non-edible olive oil as unusually fatty material to produce a fine castile soap (high smooth surface, fairly lather and high glossy appearance) as an alternative to edible olive oil (which is very expensive) and also to reduce the cost of castile soap manufacturing.