Changes In Oxidative Stability Research Articles

Differential scanning calorimetry as a tool to assess the oxidation state of cold-pressed oils during shelf-life

AbstractCold-pressed oils are highly prone to the peroxidation process, which causes a rapid decline in quality. Thus, there is a need to develop instrumental methods instead of conventional chemical analysis consuming large quantities of harmful chemicals. Differential scanning calorimetry (DSC) is a valuable analytical tool for assessing the oxidative stability of oils. Cold-pressed flaxseed, camelina and hemp seed oils from different cultivars, which had been stored for six months in room conditions under natural light exposure, were tested. Chemical methods for measuring changes in oxidative stability during storage of oils included determination of peroxide value (PV), p-Anisidine value (p-AV), total oxidation value (TOTOX) value and acid value (AV). Parameters like oxidation induction time (OIT) in isothermal mode (120, 140 °C) and onset temperature (Ton) in non-isothermal mode (heating rate 2, 5 °C/min) were established from DSC curves. Data for OIT and Ton plotted against time showed a strong, significant (p ≤ 0.05) descending trend for all oils. However, flaxseed and hempseed oils revealed a more rapid deterioration during storage compared to camelina seed oils. All DSC results showed promising repeatability of the oxidative characteristics for three types of cold-pressed oils, regardless of their origins in different cultivars. However, the most suitable for monitoring the deteriorative changes in oils during storage was the isothermal test carried out at a temperature of 120 °C, for which the correlations with chemical indicators (PV, p-AV, TOTOX) were highly significant (p ≤ 0.0001). Linear discriminant analysis (LDA) based on the DSC results revealed, that the first discriminating function significantly separated the fresh oils from stored oils. The study showed that, based on a starting point defined for fresh oils, the DSC technique can be used to effectively and ecologically monitor the deterioration of oils by oxidation, instead of harmful chemical analyses.

Changes in oxidative stability of rapeseed oils under microwave irradiation: The crucial role of polar bioactive components

To investigate the effects of microwaves on the quality of oils, 33 different rapeseed oil samples were treated with microwave heating (MH) and conventional heating (CH) at the same heating curve. The oxidation indices showed that, compared to CH, the rapeseed oil samples exhibited varying degrees of oxidation under MH, which could be divided into three categories. Analysis of the bioactive components of rapeseed oils indicated strong negative correlations between the degree of oxidation and the polyphenol, tocopherol, phytosterol, and squalene contents. Moreover, oxidation positively correlated with the degree of unsaturation and water content, but did not relate to the contents of chlorophylls and β-carotene. Principal component analysis (PCA) and hierarchical clustering analysis (HCA) indicated that the oxidation process of oils subjected to MH may be primarily influenced by water, γ-tocopherol, and polyphenols, possibility due to their polar structure/moiety or antioxidant nature. Overall, this study indicated that some oils are suitable for MH because of the oxidative resistance originating from their bioactive components.

The Effect of Dietary Dry Distilled Rose Petals or Dihydroquercetin Supplementation on the Oxidative Stability and Quality of Lamb Muscles and Fat

The study's objective was to determine the changes in oxidative stability of m. Longissimus dorsi, m. Semimembranosus and perirenal adipose tissue from lambs fed a diet supplemented by 7.5 mg dihydroquercetin/kg life wight/d or 545 mg dry distilled rose petals (DDRP)/kg life wight/d.The experiments were performed with 30 male lambs aged 65 days. They were divided into three groups of 10 animals fed 50 days ad libitum: the control group (with ground alfalfa + granulated compound feed) and two experimental ones (with the same diet + phytonutrients). Samples stored 7 days at 0-4°C were examined. After 7 d of storage in both muscles, the addition of 545 mg DDRP/kg life wight/d contributed to the reduction of α-aminoacidic nitrogen with approximately 0.5 mg Leu/g and the FFA with 0.5-2%. The addition of 7.5 mg dihydroquercetin contributed to the reduction of TBARS with 0.14-0.21 mg MDA/kg, the total color difference, and a slight increase in the share of the MUFA more pronounced in m. Longissimus dorsi. The reduction of aerobic plate count and total yeasts and molds count were determined too. Further studies with higher doses of phytonutrient’s supplementation are needed to determine if it will provoke a more pronounced oxidative stability.

Changes in oxidative stability and phytochemical contents of microencapsulated wheat germ oil during accelerated storage

Wheat germ oil (WGO) contains high amounts of tocopherols, phytosterols, and carotenoids. The high amount of unsaturated fatty acid content of WGO increases sensitivity to oxidative degradation. This study aimed to assess the efficacy of WGO microencapsulation in buttermilk (BM) to prevent oxidative degradation. A mixture consisting of WGO:BM (1:2) and water (60%) was emulsified by a high-pressure homogenizer, and then freeze-dried. Both bulk and microencapsulated WGO samples were kept at 60 °C for 24 days to evaluate oxidative stability, changes in contents of tocopherol, phytosterol, and carotenoid. Peroxide and p-anisidine values of microencapsulated WGO were significantly lower than the bulk WGO throughout the storage days (p < 0.05). Similarly, tocopherols, phytosterols, and carotenoid contents degraded less in microencapsulated WGO than those in bulk WGO (p < 0.05). Improved stability of the sensitive compounds in WGO through microencapsulation can extend the potential use of WGO's as a functional ingredient in food formulations.

Collaborative effect of fat reduction and α-tocopherol incorporation on oxidative stability in beef sausages

This study focuses on the changes in oxidative stability and sensory properties of reduced fat and/or α-tocopherol incorporated sausages during storage at 4°C for 3 months. In order to examine these changes, sausages were formulated with 20% fat and 20% fat+200 ppm α-tocopherol, coded as C20A0 and C20A1, respectively. Sausages formulated with 10% fat (C10A0) and 10% fat+200 ppm α-tocopherol (C10A0) were low fat sausages. Reduction of fat by 50% or adding α-tocopherol initially increased the peroxide values of sausages, but at the end of storage, conversely, reduction of fat and α-tocopherol addition retarded lipid peroxidation as well as malonaldehyde generation (p<0.05). The highest thiobarbituric acid reactive substance values were recorded for C20A0 sausages initially and at the end of the storage (p<0.05). Even though thiobarbituric acid reactive substance values of sausages with 20% fat were higher, the initial rancid taste of all sausages were similar at month 0, but differences in the rancid taste of sausages began to be revealed with increasing storage time (p<0.05). No significant differences were found in the general acceptability of all the sausages during the 3-month storage period (p>0.05).

Changes in oxidative stability and protein profile of flaxseeds resulting from thermal pre-treatment.

The oxidative stability of oilseeds is crucial for their technological/nutritional quality and shelf life. This research aimed to evaluate the effect of thermal pre-treatment (steaming and roasting under various time/temperature conditions) on flaxseed oil and protein stability. The monitoring of changes in oil oxidation in situ and protein profiles (SDS-PAGE) and analysis of the antiradical activity of ethanolic and aqueous fractions were included in the study. Flaxseed stability during storage was considerably affected by thermal pre-treatment conditions. Dynamics of oil oxidation was accelerated at 160 °C and 180 °C but slowed at 200 °C. Influence of pre-treatment conditions on the antiradical activity of the aqueous fraction was clearly observed and no effect concerning the ethanolic fraction was found. The most significant changes in protein profile of 200 °C-roasted flaxseed were found with the observed disappearance of 19 kDa protein. A treatment-dependent decrease in the 13 kDa protein was also detected. Based on the aqueous extract protein profiles, roasting conditions were found to be crucial for protein extractability. The study has broadened knowledge of the consequences of flaxseed thermal treatment. The deterioration of flaxseed oil oxidative stability is shown. The changes of 19 and 13 kDa proteins suggest their sensitivity to thermally induced aggregation and/or cross-link. © 2018 Society of Chemical Industry.

Effect of roasting on physico-chemical properties, antioxidant capacity, and oxidative stability of wheat germ oil

Wheat germ oil (WGO) is rich in highly concentrated nutrients, especially vitamin E and polyunsaturated fatty acids. In this study, changes in oxidative stability, bioactive components, volatile compounds, and antioxidant capacity of WGO extracted from wheat germ roasted at 180 °C for 0–20 min were investigated. In general, antioxidant capacity and oxidative stability of WGO increased with roasting. Compared to oil from unroasted wheat germ, oil from wheat germ roasted for 20 min demonstrated the highest total phenolics, but a slight reduction in total tocopherols and β-carotenoids content. Fatty acid profiles were not affected, whereas hydroxymethylfrufural (HMF) content increased significantly, suggested the extent of Maillard reaction increased significantly with roasting. Among volatiles, esters such as n-butyl acrylate and acids such as hexanoic acid prevailed in WGO from unroasted wheat germ. However, after roasting, the levels of these compounds decreased or disappeared and furfurans, pyranes, pyrazines, and pyrroles with high odor activity became the most abundant.

Biodiesel blend (B10) treated with a multifunctional additive (biocide) under simulated stored conditions: a field and lab scale monitoring

Microbial contamination of stored diesel/biodiesel fuel over time and the consequent changes in the fuel chemical composition is of serious concern. The use of biocides has also been shown to be an effective strategy to address this challenge but in some countries like Brazil, no products have been released and licensed to be used yet. The aim of this study was to evaluate the effectiveness of a multifunctional additive containing a biocide (i.e., 3,3-methylenebis(5-methyloxazolidine); in short MBO) as 50% of its formulation (AM-MBO50) for controlling microbial contamination under simulated storage conditions. The experiment was conducted under two conditions: at lab-scale and in the field (real-world condition). In both experiments, B10 blend treated with AM-MBO50 as well as the untreated fuel blend were stored under simulated storage conditions for 35 and 90 d, respectively. The additive effectiveness and the changes in oxidative stability, water content, density, and viscosity were monitored. The results showed that the evaluated product was an efficient treatment to control microbial growth at 1000 ppm concentration, presenting a biocide action after 7 d in the tanks containing the treated fuel and with a low microbial challenge and a biostatic action in the tanks containing the treated fuel and with a high microbial challenge. In the tanks containing the fuel treated with AM-MBO50, no adhesion of biofilm in the oil/water interface nor meaningful changes in the quality parameters such as oxidative stability, water content, viscosity, and density were observed after 90 d. A comparison between the lab-scale and field results showed that the application conditions determined at the lab-scale can only serve as preliminary guidance for the field (real-world) application and that they should be monitored and adjusted for each specific system.

Pigmented rice oil: Changes in oxidative stability and bioactive compounds during storage of whole grains

This study evaluated the effects of storage temperature on the oxidative stability and bioactive compounds present in oil extracted from whole rice grains. Whole rice grains (brown, black, and red pericarps) were stored at temperatures of 16, 24, 32, and 40 °C for 6 months. Oil extraction was carried out on samples at the beginning, and after 6 months, of storage. Oil acidity, extinction coefficients (K232 and K270), fatty acid profiles, γ-oryzanol, carotenoid, and tocopherol contents were evaluated. Oil extracted from rice grains with black pericarps showed the highest concentrations of γ-oryzanol, carotenoids, and tocopherols, followed by oil extracted from grains with brown and red pericarps. A storage temperature of 16 °C was effective for maintaining good oil quality and bioactive compounds extracted from the oil when stored for 6 months. Practical application The consumption of nutraceutical and bioactive foods has gained importance in recent years, highlighting the use of whole pigmented rice grains. A great amount of the rice grains used in the world's food industry are stored for periods up to 12 months prior to their use. This study presents the changes in the quality of oil and bioactive compounds present in the oil extracted from rice grain with brown, black and red pericarp as a function of storage conditions during long-term and may help food industries to elucidate the differences in quality of oil and bioactive compounds in rice oil. The proper handling of post-harvest rice grains is important to increase economic gains for the processing industries and maintain the quality of oil for human consumption and industrial use.

Microwave pretreatment effects on the changes in seeds microstructure, chemical composition and oxidative stability of rapeseed oil

Abstract The purpose of the present study was to investigate the effect of microwave (MV) irradiation on the microstructure of rape seeds, recovery of oil, and to examine changes in oxidative stability, composition of FA, and contents of tocochromanols and canolol of rapeseed oil. Rapeseeds (Brassica napus) of two varieties, Kana and Bakara, adjusted to moisture contents of 7 and 9%, undergone MV pretreatment under 800 W for 0, 3, and 7 min, prior to oil extraction by cold-press. Tocochromanol contents were differently affected by the MV pretreatment of rapeseed prior to pressing. Depending on the adjusted seed moisture content both individual and total tocopherol contents increased to the maximum at different microwave times. The amount of canolol detected in cold-pressed oil samples ranged from 16.34 to 16.97 μg/g of oil; this was increased to 926.42 and 821.86 μg/g by MV pretreatment for 7 min (at 7% moisture level). The oxidative stability prolongation from 3.64 to 4.09 h up to 11.52–12.75 h was observed. Regarding the FA composition of the oils, no significant changes (P > 0.05) in the fatty acid composition occurred during seeds MV pretreatment.

In Vivo Oxidative Stability Changes of Highly Cross-Linked Polyethylene Bearings: An Ex Vivo Investigation

The development of highly cross-linked UHMWPEs focused on stabilizing radiation-induced free radicals as the sole precursor to oxidative degradation. However, secondary in vivo oxidation mechanisms have been discovered. After a preliminary post-operative analysis, we subjected highly cross-linked retrievals with 1–4years in vivo durations and never-implanted controls to accelerated aging to predict the extent to which their oxidative stability was compromised in vivo. Lipid absorption, oxidation, and hydroperoxides were measured using infrared spectroscopy. Gravimetric swelling was used to measure cross-link density. After aging, all retrievals, except vitamin E-stabilized components, regardless of initial lipid levels or oxidation, showed significant oxidative degradation, demonstrated by subsurface oxidative peaks, increased hydroperoxides and decreased cross-link density, compared to their post-operative material properties and never-implanted counterparts, confirming oxidative stability changes.

Effect of Immersed Herbs on the Oxidative Stability of Edible Oils

The improvement of the oxidative stability of edible oils is in the focus of scientific and consumer interest. In the present work the effect of immersion of herbs in edible oils was performed and changes in oxidative stability were measured. Sage and oregano were chosen as herbs and linseed oil, corn germ oil as well as walnut oil as lipid media. Immersion parameters were 3%, 5%, and 7% (w/w) herb/oil, duration: 10 days, temperature: 30°C. Oxidative stability was measured by Rancimat test and FRAP analysis. Results showed that the oxidative stability of the highly sensitive oils -such as linseed and walnut oil- was successfully improved by immersion of herbs. Corn germ oil, which contains a high amount of tocopherols, became similarly more stable, however, only moderately.

Degradation of selected nutrients in sunflower oils during long-term storage

We investigated the influence of long-term storage (10 months) at an average ambient temperature of 25&amp;deg;C on oxidative stability of sunflower oils (made in Slovakia, Czech Republic, Austria, and Hungary) and their nutrients. Chemical properties were determined and changes in oxidative stability monitored. Oil samples were collected and analysed for the content of tocopherols and &amp;beta;-carotene. Degradation of nutrients depends on chemical composition of oils and storage conditions. It was found that the concentration of both antioxidants decreased in all the samples with the increase in storage time. According to the results, losses of total tocopherols and &amp;beta;-carotene in refined sunflower oils stored in transparent 5-l PET bottles and exposed to daylight at ambient temperature were found to be 52&amp;ndash;64% and 63&amp;ndash;65%, respectively. The country of origin had no statistically significant impact on the oxidative stability of stored sunflower oils. &amp;nbsp;

Comparison of the Rancimat and the ACL Instrument for Measuring the Oxidative Stability of Corn Oil

AbstractA comparison was undertaken between two machines that utilise accelerated methods to measure oxidative stability: the Rancimat (Metrohm, Switzerland) and the single channel chemiluminescence instrument (ACL Instruments, Switzerland). The results from the machines showed good correlation for the measurement of the oxidation induction time of corn oil. For the ACL Instrument, the effect of the sample holder material (aluminium or borosilicate glass) was also investigated and clear differences were noted. Finally, a stability study was carried out over a period of 6 months, with corn oil, stored in the dark at three temperatures: ~4, ~27, ~40 °C and it was observed that it was possible to track subtle changes in oxidative stability using chemiluminescence.

Changes in oxidative stability, antioxidant capacity and phytochemical composition of Pistacia terebinthus oil with roasting

The effect of roasting on oxidative stability, antioxidant capacity and the content of antioxidant phytochemicals in Pistacia terebinthus oil was investigated. Oils were extracted from P. terebinthus fruits roasted at 180°C for 0–40min. Roasting was found to cause an increase in the passage of phenolic compounds to the oil whereas the level of tocopherols, lutein and β-carotene was decreased. Antioxidant capacity and oxidative stability of P. terebinthus oil increased with roasting. As an indicator of the presence of Maillard reaction products in oil, hydroxymethylfurfural (HMF) level and colour intensity was measured and found to increase with increasing roasting time. Fatty acid composition was not affected significantly by roasting.

Roasting‐Related Changes in Oxidative Stability and Antioxidant Capacity of Apricot Kernel Oil

AbstractApricot kernels were roasted for various lengths of time (0–30 min) at 180 °C and changes in the oxidative stability, antioxidant capacity, color, as well as the level of tocopherols and fatty acids of the apricot kernel oil (AKO) were monitored. While the level of tocopherols decreased, the oxidative stability and antioxidant capacity of AKO increased with roasting, probably due to the formation of antioxidative Maillard reaction products (MRPs) during the roasting. Medium roasted samples (15–20 min) were found to be more resistant to oxidative deterioration. The oil from the 30‐min roasted sample was more susceptible to oxidation compared to the oil from the 20‐min roasted sample in most of the stability tests. Relatively shorter roasting periods (5–10 min) also led to a decrease in oxidative stability in comparison to the unroasted sample. Brownish color and antiradical activity increased with roasting and the highest values were measured in the 30 min roasted sample.

Oxidative stability and tocopherol content of refined sunflower oil during long-term storage in different commercial packagings

The study was undertaken to monitor the changes in oxidative stability and �-tocopherol content of refined sunflower oil during 12 months of storage at room temperature in different commercial packagings: Tetra brick, polyethylene terephthalate (PET) bottles and polyethylene (PE) canisters. The results showed significant influence of packaging type on the oxidative stability of oil. The largest changes were determined in oil packed in PE canisters (volume 5 l), where the peroxide values (PV) after 12 months were 9.34 and 10.46 mmol kg –1 , while the lowest increase in PV were 1.05 and 1.67 mmol kg –1 in Tetra brick packaging. The highest increase in specific absorbances was also noticed for oil packed in PE canister. It came to loss of tocopherol during storage in accordance with the degree of oil oxidation. In oil packed in Tetra brick 6.52 and 8.14% losses of tocopherol (compared to the initial value) were found, while the losses in canister were found to be 14.18 and 17.88%. The results of Schaal-oven test also indicated decrease of oxidative stability during storage in accordance with protective properties of packagings and packing conditions.

Loss in tocopherols and oxidative stability during the frying of frozen cassava chips

The present study was aimed at verifying tocopherols losses and oxidative stability changes in vegetable oils used in discontinuous frying. The frying of frozen cassava chips was carried out in a household electric frying pan, where the oil was heated to a temperature of 180°C for 25 hours, with fresh oil replacement. The results obtained from the analytical determinations were submitted to variance analysis, in a factorial scheme, using a completely randomized design, making it possible to determine the influence of the type of oil and frying times on changes in the oil. The data show that the smallest changes occur in palm oil, which is more saturated. For sunflower and cottonseed oils, which are more unsaturated, there was a clear decrease in both tocopherol concentration and oxidative stability.

Effect of olive fruit freezing on oxidative stability of virgin olive oil

AbstractSeveral studies have suggested that the phenolic fraction plays an important role during storage and therefore in the shelf life of virgin olive oil. This investigation examines the effect of freezing olives (–18 °C) before processing into oil on the transfer of the phenolic compounds into the subsequent oil, and the consequential changes in oxidative stability. Oil samples obtained from frozen olives (24 h at –18 °C), crushed with and without preliminary thawing, were compared to a control sample; both oils were obtained using a two‐phase low‐scale mill. The oxidative stability in different samples was assessed in terms of primary and secondary oxidation products as measured by peroxide values and oxidative stability index times, respectively. The quality of the oil samples was also checked through the percentage of free acidity and the phenolic content. Phenols were determined by both spectrophotometric assays (total phenols and o‐diphenols) and HPLC‐DAD/MSD. The antiradical capacity of the phenolic fraction was determined by DPPH and ABTS spectrophotometric tests. These analyses showed that thawing of olives before oil extraction led to a significant loss of oxidative stability and phenols; in contrast, samples obtained from frozen olives that were not thawed before crushing showed qualitative characteristics similar to control samples.

Microwave roasting effects on the physico‐chemical composition and oxidative stability of sunflower seed oil

AbstractThe purpose of the present study was to explore the influences of microwave heating on the composition of sunflower seeds and to extend our knowledge concerning the changes in oxidative stability, distribution of FA, and contents of tocopherols of sunflower seed oil. Microwaved sunflower seeds (Helianthus annuus L.) of two varieties, KL‐39 and FH‐330, were extracted using n‐hexane. Roasting decreased the oil content of the seeds significantly (P&lt;0.05). The oilseed residue analysis revealed no changes in the contents of fiber, ash, and protein that were attributable to the roasting. Analysis of the extracted oils demonstrated a significant increase in FFA, p‐anisidine, saponification, conjugated diene, conjugated triene, density, and color values for roasting periods of 10 and 15 min. The iodine values of the oils were remarkably decreased. A significant (P&lt;0.05) decrease in the amounts of tocopherol constituents of the microwaved sunflower oils also was found. However, after 15 min of roasting, the amount of α‐tocopherol homologs was still over 76 and 81% of the original levels for the KL‐39 and FH‐330 varieties, respectively. In the same time period, the level of σ‐tocopherol fell to zero. Regarding the FA composition of the extracted oils, microwave heating increased oleic acid 16–42% and decreased linoleic acid 17–19%, but palmitic and stearic acid contents were not affected significantly (P&lt;0.05).