Cholesterol Oxidation Products Concentration Research Articles

Current Knowledge about Oxysterols: A Review.

For years food consumers have been warned that a cholesterol-rich diet may result in atherosclerosis. It is also well known that consumption of large amounts of phytosterols decreases concentration of low-density lipoproteins (LDLs) in blood (LDLs are regarded a key risk factor in development of cardiovascular diseases). However, no scientific evidence has unambiguously proved any direct connection between amount of consumed cholesterol and LDL level in blood. On the other hand, concentration of cholesterol oxidation products, oxysterols, seems to be indeed relevant; for example, they significantly impact appearance of atherosclerotic lesions (plaques). Phytosterols (like sitosterol or campasterol) decrease LDL level in blood, but on the other hand products of their oxidation are toxic. Therefore, it is worth to know influence of phytosterols on living organisms, processes which lead to their formation, and their levels in popular foodstuffs. This paper is an attempt to review literature data on the above aspects, as well as on impact on living organisms of oxidation products of popular sterols.

Formation of cholesterol oxidation products (COPs) and loss of cholesterol in fresh egg pasta as a function of thermal treatment processing

The aim of this paper was the quantification of cholesterol loss and of its oxidation products in fresh egg pasta submitted to different thermal treatments. COPs were analysed by LC-MS/MS. The results showed that the COP concentration increased with increasing heating severity (expressed as F 100/10 value) from 66.44μg/g in the raw pasta up to 117.9μg/g after 120min at the reference temperature of 100°C; under the same processing conditions, the cholesterol loss reached 75%. This study revealed that 7-ketocholesterol (7-keto) is the main COP found and showed a linear correlation between its concentration and (i) total COP amount (r2=0.981; p<0.05), (ii) TBARS value (r2=0.969; p<0.05) and (iii) heating time expressed as a logarithm of F 100/10 value (r2=0.999 e p<0.01). The total amount of COPs found in the product was very low when compared to literature values reported for dried egg pasta and did not exceed 0.32mg/kg.

Effect of mustard on lipid oxidation in model pork meat product

The effect of ground mustard seed on the formation of cholesterol oxidation products (COPs) and malondialdehyde was evaluated by comparing their concentration in fresh and stored cooked model pork meat product prepared with addition of two levels of mustard seed and without this flavoring. The sensory quality of product was also determined using quantitative descriptive analysis. Obtained results pointed out that the addition of mustard seed to the composition of cooked model meat products decreased TBARS values. The concentration of cholesterol oxides in model meat product samples was between 5.14 and 30.42 µg/100 g product during 12 days of chilling storage. The results showed that a low amount (0.5%) of ground mustard seed was effective in inhibiting the formation of oxysterols. The highest effectiveness of mustard seed was observed in case of 7‐ketocholesterol and 7β‐hydroxycholesterol formation. The results of sensory evaluation indicated that mustard seed at the level of 0.2 and 0.5% of model pork products had positive effects on their sensory qualities. The lower concentration of COPs in the investigated cooked meat product with mustard seed addition at 1 day since the production may be connected with the presence of phenolic compounds generated during heat‐treatment of meat product such as canolol.Practical application: Oxidation processes are one of the major problems encountered in meat processing and storage. The addition of natural antioxidants is a major way to inhibit oxidation processes in meat products. Mustard seeds are excellent source of phenolic compounds, which have been reported to show good antioxidant activity. The results of this study suggest that incorporation of ground mustard into cooked meat product can improve lipid stability and functional value for consumers. Therefore, mustard seed can serve as an ingredient in developing healthy meat products.

Thermo-oxidation of cholesterol: Effect of the unsaturation degree of the lipid matrix

The influence of the unsaturation degree of different triacylglycerols (tristearin, triolein, trilinolein and trilinolenin) on cholesterol oxidation at 180°C, was evaluated. Cholesterol degraded faster when heated alone than in the presence of triacylglycerols; moreover, the more unsaturated the matrix, the slower the degradation of cholesterol. Both cholesterol and triacylglycerols degradation fit a first order kinetic model (R2>0.9), except for the tristearin sample. Cholesterol oxidation products (COPs) and peroxides were formed during the heating treatment. The presence of any type of lipid matrix postponed and decreased the maximum concentration of both oxidation parameters. Maximum total COPs concentrations were achieved at 20min in neat cholesterol, 120min in tristearin and triolein and 180min in polyunsaturated matrix samples. 7-Ketocholesterol was the main COP in most cases during the whole heating treatment. Both the presence of triacylglycerols and their unsaturation degree inhibited cholesterol thermooxidation at 180°C.

Red wine prevents the postprandial increase in plasma cholesterol oxidation products: a pilot study

Moderate wine consumption has been shown to lower cardiovascular risk. One of the mechanisms could involve the control of postprandial hyperlipaemia, a well-defined risk factor for atherosclerosis, reasonably by reducing the absorption of lipid oxidised species from the meal. The objective of the present study was to investigate whether wine consumption with the meal is able to reduce the postprandial increase in plasma lipid hydroperoxides and cholesterol oxidation products, in human subjects. In two different study sessions, twelve healthy volunteers consumed the same test meal rich in oxidised and oxidisable lipids (a double cheeseburger), with 300ml of water (control) or with 300ml of red wine (wine). The postprandial plasma concentration of cholesterol oxidation products was measured by GC-MS. The control meal induced a significant increase in the plasma concentration of lipid hydroperoxides and of two cholesterol oxidation products, 7-β-hydroxycholesterol and 7-ketocholesterol. The postprandial increase in lipid hydroperoxides and cholesterol oxidation products was fully prevented by wine when consumed with the meal. In conclusion, the present study provides evidence that consumption of wine with the meal could prevent the postprandial increase in plasma cholesterol oxidation products.

Correlation between serum content of the main COPs (cholesterol oxidation products) from autoxidation and cardiovascular risk factors

Risk factors for cardiovascular disease (CVD) have been proven to be associated with an increased oxidative stress. Several studies have considered cholesterol oxidation products (COPs) as specific in vivo markers of oxidative stress. The aim of this study was to investigate the association between the levels of COPs derived from autoxidation processes and established cardiovascular risk factors, comparing the levels of serum COPs in subjects with or without showing values out of the reference ranges. It was a cross-sectional study in which 88 subjects were recruited and individual and total COPs from autoxidation origin was analyzed in serum by GC-MS. The simultaneous correlation of COPs with different CVD risk factors have been analyzed. A great variability of total COPs concentrations were found. Subjects presented total COPs values from 0.091 to 2.052 μg/mL. Total COPs were significantly higher (p < 0.05) in patients with hypertriglycerolemia, hypertension, diabetes and overweight/ obesity status compared to those subjects who did not present those CVD risk factors. Moreover, 7α and 7β hydroxycholesterol and 7-ketocholesterol were significantly higher (p < 0.05) in patients with hypertension and diabetes. No significant differences in total COPs were found between patients with and without hypercholesterolemia. The obtained results showed that the analyzed COPs correlate well with at least 4 out of 6 risk factors of development of CVD.

Inhibition of Serum Cholesterol Oxidation by Dietary Vitamin C and Selenium Intake in High Fat Fed Rats

Cholesterol oxidation products (COPs) have been considered as specific in vivo markers of oxidative stress. In this study, an increased oxidative status was induced in Wistar rats by feeding them a high-fat diet (cafeteria diet). Another group of animals received the same diet supplemented with a combination of two different antioxidants, ascorbic acid (100 mg/kg rat/day) and sodium selenite (200 microg/kg rat/day) and a third group fed on a control diet. Total and individual COPs analysis of the different diets showed no differences among them. At the end of the experimental trial, rats were sacrificed and serum cholesterol, triglycerides and COPs were measured. None of the diets induced changes in rats body weight, total cholesterol and triglycerides levels. Serum total COPs in rats fed on the high-fat diet were 1.01 microg/ml, two times the amount of the control rats (0.47 microg/ml). When dietary antioxidant supplementation was given, serum total COPs concentration (0.44 microg/ml) showed the same levels than those of the rats on control diet. 7beta-hydroxycholesterol, formed non-enzymatically via cholesterol peroxidation in the presence of reactive oxygen species, showed slightly lower values in the antioxidant-supplemented animals compared to the control ones. This study confirms the importance of dietary antioxidants as protective factors against the formation of oxysterols.

Concentrations of cholesterol oxidation products in raw, heat-processed and frozen-stored meat of broiler chickens fed diets differing in the type of fat and vitamin E concentrations

The present study was performed to investigate the effect of dietary fat and vitamin E on concentrations of cholesterol oxidation products (COP) in broiler muscle. A total of 144 1-d-old broiler chicks were fed diets with either palm oil, soyabean oil or linseed oil and vitamin E concentrations of 20, 40 or 200 mg/kg for 35 d. COP concentrations were analysed in raw, heat-processed (180 degrees C, 20 min) and frozen-stored (-20 degrees C, 6 months) breast and thigh muscles. COP concentrations were influenced by dietary vitamin E concentration, dietary fat, treatment and type of muscle (P<0.001). Increasing the dietary vitamin E concentration generally reduced the concentration of COP. This effect was strongest in broilers fed linseed oil and weakest in broilers fed palm oil; the effect of vitamin E was also stronger in heated muscles than in raw or frozen-stored muscles. Moreover, the concentration of COP in thigh muscle was more strongly influenced by dietary vitamin E than that in breast muscle. COP concentrations in muscles were on average highest in broilers fed linseed oil and lowest in broilers fed palm oil, but the effect of the dietary fat also depended on the vitamin E concentration, the treatment and the type of muscle. In conclusion, our study shows that dietary fat and vitamin E influence the concentrations of total COP in broiler muscle. However, the effects of these factors were not only influenced by interactions between each other, but also depended on the treatment of the muscle and the type of muscle.

Oxidised cholesterol in milk and dairy products

Cholesterol is found in animal foods. It can be oxidised in various ways and cholesterol oxidation products (COPs) are formed. Such products are often found in animal foods including dairy products. Recently published results suggest that the contents of COPs in milk and dairy products is very small and does not confirm the results of earlier studies. A higher concentration of COPs can be found only in processed dairy products exposed to harsh storage conditions where the impact of oxygen and light or oxygen and low water activity are concomitant.

Kinetic Studies of Cholesterol Oxidation as Inhibited by Stearylamine during Heating

The formation of cholesterol oxidation products (COPs) during heating in the presence of stearylamine at 140 degrees C was analyzed by high-performance liquid chromatography (HPLC) and kinetically studied by use of nonlinear regression models. Results indicated that the COPs concentration increased with increasing heating time, and stearylamine was shown to reduce both oxidation and degradation rates of cholesterol. Without stearylamine, the highest rate constant (per hour) was observed for epoxidation (545.4), followed by free radical chain reaction (251.0), reduction (147.3), dehydration (95.8), triol dehydrogenation (4.7), degradation (0.34), triol formation (0.31), and dehydrogenation (0.13). With stearylamine, the epoxidation and free radical chain reaction rates could be reduced by about 800- and 3.4-fold, respectively, and triol formation during oxidation could be completely inhibited. In addition, the reactions for reduction, dehydration, degradation, and dehydrogenation could proceed slower in the presence of stearylamine. The kinetic model developed in this study can be used to predict the inhibition of COPs formation by stearylamine during heating of cholesterol.

Photoxidation of cholesterol and lipids of turkey meat during storage under commercial retail conditions

Photoxidation of cholesterol and lipids of raw turkey patties packed in vessels with transparent shrink film was studied during storage at 4 °C under commercial retail conditions. Two different storage periods were applied: a 3-day storage and a 11-day storage. When meat was stored in the dark at 4 °C, the maximum peroxide number was reached after 5 days and the maximum concentration of cholesterol oxidation products was attained only after 7 days. Turkey meat exposed to the white fluorescent light (under a daylight lamp) showed a maximum COPs concentration and peroxide value after just 1 day of storage (12 h effective light exposure). A lamp with low emission in the blue band (warm-tone lamp) was useful for lowering peroxidation and cholesterol oxidation, thus being a suitable solution for the exhibition of meat products in supermarkets or meat processing industries.

Absorption of Cholesterol Oxidation Products from Ordinary Foodstuff in Humans

Background: Information on the absorption of cholesterol oxidation products (COP) from ordinary foodstuff in humans is scarce. Methods: Five healthy young men were offered a salami- and Parmesan-containing meal naturally rich in COP. Plasma and lipoprotein COP concentrations were measured over the following 9 h. Results: The mean plasma free (nonesterified) COP concentration showed its maximal increase 3 and 5 h after meal consumption. In contrast, the raise in plasma total COP concentration began 6 h after the meal with a maximum at 8 h and was statistically significant for 7α- and 7β-hydroxycholesterol and 7-ketocholesterol. The increase in plasma total cholesterol concentration was comparable to that of total COP. Comparing the COP composition of the chylomicrons and the test meal, cholestanetriol, 7-ketocholesterol, and to a lesser extent cholesterol-α-epoxide were underrepresented in the chylomicrons as was the opposite for 7β-hydroxycholesterol. In very-low-density lipoprotein, a steady increase in the COP:cholesterol ratio was observed from 6 h on. Conclusion: COP from ordinary foodstuff were absorbed in the human intestinal tract but differences in the bioavailability of the single COP compounds were found.

Kinetic Model of the Cholesterol Oxidation during Heating

The formation of cholesterol oxidation products (COPs) during heating of cholesterol at 150 °C for up to 30 min was kinetically studied using nonlinear regression models. The various COPs were analyzed by TLC and HPLC. Results showed that the COPs concentration increased with increasing heating time, and the cholesterol loss reached 64.8% after 30 min of heating. In the early stage of oxidation, the highest rate constant (h-1) was observed for 7-hydroperoxycholesterol (7-OOH) formation, followed by epoxidation, dehydration, reduction, and dehydrogenation. The reactions for formation of 7-OOH (7α-OOH and 7β-OOH) and 5,6-epoxycholesterol (5,6α-EP and 5,6β-EP) fit the second-order, while the other reactions fit the first-order. The correlation coefficients (r2) for the reactions ranged from 0.79 to 0.99. The kinetic model developed in this study can be used to predict the concentration changes of COPs during the heating of cholesterol. Keywords: Cholesterol oxidation; heating; kinetic model; HPLC analysis

Effect of dietary administration of oil extracts from rosemary and sage on lipid oxidation in broiler meat

1. Oxidation of meat and membrane from broilers fed on a diet containing 500 mg/kg rosemary and sage extracts was compared to meat and membrane oxidation from broilers receiving a control diet (not enriched with antioxidants) and a diet enriched in alpha-tocopheryl acetate (200 mg/kg). 2. After 9 d of refrigerated storage, thiobarbituric acid reactive substances of white meat from broilers fed on the control and the alpha-tocopheryl acetate-enriched diets were 0.51 and 0.25 mg malonaldehyde/kg meat, respectively. Values for meat from broilers fed on the diets containing the rosemary and sage extracts were in the range 0.30 to 0.35 mg malonaldehyde/kg meat, significantly lower than those from birds fed on the control diet. A similar trend was observed in the dark meat but differences were not significant at 9 d of storage. Similar trends were observed in raw samples stored at- 20C for up to 4 months and in samples cooked at 70C and kept stored under refrigeration for up to 4 d. 3. The meat from broilers fed on the diet containing spice extracts had smaller concentrations of total cholesterol oxidation products (COPS) than meat from the control group (P<0.05). Supplemental alpha-tocopheryl acetate reduced the COPS concentrations to a greater extent than did spice extracts (P<0.05). 4. A similar trend was observed in microsomal fraction isolates, in which the rate of metmyoglobin/hydrogen peroxide-catalysed lipid peroxidation was lower in animals receiving spice extracts than in those fed on the basal diet.

Effect of dietary oat administration on lipid stability in broiler meat

1. The susceptibility to oxidation of meat from broilers receiving 200 g/kg oats in the diet was compared to the stability of meat from broilers receiving a control diet (10 mg/kg of alpha-tocopheryl acetate) and a diet enriched in alpha-tocopheryl acetate (200 mg/kg). 2. After 9 d of refrigerated storage thiobarbituric acid-reactive substances (TBARS) values in raw dark meat (thigh) were 0.51 and 0.19, respectively, for broilers fed on the control and the alpha-tocopheryl acetateenriched diets. Meat from broilers fed on the diet containing oats had a lower TBARS value than the control group (P 0.05), but higher than the group receiving the supplemented diet. The same trend was observed in white meat (breast). Similar effects were observed after the frozen storage of meats, although the antioxidant effect of oats was more evident (P 0.05) than in the raw meat. 3. Cholesterol oxidation products (COPS) in broiler meat were also influenced by the dietary regimen. COPS concentration in white and dark meat, respectively, from broilers fed on the oat diet were 43% and 32% lower than those in the control samples. 4. Supplemental alpha-tocopheryl acetate reduced COPS concentration by approximately 60%. The availability of natural antioxidants and their possible synergistic effects suggest an interesting way of improving meat stability.

Isolation of cholesterol oxidation products from animal fat using aminopropyl solid-phase extraction

Cholesterol oxidation products were separated from triglycerides and cholesterol in a single step on an aminopropyl solid-phase extraction column. The products were purified by subsequent transesterification and saponication, derivatized to trimethylsilyl ethers and analyzed by gas chromatography. Heated cholesterol-containing fat samples were autoxidized by bubbling air through them. When the flow-rate of air was set at 100 ml/min, the concentration of cholesterol oxidation products in the fat increased to a maximum after 1–2 h and then decreased to almost a zero level after 8 h. The concentration of cholesterol oxidation products in the fat increased over a similar time period, without reaching a maximum, when the flow-rate of air was decreased to 5 ml/min.

Cholesterol oxidation products in small sun-dried fish

Cholesterol oxidation products (COPs) in small sun-dried fish Spratelloides gracilis and Decapterus maruodsi were extracted, separated by thin-layer chromatography, and then quantified by capillary gas chromatography after trimethylsilylation. Peak identifications were confirmed by mass spectrometry. Four major COPs including 7α- and 7β-hydroxycholesterol, 7-ketocholesterol, and 5, 6α-epoxycholesterol, were identified in small sun-dried fish which were stored at ambient temperature for c. 3 months under air. The total concentration of COPs in small sun-dried fish ranged from 4·82 ppm to 65·7 ppm, with 7α-hydroxycholesterol appearing as the predominant product.

Quantification of Cholesterol Oxidation Products In Egg Yolk Powder Spray‐dried with Direct Heating

ABSTRACTA direct‐heated spray dryer with an evaporative capacity of up to 7 kg H2O/hr was used to identify processing conditions responsible for formation of cholesterol oxidation products (COPS) in spray‐dried egg yolk. Outlet air temperature and nitrogen oxides (NOx) in the combustion gases were the only conditions that affected COPS levels. At outlet temperature 150°C, total COPS concentrations in the spray‐dried product were 75 ppm at 5 ppm NOx and 213 ppm at 300 ppm NOx. In products dried at 75°C outlet temperature, total COPS concentrations were 21 ppm at 5 ppm NOx and 58 ppm at 300 ppm NOx. In general, individual COPS responded to outlet temperature and NOx in the same manner as total COPS.

Plasma Cholesterol Oxidation Products (Oxysterols) in Human Subjects Fed a Meal Rich in Oxysterols

ABSTRACTThere is no evidence whether humans absorb cholesterol oxidation products (COPS) from food sources. Therefore, (after‐meal) absorption of COPS in humans was studied following consumption of a powdered egg meal containing 30–90 ppm each of four different COPS. Both total plasma and plasma chylomicron COPS concentrations increased. By contrast, subjects consuming fresh eggs containing very low levels of the same four COPS (0–2 ppm) demonstrated no significant rise in plasma COPS. We concluded that the human subjects studied had the capacity to absorb COPS from food sources. The brief residence time of COPS observed in both chylomicrons and plasma suggested rapid transfer of COPS among lipoprotein fractions and/or clearance from plasma.