Effect of cooking and storage on lipid oxidation and development of cholesterol oxidation products in water buffalo meat

Buffalo meat was subjected to two cooking methods viz. broiling and pressure cooking and two storage procedures viz. refrigerated (4 °C) storage for six days and frozen (-10 °C) storage for 90 days. Changes in lipid oxidation and development of cholesterol oxidation products were studied in raw as well as cooked meat samples. Total lipid, phospholipid, cholesterol, free fatty acid, glycolipid and glyceride contents increased significantly on cooking of meat but did not show any significant changes during either refrigerated or frozen storage except for free fatty acid content which showed an increase. The TBA values also increased during storage but not to the extent of indicating rancidity. Cholesterol oxidation products separated by thin layer chromatography were: cholestanetriol, 7-α-hydroxycholesterol, 19-hydroxycholesterol, 7-ketocholesterol, cholesterol-α-epoxide, cholesterol-β-epoxide and an unidentified fraction. All these fractions, except for the unidentified fraction, increased on cooking and storage. The cholesterol-β-epoxide fraction was resistant to changes. Changes in broiled meat were more pronounced compared to pressure cooked meat. Frozen storage did not prevent the development of cholesterol oxidation products in buffalo meat.     

Effect of processing and storage on neutral lipids of buffalo meat

Three muscles viz. Triceps brachii (TB), Longissimus dorsi (LD) and Biceps femoris (BF) from different anatomical locations of adult male buffaloes were stored after broiling and pressure cooking under refrigerated (4°C) condition for 3, 6, 9 days and 30, 60, 90 days under frozen (-10°C) storage. At the end of each storage interval they were analysed for total lipids, cholesterol contents and glyceride fractions i.e. monoglycerides (MG), diglycerides (DG), and triglycerides (TG). Muscles differed significantly in total lipids as well as contents of all glyceride fractions. Muscle LD had significantly higher total lipid content than TB and BF. Muscles differed significantly in their esterfied cholesterol (EC) contents. Heat processing increased total lipids, cholesterol, MG, DG and TG contents of all the buffalo muscles studied. Total cholesterol contents remained unchanged during refrigerated and frozen storage. However, EC, MG, DG and TG contents declined during storage. The influence of anatomical locations on fatty acid composition of neutral lipids was observed. The ratio of unsaturated to saturated fatty acids increased due to cooking. A gradual decrease in mono- and polyunsaturated fatty acids was recorded during refrigerated and frozen storage.     

Wide-Bore Capillary Gas Chromatographic Method for Quantification of Cholesterol Oxidation Products in Egg Yolk Powder

A wide-bore capillary gas chromatographic (GC) method was developed for quantification of cholesterol oxidation products in egg yolk powder. Baseline separations were achieved between 7α- and 7β-hydroxycholesterol, cholesterol, cholesterol-5α,6α-epoxide, cholesterol-5β,6β-epoxide and 7-ketocholesterol chromatographed as the trimethylsilylated sterols. Excellent response linearity was obtained for each cholesterol oxidation product, permitting reliable quantification. Recoveries from freeze-dried egg yolk spiked with various levels of cholesterol oxidation products ranged from 78.2 to 95.1%. The coefficients of variation compared favorably to those for packed column GC methods.     

Quality characteristics of pork patties irradiated and stored in different packaging and storage conditions

Patties were made from pork loin, individually vacuum- or aerobic-packaged and stored either at 4 or -40°C. Refrigerated patties were irradiated at 0, 1.5, 3.0 or 4.5 kGy absorbed dose, and frozen ones were irradiated at 0, 2.5, 5.0, or 7.5 kGy. Samples were analyzed for lipid oxidation, volatile production and odor characteristics. Refrigerated samples were analyzed at 0, 1 and 2 weeks, and frozen ones after 0, 1.5 and 3 months of storage. With vacuum packaging, the lipid oxidation (TBARS) of both refrigerated and frozen patties was not influenced by irradiation and storage time except for the patties irradiated and refrigerated at 7.5 kGy. With refrigerated storage, panelists could detect irradiation odor at day 0, but not after 1 week at 4°C. With frozen storage, however, irradiation odor was detected even after 3 months of storage. With aerobic packaging, the TBARS of refrigerated pork patties increased with storage time. The TBARS of pork patties increased as irradiation dose increased at day 0, but the effect disappeared after 1 week at 4°C. Nonirradiated patties were preferred to the irradiated ones at day 0 because of the significant irradiation odor in the irradiated ones, but the off-odor disappeared after 1 week at 4°C. With frozen storage, patties irradiated at 7.5 kGy had higher TBARS than those irradiated at lower doses. Nonirradiated patties had higher preference scores than the irradiated ones for 1.5 months in frozen storage. Sulfur-containing compounds were responsible for most of the irradiation off-odor, but these volatilized quickly during storage under aerobic conditions. Overall, vacuum packaging was better than aerobic packaging for irradiation and subsequent storage of meat because it minimized oxidative changes in patties and produced minimal amounts of volatile compounds that might be responsible for irradiation off-odor during storage.     

High-Resolution NMR Detection of Cholesterol Oxides in Spray-Dried Egg Yolk

A new approach, alternative to currently available methods, for studying cholesterol oxidation in egg powder is reported. The quantitative analysis of cholesterol oxides was carried out by high-resolution proton nuclear magnetic resonance (¹H-NMR). The following oxides were isolated from spray-dried egg powder by rapid chromatographic procedures and detected by selecting “marker”¹H-NMR signals: 7-ke-tocholesterol, 7α-hydroxy-cholesterol, 7β-hydroxy-cholesterol, cholesterol-α-epoxide and cholesterol-β-epoxide. The quantified cholesterol derivatives ranged from 4.9 to 9.1 ppm with a detection limit of 0.3 ppm (5 μ.g from 16g of matrix). The main usefulness of the method should be in investigating intermediates and products due to chemical transformation of cholesterol during storage and heating of foodstuffs.     

Enzymatic Determination of Cholesterol Oxides

For measurement of the concentration of oxidised cholesterols in foodstuffs, a method was developed by adapting the well-known enzymatic determination of cholesterol. A linear correlation was found between the absorbance measured after enzymatic reaction and the concentrations of 7α-hydroxycholesterol, 7β-hydroxycholesterol, 7-ketocholesterol, cholesterol-5α, 6α-epoxide in the range 1–12 μg. The usefulness of this method was demonstrated by determination of the four cholesterol oxidation products separated by TLC from the non-saponifiable lipid fraction of 5-month-old whole-egg powder (stored under different conditions) and of biscuit enriched with egg powder. The main advantages of the combination of TLC and the enzymatic method, beyond its rapidity and sensitivity, are that the determination of cholesterol oxidation products can be carried out in parallel with many samples containing small amounts of oxidised cholesterols even in the presence of a large quantity of cholesterol.     

Changes in phospholipids of buffalo meat during processing and storage

Effect of broiling and pressure cooking as well as alterations during refrigerated (4°C) and frozen (-10°C) storage on the phospholipids of adult male buffalo muscles viz. Triceps brachii (TB), Longissimus dorsi (LD) and Biceps femoris (BF), i.e. from three different locations were studied. Muscles differed significatly in their total lipid and phospholipid content. Cooking methods significantly altered the total phospholipid content and its fractions. Storage period did not show any significant effect on total phospholipids during refrigerated and frozen storage, whereas certain phospholipid classes viz. lysophosphatidyl choline and lysophosphatidyl ethanolamine + sphingomyelin increased significantly and major phospholipid classes viz. phosphatidyl choline and phosphatidyl ethanolamine decreased significantly. The changes in phospholipid classes were similar both in refrigerated and frozen samples but relatively more pronounced in the former. Palmitic, stearic, oleic and linoleic acids were the four predominant fatty acids in the phospholipids of buffalo meat. The effects associated with the location of muscles were evident. Differences in fatty acid composition of individual muscles in response to heat processing were observed. Heat processing significantly increased the total saturates in TB and LD muscles while it decreased in BF. The total monounsaturated and total polyunsaturated fatty acids of phospholipids decreased during refrigerated and frozen storage indicated by a significant decreass in oleic, linoleic and arachidonic acids.     

Lipid and cholesterol oxidation in chicken meat are inhibited by sage but not by garlic

The effects of the addition of sage and garlic in chicken meat on lipid and cholesterol oxidation, having as prooxidant factors the addition of salt, thermal treatment, and frozen storage, were evaluated. The content of unsaturated fatty acids did not change in the presence of sage; on the contrary, with garlic, the content of these fatty acids decreased after cooking and storage. Hexanal and pentanal contents were lower in patties containing sage, and higher in those with garlic. The 7-ketocholesterol was the cholesterol oxide found in higher amount in raw chicken on day 0, while the formation of 7β- and 7α-hydroxycholesterol was verified only from day 30 on. Cooking and storage resulted in increase of total cholesterol oxides and decrease of α- and γ-tocopherol. Sage was effective in controlling lipid and cholesterol oxidation, minimizing the prooxidant effects of salt, cooking, and storage. However, garlic presented no effect as antioxidant and accelerated lipid oxidation. PRACTICAL APPLICATION: The addition of sage to chicken meat (0.1 g/100 g) is a good alternative to prevent and delay the formation of compounds derived from lipid oxidation that are responsible for off-flavors and loss of nutritional quality during long-term frozen storage. Care must be taken when using garlic to seasoning chicken meat products, such as hamburgers and meatballs, especially cooked or precooked due to its potential to promote lipid oxidation and consequently raising the risk of having the product rejected by the consumer.     

Cholesterol Oxidation Products in Some Muscle Foods

Cholesterol oxidation products were estimated in some meat products by capillary gas chromatography after trimethylsilylation. Peak identities were confirmed by mass spectrometry. Freeze-dried pork, stored in contact with air at 22°C for ca. 3 yr, revealed 7α- and 7β-hydroxycholesterol, 7-ketocholesterol, α- and β-epoxide and cholestane-triol. The total concentration of oxidation products reached almost half of the remaining cholesterol content with 7-ketocholesterol as the predominant species. Some oxidation products were noted at a few ppm levels in broiled beef steaks, but not in precooked beef products. As rancidity development advanced in comminuted and cooked meats during storage, the oxidation of cholesterol became apparent.     

Antioxidant Inhibition of Cholesterol Oxidation in a Spray-Dried Food System during Accelerated Storage

Spray-dried egg yolk was used to evaluate antioxidant inhibition of cholesterol oxidation during accelerated (CU⁺² and heat) storage. Liquid yolk was treated with equimolar amounts of BHA (0.01%, w/w of lipid), ascorbyl palmitate (0.023%), or a tocopherol blend (0.023%). Yolk batches were spray-dried, stored at 60 ± 2°C for up to 28 days, and analyzed for cholesterol oxidation products (COPS) using gas chroma-tography. COP levels generally increased during storage with 7-ketocholesterol predominant. Significant antioxidant effects were manifest in decreased levels of 7-ketocholesterol, 7α- and 7β-hydroxycholesterol; while cholestane-triol and cholesterol-5,6-epoxide levels were not affected. All antioxidants showed significant inhibitive effects relative to the control, and tocopherols were more effective than ascorbyl palmitate.     

Effect of dietary α-tocopherol supplementation and gamma-irradiation on α-tocopherol retention and lipid oxidation in cooked minced chicken

The effects of dietary α-tocopherol supplementation and gamma-irradiation on α-tocopherol retention and lipid oxidation in cooked minced chicken during refrigerated storage were studied. Minced breast and thigh meat from broilers fed diets supplemented with 100, 200 or 400 mg α-tocopheryl acetate/kg feed was irradiated at 2.5 or 4.0kGy. Cooked irradiated and unirradiated meat was stored at 4 °C for 5 days. α-Tocopherol concentrations increased with increasing dietary supplementation. Concentrations decreased during storage, but retention was not affected by irradiation. Lipid stability was determined by measuring the formation of thiobarbituric acid-reacting substances (TBARS) and cholesterol oxidation products (COPs) during storage. TBARS and COPs increased during storage and were reduced by increasing levels of dietary α-tocopheryl acetate supplementation. Irradiation accelerated TBARS formation during storage, but this was prevented by supplementation with 200 mg α-tocopheryl acetate/kg feed. Irradiation tended to increase COPs during storage, although no consistent effects were observed. In general supplementation with over 400 mg α-tocopheryl acetate/kg feed may be required to control cholesterol oxidation in minced chicken. The results suggest that, overall, irradiation had little effect on lipid stability in α-tocopherol-supplemented meat following cooking and storage.     

Evaluation of cholesterol and lipid oxidation in raw and cooked minced beef stored under oxygen-enriched atmosphere

Oxygen-enriched modified atmosphere packaging (MAP) represents an important means to stabilize meat colour but may lead to an increase in lipid oxidation, influencing the acceptability and safety of the product. In this work, the effect on cholesterol and lipid susceptibility to oxidation was investigated in commercial minced beef held under MAP (80% O(2)/20% CO(2)). Cholesterol oxidation products (COPs), peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) were determined, before and after pan frying, at 1, 8 and 15 days since packaging under refrigerated storage (3-4°C). 7α-Hydroxycholesterol, 7β-hydroxycholesterol and 7-ketocholesterol were the more abundant COPs identified. COPs significantly increased in raw beef during storage: after 1, 8 and 15 days since packaging COPs were at the levels of 10.4, 30.7 and 60.5μg/g of fat, respectively. Cooking did not affect cholesterol oxidation in freshly packaged minced beef but led to a rise in COPs amount with respect to raw muscle after 8 and 15 days of storage. The trend in cholesterol oxidation reflected the progressive increase in lipid peroxidation rate brought by MAP conditions.     

Effect of irradiation and packaging conditions after cooking on the formation of cholesterol and lipid oxidation products in meats during storage

The effect of irradiation and packaging conditions on the content of cholesterol oxidation products (COPs) and lipid oxidation in cooked turkey, beef, and pork during storage was studied. Ground turkey leg, beef, and pork were cooked, packaged either in oxygen-permeable or oxygen-impermeable bags, and irradiated at 0 or 4.5 kGy. Lipid oxidation and COPs were determined after 0 and 7 days of storage at 4°C. Packaging of cooked meat was more important than irradiation in developing COPs and lipid oxidation in cooked meats during storage. 7-Hydroxycholesterol, 7β-hydroxycholesterol, β-epoxide, and 7-ketocholesterol were among the major COPs formed in cooked turkey, beef, and pork after storage, and their amounts increased dramatically during the 7-day storage in aerobic conditions. Irradiation had no significant effect on the amounts of any of the COPs found in cooked turkey and beef, but increased (P<0.05) the amounts of - plus 7β-hydroxycholesterol, β-epoxide, 7-ketocholesterol, and total COPs in aerobically packaged cooked pork. The amounts of COPs and lipid oxidation products (TBARS) closely related to the proportion of polyunsaturated fatty acids in meat. The results indicated that the composition of fats in meat is important on the oxidation rates of lipids and cholesterol, and packaging is far more important than irradiation in the formation of COPs and lipid oxidation in cooked meat.     

Effect of frozen storage duration and cooking on physical and oxidative changes in M. Gastrocnemius pars interna and M. Iliofiburalis of Rhea americana

This study was conducted to evaluate the effect of frozen storage time (30, 60, 90 or 180 days) and cooking (100 °C, 30 min) on the physical characteristics and oxidative stability of M. Gastrocnemius pars interna (GN) and M. Iliofiburalis (IF) of rhea americana. Physical parameters measured included thawing and cooking loss, colour parameters (L*a*b*), while oxidation was assessed by determining the TBA-RS, carbonyl and aromatic amino acid content. Prolonged frozen storage of rhea meat decreased lightness (L*), yellowness (b*), and increased the discoloration parameter hue angle and redness a*. During storage, muscle IF was more prone to lipid and myoglobin oxidation than muscle GN. Cooking loss declined with the increase of storage time and was higher in GN than in IF muscle. With cooking, TBA-RS, carbonyl content, and aromatic amino acids (phenylalanine, tyrosine, and tryptophan) were highly affected, but the extent of oxidation ranged according to muscle and duration of frozen storage.     

Effect of different cooking methods on some lipid and protein components of hamburgers

The effects of different cooking methods on the lipid and protein fractions of hamburger were evaluated. The lipid component was subjected to the following analyses: peroxide value; p-anisidine; total and free fatty acids; cholesterol and its oxidation products (quantified as 7-ketocholesterol). Lysinoalanine (LAL), free amino acids and D-amino acids (D-AA) were also determined in the protein fraction. All results were compared with a raw control. No significant differences were found among the cooking treatments with respect to D-AA and LAL. The degree of proteolysis, lipolysis and lipid oxidation varied depending on the treatment conditions. Regarding cholesterol oxidation, the combination of roasting and microwave heating caused more oxidation than the other treatments. The raw meat, however, showed an advanced degree of oxidation (25.2 ppm of total 7-ketocholesterol/120 g ground meat).     

Effect of carnosine, salt and dietary vitamin E on the oxidative stability of chicken meat

The effect of carnosine on lipid and cholesterol oxidation in salted chicken thigh meat and its relationship to dietary α-tocopherol supplementation was examined. Broilers (Cobb 500) were fed diets with a basal (30 mg kg(-1)) or supplemental (200 mg kg(-1)) level of α-tocopheryl acetate for 6 weeks. Thigh meat patties were prepared with carnosine (1.5%), salt (1%) or salt plus carnosine. Salt accelerated lipid and cholesterol oxidation following cooking and refrigerated storage. However, carnosine inhibited lipid and cholesterol oxidation in salted patties. Dietary α-tocopherol supplementation also reduced the extent of lipid and cholesterol oxidation in salted patties. The combination of carnosine and dietary α-tocopherol resulted in the greatest lipid and cholesterol stability in salted meat.     

Effect of dietary α-tocopheryl acetate supplementation on α-tocopherol distribution in raw turkey muscles and its effect on the storage stability of cooked turkey meat

Day-old turkey chicks (n = 99) were divided at random into three groups (n = 33) and fed diets containing 20 (E20), 300 (E300) and 600 (E600) mg all-rac-α-tocopheryl acetate per kg feed per day for 21 weeks prior to slaughter. After slaughter, breasts and legs were removed and examined for α-tocopherol content. Breast muscle from birds fed the three diets was oven cooked, cooled, sliced and overwrapped. The oxidative and colour stability of the slices was examined. Mean α-tocopherol levels in turkey muscle were significantly (p < 0.05) higher in the E300 and E600 groups compared to the control group fed the E20 diet. α-Tocopherol levels in the E300 and E600 groups showed that concentrations in leg muscle were significantly (p <0.05) higher than in breast muscle. α-Tocopherol levels in leg and breast muscles from birds fed E20 and E600 diets decreased significantly (p < 0.05) during 12 months of frozen (-20 °C) storage. TBARS numbers for breast slices from all three dietary groups, cooked both 24 hr after slaughter and following frozen (-20 °C × 11 months) storage, increased during refrigerated (4 °C) display for 10 days. TBARS numbers for slices produced from meat previously held in frozen storage increased more rapidly than those for meat cooked following slaughter. In both cases, E300 and E600 diets significantly (p < 0.05) suppressed lipid oxidation compared to E20 samples. In general, Hunter a values for meat slices from turkeys fed the E300 and E600 diets were higher than those for meat slices from turkeys fed the E20 diet.     

Refrigerated shelf life of vacuum-packaged, previously frozen ostrich meat

Previously frozen ostrich meat was evaluated over 28 days to determine the refrigerated shelf life. Intact steaks and ground meat from three ostrich carcasses were vacuum-packaged, frozen to -40°C for 5 days, and stored in a 0°C walk-in cooler. Instrumental analysis of CIE L*a*b* values indicated that ostrich meat was very dark in color, initially and over time. Microbial growth stayed slightly below 1.0 × 10(7) CFU/g for up to 21 days of refrigerated storage. Sensorially evaluated color showed an increase (p <0.05) in darkness over time. Percentage of browning increased (p<0.05) over time from 1% initially to 55% for intact steaks and 75% for ground meat by 28 days. Sensory aroma scores significantly (p<0.05) changed over time, with unacceptable aroma occurring by 14 days. Previously frozen, vacuum-packaged ostrich meat stored under refrigerated conditions should be used within 10 days.     

Antioxidative activity of α-tocopherol in cooked and uncooked ground pork

The effect of α-tocopherol (0, 100, 200 ppm) on lipid oxidation either in cooked or uncooked ground pork was studied during aerobic storage at 4°C and -20°C. Lipid oxidation was measured using the 2-thiobarbituric acid (TBA) method and rancidity development was scored by a trained sensory panel. Alpha-tocopherol slowed the rate of oxidation in cooked ground pork stored at either 4°C or -20°C and uncooked samples refrigerated for extended periods of time (12 days). In cooked product stored at 4°C where oxidation development was intense and off-flavors were strong, panelists did not detect flavor differences due to treatments. But in cooked product stored at -20°C sensory results were consistent with TBA analysis. Pre-rigor grinding, known to induce a high pH and inhibit lipid oxidation in uncooked fresh pork, had no protective effect on lipid oxidation as measured by TBA values in cooked ground pork, regardless of storage condition. TBA numbers increased during storage of cooked product at 4°C with an increase in internal cooking temperature between 50°C and 80°C. Internal cooking temperatures of 70°C or higher induced a rapid rate of oxidation when stored at 4°C.     

DIETARY OILS AND TOCOPHEROL SUPPLEMENTATION ON CHOLESTEROL OXIDE FORMATION IN FREEZE-DRIED CHICKEN MEAT DURING STORAGE

The influence of dietary oils [fish (FO), flax (LO), palm (PO) and sunflower (SO) oil] and tocohperol supplementation on the oxidation of cholesterol and lipids of chicken meat was investigated. Lipid oxidation in chicken meat powders was determined by thiobarbituric acid reactive substances (TBARS) and cholesterol oxidation products were estimated by capillary gas chromatography (GC) after trimethylsilylation. Peak identities from GC were confirmed by mass spectrometry. Freeze-dried chicken meat powder, stored in contact with air at room temperature for four months showed the presence of 7α- and 7β-hydroxycholesterol, 7-ketocholesterol, α and β-epoxide, and cholestane-triol. Total cholesterol oxides contents significantly (P < 0.05) increased with storage. The amount of cholesterol oxides in the meat powder was the highest in FO and SO group, and lowest in PO group. Lipid and cholesterol oxidation were accelerated by the presence of long-chain PUFA. Lipid and cholesterol stability of chicken meat were improved by the dietary supplementation of tocopherol.