Search

Forty-eight 27-wk-old White Leghorn hens were assigned randomly to four diets containing 0, 1.25, 2.5, or 5.0% conjugated linoleic acid (CLA). Hens were fed the CLA diets for 2 wk before eggs were collected for the study. Classes of egg yolk lipids were separated, and fatty acid concentrations in total lipid, triglyceride (TG), phosphatidylethanolamine (PE), and phosphatidylcholine (PC) were analyzed to determine the incorporation of dietary CLA isomers into different classes of egg yolk lipids. The amounts of CLA incorporated into lipid, PC, PE, and TG of egg yolk were proportional to the levels of CLA in the diet. However, more CLA was incorporated in TG than in PC and PE. The incorporation rates of different CLA isomers into different classes of lipids also were significantly different: cis-9, trans-11 and cis-10, trans-12 CLA were deposited more in TG, but cis-11, trans-13 CLA deposition in TG was significantly less. There were large differences in the concentrations of cis-8, trans-10 CLA in PC and PE. The inclusion of CLA into the diet influenced the metabolism of polyunsaturated fatty acids. The contents of 5,8,11,14-eicosatetraenoic, 9,12-octadecadienoic, and 9,12,15-octadecatrienoic acids were decreased as dietary CLA increased. Three isomers of hexadecadienoic acid were found in egg yolk lipids from hens fed 5% dietary CLA. The detection of hexadecadienoic acid isomers in lipid indicates that the utilization of CLA as an energy source after the first round of beta-oxidation may be less favorable than that of 9,12-octadecadienoic acid.

Twenty-four, 79-wk-old White Leghorn hens were assigned randomly to three diets containing 0, 2.5, or 5.0% conjugated linoleic acid (CLA). The diets were fed for 4 wk to determine the effect of dietary CLA on quality characteristics of eggs. Eggs were collected daily and stored at 4 C for 1, 7, 21, or 49 d. At the designated times, the eggs were processed to evaluate water content, fatty acid composition, color, proportions and pH of yolk and albumen. Firmness of yolk after the eggs were hard-cooked was also determined. The proportions of myristic, palmitic, stearic, CLA (9-cis, 11-trans CLA and 10-trans, 12-cis CLA isomers), and unidentified fatty acids in egg yolk lipids were increased as dietary CLA increased, but those of palmitoleic, oleic, linoleic, linolenic, arachidonic, and docosahexaenoic acid were decreased. Duration of refrigeration increased the proportion of egg yolk but decreased the contents of albumen and yolk lipids after 21 d or longer of storage. Egg yolk pH increased as refrigeration time increased, regardless of dietary treatment, but the increase was greater in the eggs produced by hens fed the CLA diets. Albumen pH increased significantly after 7 d of storage but remained unchanged until 21 d and then decreased by 49 d. Dietary CLA had no effect on the pH of albumen until 49 d of storage. After 49 d storage, egg albumen pH from hens fed CLA diets was lower than that of albumen from hens fed the control diet. Yolk color was not influenced by the dietary CLA and storage, but the egg yolk surface from hens fed CLA diets sometimes had relatively dark color with light spots. Dietary CLA and storage of CLA eggs increased the firmness of hard-cooked egg yolk. The texture of yolks from hard-cooked CLA eggs was rubbery and elastic, and the yolks were more difficult to break using an Instron. It was speculated that the quality changes of CLA eggs were related to the increase of yolk water content, the movement of ions between yolk and albumen through yolk membrane, and the changes of egg yolk pH during storage.

A study was conducted to develop a solvent system that will clean egg yolk samples and concentrate cholesterol oxides effectively before analysis. Cholesterol oxide standards or lipid samples (0.2 g) loaded onto a silicic column were washed with a portion of Solvent I (hexane/diethyl ether, 9:1, vol/vol) and then with Solvent II. Four different Solvent II preparations (Solvent IIa, hexane:ethyl acetate = 4:1; Solvent IIb, hexane:ethyl acetate = 1:1; Solvent IIc, hexane:ethyl acetate:diethyl ether = 2:1:1; Solvent IId, hexane:ethyl acetate:diethyl ether = 4:1:2, vol/vol/vol) were prepared and the purification efficiencies of Solvent II solutions for neutral lipids, cholesterol, and phospholipids in the column were compared. Yield study using cholesterol oxide standards showed that one or more of the cholesterol oxide standards were eluted by the Solvent IIb and Solvent IIc, but Solvent IIa and Solvent IId did not elute any of the cholesterol oxides during washing. Egg samples prepared with Solvent IIa showed greater amount of cholesterol oxides than those prepared with Solvent IId, probably due to incomplete purifying of phospholipids and interference. However, the amounts of cholesterol oxides in cooked meat prepared with the two purification solvents were not different. Because egg yolk contains very large amounts of phospholipids and cholesterol compared with other foods, at least twice as much Solvent IIa as Solvent IId was required to properly clean egg yolk samples. It was concluded that purification solvents should be selected by sample types, and Solvent IId (hexane:ethyl acetate:diethyl ether = 4:1: 2) was superior to Solvent IIa (hexane:ethyl acetate = 4: 1) for egg yolk samples.

Pork sausages were prepared with lean pork meat, fat from different sources [backfat (BF), corn oil (CO) or flaxseed oil (FO); 10% of lean meat], NaCl (2%), and ice water (10%). The emulsified meat batters were stuffed into casings (3 cm in diameter) and cooked to an internal temperature of 72°C. Cooked sausages were sliced and vacuum- or aerobic-packaged individually. Sausages were irradiated at a 0, 2.5, or 4.5 kGy dose and stored in a 4°C refrigerator for 8 days. Aerobic-packaged, irradiated cooked sausages prepared with BF and FO showed higher Hunter L-values than nonirradiated controls at day 0, but the difference disappeared at day 8. Irradiation increased the Hunter a-value in vacuum-packaged cooked pork sausages regardless of the fat source used, and the increase of the Hunter a-value was dose-dependent. In contrast, the Hunter a-value decreased by irradiation in aerobic-packaged cooked pork sausages prepared with BF or FO. The Hunter a-value of cooked pork sausage with aerobic packaging was significantly reduced at day 8. Hunter b-values increased at Day 8 in irradiated cooked pork sausages except for the sausage prepared with CO at 2.5 kGy. Cooked pork sausages prepared with CO were lighter, and sausage prepared with FO was redder and more yellow (p

Longissimus dorsi muscle strips, approximately 20 mm long, 40 mm wide, and 5 mm thick (4 g), of pig were randomly placed in a single layer into labeled bags (four strips per bag) and packaged either aerobically or under vacuum. Samples in the bags were irradiated at 0, 5, or 10 kGy and stored at 4°C for 5 days. Lipid oxidation, the amount and identity of volatile components and sensory characteristics of raw pork strips were determined at 0 and 5 days of storage. Irradiated muscle strips produced more 2-thiobarbituric acid reactive substances (TBARS) than nonirradiated only in aerobic packaging during storage. Irradiation had no effect on the production of volatiles related to lipid oxidation, but produced a few sulfur-containing compounds not found in nonirradiated meat. This indicates that the major contributor of off-odor in irradiated meat is not lipid oxidation, but radiolytic breakdown of sulfur-containing amino acids. Many of the irradiation-dependent volatiles reduced to 50 to 25% levels during the 5-days storage under aerobic conditions. Irradiated muscle strips produced stronger irradiation odor than nonirradiated, but no irradiation dose or storage effect was found. Irradiation had no negative effect on the acceptance of meat, and approximately 70% of sensory panels characterized irradiation odor as barbecued-corn-like odor.

Mechanisms of superoxide.O2--generating systems on the pro-oxidant effect of iron from various sources were studied. Reaction mixtures were prepared with distilled water, oil emulsion, or meat homogenates. Free ionic iron (ferrous and ferric), ferritin and hemoglobin (Hb) were used as iron sources, and KO2 and xanthine oxidase (XOD) systems were used to produce .O2-. Thiobarbituric acid reactive substances (TBARS) values and iron contents of the reaction mixtures were determined. Ferric iron and ferritin, in the presence or absence of superoxide-generating systems, had no catalytic effect on the oxidation of oil emulsion but became pro-oxidants when reducing agent (ascorbate) was present. Ferrous iron and Hb had strong catalytic effects on the oxidation of oil emulsion as shown by TBARS values. Superoxide and H2O2, generated from superoxide-generating systems, oxidized ferrous iron and ascorbate, and lowered the pro-oxidant effect of ferrous iron in oil emulsion. Addition of ferric or ferrous iron increased but Hb did not have any effect on the TBARS values of raw meat homogenates. The reaction mechanisms of superoxide and the superoxide-generating systems on the prooxidant effect of various iron sources indicated that .O2- was a strong oxidizer rather than a reducing agent, and the antioxidant effect of XOD system in oil was caused by the oxidation of ferrous iron to the ferric form by .O2- and/or H2O2.

A study was conducted to determine the effect of egg size and the age and strain of hens on the content of egg solids. Eggs were obtained from commercial farms from four strains of hens with similar age groups and received diets formulated to contain the same dietary energy and protein levels across the strains within a farm. Eggs were collected on 2 different d when the flocks reached the average ages of 28, 55, 75, and 97 wk. The eggs collected form each farm were pooled and sorted by size. Each individual egg was used as a replicate for yolk:white ratio; however, five yolks, five whites, and five whole eggs from each strain at each age period were pooled, homogenized, and then used as a replicate to determine the solids contents of yolk, white, and whole eggs. The yolk:white ratio of eggs from 28-wk-old hens was the lowest, that from 55- and 78-wk-old hens was the highest, and that from 97-wk-old hens was intermediate; however, the solids content (percentage) of whole eggs increased with the age of the hens. The solids content of egg white was highest in eggs from 28-wk-old hens. The white solids content of extra large eggs was greater than that of medium eggs, and yolk solids increased with egg size; however, the solids of whole egg were not affected by egg size. The strain of hens had a significant effect on the solids of whole egg, white, and yolk; however, the strain effect on yolk:white ratio was not significant. The results showed that young (28-wk-old) and old birds (97-wk-old) produced eggs with low solids content and intermediate aged hens (55- to 78-wk-old) produced eggs with high solids content. Therefore, it may be more beneficial for egg producers and processors to use young (28-wk-old) and old birds (97-wk-old) for table egg production and birds of intermediate age (55- to 78-wk-old) for liquid egg production.

Two studies were conducted to determine 1) the effect of post-mortem time before chilling on hot boned prerigor breast muscle water-holding capacity (WHC), and 2) post-mortem temperature effect on sarcomere length and drip loss of uncooked breast, and shear force and WHC of turkey breast muscle that is hot-boned, marinated, and cooked. In Study 1, the turkey breast muscle was excised immediately after slaughter and chilled at 0 C. The effect of post-mortem time (15, 30, 45, 60, 90, and 120 min) before chilling on muscle pH, drip loss, and WHC (measured by homogenate cooking yield) was determined. In Study 2, hot boned prerigor breast slices were held at either 0 or 12 C and then at 3 h post-mortem stored at 2 C. Sarcomere length and drip loss of uncooked breast, and the shear force and WHC (measured by cooking yield) of cooked breast muscles with water, salt, and sodium tripolyphosphate were determined. Results indicated that pH on Day 1 post-mortem and cooking yield of water homogenates were not influenced by the post-mortem time before chilling. Drip losses increased as the post-mortem time before chilling was increased. Cooking yield of homogenate with water, salt, and sodium tripolyphosphate was decreased when breast muscle was chilled after 60 min post-mortem. Drip loss of breast was less at 0 C than at 12 C, but cooking yield and shear force were not affected by post-mortem chilling temperature. It was concluded that the post-mortem time before chilling has an influence on uncooked and cooked muscle WHC, but the differences found in uncooked muscle drip loss were not reflected in WHC or shear force of cooked muscle with water, salt, and sodium tripolyphosphate added.

Single Comb White Leghorn laying hens were fed diets high in oleic, linolenic, or linoleic acid prepared by incorporation of high oleic acid sunflower seed (HOAS), full-fat flax seed (FLAX), or regular high linoleic acid sunflower seed (HLAS), respectively, to investigate the effects of dietary fats on the fatty acid compositions of major lipid classes of chicken eggs. Egg production, Haugh units, specific gravity, and yolk total lipid content were measured. After 3 wk of feeding, the fatty acid compositions of yolk total lipids, triglycerides, phosphatidylcholine (PC), and phosphatidylethanolamine (PE) were measured by gas chromatography. Dietary treatments had no effect on egg production, Haugh units, specific gravity, or yolk total lipid content. Feeding HOAS increased yolk oleic acid by 17%, and the change was only in triglycerides. The increases of yolk linoleic and arachidonic acids upon HLAS feeding were distributed evenly among triglycerides and PC, with moderate effect in the PE fraction. The enrichment of linolenic acid in eggs from the FLAX regime was mainly in triglycerides. The longer chain n-3 fatty acids, such as eicosapentaenoic, dososapentaenoic, and docosahexaenoic acids, were deposited exclusively in phospholipids, particularly in PE. The contents of the longer chain n-3 fatty acids in PE were three to seven times those in PC, indicating a preferential incorporation of these fatty acids into PE.

The mechanisms and antioxidant activities of six natural phenolics against lipid oxidation induced by ultraviolet (UV) radiation or Fe 2+ were studied. An oil emulsion was pre- pared with flax oil and the thiobarbituric acid-reactive sub- stances (TBARS) method was used to determine lipid oxidation. The antioxidant activities of the six phenolics against UV-in- duced lipid oxidation were as follows: quercetin > rutin = caf- feic acid = ferulic acid = sesamol > catechin. The inhibitory concentrations (IC 50 ) showed that the effectiveness of these an- tioxidants against Fe 2+ -induced lipid oxidation was in the order quercetin (1.7 µM) > rutin (10.3 µM) > catechin (14.9 µM) > sesamol (18.5 µM) > caffeic acid (19 µM) > ferulic acid (>250 µM), and quercetin was more efficient than butylated hydroxy- toluene (BHT) (2.9 µM). Quercetin and rutin had absorption maxima at the UV-A (320-380 nm) region, while the other phe- nolics tested had absorption maxima near (catechin, 278 nm) or at the UV-B (280-320 nm) region. The stoichiometric ratios of quercetin, rutin, catechin, and caffeic acid to Fe 2+ were 3:1, 2:1, 1:1, and 1:1, respectively. Although free-radical scaveng- ing capability of antioxidants was the most critical, UV absorp- tion and/or Fe 2+ -chelation properties of natural phenolics also contributed significantly to the control of lipid oxidation in- duced by UV or Fe 2+ in oil systems. JAOCS 75, 1717-1721 (1998).

The concentrations of nitrate and nitrite in raw turkey breast meat and the microbial conversion of nitrate to nitrite in an uncured tumbled breast meat product were studied to assess their involvement in the formation of undesirable pinkness. Nitrate concentration in raw turkey breast meat ranged from 3.8 to 21 ppm and nitrite varied from 0 to .7 ppm. Microorganisms in the tumbled meat sample converted the nitrate to nitrite; 5.2 ppm of nitrite (NaNO2) were formed from 100 ppm of added nitrate (KNO3) during 40 h of storage at 4 C. It was concluded that if a high amount of nitrate and a long storage period were combined in tumbled turkey breast meat, the probability of the development of a pink color in the oven-roasted product would be very high.

Eight combinations of sodium chloride (0, 2.5%), sodium tripolyphosphate (0, .5%) and dextrose (0, 1%) were dissolved in phosphate buffer containing .5 mg myoglobin (Mb), hemoglobin (Hb), or cytochrome c per milliliter. These solutions were heated to 68 C, 74 C, 80 C, or 85 C to determine ingredient effects on the heat stability of purified Mb, Hb, and cytochrome c. Salt significantly decreased the heat stability of Mb at all temperatures studied, and Hb at 68 C and 74 C. However, salt significantly increased the heat stability of cytochrome c. Phosphate increased the heat stability of Mb but decreased that of cytochrome c due to a pH increase. Dextrose increased the heat stability of Hb at 68 C, and that of cytochrome c at 85 C.

Ground turkey breast meat treatments were prepared with 16 combinations of myoglobin (0, .4 mg/g meat), cytochrome c (0, .1 mg/g meat), salt (NaCl; 1, 2.5%), and sodium tripolyphosphate (0, .5%) before cooking to determine their effect on meat color, water extractable pigments, total pigment, and oxidation-reduction potential in cooked turkey breast meat Addition of myoglobin did not increase extractable pigment but significantly (P

Sixteen combinations of nitrite [0, 1, 10, 50 parts per million (ppm)], sodium chloride (0, 2%), and phosphate (0, .5%) were mixed with turkey breast meat before cooking to determine the main effects and interactions on color (redness, a; yellowness, b; lightness, L) value, nitrosoheme pigment, total pigment, and residual nitrite in oven-roasted turkey breast meat. Addition of 1 ppm nitrite caused a significant color change in oven-roasted turkey breast meat. By increasing nitrite level, a values, nitrosoheme pigment, total pigment, and residual nitrite significantly (P Sodium chloride increased a values (P A salt × phosphate interaction decreased L values at all nitrite levels except that of 10 ppm added nitrite, but significantly (P

Raw turkey breasts were aerobically or vacuum-packaged, irradiated with a linear accelerator, and frozen for 0, 1.5, or 3 mo. Lipid oxidation, volatiles, color values, gas production, and oxidation-reduction potential of the samples were determined. Irradiation produced off-odor volatiles associated with lipid oxidation and sulfur-volatiles; the off-odor was much higher in aerobic packaging. Volatiles increased with irradiation dose, aerobic packaging, and storage time. Irradiation increased stable pink color with both aerobic and vacuum-packaging. Irradiation increased the production of carbon monoxide (CO) and reducing property, indicating that CO-myoglobin could be responsible for the pink color. Lipid oxidation and color changes were not related in irradiated frozen turkey.