Irradiation effects on meat flavor: A review.

Irradiating fresh meat, even at low doses, can result in off-odors and flavors which have been described as rotten egg, bloody, fishy, barbecued corn, burnt, sulfur, metallic, alcohol or acetic acid. The odors vary with the type of meat, temperature during irradiation, oxygen exposure during and/or after the irradiation process, packaging and presence of antioxidative substances. Irradiation can induce formation of isooctane-soluble carbonyl compounds in the lipid fraction and low molecular weight, acid-soluble carbonyls in the protein fraction of meat. Increasing irradiation dose increases these compounds however, cooking reduces them. Among the volatile components, 1-heptene and 1-nonene are influenced most by irradiation dose, and aldehydes (propanal, pentanal, hexanal) are influenced most by packaging type (aerobic vs vacuum). Sulfur-containing volatiles formed from sulfur-containing compounds (primarily amino acids) also contribute to irradiation odor. Dimethyltrisulfide is one of the most potent off-odor compounds, contributing fishy, putrid odors, followed by bismethylthiomethane (sulfurous). Reducing the temperature during the irradiation process reduces the effects on odor/flavor because free radical generation and dispersion are reduced. Ultimately, radiolysis of water into free radical species (OH,H, H(3)0(+), e(aq)(-)) may be the initiators of both lipid oxidation breakdown products and sulfur-containing volatiles responsible for irradiation odor. Methods to decrease the detrimental effects of irradiation include oxygen exclusion (vacuum packaging), replacement with inert gases (nitrogen), addition of protective agents (antioxidants), and post-irradiation storage to allow flavor to return to near-normal levels (re-packaging or double packaging in oxygen permeable film).

Effects of carbon monoxide-modified atmosphere packaging and irradiation on E. coli K12 survival and raw beef quality.

The objective of this study was to evaluate the combined effects of irradiation and carbon monoxide in modified atmosphere packaging (CO-MAP) on total plate counts, Escherichia coli K12, color, and odor of fresh beef during refrigerated storage. Beef was packaged aerobically or in CO-MAP, and irradiated at 0, 0.5, 1.0, 1.5 or 2.0kGy then held at 4°C for 28days. Raw beef odor decreased and acid/sour, rancid and grassy odors increased starting on day 14. Initially, no difference existed for visual green color scores due to gas atmosphere. After 14days of storage, aerobically packaged beef was greener and less red than CO-MAP packaged beef. The a∗ value of CO-MAP packaged beef was higher than that of aerobically packaged beef. Red color of CO-MAP packaged samples decreased slightly in some irradiated samples after 14days of storage. On day 0 and thereafter, no coliforms were detect after irradiation at 1.5 or 2.0kGy regardless of packaging format. These findings suggest that CO-MAP could be used to preserve beef color irradiated at doses sufficient to reduce microbial loads to safe levels during 28days of storage.

Characterization of striping in fresh, enhanced pork loins.

To investigate the striping phenomenon in fresh, enhanced pork, a series of experiments were undertaken to identify possible causes of the problem. No one factor (individual brine components, brine pH, ingredient concentration, enhancement pressure, meat and brine pH, or enhancement level) was specifically identified, which could be used to reduce the severity of the striping problem. Furthermore, tumbling the product for 2h, did not reduce the amount of striping, indicating once striping has occurred, it is permanent. Evaluation of the striping pattern indicates that the stripes are formed not only at the needle injection site, but also follow the muscle fiber orientation. The use of darker pork provided more of a contrast when evaluating striping, thus exacerbating the perceived level of striping.

Effect of different dietary levels of natural-source vitamin E in grow-finish pigs on pork quality and shelf life.

Improving pork quality and shelf life is important in today's swine industry because higher levels of DDGS are incorporated into pig diets. Relatively high level of poly-unsaturated fatty acids (PUFA) in DDGS may increase pork susceptibility to lipid oxidation and thus reduce pork shelf life. Antioxidants such as vitamin E may delay the onset of pork lipid oxidation when used as an ingredient in the diet. This experiment examined carcass characteristics, meat quality, shelf life, and color stability in pork from pigs (n=150) fed five levels of a natural vitamin E (Nova-E) and one level of synthetic vitamin E. Natural vitamin E and synthetic vitamin E had no effect on carcass characteristics or meat quality. Increasing dietary natural vitamin E from 10 to 200mg/kg decreased lipid oxidation. Lipid oxidation of pork chops and ground pork was similar between pigs fed 40mg/kg and higher levels of natural vitamin E, indicating no additional benefits from supplementing beyond 40mg/kg natural vitamin E. Supplementing 200mg/kg synthetic vitamin E decreased pork lipid oxidation when compared to supplementing 10mg/kg natural vitamin E. High levels of natural vitamin E or synthetic vitamin E, however, did not prevent discoloration of loin chops. These data indicate that natural vitamin E was effective to help reduce lipid oxidation and the effective minimal level of dietary supplementation appeared to be 40mg/kg.

Effect of enhancement and ageing on flavor and volatile compounds in various beef muscles.

To identify and quantify selected flavor-active volatile compounds and relate them to sensory characteristics, the gluteus medius (round), rectus femoris (round), vastus lateralis (round), vatsus medialis (round), teres major (chuck), infraspinatus (chuck), complexus (chuck), serratus ventralis (chuck), psoas major (loin) and longissimus dorsi (loin) were removed from heifer carcasses, enhanced, vacuum packaged, aged for 7 or 14days, steaks were cut, vacuum packaged and frozen (48h). Flavor-active volatiles affected by enhancement and ageing in the various muscles included nonanal, 2,3-octanedione, pentanal, 3-hydroxy-2-butanone, 2-pentyl furan, 1-octen-3-ol, butanoic acid, pentanal and hexanoic acid, compounds often associated with lipid oxidation. Enhancement decreased hexanal and hexanoic acid. Ageing decreased butanoic acid. Pentanal content varied among muscles depending on enhancement and ageing. Livery off-flavor was positively correlated with pentanal, hexanal, 3-hydroxy-2-butanone and hexanoic acid. Rancid off-flavor was correlated with pentanal and with 2-pentyl furan but not with hexanal.

Effect of carbon monoxide in modified atmosphere packaging, storage time and endpoint cooking temperature on the internal color of enhanced pork.

The objective of this research was to evaluate the effects of gas atmosphere, refrigerated storage time, and endpoint temperature on internal cooked color of injection-enhanced pork chops. Enhanced chops were packaged in 0.36% CO/20.34% CO(2) (CO-MAP), 80% O(2)/20% CO(2) (HO-MAP), or PVC-overwrapped (PVC-OW; controls), stored at 4°C for 0, 12, 19 or 26 days, displayed for 2 days then cooked to six endpoint temperatures (54, 60, 63, 71, 77, and 82°C). L(∗), a(∗), and b(∗) values, hue angle and chroma were determined on the internal cut surface of cooked chops. Chops packaged in CO-MAP had the highest a(∗) values; a(∗) value began increasing on day 14. The lowest hue angles occurred in chops cooked to lower endpoint temperatures. Chops in CO-MAP had lower hue angles and higher chroma than those in HO-MAP and PVC-OW. Above 71°C, hue angle and chroma increased. Overall, CO-MAP packaged chops stored for longer time periods then cooked to lower endpoint temperatures appeared reddest. HO-MAP packaged chops were less red, did not change over time, and appeared more well done at lower endpoint temperatures than those in other gas atmospheres. CO-MAP packaged chops retained redness even after cooking at 82°C.

The effects of shelf-life enhancers on E. coli K12 survival in needle-injected, surface contaminated beef strip steaks enhanced using recycled solutions.

The objective of this study was to evaluate the efficacy of shelf-life enhancers (sodium lactate [SL] or sodium lactate+sodium diacetate [SLDA]) on limiting the growth of Escherichia coli K12 in needle-injecting surface-contaminated beef strip steaks with recycled enhancement solutions. Strip loins were injected to 10% over initial weight. SLDA was most effective in controlling bacterial growth followed by SL alone. The salt/phosphate combination in the enhancement solution was ineffective. SL decreased a(∗) (less red) and b(∗) values (less yellow) of the steaks compared to the salt/phosphate control. SLDA decreased L(∗) values compared to SL alone. SL and SLDA were equally effective in reducing purge loss from the steaks. Steaks enhanced with a "fresh" enhancement solution had higher a(∗) values (more red) and higher E. coli contamination levels than steaks enhanced with recycled solutions. Recycling did not affect L(∗) value, b(∗) value, or purge loss.

The effects of shelf-life enhancers on E. coli K12 survival in needle-injected, surface contaminated beef strip steaks enhanced using recycled solutions.

The objective of this study was to evaluate the efficacy of shelf-life enhancers (sodium lactate [SL] or sodium lactate + sodium diacetate [SLDA]) on limiting the growth of Escherichia coli K12 in needle-injecting surface-contaminated beef strip steaks with recycled enhancement solutions. Strip loins were injected to 10% over initial weight. SLDA was most effective in controlling bacterial growth followed by SL alone. The salt/phosphate combination in the enhancement solution was ineffective. SL decreased a(∗) (less red) and b(∗) values (less yellow) of the steaks compared to the salt/phosphate control. SLDA decreased L(∗) values compared to SL alone. SL and SLDA were equally effective in reducing purge loss from the steaks. Steaks enhanced with a "fresh" enhancement solution had higher a(∗) values (more red) and higher E. coli contamination levels than steaks enhanced with recycled solutions. Recycling did not affect L(∗) value, b(∗) value, or purge loss.

Instrumental evaluation of pH effects on ability of pork chops to bloom.

Color plays an important role in consumer purchase decisions of pork. For this reason, the objective of this study was to determine the usefulness of instrumental measures of bloom and bloom as a function of pH. Color was measured with two instruments on pork chops of varied ultimate pH (5.1-6.1) in a vacuum package and again after blooming. During bloom, Hunter a* increased while Minolta a values changed little. Bloom had no effect on either measure of lightness (L* or L). With bloom, Hunter Hue Angle decreased indicating an increase in red color, while Minolta Hue Angle measurement increased with bloom, implying a decrease in true red color. Although lightness was unaffected by bloom, pH had a significant effect on Hunter L* and Minolta L values. Increasing pH resulted in an increase of Hunter a*, but not Minolta a, in both unbloomed and bloomed chops. Hunter Hue Angle was consistently higher than Minolta Hue Angle regardless of bloom status or pH.

Antioxidant and modified atmosphere packaging prevention of discoloration in pork bones during retail display.

The objective of this study was to evaluate the ability of antioxidants to prevent discoloration in pork rib bones. Pork rib bones were removed from carcasses, frozen (-20°C, 24h), split lengthwise, exposed to antioxidant solutions (ascorbic acid, citric acid, propyl gallate or ascorbic/EDTA mix), packaged (modified atmosphere [80% O(2) and 20% CO(2)] or air), then displayed in a retail case at 4°C for 8days. Dark pigment formation was visually evaluated during the display period. Instrumental color was determined at the end of the 8-day display period. Visual bone discoloration increased over time for all treatments. After 2days of display, samples treated with propyl gallate were visually redder, less discolored and less green/black than samples treated with other antioxidants. After 8days of display, propyl gallate-treated samples had higher a* and b* values, as well as chroma (intensity). However, this difference was no longer large enough to be visually detected.

Effect of carbon monoxide and high oxygen modified atmosphere packaging and phosphate enhanced, case-ready pork chops.

The objective of this study was to evaluate the effects of CO-MAP compared to traditional high oxygen MAP (HiOx-MAP) packaging and enhanced with different phosphate on enhanced pork quality. Pork loins were enhanced to 10.5% over initial weight to contain 0.3% salt and 0.4% phosphate (either sodium tripolyphosphate [STP] or a blend of STP and sodium hexametaphosphate) on a finished weight basis. Chops were cut, packaged in atmospheres containing 0.4% CO/30.0% CO(2)/69.6% N(2) (CO-MAP) or 80% O(2)/20% CO(2) (HiOx-MAP), aged in the dark, then placed in a lighted retail display case for 48h. Chops packaged in CO-MAP were redder (higher Minolta a(∗) values) and darker (lower Minolta b(∗) values) than chops packaged in HiOx-MAP. Based on sensory scores, the CO-MAP chops were pinker than the HiOx chops after cooking. CO-MAP chops also experienced less purge loss than chops in HiOx-MAP. Results indicate that CO-MAP had no effect on flavor or consumer acceptability and only minimal effects on other characteristics.

Primary malignant melanoma of the common bile duct.

Biliary tract obstruction in a 30-year-old man was found to be caused by a malignant melanoma in the common bile duct. Melanin pigment was demonstrated by immunohistochemistry and electron microscopy. Extensive search for a primary malignant melanoma elsewhere was unsuccessful. No pigmented lesions had been removed previously. There were junctional changes in the mucosa of the common bile duct close to the tumor. The malignant melanoma in the common bile duct therefore is considered to be primary. Only one other case of primary malignant melanoma in the common bile duct has been described in the literature, whereas metastases to the major bile ducts in one autopsy study of malignant melanoma in the more common locations were found with a frequency of 6 per cent.

Management of the pancreatic stump during the Whipple operation.

A method of managing the pancreatic stump during the Whipple operation is described. Using this method has resulted in no pancreatic leaks and no postoperative deaths.

Alterations in taste thresholds in men with chronic obstructive pulmonary disease.

OBJECTIVE: Weight loss is a common occurrence in chronic obstructive pulmonary disease (COPD), and efforts to increase energy intake are often unsuccessful. The objectives of this study were to determine if there were any taste threshold differences between normal-weight and underweight men with COPD, and to determine if there was any association between absolute and recognition taste thresholds and biochemical data associated with COPD. DESIGN: Cross-sectional comparative. SUBJECTS/SETTING: Potential subjects were identified by their physicians. Forty-six men were willing and eligible to participate. Subjects were given sets of triangle taste tests for 4 tastants: sweet, salty, bitter, and sour. Additional information collected included health history data and biochemical data. Subjects were classified as underweight or normal weight for comparison. STATISTICAL ANALYSES PERFORMED: Independent t tests and one-way analysis of variance were used to determine differences between persons in the underweight (n = 17) and normal-weight (n = 29) groups, and the influence of confounding variables. Bivariate correlations were used to determine associations between tastant thresholds and biochemical indexes for the entire group (N = 46). Stepwise regression analysis was used to determine significant variables in prediction of thresholds of the 4 tastants for the entire group (N = 46). RESULTS: Underweight subjects had a significantly higher bitter taste threshold than normal-weight subjects (5.76 vs 5.10, P = .016). A significant negative correlation was found between absolute bitter and bicarbonate (r = -.39, P = .01) and PCO2 (r = -.34, P = .02). A significant regression equation for absolute bitter taste threshold was determined (P = .011) on the basis of bicarbonate values; and upon body mass index for bitter taste recognition threshold (P = .031). APPLICATIONS: Recognition that patients with COPD may have alterations in taste that are associated with weight status and/or biochemical status can guide dietitians in their recommendations for meal plans targeting individual weight goals.

Incubation temperature effects on physical characteristics of normal, dark, firm and dry, and halothane-carrier pork longissimus.

Pigs (n = 18) were selected to represent three different muscle conditions (six pigs per condition): normal: dark, firm, and dry; and halothane carrier. A 45-cm-long longissimus section was excised from each side of the carcass at 30 min postmortem and cut into six sections. Right side sections were assigned to the intermediate temperature incubation (23 degrees C), and left side sections were designated high temperature incubation (40 degrees C). Sections were randomly assigned to incubation times (0, 1, 2, 4, 6, or 8 h). The 0 h section from each incubation treatment was designated as a control and was placed directly into a 4 degree C cooler. Temperature and pH were evaluated on the control section and for each loin section a the end of the incubation time. Color (L*, a*, and b* values), percentage of purge loss, water-holding capacity, and drip loss were determined. Incubation treatment did not alter pH decline in dark, firm, and dry muscle; however, high temperature increased pH decline in normal and halothane carrier samples. Results suggest that there is a strong interaction between pH and temperature that affects pork quality attributes. High incubation temperature had a negative effect on most quality variables; however, muscle condition (normal or halothane carrier) had limited effects on muscle quality.

Pork carcass composition: I. Interrelationships of compositional end points.

Thirty pork carcasses were used to evaluate the interrelationships between compositional end points and the accuracy of predicting various end points from one another. Right sides were fabricated into Boston butt, picnic, anterior belly, posterior belly, anterior loin, posterior loin, and ham. Carcass composition was determined on the right side using physical dissection and chemical analyses of soft tissue. Left sides were ground (whole-side grind). Linear measures and chemical composition were made on left sides. Using dissectable components, high (r > .85) correlations occurred between percentage of fat-free lean and percentage of lipid, percentage of dissectable fat, and lipid in the whole-side grind; between weights of dissectable lean and fat-free lean; and between weights of lipid in the whole-side grind and lipid, dissectable fat, and dissectible lean. Dissectable lean percentage and fat (percentage and weight) could be predicted using weight of lipid, weight of fat-free lean, and side weight. Any physical measure could be accurately estimated from any compositional end point (r2 = .79 to .93). Regression equations using 10th-rib linear measures and hot carcass weights predicted compositional end points with R2 > or = .80, with the exception of dissectable lean (R2 = .56).

Pork carcass composition: II. Use of indicator cuts for predicting carcass composition.

Right sides of 30 pork carcasses were fabricated into indicator cuts (Boston butt, picnic, anterior belly, posterior belly, anterior loin, posterior loin, and ham) and used to determine carcass composition by physical dissection and chemical analysis of soft tissue. Linear measures and chemical composition of whole-side grind were collected from left sides. Dissection of indicator cuts to predict dissectable composition of the side were much better indicators than linear measures (R2 = .70 to .94). Chemical analyses of soft tissue (lean + lipid) from the loin and anterior belly were better predictors of fat-free lean and extractable lipid composition of the side than linear measures; 89% of the variation in dissectable lean of the side was explained by the use of dissectable components of the anterior loin. The loin served as the best overall indicator cut across the various end points evaluated; 92% of the variation in dissectable lean of the side was explained using dissectable components of the shoulder. The anterior belly was a good indicator for percentage of dissectable lean, fat, fat-free lean, and extractable lipid.

Cooking rate, pH and final endpoint temperature effects on color and cook loss of a lean ground beef model system.

To assess the effects of pH, heating rate and endpoint temperature on instrumental and visual color of ground beef, pH was adjusted to 5.2-6.4, samples were heated at 0.7°C or 3°C/min to 55, 60, 65, 70, 75 or 80°C in a water bath. Cooking rate had no effect on cook loss, instrumental or visual color. Regression equations for linear, quadratic and/or cubic effects of pH and/or endpoint temperature were significant for most color indices. Amount of variance explained by the model and R(2) was increased by adding the calculated percentages of metmyoglobin and/or deoxymyoglobin to the regression models. The predicted sensory brownness score (0=very pink, 7.5=intermediate pink/brown, 15=intense brown) for samples with pH 5.75 cooked to 70°C was 9.75. Samples with a pH of 5.5 achieved this brownness score at 67°C. Samples with a pH of 5.2 achieved this brownness at 58°C.

Effects of pH and temperature on metmyoglobin solubility in a model system.

From a series of experiments heating metmyoglobin solutions at pH 5.0 through 7.0, the effects of temperature and pH on the thermal stability of metmyoglobin were investigated. The percent metmyoglobin denatured at temperatures from 25 to 80 °C was determined. pHs lower than 6.5 caused metmyoglobin denaturation at various temperatures from 25 to 80 °C, but it was particularly apparent when pH was < 5.6. Thermal stability of metmyoglobin increased as pH increased. Metmyoglobin denaturation occurred at 55 °C at pH 5, however, denaturation did not occur until 60 °C at pHs from 5.3 to 7.0. A slower heating rate (0.9 °C/min) resulted in more metmyoglobin thermal denaturation than a faster heating rate (1.3 °C/min) when the temperature was above 55 to 60 °C. The denaturation caused by low pH alone was reversible, while that caused by high temperature was not. Techniques which increase muscle pH, such as the injection of sodium bicarbonate, could effectively improve the color condition of PSE meat.

Effects of urea denatureation and pH on the ability of porcine myoglobin to undergo reduction.

To determine the effects of globin moiety denaturation and pH on the ability of metmyoglobin (MetMb) to undergo reduction, MetMb isolated from porcine hearts was denatured in 8.5M urea. Both native and denatured MetMb solutions were serially reduced with Na(2)S(2)O(4) (0, 7.5, 15, 18.75, 22.5, 26.25, 30, 30.75, and 45 umol). Reduction was conducted at pH 5, 5.2, 5.4, 5.6, 6, 6.2, 6.4, 6.6, and 7. After reduction, absorbance was determined at 635 nm and the percent of the original MetMb which was reduced was calculated. The average percent MetMb reduced from the native and denatured forms was 35 and 25%, respectively. pH significantly influenced the percentage of MetMb reduced, especially when pH was <6. If the MetMb was denatured prior to reduction, the influence of pH on its ability to undergo reduction was slight. The percentage of denatured MetMb reduced was higher at pH 7 than at all other pHs. High pH enhanced the ability of MetMb to undergo reduction; while low pH decreases it. Low pH may have denatured the native globin moiety.