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Department of Animal Sciences, University of Kentucky, Lexington 40546
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Beef • Meat Quality • Packaging • Steaks
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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For years, case-ready packaging technologies have been evaluated as methods to improve shelf life and maintain the quality of fresh meat. Case-ready packaging includes two major types of packaging: vacuum-packaging and modified-atmosphere packaging (MAP). These two types of packaging systems differ considerably, and each has proven to have considerable advantages when compared to traditional polyvinyl chloride (PVC) over-wrap (Blinkstad, et al., 1981
; Asenio et al., 1988; Gill and McGinnis, 1995). Therefore, the objective of this study was to evaluate the visual and chemical benefits of high-oxygen (80% O2/20% CO2) MAP on steaks from three muscles of the beef round from three USDA quality grades.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Beef carcasses obtained from New Horizons Packing (Cincinnati, OH) were ribbed between the 12th and 13th ribs for yield and quality grade determination (USDA, 1997) following a 24-h chill period at 1°C. Carcasses (n = 9) were selected for the study based on USDA quality grades to include three each of Select (Slight10 to Slight50), low Choice (Small30 to Small70), and high Choice (Moderate60 to Moderate100). Rounds from each carcass were fabricated into the semitendinosus (ST), semimembranosus (SM), and biceps femoris (BF). Each muscle was cut in half (ST was cut lengthwise; SM and BF were bisected by the width of the muscle perpendicular to the aitch bone) and muscle halves were allocated randomly to either high-oxygen (80% O2/20% CO2) MAP or PVC over-wrap (OTR = 6,500 cc/M2, 24 h, atm, 25°C) packaging. Muscles were labeled according to corresponding carcass, vacuum-packaged, and held at 4°C for 24 h.
On d 6 postmortem, half of each muscle was transported on ice and monitored for temperature control (remaining <4°C) to the Cryovac/Sealed Air Corp. Research and Development Facility (Duncan, SC) for packaging in high-oxygen MAP. Five 2.54-cm-thick steaks were sliced from each muscle and placed in a barrier foam tray (Cryovac/ Sealed Air Corp.), flushed with a 80% O2/20% CO2 mixture, hermetically sealed using an Inpack Nema 4X (Ross, Midland, VA) MAP machine, and randomly assigned to evaluation day. Steaks were then transported in ice chests at <4°C to the University of Kentucky Meat Science Laboratory (Lexington, KY). Five 2.54-cm-thick PVC steaks were sliced from the other half of the corresponding muscles, placed on styrofoam trays, overwrapped using an oxygen-permeable PVC film, and then randomly assigned to evaluation day. All steaks were placed under simulated retail display conditions (on a table 1.25 m directly under the light source; defrost cycles occurred every 4 h for 7 min, maintaining the temperature at ± 1°C) for 1, 3, 5, 7, and 10 d under constant illumination from cool white fluorescent lights (Osram Sylvania Products, Inc., Versailles, KY; model F40/DWWPlus, 3,300 lumens, 750 lx) at 4°C.
Fat Content
Intramuscular fat content for each carcass and muscle was determined from each d-1 steak. Each sample was ground and sent to an independent laboratory; petroleum ether procedures for evaluating fat content followed AOAC (1990) guidelines.
Visual Evaluation
Steaks for each of the evaluation days were visually evaluated on the given assigned day (1, 3, 5, 7, and 10 d) by a five-member trained panel before removal from the package. The panel was trained according to AMSA (1995) guidelines. Each steak was evaluated for lean color and assigned a score from 8 (bright cherry-red) to 1 (extremely brown or green). Surface discoloration was also evaluated, with scores ranging from 11 (0% surface discoloration) to 1 (90 to 100% surface discoloration; AMSA, 1995).
Colorimeter Evaluation
A Minolta Chroma Meter CR-310 (Minolta Co., Ramsey, NJ) with a pulse xenon arc lamp (D65) with a 50-mm aperture size was calibrated each day using a standard white tile and used to examine L* and a* color space value on d 1, 3, 5, 7, and 10 of simulated retail display. Each package was opened and values were recorded (and averaged) from two locations of the cut surfaces of the ST, SM, and BF.
Metmyoglobin Content
Using the procedure of Krzywicki (1982), the relative metmyoglobin content was determined on d 1, 3, 5, 7, and 10 of display. A 4.0-g sample from each steak was blended with 36 mL of a 40 mM PBS (pH 6.8) in a Waring blender (New Hartford, CT). The homogenate was placed into a 50-mL centrifuge tube, placed on ice for 2 h, and then centrifuged at 5°C for 60 minutes at 30,000 x g. The supernatant was filtered using Whatman No. 1 filter paper, and absorbance was recorded at 525, 545, 565, and 572 nm with a spectrophotometer (model 690 STC#690-001; Mountain View, CA) and recorded. Exposure to light was avoided throughout the procedure to reduce further oxidation of the pigment. Metmyoglobin content (mg/g) was calculated from the following formula:
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where, R1, R2, and R3 are the absorbance ratios of A572/A525, A565/A525, and A545 /A525, respectively.
Statistical Analysis
Data were analyzed using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC) as a split-plot design with carcass as the whole plot experimental unit and quality grades (high Choice, low Choice, and Select) as treatments. The whole plot error term was quality grades nested within carcasses. The subplot experimental unit was muscle (SM, ST, or BF) with packaging method (MAP or PVC) and display time (1, 3, 5, 7, or 10 d) as treatments (Figure 1). The experiment was replicated three times, and all possible pair-wise comparisons were made with a significance level of 5% for the response variables. Main effects were separated using LSD and interactive effect means were separated using the PDIFF option of SAS.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Select carcasses had a lower (P < 0.05) intramuscular fat content (2.02%) than low Choice and high Choice carcasses (3.76 and 5.69%, respectively). Although there were no differences (P > 0.05) between muscles, steaks from the BF tended to have numerically higher intramuscular fat contents (4.71%) than both ST (3.56%) and SM (3.20%) muscles (data not shown).
Color
Visual Lean Color.
Results indicated that low Choice steaks received higher (P < 0.05) lean color values (6.4) than either high Choice or Select steaks (5.8 and 5.9, respectively). Many consumers evaluate steak quality by using color to make their purchasing decision. Beefsteak quality has been equated to a bright red color. Consumers look unfavorably toward discoloration and any variation from this bright red standard. Kennick et al. (1971) reported color desirability was higher for steaks in the Choice grades then those in the Select and Prime grades.
Evaluation of quality grades in different packaging types displayed differences at d 5, 7, and 10 for lean color (packaging method x quality grade; P < 0.05), with low Choice steaks in MAP and PVC receiving the highest (P < 0.05) in lean color values and high Choice steaks in PVC receiving the lowest (P < 0.05) on d 5, 7, and 10 (Figure 2, Panel A). Moreover, lean color scores were higher (P < 0.05) for steaks packaged in MAP than PVC (6.3 vs. 5.9). The interactive effect (P < 0.05) of packaging method and muscle suggested inherent differences in muscles affected their reaction to packaging. Both ST and BF steaks were rated higher (P < 0.05) for lean color in MAP than PVC, whereas packaging method did not (P > 0.05) affect color scores of steaks from the SM (Figure 2, Panel B). Even though lean color values decreased (P < 0.05) with increasing display time (data not shown), ST steaks in MAP were rated higher (P < 0.05) for lean color on d 5, 7, and 10, whereas BF steaks in PVC, and SM steaks in PVC and MAP, received the lower (P < 0.05) lean color scores after 5, 7, and 10 d of simulated retail display (Figure 2, Panel B). The lean color values decreased (P < 0.05) as display time increased. Much of the variation in lean color could be attributed to overall oxidation levels of the cuts from increased metmyoglobin formation and possible lipid oxidation.
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, Panel A). The BF and ST muscles packaged in MAP had less (P < 0.05) discoloration than corresponding muscles packaged in PVC, whereas discoloration scores were similar (P > 0.05) in the SM regardless of packaging method (Figure 3, Panel B). Furthermore, there was less (P < 0.05) discoloration at d 7 and 10 for ST steaks compared with steaks from either the BF or SM; however, on d 1, 3, and 5, there were no (P > 0.05) differences between muscles (Figure 3, Panel A). There was a noticeable increase (P < 0.05) in discoloration after 5 d; however, Sorheim et al. (1999) reported color scores were stable throughout 11 d of storage. Panel evaluation scores were different between packaging with less (P < 0.05) discoloration for MAP than PVC steaks (8.3 vs. 7.8).
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Lightness (L*) Values.
There was a packaging x muscle interaction (P < 0.05) of for L* values (Figure 4, Panel B). Steaks from the ST in MAP displayed the highest (P < 0.05) L* values after 3, 5, 7, and 10 d of simulated retail display. Additionally, ST steaks were lighter (P < 0.05) than either BF or SM steaks (41.7, 38.9, and 40.7, respectively; data not shown). High Choice steaks were darker (lower L* value) than low Choice and Select steaks (39.2, 41.1, and 41.1, respectively; data not shown). In addition, L* values were higher (P < 0.05) for MAP (41.4) steaks than PVC (39.5) steaks. The low Choice and Select steaks packaged in MAP had higher L* values than low Choice and Select steaks packaged in PVC and high Choice steaks in either packaging type (quality grade x packaging interaction; P < 0.05; Figure 4, Panel A).
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, Panel A). Steaks package in MAP had higher (P < 0.05) a* values than steaks packaged in PVC, with the greatest difference between packaging methods occurring after 5 d of display (data not shown), and the magnitude of the difference between packaging methods was most noticeable in steaks from the BF and ST muscles (Figure 5, Panel B). Moreover, ST steaks in MAP tended to have greater (P < 0.05) a* values after 3, 5, 7, and 10 d of simulated retail display than BF steaks in MAP. Sorheim et al. (1999) reported a* values after 3 d of display for steaks packaged in high oxygen were also redder; however, these beef loin steaks discolored gradually between d 3 and 10 of display.
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Metmyoglobin conversion in beef products is very important because consumers’ purchasing decisions of red meats are based, to a high degree, on product color. High Choice steaks had higher (P < 0.05) metmyoglobin concentrations than low Choice and Select steaks. Initial (d 1) values indicated that no metmyoglobin formation had yet occurred. Correal et al. (1986) also found differences in metmyoglobin content among strip steaks from the three grades (Prime, Choice, and Good) and attributed the differences to inherent characteristics of the muscles. Low Choice steaks in MAP presented the lowest metmyoglobin formation after 10 d of display (quality grade x packaging interaction; P < 0.05; Figure 6, Panel A).
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reported color stability is largely a matter of slowing or preventing the formation of brown metmyoglobin at the muscle surface. Metmyoglobin content was not different (P > 0.05) between PVC (0.27 mg/g) and MAP (0.29 mg/g). In contrast, Ordonez and Ledward (1977) reported an increase in oxygen concentration caused a significant decrease in the rate of metmyoglobin content, indicating that less than 30% of the total surface pigment concentration was metmyoglobin even after 15 d of storage in 80% O2/20% CO2.
In the present study, despite the increase in oxygen concentration in the packaging system, the concentrations of metmyoglobin continued to increase over display time, indicating stability of oxymyoglobin can be affected by the differences in the muscle’s chemical makeup. Semitendinosus steaks had less (P < 0.05) metmyoglobin formation than steaks for BF and SM muscles, regardless of packaging method (0.22, 0.28, and 0.35 mg/g, respectively). Metmyoglobin content for muscle x packaging increased over time for all muscles (Figure 6
), which is consistent with Ordonez and Ledward (1977), who reported a 55% increase in metmyoglobin over display time.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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2 Present address: Department of Animal Science, Texas A & M University, College Station 77843.
3 Correspondence: 205 W. P. Garrigus Bldg. (phone: 859-257-7550; fax: 859-257-5318; E-mail: wmikel{at}ca.uky.edu).
Received for publication May 14, 2002. Accepted for publication May 29, 2003.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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