Animal age, packaging and antioxidant treatment effects on sensory characteristics of beef Infraspinatus muscle

Abstract

The objective was to determine effects of animal age, packaging and antioxidant treatment on colour and sensory characteristics of infraspinatus (IF) muscle of the beef shoulder (chuck). IF steaks from older animals (USDA commercial grade; >42 months age) had higher (P < 0.05) muscle pigment levels and redness than young select grade steaks. Steaks in 80% oxygen-modified atmospheric packaging (O₂-MAP) had higher (P < 0.05) thiobarbituric acid values than steaks in 0.4% carbon monoxide-modified atmospheric packaging (CO-MAP) (1.30 and 0.41, respectively). Descriptive rancidity scores were lowest for select grade steaks in CO-MAP (1.03). Beef flavour intensity was higher (P < 0.05) for steaks in CO-MAP, even though steaks were held longer (21 days) before cooking. Sour/grassy scores were highest (P < 0.05) for steaks in polyvinyl-chloride film (5 days storage), and lowest (P < 0.05) for steaks in CO-MAP, indicating that sour/grassy flavour dissipated at longer storage times.

Introduction

Animal age at harvest is an important factor that affects meat quality in general and flavours in particular (Morgan et al., 1991). Animal diet also plays a vital role in ultimate meat quality (Liu et al., 1995; Crouse et al., 1984; Muir et al., 1998; Mandell et al., 1998), affecting fat content and composition, and the concentration of fat-soluble and water-soluble flavour compounds (Hornstein & Crowe, 1960; MacLeod & Coppock, 1976). Many of the flavour and aroma compounds are lipophilic and associated with the fat, developing a typical flavour profile, sometimes including off-flavours in beef muscles from older animals. Off-flavours of concern include sour/grassy and liver-like. Desirable sweet, meaty and savoury or umami flavour notes are associated with grain-fed beef (Melton et al., 1982; Macleod, 1994; Spanier et al., 1992; Brewer, 2010), while grass and hay-based diets are more likely to produce sour and grassy flavours (Calkins & Hodgen, 2007). Liver-like is another flavour note sometimes associated with older animals, or forage-fed animals (Brewer, 2010; Boleman et al., 1997). It has been reported that liver-like off-flavours were specific to individual animals, and that pH and haem iron were not strongly related to off-flavour notes (Meisinger et al., 2006). However, Wadhwani et al. (2010) found that the infraspinatus (IF) muscles were more prone to liver-like off-flavours, compared to other muscles of the beef shoulder (chuck). On the other hand, Miller (2001) reported that beef cuts with higher levels of myoglobin, higher degree of doneness or with higher degree of lipid oxidation typically express liver-like or metallic flavours. If liver flavours are indeed products of lipid oxidation in beef muscles, prevention may be possible by antioxidant injection combined with anaerobic packaging. Lipid oxidation and rancidity of beef rib steaks or ground beef were inhibited by vacuum packaging or anaerobic-modified atmosphere packaging (MAP) with 0.4% carbon monoxide (John et al., 2004, 2005).

Injection of fresh beef steaks and roasts with a solution of ascorbic acid and sodium tripolyphosphate (STP) is now permitted by the United States Department of Agriculture (USDA). Thus, ‘enhancement’ injection of fresh beef is increasingly used, particularly in MAP products. Injection of beef loin strips with phosphate, lactate and sodium chloride improved beef tenderness and juiciness (Vote et al., 2000). Mancini et al. (2005) used enhancement solutions of lactate and rosemary to improve strip loin steak colour stability and reported that lactate-enhanced products were darker but had a more stable red colour.

This experiment was designed to evaluate three packaging methods [PVC, 80% O₂-MAP and 0.4% carbon monoxide-modified atmospheric packaging (CO-MAP)] and antioxidant treatments (0.3% STP + 500 ppm ascorbic acid) on colour, sensory characteristics (flavour and tenderness) and thiobarbituric acid (TBA) values of IF steaks from young (select grade; <30 months of age) and old (commercial grade; >42 months of age) animals.

Materials and methods

Sample procurement

Infraspinatus muscles of beef chuck (shoulder clod) were obtained from local meat plants. The muscles were of two USDA grades: commercial (from animals >42 months age) and select (<30 months age).

Select grade

Select grade muscles were from light carcasses (<272 kg) and had slight marbling score as per the USDA select grade. Vacuum-packed boneless beef chuck shoulder clods (Institutional Meat Purchase Specifications (IMPS) no.114) were purchased and brought to the Utah State University (USU) meat laboratory within 48 h postmortem. The IF was removed, and then steaks (1.9 cm thick) were knife-cut and packaged in styrofoam trays over-wrapped with oxygen-permeable polyvinyl chloride (PVC) film, or in 80% oxygen-modified atmospheric packaging (O₂-MAP), or 0.4% CO-MAP. The packaged muscles were stored at 2 °C (aged) in the dark for a period typical for each packaging method, as follows: PVC wrap for 5 days; O₂-MAP for 10 days; and CO-MAP for 21 days.

Commercial grade

Infraspinatus muscles from grain-fed dairy cattle were purchased from a local processor and transported on ice to the USU meat laboratory, on the same day as harvested, then held at 2 °C. IF steaks (1.9 cm thick) were knife-cut and packaged in either PVC, 80% O₂-MAP, or 0.4% CO-MAP within 48 h postmortem, and stored as described above for select grade steaks. Nine steaks were required from each IF muscle. Thus, a steak thickness of 1.9 cm was used, typical of retail beef steaks in the USA.

Total pigment extracted in phosphate buffer

Finely minced beef samples (3 g) were diluted with 25 mL of cold 0.04 m sodium phosphate buffer (pH 6.8) in 50 mL polypropylene tubes (Cole-Palmer Instrument Company, Vernon Hills, IL, USA) (Trout, 1989). The samples were mixed with a glass rod, and the tubes were kept in ice for 1 h. Tubes were then centrifuged (Model RC5C; Sorvall Instruments, Dupont, Wilmington, DE, USA) at 21 500 g for 30 min at 2 °C. The supernatant was collected, and absorbance was read at 525 and 700 nm using a Model UV-2100 UV-VIS recording spectrophotometer (Shimadzu Co., Kyoto, Japan) against blank phosphate buffer. Pigment concentration (myoglobin + haemoglobin mg g⁻¹ muscle) was calculated using the following equation:

Total soluble haem (mg g⁻¹) = (A₅₂₅ − A₇₀₀) × 2.303 × dilution factor, where; A₅₂₅ was the isobestic point, i.e. the point on the visible spectra where myoglobin or haemoglobin forms (oxy, deoxy or met) have equal absorbance. Soluble pigment concentration was corrected for turbidity by subtraction of the absorbance at 700 nm.

Total pigment extracted in acidified acetone

Total pigment as acid haematin was determined using the acidified acetone extraction of Hornsey (1956), with slight modification. Reagent used was acetone b (prepared by mixing 20 mL concentrated HCl to a final volume of 100 mL with deionised water). The diluted HCl was then transferred to a 1-L volumetric flask and brought to volume with acetone. The sample preparation and procedures were conducted in dim light to minimise pigment fading. Minced beef samples (2 g) were weighed into Pyrex tubes, 9.0 mL acetone b was added, and samples were macerated using a glass rod (Pearson & Tauber, 1984). The tubes were capped and allowed to stand for 1 h before filtering through Whatman 42 filter paper. Filtrate absorbance was read at 640 nm against a blank that contained all the reagents except beef sample. Total pigment (ppm haematin) was calculated as described by Hornsey (1956): ppm total pigment = A₆₄₀ × 680.

High-performance liquid chromatography

Blood haemoglobin contribution to IF muscle pigments was determined using an HPLC method as described by Oellingrath et al. (1990) and modified by Wadhwani et al. (2010). Ground beef IF samples (10 g) were diluted with 30 mL of 0.1 m sodium phosphate buffer pH 7.0 in a standard stomacher bag with 400 mL capacity (VWR, Batavia, IL, USA) and mixed for 1 min at high speed using a Colworth Stomacher 400 Model BA7021 (London, UK). The entire mixture was transferred to a 50-mL polypropylene tube and centrifuged (Model RC 5C; Sorvall Instruments) at 21 500 g for 30 min at 2–5 °C. The supernatant was then filtered through a 0.45-micron membrane filter disc (Millipore, Billerica, MA, USA). A 2-mL portion of filtered solution was diluted to 10 mL with 0.1 m sodium phosphate buffer. A few grains of potassium cyanide were added to maintain the haem pigments in their cyano-ferric form. Filtered samples (40 μL) were transferred to a 100-μL plastic, tapered bottom vial. The vial was placed on the holding rack of the HPLC autosampler. The autosampler was set to withdraw 25 μL from each sample vial for pigment separation and quantitation (Wadhwani et al., 2010).

Antioxidant and packaging treatment

The experiment was a factorial design, with three packaging methods (0.4% CO-MAP, 80% O₂-MAP, PVC wrap), and two antioxidant treatments (control noninjected or injected with a solution of 0.3% STP + 500 ppm ascorbic acid). IF steaks were injected manually using a 30-cc plastic syringe (VWR, Arlington Heights, IL, USA) to obtain a 6% weight gain. MAP was done as described by John et al. (2005). Individual steaks in triplicate were placed in trays for PVC and vacuum bags (15 × 25 cm; Koch, Kansas City, MO, USA) for 80% O₂-MAP and 0.4% CO-MAP. The PVC pack consisted of foam tray and a clear top film that were both oxygen and moisture impermeable. The barrier foam tray had a maximum oxygen transmission rate of 0.1 cc m⁻² at 23 °C, 0% relative humidity and maximum moisture vapour transmission rate of 2.0 g/(24 h, 254 cm²) at 100% relative humidity and 38 °C (Cryovac Sealed Air Corp., Duncan, SC, USA). The oxygen barrier film had a maximum oxygen transmission rate of 20 cc/ (24 h, 254 cm²) and moisture vapour transmission rate of <0.10 g/(24 h, 254 cm²). The vacuum bags used for packaging were 3 mil thickness (0.75 gauge nylon, 2.25 gauge polyethylene) with an oxygen permeability of 0.6 cm³/100 m²/24 h at 0 °C and a water vapour transmission rate of 0.6 g/100 m²/24 h at 38 °C and 100% relative humidity. Ambient air was removed by vacuum, and the desired atmosphere was flushed into the bag. Packages were heat sealed. Cylinders certified to contain the desired gas composition (0.4% CO + 30% CO₂+ 69.6% N₂; or 80% oxygen + 20% CO₂) were obtained from Air Gas Corp, Salt Lake City, UT, USA). The levels of O₂ and CO (80% and 0.4%, respectively) were chosen because these levels are typically used in modified atmospheric packaging in commercial (retail) meat packages in the United States. Initial packages from each packaging run were tested to verify that oxygen concentrations were less than 10 ppm in CO-MAP packages, and 80 ± 2% in high oxygen packaging, using an Illinois Instruments Oxygen Analyzer (Model 3500; Illinois Instruments, Ingleside, IL, USA). Packaged steaks were stored at 2 °C in the dark for a period typical for each packaging method, as follows: CO-MAP for 21 days, 80% O₂-MAP for 10 days and PVC wrap for 5 days. At the end of the storage period, two steaks/replication (three replicates) were used for measurement of visual and Hunter colour measurements. The remaining steak in each replication was cooked to an internal temperature of 71 °C for sensory evaluation of flavour intensity.

Colour measurement

The colour of the IF muscle was measured using a Hunter Lab Miniscan portable colourimeter (Reston, VA, USA). The instrument was standardised using white and black standard plates covered with the same plastic film used for meat colour measurements. CIE L* (lightness), a* (redness) and b* (yellowness) values were measured on meat samples using illuminant D65. The a* value represents redness, so brighter red beef muscle samples had higher a* values. Hue angle was also calculated as arctangent (b*/a*), where hue angle values near zero are red and higher values are increasingly less red and more yellow.

Sensory analysis

A sensory panel (eight panellists) was trained for descriptive analysis of beef muscle flavour profile and tenderness. Panellists were trained to recognise intensity of normal beef flavour as well as off-flavours including rancid, metallic and sour/grassy. The panellists were trained by providing standard samples for each sample (Meilgaard et al., 1991). For liver flavour, beef liver was cooked to 71 °C internal temperature and served warm. For rancid or oxidised flavour, steaks were cooked to 71 °C on the previous day, kept at 2 °C and served the next day after warming in a microwave for 1 min. For beef flavour, fresh beef top loin steaks were cooked as described previously and served. All sensory traits were evaluated for intensity using a five-point category scale where 1 = no flavour/tenderness; 2 = slightly intense flavour/tenderness; 3 = moderately intense flavour/tenderness; 4 = very intense flavour/tenderness; and 5 = extremely intense flavour/tenderness. The panellists were trained to recognise the select grade top loin beef steak samples as 3 (moderately intense) for beef flavour intensity and instructed to compare experimental steaks with the standards used during training. The training was conducted in two sessions. In the first session, panellists were familiarised with the five-point scale and its usage. In the second session, cooked beef samples were evaluated for intensity of different flavours. Group discussion was conducted regarding sample flavour, tenderness and toughness attributes. IF muscle from select and commercial grade animals was cooked to an internal temperature of 74 °C on an electric grill preheated to 177 °C (Circulon Hi-flow system, Hong Kong, China), and temperature was monitored using a thermocouple thermometer (Atkins Temptec, Gainesville, FL, USA). The thermometer probe was inserted horizontally from the side of a steak to the geometric centre to monitor the cooking temperature. Panellists were seated in individual sensory booths equipped with computers. Samples were coded with three digit numbers (balanced and randomised) prior to serving. Distilled water and unsalted crackers were available to cleanse the palate between samples. Panellist responses were recorded by the SEnsory INformation MAnagement SYstem 2000 software version 6 (Morristown, NJ, USA) and were analysed using Sas (SAS, 1999) software for mean values and comparison of means by analysis of variance (Anova).

Warner Bratzler Shear force (WBSF) test

The firmness/tenderness of commercial grade IF steaks was measured using a Warner-Bratzler Shear Press (G.R. Electric Man. Co., Manhattan, KS, USA) to measure the force (kg) applied to completely shear the sample (Quinton et al., 1997). Each steak was cooled to room temperature, and three 1.27-cm-diameter cores were removed from each steak parallel to the muscle fibre orientation using a manual-coring device. A single peak shear force measurement was obtained for each core using the WBSF instrument. Peak WBSF values from each steak were averaged for statistical purposes (Roeber et al., 2005).

pH

The pH values for fresh samples were measured by adding 90 mL deionised water to 10 g of finely chopped meat then thoroughly mixed. After about 10 min at room temperature, samples were filtered through Whatman filter paper no. 2 (Fisher Scientific, Salt Lake City, UT, USA). The pH of the filtrate was measured using a pH meter (Fisher Chemicals, Fair Lawn, NJ, USA) calibrated at pH 4.0 and 7.0.

Thiobarbituric acid method

Thiobarbituric acid reactive substances were measured as described previously (Buege & Aust, 1978; Wadhwani et al., 2010). Duplicate samples (0.5 g) were weighed in two tubes with 2.5-mL stock solution containing 0.375% TBA (Sigma Chemical Co., St Louis, MO, USA), 15% TCA (Mallinckrodt Baker Inc., Paris, KY, USA) and 1.0 N HCL. Sample tubes were heated in hot boiling water bath for 10 min to develop pink colour and then cooled under running tap water. Samples were centrifuged (Model RC 5C; Sorvall Instruments) at 12 465 g for 25 min. Absorbance of supernatant was read at 532 nm using a spectrophotometer, against a blank sample having all reagents except the beef sample. The malonaldehyde (MDA) concentration was calculated using a chromogen extinction coefficient of 1.56 × 10⁵ m⁻¹ cm⁻¹ (Sinhuber & Yu, 1958). The MDA concentration was converted to TBA number (mg MDA kg⁻¹ meat sample) as shown below:

• 1

  TBA # (mg kg⁻¹) = sample A₅₃₂ × (1 m MDA chromagen/1.56 × 10⁵) × [(1 mole L⁻¹)/m] × (0.003 L/0.5 g meat) × (72.07 g MDA mole⁻¹ MDA) × (1000 g kg⁻¹), simplified to:

• 2

  TBA # (ppm) = sample A₅₃₂ × 2.77

Statistical design and analysis

This experiment was a factorial design (3 × 2 × 2) with three packaging methods (PVC, 80% O₂-MAP, 0.4% CO-MAP), two antioxidant treatments (with or without injection of 0.3% STP + 500 ppm ascorbate) and two grades/age (select <30 months and commercial >42 months). There were three replications (steaks from three different IF muscles) per treatment. Analysis of variance was done on the data collected for each experiment using Sas 9.1.3 (SAS Inc., 1999). Post hoc mean comparison was done by Fisher’s least significant difference (LSD) test at P < 0.05. Means were considered different if the difference between means was greater than the calculated LSD value. Treatment means for sensory values and TBA values were similarly calculated and compared.

Results and discussion

Raw meat pigment measurements

Haemoglobin content of IF muscles of select and commercial grade cattle was measured by HPLC. Haemoglobin eluted at 21 min for both standard solutions and extracts of IF muscles (data not shown). No significant difference was observed in haemoglobin (Hb) content between old (commercial) and young (select) IF muscle (Table 1), but commercial grade IF tended to have higher Hb content than select grade muscles (0.35 and 0.25 mg g⁻¹ muscle, respectively). Myoglobin content of beef muscle ranged from 3.0 to 6.5 mg g⁻¹ muscle (Krzywicki, 1982), up to 9 mg g⁻¹ muscle (Wadhwani et al., 2010) depending on the method used. The low level of Hb in the IF muscles in the present study was in agreement with the values reported by Oellingrath et al. (1990), and indicative of low blood retention in these samples.

Total phosphate buffer extractable pigment in commercial grade IF muscle was higher (P < 0.05) than select grade IF muscle (8.94 and 5.73 mg haemoprotein g⁻¹ muscle, respectively; Table 1). Total haematin content was also higher (P < 0.05) in commercial grade IF muscle compared with select grade samples (229 and 127 ppm, respectively) in agreement with previous work (Smith et al., 1988; Renand et al., 2001). Colour parameters a*, b* and hue angle were also significantly different among commercial and select grade IF samples, with lower (P < 0.05) mean values for a*, b* and hue angle for commercial than select grade IF samples (Table 1), where lower hue angle indicated more red colour intensity in commercial grade steaks.

Packaging effects on colour measurement

The main effect of packaging (pooled for antioxidant treatment) on Hunter colour values of select and commercial grade IF muscles is shown in Table 2. The redness (a*) and hue angle values of select grade IF were significantly affected by packaging method (PVC, 80% O₂-MAP and 0.4% CO-MAP). Select grade IF muscle packaged in CO-MAP had dramatically higher (P < 0.05) a* values than other packaging methods (mean values of 20.9, 6.9 and 7.2 for steaks in CO-MAP, PVC and 80% O₂-MAP, respectively). Similarly for hue angle, CO-MAP packaged select grade IF had the lowest hue angle (P < 0.05) indicating more redness. The CO-MAP packaged steaks were uniformly bright red and visually attractive after 21 days refrigerated storage as previously reported for ground beef or rib steaks in this packaging method (John et al., 2004, 2005). Packaging storage times were different by design as typical for each packaging method; 5, 10, 21 days for PVC, 80% O₂, 0.4% CO, respectively. After 5 days in PVC, 10 days in 80% O₂ or 21 days in 0.4% CO, steaks maintained generally desirable red appearance, with a* values > 10 (not different from each other) for commercial grade IF steaks. The reason for high red colour stability for commercial grade steaks in all packaging methods was probably because muscles from older (commercial grade) animals have higher levels of vitamin E and other antioxidants (Yang et al., 2002) and thus are more resistance to pigment oxidation and browning than the muscles from younger (select grade) animals. Also, IF steaks from older animals simply had higher muscle pigment content than select grade IF muscle (Table 1).

Sensory evaluation, WBSF and TBA values of cooked infraspinatus steaks

Main effects

Main and interaction effects of animal grade, packaging and antioxidant treatment are summarised in Table 3. Select grade IF muscle tended to have slightly higher beef flavour intensity scores of 2.80 than the commercial grade IF muscle (2.49), though the values were not significantly different (P = 0.061). Select grade IF muscles were also scored higher for metallic and liver-like off-flavours (P < 0.05). Select grade IF had no incidence of sour/grassy off-flavour. In contrast, higher intensity of sour/grassy flavour has been reported for older (commercial grade) beef muscles (Brewer, 2010). In the present study, the trained panel reported sour/grassy off-flavour and lower tenderness scores for commercial grade IF during sensory training, whereas no such problems were reported for select grade IF muscles. Because sensory panellists did not detect sour/grassy flavour or toughness in select grade IF steaks during preliminary training in this study, sour/grassy, tenderness scores and WBSF were not measured for select grade IF steaks. Because sour/grassy flavour and less tenderness were later noted for commercial grade steaks in training sessions, these parameters were measured for commercial grade steaks.

The TBA values for select grade IF were significantly higher than the commercial grade IF muscles indicating higher rancidity for the select grade IF muscles. The lower TBA of commercial grade IF muscles could be attributed to diets of older animals which are usually pasture fed. Hence, their muscles are comparatively richer in vitamins and other antioxidants (Gatellier et al., 2004).

Comparing the three packaging methods (PVC for 5 days, 80% O₂-MAP for 10 days and 0.4% CO-MAP for 21 days), beef flavour intensity scores were significantly higher (2.72) for 0.4% CO-MAP even after 21 days of storage than other packaging methods (PVC = 2.02; 80% O₂-MAP = 2.15). PVC-overwrap had higher metallic scores (P < 0.05) than the 80% O₂-MAP and 0.4% CO-MAP, and unexpectedly, there was no difference in rancid flavour scores among the three packaging methods. It was found that liver-like off-flavour was higher (P < 0.05) in 0.4% CO-MAP than in PVC (1.50 and 1.25, respectively), but the intensity scores were below 2, indicating only a slight intensity of liver-like off-flavour. As noted earlier, sour/grassy off-flavour was only detected in commercial grade IF muscles and was absent in select grade IF muscles. This off-flavour intensity was higher (P < 0.05) for commercial-grade muscles packaged in PVC-overwrap, compared with 0.4% CO-MAP (Table 3). Tenderness of commercial grade IF muscles was also evaluated on five-point scale where 1 = not tender and 5 = extremely tender. Commercial grade IF steaks packaged in 80% O₂-MAP were less tender (2.17) than PVC (2.37).

In contrast to the sensory tenderness scores, Warner-Bratzler shear force values were significantly higher (samples were tougher) for muscles packaged in 0.4% CO-MAP (2.81) and PVC (2.70) compared with steaks in 80% O₂-MAP (2.31). However, absolute differences in WBSF among packaging treatments were small (<0.5 kg to shear sample cores). These differences, although statistically different, were not detected by the panellists. Mean differences among sensory panel scores for tenderness were also low in absolute terms. All samples were slightly tender (2–3). TBA values were higher (P < 0.05) for steaks in 80% O₂-MAP than for steaks packaged by other methods. This could be explained because of the abundance of oxygen in 80% O₂-MAP causing rancidity (Jakobsen & Bertelsen, 2000; Jayasingh et al., 2002). Antioxidant treatment as a main effect had no significant effect on any of the parameters tested.

Interaction effects

The two-way interactions between animal grade, packaging methods and antioxidant treatment for sensory scores, TBA and WBSF are also presented in Table 3. Select grade IF muscles packaged in 0.4% CO-MAP scored higher (P < 0.05) than most other samples for beef flavour intensity (3.25) even though these samples were stored 21 days of storage. The IF muscles with antioxidant injection also had high beef flavour intensity score (3.17), similar to steaks in 0.4% CO-MAP. Thus, beef flavour intensity of select grade IF could be enhanced and maintained using the 0.4% CO-MAP packaging method.

Metallic flavour scores were higher (P < 0.05) for select grade steaks in PVC (2.25), and for commercial grade steaks without antioxidant treatment (2.50), compared to other treatment combinations (Table 3). Metallic flavour scores were lower (P < 0.05), with scores ranging from 1.0 to 1.5, where 1 = not detectable metallic flavour, for steaks in 0.4% CO-MAP with and without antioxidant treatment and irrespective of animal grade.

Rancid flavour scores were significantly higher (1.93) for samples in 80% O₂-MAP w/o antioxidant treatment, and noticeably, antioxidant treatment could not significantly reduce rancid flavour score (1.71). Similarly, for PVC and 0.4% CO-MAP, rancid flavour scores were unchanged (P > 0.05) even after antioxidant treatment was applied. Select grade steaks in 0.4% CO-MAP had lowest (P < 0.05) rancid flavour scores (1.03). Liver-like flavour scores were higher (P < 0.05) for IF muscles packaged in CO-MAP w/o antioxidants (1.80), compared to most other treatment combinations. Steaks packaged in PVC w/o antioxidants also had high (P < 0.05) liver-like flavour scores (1.69). The interaction of commercial grade IF in PVC overwrap had the lowest (P < 0.05) score for liver-like off-flavour (1.00).

Sour/grassy flavour of commercial grade IF in PVC was significantly (P < 0.05) higher (2.88) than the commercial grade IF steaks in 80% O₂-MAP (2.00), or 0.4% CO-MAP (1.87). A possible explanation is that the intensity of sour/grassy flavour decreased with storage time. The PVC, 80% O₂-MAP and 0.4% CO-MAP samples were served to panellists at 5, 10 and 21 days, respectively, as is typical for the storage life of meat in these packaging methods. Sour/grassy flavour was lower (P < 0.05) for commercial grade steaks treated with antioxidant solution (1.60). The interaction of 80% O₂-MAP w/o antioxidant treatment had the highest (P < 0.05) sour/grassy flavour (3.05). Thus, it is recommended to apply antioxidant treatment when packaging commercial grade IF steaks in high oxygen atmospheres to lower sour/grassy flavour notes.

Certainly, the packaging methods used in this study (PVC; 80% O₂-MAP; 0.4% CO-MAP) affect appearance and shelf life in part through their effects on bacterial growth. For example, beef loin steaks wrapped in PVC turned brown, with aerobic plate count (APC) exceeding spoilage level (<10⁶ CFU cm⁻²) in <2 weeks at 2 °C, but remained red with APC below spoilage levels for 7 weeks in CO-MAP (Jayasingh et al., 2001). Growth of spoilage organisms on fresh meat in MAP is slowed by high CO₂ concentrations (Garcia de Fernando et al., 1995). Growth of cold tolerant pathogens (A. hydrophilia, L. monocytogenes, Y. enterocolitica) is completely inhibited under a high-CO₂, anaerobic atmosphere at 5 °C or below (Gill & Reichel, 1989). In addition to colour and appearance, spoiled-odour or flavour may limit the shelf life of retail beef products held beyond recommended sell-by dates of 7, 14 or 35 days for beef steaks packaged in PVC, 80% O₂-MAP or 0.4% CO-MAP, respectively (Jayasingh et al., 2001; Hunt et al., 2004; John et al., 2005). In the present study, steaks for sensory evaluation were within recommended shelf life limits, and panellists did not note any off-flavours associated with microbial spoilage. Possible interaction effects of packaging method and bacterial growth on steak colour and flavour were not investigated in this study.

Tenderness scores for commercial grade IF were highest (3.13) for commercial grade steaks receiving antioxidant treatment, or for steaks in PVC with antioxidant treatment (Table 3). The instrumental values for tenderness by WBSF were inconsistent among various interactions. Shear values were sometimes lower for steaks receiving antioxidant treatment. However, the interaction of commercial grade IF muscles and antioxidant treatment had a high mean shear value of 3.15, indicating tougher muscles associated with the commercial grade (Table 3).

Commercial grade IF steaks w/o antioxidant treatment had the highest (P < 0.05) mean TBA values (1.54). However, TBA values were also high (1.18; P < 0.05) for select grade IF muscles packaged in 80% O₂-MAP.

Conclusions

In conclusion, IF steaks from commercial grade (older) animals had higher meat pigment levels, and steaks were more red as compared to IF from select grade steaks. Steaks in 80% O₂-MAP had higher (P < 0.05) TBA values than steaks in 0.4% CO-MAP (1.30 and 0.41, respectively). Descriptive panel rancidity scores were also lowest for select grade steaks in CO-MAP (1.03). Beef flavour intensity was higher (P < 0.05) for steaks in CO-MAP, even though steaks were held longer (21 days) before cooking. Objectionable sour/grassy flavour scores were highest (P < 0.05) for steaks in PVC film wrap (5 days storage), and lowest (P < 0.05) for steaks in CO-MAP (21 days storage), indicating that sour/grassy flavour dissipated at longer storage times.

Acknowledgments

Financial support of this project from the National Cattlemen’s Beef Association (USA) is greatly appreciated. This manuscript is approved as Utah Agricultural Experiment Station paper no. 8252.

References