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Journal of Animal Science - Animal Products

An evaluation of the effectiveness of FreshCase technology to extend the storage life of whole muscle beef and ground beef

 

This article in JAS

  1. Vol. 94 No. 11, p. 4911-4920
     
    Received: Mar 28, 2016
    Accepted: Sept 06, 2016
    Published: October 27, 2016


    1 Corresponding author(s): dale.woerner@colostate.edu
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doi:10.2527/jas.2016-0508
  1. X. Yanga,
  2. D. R. Woerner 1a,
  3. J. D. Hastya,
  4. K. R. McCullougha,
  5. I. Geornarasa,
  6. J. N. Sofosa and
  7. K. E. Belka
  1. a Department of Animal Sciences, Colorado State University, 1171 Campus Delivery, Fort Collins 80523-1171

Abstract

The objective of this study was to identify the maximum time of refrigerated storage before aerobic psychrotrophic bacteria (APB) grew to a level indicative of spoilage (7 log cfu/g) or other indicators of spoilage were observed for whole muscle beef and ground beef packaged using FreshCase technology. Storage life for beef steaks stored in FreshCase packages at 4°C was 36 d, with ground beef stored in FreshCase packages at 4°C lasting 10 d. Additionally, greater (P < 0.05) a* (redness) values were detected in FreshCase packaged samples of both beef steaks and ground beef over storage time. At the point of spoilage, off-odors were detected at very low levels in all samples along with low thiobarbituric acid values (< 2 mg malonaldehyde/kg). Therefore, use of FreshCase technology in whole muscle beef and ground beef is a viable option to extend storage life.



INTRODUCTION

Shelf life of fresh meat is defined as the storage time until it reaches spoilage (Borch et al., 1996). Spoilage can be indicated by multiple characteristics including bacterial load, appearance or color of lean and fat, oxidative rancidity, presence of off-odors, and off-flavors. Oxygen and light exposure as well as inappropriate temperature during storage are extrinsic factors that can reduce the shelf life of meat (Lambert et al., 1991; Nychas et al., 2008). Altering the packaging technique is one of the most common methods for managing extrinsic factors negatively influencing the shelf life of meat.

Consumers tend to judge meat quality using 3 sensory properties: appearance, texture, and flavor (Liu et al, 1995). A red color/appearance is most commonly associated with fresh beef and quality by consumers (McMillin, 2008). Fresh meat color deteriorates gradually over time with extended periods of chilled storage (Greer and Jones, 1991). Consequently, the price of discolored beef is reduced by 15%, resulting in an annual revenue loss of $1 billion for the U.S. beef industry (Smith et al., 2000).

FreshCase (Bemis Company, Inc., Oshkosh, WI) is a novel packaging technology that has been shown to extend the shelf life of whole muscle beef and ground beef by fixing beef color in a fresh-appearing state. This technology refers to vacuum-packaging fresh meat with high barrier nitrite-containing film. The use of nitrite in meat packaging material results in development of a bright red surface color and reduces rates of discoloration of meat under vacuum conditions (Siegel, 2010). Due to the reduced rate of discoloration with meat packaged using FreshCase, it may give consumers a false indication of freshness.

The objective of this experiment was to identify the maximum time of refrigerated storage before aerobic psychrotrophic bacteria (APB) grew to a level indicative of spoilage (7 log cfu/g) or other indicators of spoilage, including oxidative rancidity and product odor, were observed for whole muscle beef and ground beef packaged using FreshCase technology.


MATERIALS AND METHODS

Sample Preparation

Whole Muscle Beef Steaks.

Two cases of boneless, beef strip loins (Institutional Meat Purchasing Specifications 180, USDA; 6 strip loins/case; major muscle: longissimus dorsi) were collected from a commercial processing plant 5 d postmortem and transported to the Colorado State University (CSU) Meat Laboratory (Fort Collins, CO). Case served as an experimental block and was independently processed and stored. Immediately following arrival at CSU Meat Laboratory, strip loins were cut into 2.54-cm-thick steaks using aseptic techniques. Steaks were hand trimmed to a maximum exterior fat thickness of 0.32 cm. Steaks were then randomly assigned to 1 of 2 packaging treatments (FreshCase or Control). Every other steak within a strip loin was placed into a 15.24 by 30.48 by 2.54 cm FreshCase pouch (oxygen transmission rate < 2.3 cm3/m2 per 24 h at 23°C and water vapor transmission rate < 7.6 g/m2 per 24 h at 37.8°C and 90% relative humidity; product code CURLON Grade A5105 O0, specifically designed for beef; Bemis Company, Inc.). The FreshCase pouches had high barrier film with a 4-mm thickness and had sodium nitrite incorporated into the sealant layer. Every other steak within a strip loin was placed into an identical 15.24 by 30.48 by 2.54 cm bag containing no nitrite (Control). Each pouch was individually identified and vacuum-packaged using a dual-chamber vacuum-packaging machine (model C500; Multivac Inc., Kansas City, MO) until 700 Pa of pressure was reached. Pouches were boxed according to treatment and placed under dark refrigerated (2–4°C) storage.

Ground Beef.

To achieve a lean (approximately 85% lean) ground beef product, 2 cases of beef chuck rolls (Institutional Meat Purchasing Specifications 116A, USDA; 4 chuck rolls/case) were collected from a commercial processing plant on d 2 postmortem and transported to the CSU Meat Laboratory. Case served as an experimental block and was independently stored and processed with a complete cleaning and sanitation between each. Using aseptic techniques, the chuck rolls were removed from vacuum-packages, cut into 5 by 5 cm pieces, and ground twice using a mixing grinder (model 4346; Hobart Corp., Troy, OH). The beef pieces were initially coarse ground using a 1.27-cm breaking plate and then fine ground using a 0.48-cm plate. Immediately following grinding, 454 g of ground beef was tightly stuffed, using a vacuum stuffer (model VF 50; Handtmann Inc., Lake Forest, IL), into 1 of 2 packaging treatments (FreshCase or Control). Ground beef pouches were individually packaged and labeled, identical to beef strip loin steaks.

A total of 175 (7 pouches/d × 25 d) pouches of beef steaks and 175 pouches (7 pouches/d × 25 d) of ground beef were prepared for storage. Seven Control and 7 FreshCase pouches were removed from storage for steaks and ground beef at time intervals of 1 to 6 d. Sampling intervals varied and were determined based on microbial counts to catch the end of storage life when APB on the day average count reached 107 cfu/g. Untested samples were placed into boxes, sealed, and stored at temperature of 4°C until average APB counts reached 107 cfu/g for 3 consecutive days.

Instrumental Color Measurement

On every sampling day, objective color measurements were taken for each package removed from storage using a spectrophotometer (MiniScan EZ; Hunter Association Laboratory Inc., Reston, VA). Within 10 s of opening package, surface lean color and external fat color of beef steaks was measured at 3 different locations. The 3 values for lean color and 3 values for fat color were averaged to obtain single lean color and fat color value for each sample. Surface color of ground beef was measured at 3 different locations on each sample and averaged to obtain a single value for each sample. The CIE L* (lightness), a* (redness), and b* (yellowness) values were recorded for each sample.

Microbiological Analysis

On each microbial sampling day, 7 pouches each of beef steaks and ground beef were randomly selected and analyzed for counts of total APB and lactic acid bacteria (LAB). Individual steaks (approximately 100 g of whole muscle) were aseptically cut into 1-cm cubes and placed into a Whirl-Pak filter bag (1.63 L; Nasco, Modesto, CA). For ground beef, approximately 100 g samples were transferred from each pouch into individual Whirl-Pak filter bags. Maximum recovery diluent (MRD), comprising 0.85% sodium chloride and 0.1% peptone, was added to each sample at a 1:1 ratio (sample weight to volume of diluent) followed by pummeling for 2 min (Masticator; IUL Instruments, Barcelona, Spain). Sample homogenates were serially diluted in 0.1% buffered peptone water (Difco; Becton, Dickinson and Company, Sparks, MD) and spread plated in duplicate onto tryptic soy agar (Acumedia, Lansing, MI) for enumeration of total APB. For determination of LAB counts, sample dilutions (1 mL) were mixed with 10 mL of molten (45°C) Lactobacilli MRS Agar (Difco; Becton, Dickinson and Company); this was done in duplicate. After setting, a 10 mL overlay of the molten Lactobacilli MRS Agar was added to plates. Colonies were counted after incubation of tryptic soy agar plates at 7°C for 10 d and MRS plates at 25°C for 5 d. Duplicate plate counts were averaged and a single count was reported for each sample.

pH Measurement

The pH of sample homogenates was measured after microbial analysis (same sample that was diluted with MRD at 1:1 weight ratio; pH of MRD was 7.0 ± 0.2 at 25°C), using a pH meter fitted with a glass electrode (UltraBasic-5; Denver Instrument, Arvada, CO).

Odor Panels

Panelist were trained for 5 sessions (90 min per session), prior to the actual panels, to evaluate attributes that represented odors from fresh meat to spoilage meat of each respective attribute, including putrid, acidic, sour, and rancid, using a 15-cm continuous line scale. Odors associated with rotten eggs, acetic acid (vinegar), sour milk (buttermilk), and oxidized oil served as descriptors for putrid, acidic, sour, and rancid odors, respectively. Panelists were trained to identify each odor with the following standards: yolks from overcooked hard-boiled eggs, white vinegar, buttermilk, and oxidized oil. Each standard in its pure form served as the maximum intensity (very strong presence) on the 15-cm line scale, whereas the absence of each odor served as “no presence.” Following the training and identification using the standards, the standards were mixed or blended with beef samples at various levels to train for low to high intensities of each odor attribute.

Before each odor panel, all steak and ground beef samples were divided into equal parts; one-half of each sample was designated as raw and the other half for cooked odor evaluation. Raw half of steak was cut into 1 by 1 by 1 cm pieces, 50 g of raw ground beef was measured out, and each was put into 60 mL lidded glass jars. Steaks and ground beef samples (30-g patties) designated for cooking were cooked to an internal temperature of 71°C using double-sided electric grills (Salton Clamshell Grill model number GR39A; Salton Inc., Lake Forest, IL), and put into 60-mL lidded glass jars. All jars were labeled in a completely random order for odor panels.

During an odor panel, at least 6 trained panelists who had been previously trained with sensory characteristics of meat were seated in individual booths in a light-controlled room. Each panelist received a set of 14 (7 raw and cooked beef steaks along with 7 raw and cooked ground beef) samples to evaluate off-odors and general meat odors using a 15-cm unstructured line scale, with the extreme left indicating absence of odor and extreme right indicating a very strong presence. A single sensory value was obtained for each of the following odors: putrid, acid, sour, rancidity, and meaty odor. Trained panelists marked the scale with a vertical line at the perceived intensity. Results were expressed by the distance of the vertical line from the extreme left end of the 15-cm scale.

Thiobarbituric Acid Reactive Substances Analysis

The 2-thiobarbituric acid method described by Tarladgis et al. (1960) was used to measure lipid oxidation for each sample designated for thiobarbituric acid reactive substances (TBARS) analysis. Four pouches of Control and FreshCase beef steak samples and 4 ground beef samples were selected for TBARS analysis on days indicating a significant increase in microbial growth. Thiobarbituric acid reacts with the oxidation products of fat to form malonaldehyde (MDA), which was measured on a spectrometer in solution. The TBARS value was expressed as milligrams MDA/kilogram tissue.

Statistical Analysis

The experiment was a completely randomized block design. The effect of block by case was removed from the model as it was insignificant (P > 0.05) in initial tests. A 2-way ANOVA was conducted for each variable to investigate fixed effects of packaging technology, storage time, and corresponding interactions. Odor panel scores for beef steaks were not analyzed for individual samples by day; instead, multiple sampling days were combined to represent 3 phases of APB growth. Phase of microbial growth was used as a fixed effect in the model instead of day for steak odor panel ratings. Phase 1 was the time period from d 0 to 5 (<3 logs cfu/g), phase 2 was the time period from d 10 to 20 (4–6 logs cfu/g), and phase 3 time period was d 26 to 47 (>6 logs cfu/g). Storage effect of day was used to analyze for ground beef samples.

The general linear model procedure (PROC GLM) and mixed procedure (PROC MIXED) of SAS (version 9.1; SAS Inst. Inc., Cary, NC) were used to analyze data. Microbial counts were expressed as log10 cfu per gram. Response variables such as CIE L*, a*, and b* values; microbiological loads; pH; TBARS; and sensory panel scores were evaluated and significance of differences was defined as α = 0.05. Mean separations were obtained using Fisher’s LSD test.


RESULTS

Beef Steaks

Objective Color.

Main effects of packaging technology on objective color, microbial counts, and pH are presented in Table 1. Lean L* values tended to be slightly higher (P = 0.052) for Control steaks than for FreshCase steaks, whereas lean b* values were higher (P < 0.05) for FreshCase steaks than for Control steaks. This indicates that although lean of Control steaks appeared to be lighter colored, FreshCase steaks had a brighter, more yellow appearance. External fat of FreshCase steaks had a redder/pinker appearance with higher (P < 0.0001) a* values. Control steaks had a brighter, more yellow-colored appearance with higher (P = 0.016) b* values. Main effect of storage time (day) affected steak lean (P < 0.05) L* and b* and fat L*, a*, and b* readings (Table 2). No meaningful trends were identified from values. The a* values of lean was affected by an interaction of packaging technology × storage time (day; Fig. 1). On d 0 of storage, lean a* values for both Control and FreshCase steaks were similar, but as storage time increased, lean a* values for FreshCase steaks remained higher (P < 0.05), translating to a much redder appearance.


View Full Table | Close Full ViewTable 1.

Least squares means for traits of beef steaks and ground beef stored at 4°C

 
Traits Control FreshCase1 SEM P-value
Beef steaks2
Lean L* 34.64 34.03 0.22 0.052
Lean b* 8.94b 9.35a 0.10 0.005
Fat L* 51.04 50.61 0.38 0.428
Fat a* 3.52b 5.76a 0.19 <0.0001
Fat b* 14.40a 13.90b 0.14 0.016
APB 5.48a 5.32b 0.05 0.037
LAB 6.01 5.95 0.04 0.309
pH 5.47 5.48 0.00 0.697
Ground beef
L* 39.93 39.97 0.31 0.937
APB 6.59 6.50 0.06 0.354
LAB 5.97 5.93 0.05 0.808
pH 5.61a 5.58b 0.01 0.008
a,bLeast squares means (112 samples/treatment for beef steaks and 42 samples/treatment for ground beef) within a row with different superscripts differ (P < 0.05).
1Bemis Company, Inc., Oshkosh, WI.
2L* reflects the lightness of meat color, a* reflects the redness, and b* reflects the yellowness. APB = aerobic psychrotrophic bacteria; LAB = lactic acid bacteria.

View Full Table | Close Full ViewTable 2.

Least squares means of objective color (CIE L*, a*, and b*)1 affected by storage time (day) of beef steaks for lean and fat meat stored at 4°C

 
Lean
Fat
Day L* b* L* A* b*
0 33.56c 8.04g 51.14bcde −0.01g 10.51h
5 33.91bc 9.00ef 52.23bc 2.44f 13.06g
10 37.40a 10.60ab 57.28a 5.54abc 16.43a
13 34.18bc 8.72fg 51.89bc 3.81def 13.54efg
14 34.77bc 10.67a 57.18a 4.55cde 15.68ab
15 34.49bc 8.59fg 49.34cdef 5.80abc 15.21bc
16 33.11c 9.62cde 48.14ef 5.50abc 13.89defg
17 33.46c 9.83bcd 47.82f 6.63a 14.77bcd
18 34.49bc 9.98abc 47.94f 6.31ab 15.02bcd
19 33.35c 9.12def 48.44def 5.28abcd 14.67bcde
20 34.65bc 8.33fg 52.49b 3.89def 14.07defg
26 34.07bc 8.93ef 51.10bcde 4.85bcde 14.31cdef
31 34.40bc 8.49fg 51.21bcd 3.64ef 13.25fg
36 35.53b 8.88ef 50.54bcdef 5.28abcd 14.28cdef
41 34.49bc 9.02ef 48.39def 4.75cde 13.52fg
47 33.52c 8.47fg 48.14ef 6.01abc 14.20cdef
SEM 0.62 0.29 1.08 0.55 0.41
a–gLeast squares means (7 samples per treatment per day) within a column with different superscripts differ (P < 0.05).
1CIE L* (lightness), a* (redness), and b* (yellowness).
Figure 1.
Figure 1.

Least squares means for a* (redness) value affected by packaging × storage time (d) for lean beef steaks stored at 4°C (n = 7).

 

Bacterial and pH Results.

Over all storage times, FreshCase steaks had a lower (P = 0.037) average number of APB than Control steaks (Table 1); however, the magnitude of difference is minimal. Lactic acid bacteria and pH were not affected (P > 0.05) by packaging technologies (Table 1). However, steak pH values gradually decreased (from 5.46 to 5.34) as storage time increased (P < 0.0001; data not shown).

Levels of APB and LAB were influenced (P < 0.05; Table 3) by storage time. Plate counts of APB and LAB increased (P < 0.05) over time. Initially, levels of APB and LAB were low, with counts of 2.52 and 1.75 log cfu/g, respectively. Aerobic psychrotrophic bacteria and LAB counts for beef steaks exceeded 2 logs of growth by 10 d. After 2 logs of growth for APB and LAB, plate counts were steady and seemingly linear. Aerobic psychrotrophic bacteria exceeded 7 log cfu/g on d 41 of storage for both Control and FreshCase samples, whereas LAB exceeded 7 log cfu/g 15 d before that. Regardless of treatment, as expected, these data indicated that LAB grew more rapidly than APB in vacuum-packaged beef steak samples. Regardless of packaging technology, beef steaks will expire after 36 d of storage.


View Full Table | Close Full ViewTable 3.

Least squares means of bacterial counts (log cfu/g) for beef steaks stored in different packaging types during storage time (day) at 4°C

 
APB1
LAB1
Day Control FreshCase2 Average3 Control FreshCase Average3
0 2.51 2.54 2.52h 1.78 1.72 1.75j
5 2.68 2.71 2.69h 2.98 3.14 3.06i
10 4.37 4.31 4.34g 5.55 5.19 5.37h
13 4.98 4.31 4.65fg 5.96 5.32 5.64gh
14 5.10 4.78 4.94ef 5.71 5.79 5.75g
15 5.39 5.14 5.27de 6.32 6.03 6.17f
16 5.39 5.13 5.26de 6.10 5.77 5.93fg
17 5.80 5.74 5.77c 6.47 6.66 6.57de
18 5.82 5.45 5.64cd 6.50 6.03 6.27ef
19 5.68 5.68 5.68c 6.29 6.17 6.23ef
20 5.82 5.77 5.79c 6.60 6.77 6.69cd
26 6.41 6.44 6.43b 6.91 7.27 7.09b
31 6.78 6.73 6.75ab 6.93 7.09 7.01bc
36 6.80 6.68 6.74ab 7.15 7.29 7.22ab
41 7.10 7.06 7.08a 7.49 7.47 7.48a
47 7.07 6.80 6.93a 7.49 7.46 7.47a
SE 0.18 0.22 0.14 0.17 0.26 0.12
a–jLeast squares means (7 samples per treatment per day) within a column with different superscripts differ (P < 0.05).
1Aerobic psychrotrophic bacteria (APB) grew on tryptic soy agar plates that were incubated at 7°C for 10 d; lactic acid bacteria (LAB) grew on de Man, Rogosa, and Sharpe agar plates that were incubated at 25°C for 5 d.
2Bemis Company, Inc., Oshkosh, WI.
3Because there was no interactive effect between storage time and packaging type, only day effect on the average counts of bacteria from samples stored in Control and FreshCase packages is reported in this table.

Odor Panel Scores.

Main effect of packaging technology did not affect (P > 0.05) sensory odor scores for raw or cooked beef steak samples (data not shown). Main effect of storage time (phase) influenced (P < 0.05; Table 4) odor panel scores of all attributes for raw beef steaks. As storage time increased, intensity of putrid, acid, sour, and rancid odors increased and meaty odor intensity decreased (P < 0.05) for raw beef steaks. Over storage time, cooked beef steaks intensified in sour and rancid odors (P < 0.05). Although intensity ratings increased for some attributes, all odor scores except meaty remained low (ranged from 0.02 to 2.86). Therefore, indications of spoilage based on odor remained low throughout storage. Aerobic psychrotrophic bacteria and LAB counts grew beyond the level of bacterial spoilage (7 log cfu/g) in Phase 3 and had little indication of spoilage based on odor. Additionally, throughout storage, FreshCase samples remained bright red and acceptable in appearance.


View Full Table | Close Full ViewTable 4.

Least squares means (SE) of odor panel scores (cm)1 by storage time (phase)2 effect for raw and cooked beef steaks stored at 4°C

 
Raw
Cooked
Phase Putrid Acid Sour Rancid Meaty Putrid Sour Rancid
Phase 1 0.01c (0.22) 0.05b (0.12) 0.22c (0.22) 0.16c (0.3) 3.42a (0.19) 0.02b (0.1) 0.05c (0.12) 0.12b (0.31)
Phase 2 0.70b (0.10) 0.11b (0.05) 1.19b (0.10) 2.36b (0.13) 2.77b (0.08) 0.20ab (0.04) 0.33b (0.05) 2.29a (0.14)
Phase 3 1.38a (0.16) 1.32a (0.08) 2.64a (0.15) 3.46a (0.21) 2.23c (0.13) 0.28a (0.07) 0.81a (0.08) 2.86a (0.22)
a–cLeast squares means within a column with different superscripts differ (P < 0.05).
1A 15-cm scale continuous line was used to evaluated the intensity of off-odor and meaty odor for ground beef samples. Extreme left indicated absence of odor and extreme right indicated a very strong presence of the odor. An odor panel score was expressed as the distance of a vertical line marked by a panelist from the extreme left end of the 15-cm scale.
2Phases are grouped by aerobic psychrotrophic bacterial counts from tryptic soy agar plate cutoff (log cfu/g). Phase 1: Day 0 through 5 (<3 log), 28 samples; Phase 2: Day 10 through 20 (4 log – 6 log), 77 samples; Phase 3: Day 26 through 47 (>6 log), 21 samples.

An interactive effect of packaging technology and storage time existed for acid odor intensity in cooked beef steaks (P = 0.018; data not shown). Intensity of acid odors increased over time for both treatments; however, FreshCase samples were slightly higher (0.78 versus 0.54; P < 0.05) in acid odor during the last phase of storage.

Thiobarbituric Acid.

There was an interactive effect of storage time × packaging technology (P < 0.05) on the TBARS values of beef steaks (Table 5). The level of oxidative rancidity remained low for all samples over time periods and treatments. The maximum TBARS value for Control beef steaks was 0.44 mg MDA/kg, and the maximum TBARS value for FreshCase samples was 0.32 mg MDA/kg.


View Full Table | Close Full ViewTable 5.

Least squares means of thiobarbituric acid reactive substances values (mg malonaldehyde/kg) affected by the interaction of package and storage time (day) for beef steaks stored at 4°C1

 
Day
Treatment 0 5 10 15 20 26 31 36 41
Control 0.44a 0.26bcde 0.28bcd 0.07g 0.11fg 0.33ab 0.34ab 0.23bcde 0.31bc
FreshCase2 0.18defg 0.29bcd 0.20cdef 0.15efg 0.15efg 0.20cdef 0.29bcd 0.32ab 0.18defg
a–gLeast squares means (4 samples per treatment per day) within columns and rows with different superscripts differ (P < 0.05).
1The SEM is 0.06.
2Bemis Company, Inc., Oshkosh, WI.

Ground Beef

Objective Color.

The main effect of packaging technology on objective color, microbial counts, and pH for ground beef are shown in Table 1. No effect (P = 0.937) of packaging technology was found on L* values for ground beef. Nevertheless, the main effect of storage time (day) affected (P < 0.0001) L* values of ground beef (data not shown). However, no trend was identified from values. The interaction of packaging technology × storage time (day) existed for a* and b* values (Fig. 2 and 3). On d 0 of storage, a* and b* values for FreshCase ground beef were lower, but as storage time increased, a* and b* values for FreshCase ground beef remained higher (P < 0.05), indicating a redder and more-yellow colored appearance.

Figure 2.
Figure 2.

Least squares means for the CIE a* (redness) values by packaging by storage time (d) effect of fresh ground beef during storage at 4°C (n = 7).

 
Figure 3.
Figure 3.

Least squares means for the CIE b* (yellowness) values by packaging by storage time (d) of ground beef during storage at 4°C (n = 7).

 

Bacterial and pH Results.

For both APB and LAB counts, no difference (P > 0.05; Table 1) was found between FreshCase and Control ground beef. Over storage time, pH for Control ground beef was 5.61, which was higher (P = 0.008) than pH of FreshCase ground beef, at 5.58 (Table 1). However, the small unit difference of pH was not practically significant. Ground beef pH gradually declined from 5.63 to 5.53 as storage time increased (P < 0.0001; data not shown).

Plate counts of APB and LAB increased (P < 0.05; Table 6) as storage time increased. Initially, APB and LAB counts were relatively high at 4.12 and 3.06 log cfu/g, respectively. Aerobic psychrotrophic bacteria and LAB grew rapidly and exceeded 6 log cfu/g by 10 d of refrigerated storage. Both classifications of bacteria exceeded 7 log cfu by d 12 of storage. Ground beef storage life, regardless of packaging technology, expired after 10 d of storage.


View Full Table | Close Full ViewTable 6.

Least squares means of bacterial counts (log cfu/g) for ground beef stored in different packaging types during storage time (day) at 4°C

 
APB1
LAB1
Day Control FreshCase2 Average3 Control FreshCase Average3
0 4.14 4.10 4.12e 3.09 3.03 3.06e
5 5.31 5.13 5.21d 4.82 4.91 4.87d
10 6.82 6.71 6.76c 6.54 6.30 6.42c
12 7.37 7.36 7.37b 7.15 6.98 7.07ab
13 7.86 7.89 7.88a 7.25 7.36 7.31a
14 8.03 7.85 7.94a 6.99 6.97 6.98b
SEM 0.15 0.15 0.1 0.15 0.14 0.1
a–eLeast squares means (7 samples per treatment per day) within a column with different superscripts differ (P < 0.05).
1Aerobic psychrotrophic bacteria (APB) grew on tryptic soy agar plates that were incubated at 7°C for 10 d; lactic acid bacteria (LAB) grew on de Man, Rogosa, and Sharpe agar plates that were incubated at 25°C for 5 d.
2Bemis Company, Inc., Oshkosh, WI.
3Because there was no interactive effect between storage time and packaging type, only day effect on the average counts of bacteria from samples stored in Control and FreshCase packages is reported in this table.

Odor Panel Scores.

The main effect of packaging technology did not (P > 0.05) influence panel scores of putrid, acid, sour, rancid, and meaty odors for raw ground beef samples (Table 7). Putrid and meaty odors for cooked ground beef samples were not affected (P > 0.05) by packaging technology, either. Cooked FreshCase samples had lower (P < 0.05) intensity of sour and rancid odors. Over storage, odor panel ratings of raw and cooked ground beef were low for all attributes indicating spoilage (range from 0.06 to 1.32; Table 7). Storage time (phase) affected (P < 0.05; Table 8) odor panel scores of attributes for raw ground beef. As storage time increased, intensity of putrid, sour, and rancid increased for raw ground beef (P < 0.05). Similarly, putrid and rancid odor intensity increased in cooked samples over time. Intensity of sour odor remained the same throughout storage (excluding d 13). Meaty odor remained the same throughout storage (excluding d 10). Intensity ratings for attributes (excluding meaty odors) remained low (ranged from 0.02 to 2.65) for raw and cooked ground beef. Therefore, in reference to product odor, indications of spoilage remained low throughout storage. In Phase 3, APB and LAB counts grew beyond the recognized level of bacterial spoilage (7 log cfu/g), and there was little indication of spoilage via product odor. Additionally, the color of FreshCase samples remained bright red and acceptable in appearance throughout storage.


View Full Table | Close Full ViewTable 7.

Least squares means of odor panel scores (cm)1 by package effect for ground beef stored at 4°C.

 
Sensory traits Control FreshCase2 SEM P-value
Raw
Putrid 0.38 0.39 0.12 0.97
Acid 0.06 0.09 0.04 0.56
Sour 0.54 0.42 0.10 0.21
Rancid 1.08 0.98 0.15 0.51
Meaty 3.13 3.12 0.11 0.91
Cooked
Putrid 0.21 0.19 0.06 0.71
Sour 0.73a 0.32b 0.13 0.004
Rancid 1.32a 0.8b 0.14 0.001
Meaty 8.23 8.17 0.15 0.71
a,bLeast squares means (21 samples/treatment) within a row with different superscripts differ (P < 0.05).
1A 15-cm scale continuous line was used to evaluated the intensity of off-odor and meaty odor for ground beef samples. Extreme left indicated absence of odor and extreme right indicated a very strong presence of the odor. An odor panel score was expressed as the distance of a vertical line marked by a panelist from the extreme left end of the 15-cm scale.
2Bemis Company, Inc., Oshkosh, WI.

View Full Table | Close Full ViewTable 8.

Least squares means of odor panel scores (cm)1 by storage time (day) for raw and cooked ground beef stored at 4°C

 
Raw
Cooked
Day Putrid Acid Sour Rancid Meaty Putrid Sour Rancid Meaty
0 0.33ab 0.05b 0.02d 0.23d 2.50c 0.03d 0.11b 0.21c 8.46a
5 0.10b 0.02b 0.12d 0.16d 3.33ab 0.31ab 0.10b 0.58bc 8.22a
10 0.05b 0.10ab 0.33cd 1.03bc 3.21ab 0.13bcd 0.07b 0.80b 6.94b
12 0.67a 0.24a 0.75ab 0.8c 3.03b 0.1cd 0.15b 0.68bc 8.52a
13 0.41ab 0.01b 0.64bc 1.34b 3.49a 0.28abc 0.19a 1.90a 8.66a
14 0.75a 0.03b 1.04a 2.65a 3.22ab 0.39a 0.06b 2.34a 8.39a
SEM 0.15 0.05 0.12 0.19 0.13 0.07 0.16 0.17 0.18
a–dLeast squares means with a column with different superscripts differ (P < 0.05).
1A 15-cm scale continuous line was used to evaluated the intensity of off-odor and meaty odor for ground beef samples. Extreme left indicated absence of odor and extreme right indicated a very strong presence of the odor. An odor panel score was expressed as the distance of a vertical line marked by a panelist from the extreme left end of the 15-cm scale.

An interactive effect of packaging technology × storage time (P = 0.002) was found on acid odor intensity for cooked ground beef (data not shown). However, there was no trend in the values. The intensity of acid odor remained low (odor panel scores ranged from 0 to 0.34) for both Control and FreshCase samples throughout storage.

Thiobarbituric Acid Reactive Substances Values.

Thiobarbituric acid reactive substances values of ground beef are displayed in Table 9. Statistically, there was a packaging technology × storage time interactive effect (P < 0.0001) on TBARS values for ground beef. Thiobarbituric acid reactive substances values for Control samples increased with storage time from 0.29 to 1.19 mg MDA/kg and TBARS values for FreshCase ground beef samples increased from 0.25 to 0.82 mg MDA/kg through d 0 to 13 but ended with 0.41 mg MDA/kg on d 14.


View Full Table | Close Full ViewTable 9.

The interactive effect of package and storage time on the least squares means of thiobarbituric acid reactive substances (TBARS) values1 for ground beef stored at 4°C

 
Day
Sample 0 5 10 12 13 14
Control 0.29d 0.75bc 0.95b 0.78bc 0.95b 1.19a
FreshCase2 0.25d 0.75bc 0.74c 0.76bc 0.82bc 0.41d
a–dLeast squares means for columns and rows with different superscripts differ (P < 0.05).
1TBARS values (4) were expressed as milligrams malonaldehyde/kilogram and the SEM was 0.07.
2Bemis Company, Inc., Oshkosh, WI.


DISCUSSION

Results from this study showed beef steaks and ground beef packaged in FreshCase to be redder in color (greater a* values) during storage. This is supported by other studies that show the use of nitrite to improve and stabilize the red color of meat (McClure, et al., 2011; Skibsted, 2011). Additionally, the development of nitric oxide myoglobin did not immediately occur, because the a* value of beef steaks packed in FreshCase was not redder than that of beef samples packed in Control on Day 0 when samples were stored in the packages for several minutes, but the development of redder color of nitric oxide myoglobin was detected on Day 5 for FreshCase samples.

This study shows that a* values of beef steaks and ground beef were affected by storage time without a meaningful trend; this was different from results of papers that show a* values for meat in vacuum-packages tend to decrease over storage time (Luño et al., 1998; Jeremiah and Gibson, 2001). However, studies by Filgueras et al. (2010) and Suman et al. (2010) found redness of muscle color to be highly stable in vacuum-packages during the storage. A study by Grobbel et al. (2008) concluded that vacuum-packages or modified-atmosphere packages (64.6% N2, 35% CO2, and 0.4% CO) allowed a longer stabilization period of myglobin in red color from delaying the onset of metmyoglobin, which is brown due to oxidation of myoglobin. Moreover, Claus and Du (2013) concluded that nitrite-embedded film extended bright red color for both fresh and frozen beef products and it also helped cooked beef products display redder color compared with non-nitrite film packages based on CIE a* and R610/R525 (the percentage reflectance at 610 nm divided by the percentage reflectance at 525 nm).

Nitrite can be used as an antioxidant in cured meat (Skibsted, 2011). When an oxygen molecule reacts with unsaturated fat, lipid oxidation begins, resulting in development of rancid odor and flavor in meat (Campo et al., 2006). Nitric oxide from nitrite can scavenge the lipid derived radicals and form nonradical products. Additionally, nitric oxide can deactivate peroxide without forming hypervalent heme pigment, which is responsible for the initiation of lipid and protein oxidation (Kanner et al., 1991; Carlsen et al., 2005). This may explain why the TBARS value of ground beef in FreshCase packages was lower than Control. Moreover, lipid oxidation accelerates oxidation of myoglobin, resulting in the formation of metmyoglobin, which is responsible for brown color of meat (Lynch and Faustman, 2000; Faustman et al., 2010). Meat stored in high-O2 modified-atmosphere packages has a bright red color that is stabilized because of the high concentration of oxygen-forming oxymyoglobin. However, over time, metmyoglobin will be formed with higher TBARS values (more than 2 mg MDA/kg), indicating high levels of oxidative rancidity (Zhou, et al., 2010; Bingol and Ergun, 2011). The TBARS values for both beef steaks and ground beef samples stored in vacuum-packages (Control and FreshCase) remained lower than the minimum TBARS value for strong off-odor, especially rancid odor development to reject beef at 2 mg MDA/kg (Campo et al., 2006). Therefore, even when an extended period of storage was reached and APB and LAB counts exceeded 7 log cfu/g, oxidative rancidity was not reached. These findings support the low intensity levels of putrid and rancid odors for ground beef from the sensory portion of this study.

Therefore, the use of FreshCase packaging technology will control oxygen level, minimizing lipid oxidation, but minimize the oxidation of pigment, maintaining the fresh meat red color by nitrite in package films.

Shelf life of ground beef could be extended with changes of storage conditions. Initial bacterial load is important to meat shelf life (Lambert et al., 1991). All other factors being constant, lower initial bacteria counts can extend shelf life of meat. Beef stored at 0°C with initial microbial counts at 6 × 104 cfu/cm2 had a shelf life of 11 d, whereas beef stored at 0°C with an initial load of 65 cfu/cm2 displayed spoilage by d 21 (Ayres, 1960). Storage life is inversely related to storage temperature (Lee et al., 1983). Generally, meat shelf life decreases in proportion to increased storage temperature. Gill and Shand (1993) concluded that 100% of the storage life attainable is obtained at temperature of -1.5°C; 50% of storage life attainable is obtained by storing at 2°C, and 15% of storage life attainable is achieved at the temperature of 10°C. Beef stored in vacuum-packages at −1.5°C has a shelf life of up to 14 wk when bacterial counts reach 107 cfu/cm2 but only 3 wk when stored at 4°C (Borch et al., 1996). In this study, ground beef with an initial microbial load of 4.12 log cfu/g stored at 4°C had a shorter storage life of 10 d compared with using the same packaging technology with a lower initial microbial level of 3.84 log cfu/g and stored in lower temperature at 1°C, resulting in 35 d of storage (X. Yang, unpublished data).

Conclusion

Results from this study identified shelf life of whole muscle beef and ground beef stored at 4°C of 36 and 10 d, respectively. Also, storage life of whole muscle beef and ground beef can be extended by using FreshCase packaging technology, displaying a redder color than beef stored in regular vacuum-packages, without any adverse changes on meat quality. Further research needs to be done to evaluate the effect of FreshCase packaging technology on display color for beef and pork in retail. Additionally, consumer panels on visual color of meat should be conducted to compare the results of objective color measurement.

 

References

Footnotes


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