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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 pork and ground pork sausage

 

This article in JAS

  1. Vol. 94 No. 11, p. 4921-4929
     
    Received: Mar 28, 2016
    Accepted: Aug 30, 2016
    Published: October 13, 2016


    1 Corresponding author(s): dale.woerner@colostate.edu
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doi:10.2527/jas.2016-0509
  1. X. Yanga,
  2. D. R. Woerner 1a,
  3. K. R. McCullougha,
  4. J. D. Hastya,
  5. I. Geornarasa,
  6. G. C. Smitha,
  7. J. N. Sofosa and
  8. 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 grew to a level indicative of spoilage (7 log cfu/g) or other indicators of spoilage were observed for whole-muscle pork and ground pork sausage packaged using FreshCase technology. Pork chops and pork sausage were packaged using conventional vacuum packaging without nitrite in film (Control) or using FreshCase technology and were compared with respect to microbial counts, pH, instrumental color measurements, lipid oxidation level, and sensory properties. The storage life was 45 d for pork chops stored in FreshCase packages at 1°C and 19 d for ground pork sausage stored under the same condition. Results indicated that both pork chops and sausage stored in FreshCase packages retained redder color (P < 0.05) than those stored in Control packages. No differences (P > 0.05) existed between Control and FreshCase packaged samples for any off-odor detection for either pork chops or sausage. Moreover, levels of oxidative rancidity in all packages had low thiobarbituric acid reactive substances values. The results indicated that FreshCase technology can be used to extend storage life of pork products without having adverse effects on pork quality.



INTRODUCTION

Meat and meat products are highly perishable products. Shelf life of meat is the period of time between packaging and adverse changes in texture, flavor, odor, color, and nutritional value to an unacceptable level (Gray et al., 1996). Off-odors and slime can form on meat when bacterial populations grow to 107 and 108 cm−2, respectively (Ayres, 1960).

Meat shelf life can be shortened by a high concentration of oxygen causing microbial growth, development of off-flavors, off-odors, color deterioration, and nutritional losses (Kerry et al., 2006). Vacuum packaging is a common method used to control levels of oxygen in wholesale meat marketing (Lambert et al., 1991). Vacuum packaging can extend shelf life 5 times longer than overwrapped packages in primal cuts with low or normal pH (Johnson, 1974; Seman et al., 1988). However, vacuum packaging causes the formation of deoxymyoglobin, creating a purple color proven less desirable for consumers. Consumers use meat color as an indicator of freshness and palatability (Jeremiah, 1982; Brewer et al., 2002). Therefore, it is important to keep color attractive to consumers, which plays a major role in influencing their purchasing decisions (Sørheim et al., 1999; Kennedy et al., 2004; Viana et al., 2005).

FreshCase technology refers to vacuum packaging fresh meat with high-barrier nitrite-containing film. Nitrite and myoglobin react to form nitric oxide, causing a bright red color on the surface of meat. However, microbiological studies need to be done on FreshCase packaged pork to indicate spoilage.

The aim of this research was to identify storage life, which is defined by the number of days required to reach an aerobic psychrotrophic bacteria (APB) plate count of 7 log cfu/g, of whole-muscle pork and pork sausage and also to evaluate the effects of FreshCase Technology on the objective color and organoleptic properties of whole-muscle pork and pork sausage.


MATERIALS AND METHODS

Sample Preparation

Pork Chops.

Two cases of 16 boneless pork loins (NAMP 413B, USDA) were collected from a commercial processing facility on d 3 postmortem and transported to the Colorado State University (CSU) Meat Laboratory. Case served as an experimental block and was processed and stored independently. Upon arrival at CSU, pork loins were sliced into 2.54-cm pork chops (20 chops per loin). Each chop had a maximum exterior fat thickness of 0.64 cm. Every 2 pork chops were randomly assigned to 1 of 2 packaging treatments (FreshCase or Control). Every other 2 pork chops within a pork loin were placed into a 15.24 × 30.48 × 2.54 cm FreshCase pouch (FreshCase; oxygen transmission rate <2.3 cm3·m−2·24 h−1 at 23°C, water vapor transmission rate <7.6 g·m−2·24 h−1 at 37.8°C and 90% relative humidity; product code CURLON Grade A5105 O0, specifically designed for pork, BEMIS Company Inc., Oshkosh, WI) or a 15.24 × 30.48 cm × 2.54 cm bag (same parameters as the FreshCase bag but containing no nitrite in the film; Control). The FreshCase pouches had a high-barrier film 4 mm thick and sodium nitrite incorporated into the sealant layer. Each pouch (experiment unit) was individually identified and vacuum packaged using a dual-chamber vacuum-packaging machine (Multivac Inc., Kansas City, MO) until 7 mbar of pressure were reached. Pouches were boxed and placed into dark storage (0°C to 2°C).

Pork Sausage.

To achieve a lean specification of approximately 60%, 2 cases of pork shoulder, Boston butts (NAMP 406), were collected from a commercial processing facility on d 3 postmortem and transported to CSU. Case served as an experimental block and was processed and stored independently. Upon arrival at CSU, using aseptic techniques, butts were cut into 5 × 5 cm pieces and ground twice. Using a mixing grinder (Hobart Corp., Troy, OH), pork pieces were coarse ground with a 1.27-cm breaking plate. Coarse-ground pork was mixed with a commercially irradiated pork sausage seasoning (Legg’s Old Plantation Seasonings, blend WS-00-027-001, A. C. Legg Inc. Calera, AL). Seasoning blend did not contain nitrites. Mixed pork was ground a second time using a 0.48-cm plate. Following grinding, 454 g of ground pork sausage were stuffed using a vacuum stuffer (Handtmann, Model VF 50) into 1 of 2 packaging treatments (FreshCase or Control). Ground pork sausage packages were individually labeled and packaged identically as described for pork loins.

A total of 150 (6 pouches/d × 25 d) pouches of pork chops and 150 (6 pouches/d × 25 d) pouches of ground pork sausage were stored. Six Control and 6 FreshCase chop and sausage packages were removed from storage at intervals of 1 to 5 d. Intervals varied and were determined by APB counts on the day when count reached 7 log cfu/g. Intervals between sampling decreased as bacterial growth reached spoilage limit to determine the exact day when 7 log cfu/g APB occurred. Storage of untested samples continued until APB counts were 7 log cfu/g for 3 consecutive days.

Instrument Color Measurement

On each sampling day, objective color measurements were taken using a MiniScan EZ spectrophotometer (model 4500 S; Hunter Association Laboratory Inc., Reston, VA) equipped with a 6-mm port size, calibrated at an illuminant D65 and 10° standard observer angle. Spectrophotometers were calibrated using the black glass and white tile before each use. The color was presented in terms of CIE L* (lightness), a* (redness), and b* (yellowness) values. Within 10 s of opening a package, surface lean color and external fat color of pork chops were measured at 3 different locations. The 3 values for lean color and 3 values for fat color were averaged to obtain a single lean color and fat color value for each sample. The surface color of ground pork sausage was measured right after removing the packages at 3 different locations on 6 pouches of ground pork sausage and averaged to obtain a single value for each sample.

Microbiological Analysis

On each microbial sampling day, 6 pouches each of chops and sausage were randomly selected and analyzed for counts of total APB and lactic acid bacteria (LAB). Individual chops (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). Approximately 100 g of sausage were placed 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 diluent weight) 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, Sparks, MD) and spread plated in duplicate onto tryptic soy agar (TSA; Acumedia, Lansing, MI) for enumeration of total APB. For LAB counts, sample dilutions (1 mL) were mixed with 10 mL of molten (45°C) Lactobacilli MRS agar (Difco); this was also done in duplicate. After setting, a 10-mL overlay of the molten lactobacilli MRS agar was added to each plate. Colonies were counted after incubation of TSA 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 (meat: MRD = 1:1 weight ratio; described in the previous section) was measured after microbial analysis, using a Denver Instruments pH meter fitted with a glass electrode (UltraBasic-5, Arvada, CO). The pH meter was calibrated with standard buffers of pH 4.0 and 7.0 and measured at room temperature (25°C).

Odor Panels

Prior to odor panel, 4 packages of chops and sausage samples were cut into equal parts; half of each sample was designated for raw odor evaluation, and the other half was designated for cooked odor evaluation. Raw portions of chops were cut into 1 × 1 × 1 cm pieces, and 50-g portions of raw ground pork were measured, and both were placed into 60-mL lidded jars. Samples designated for cooked odor evaluation were cooked to an internal temperature of 71°C using double-sided electric grills (Salton Clamshell Grill model GR39A, Salton Inc., Lake Forest, IL). Cooked meat was portioned out and placed into 60-mL lidded glass jars. Jars were labeled randomly for panel evaluation.

Panelists were trained for 1 wk 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 pork sample at various levels to train for low to high intensities of each odor attribute. During each panel, at minimum 6 (maximum 8) trained panelists were seated in individual booths in a light-controlled room for each odor panel. Each panelist received a set of 8 (2 raw and 2 cooked pork chops with 2 raw and 2 cooked ground pork sausages) samples to evaluate off-odors and general meat odors using a 15-cm unstructured line scale anchored on the extreme left indicating absence of odor and the extreme right indicating a strong presence. Trained panelists marked the scale with a vertical line at perceived intensity of each attribute. Results were expressed by the distance of the marked vertical line from the extreme left end of the 15-cm scale. A single sensory value was obtained for each of the following odors: putrid, acid, sour, rancid, and meaty odors.

Thiobarbituric Acid Reactive Substances

The 2-thiobarbituric acid reactive substances (TBARS) steam distillation method described by Tarladgis et al. (1960) was used to evaluate lipid oxidation of each sample. The pink chromogen formed by the reaction of 1 molecule of malondialdehyde (MDA) with 2 molecules of 2-thiobarbituric acid with known absorption spectra (530 to 532 nm) was measured using a spectrophotometer. Four Control and 4 FreshCase packages for both chops and sausages were selected for TBARS analysis on days (d 0, 10, 20, 30, 36, 38, 40, 42, 45, 46) indicating a significant increase in microbial growth. Each TBARS value was expressed by milligrams of MDA per kilogram of tissue.

Statistical Analysis

The experiment was a completely randomized block design. Experimental block was found to be insignificant in initial tests and was removed from the model. A 2-way ANOVA was conducted for each variable to investigate the fixed effects of packaging treatment, storage time, and corresponding interactions. Rather than analyzing odor panel scores for individual samples by day, multiple sampling days were combined to represent 3 phases designated by microbial growth. Phase of microbial growth was used as a fixed effect in place of day for chops and sausage odor panel ratings. For chops, phase 1 was the time period from d 0 to 10; phase 2 was the time period from d 15 to 37, and the time period of d 38 to 50 was grouped in phase 3. For sausage, phase 1 was the time period from d 0 to 5; phase 2 was the time period from d 10 to 19, and phase 3 was the time period from d 20 to 23.

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. The response variables (CIE L*, a*, and b* values, microbiological loads, pH, TBARS, and sensory panel scores for meaty odor) were evaluated, and significance of differences was defined as α = 0.05. Since the unequal variances were observed on sensory panel scores for off-odor (putrid, acid, sour, and rancid) and meaty odor, the generalized linear mixed model (PROC GLIMMIX) with the ddfm = kr option was used to allow different variances for different phases. The mean separations were obtained using Fisher’s LSD test.


RESULTS

Pork Chops

Objective Color.

The main effects of packaging treatment on objective color, microbial counts, pH, and TBARS values are presented in Table 1. Lean L* and b* values were lower (P < 0.05) for FreshCase chops vs. Control chops. Likewise, external fat of FreshCase chops had lower (P < 0.05) L* and b* values. This indicates control chops appeared lighter and more yellow in color. Both lean and external fat color of FreshCase chops displayed a redder/pinker appearance with greater (P < 0.05) a* values. Storage time affected (P < 0.05) chops’ L*, a*, and b* readings (Table 2). However, there were no discernible trends identified from values.


View Full Table | Close Full ViewTable 1.

Least squares means (LSM) of traits by packaging treatment for pork chops and ground pork stored at 1°C

 
Traits1 Control FreshCase SEM P-value
Pork chops
Lean L* 47.58a 46.75b 0.25 0.017
Lean a* −1.47b 0.71a 0.08 <0.0001
Lean b* 6.23a 5.83b 0.10 0.007
Fat L* 68.48a 67.77b 0.18 0.007
Fat a* 0.44b 1.18a 0.08 <0.0001
Fat b* 10.85a 9.93b 0.14 <0.0001
APB 5.41 5.26 0.06 0.088
LAB 5.49 5.41 0.06 0.325
pH 5.74 5.75 0.01 0.501
TBARS 0.27b 0.33a 0.01 0.0002
Ground Pork
L* 47.79 47.50 0.27 0.453
a* 6.05b 6.69a 0.08 <0.0001
b* 14.59 14.65 0.12 0.727
APB 6.03 5.98 0.03 0.202
LAB 5.98 5.94 0.03 0.252
pH 6.25b 6.28a 0.01 0.005
a,bLSM with different superscripts within row are different at P < 0.05.
1L* reflects the lightness of meat color, a* reflects the redness, and b* reflects the yellowness. APB: aerobic psychrotrophic bacteria; LAB: lactic acid bacteria; TBARS: thiobarbituric acid reactive substance.

View Full Table | Close Full ViewTable 2.

The effect of storage time (phase) on instrumental color (least squares means; CIE L*, a*, b*) of pork chops stored at 1°C1

 
Lean3
Fat3
Phase2 L* a* b* L* a* b*
Phase 1 45.89b (0.66) −0.34a (0.17) 5.62b (0.22) 68.34b (0.69) 0.33b (0.17) 9.48b (0.33)
Phase 2 49.03a (0.38) −0.82b (0.1) 5.74b (0.13) 71.21a (0.4) 0.6b (0.1) 10.18a (0.19)
Phase 3 46.16b (0.32) −0.08a (0.08) 6.33a (0.1) 65.94c (0.33) 1.07a (0.08) 10.75a (0.16)
a–cMeans with different superscript within columns are different at P < 0.05
1SE are given in parentheses.
2Phases are grouped on the basis of aerobic psychrotrophic bacteria plate count cutoff (log cfu/g). Phase 1: d 0 to 10 (<2 log cfu/g); phase 2: d 15 to 37 (2 to 6 log cfu/g); phase 3: d 38 to 50 (>6 log cfu/g).
3L* reflects the lightness of meat color, a* reflects the redness, and b* reflects the yellowness.

Bacteria and pH.

The pH values, as well as microbial counts for APB and LAB, were not affected (P > 0.05) by packaging types (Table 1). Storage time positively affected (P < 0.05; data not shown) pH. A slight increase in pH by storage time was observed, and the average pH values of chops stored in both types of packages ranged from 5.56 to 5.92 (data not shown).

Plate counts of APB and LAB increased (P < 0.05) throughout storage time (day; Table 3). Initially, levels of APB and LAB were relatively low, with counts of 1.53 and 1.56 log cfu/g, respectively. Both APB and LAB counts for pork chops exceeded 3 logs of growth by 25 d of refrigerated storage. After 3 logs of growth were observed, sampling became more frequent, and plate APB and LAB counts were steady and seemingly linear. Aerobic psychrotrophic bacteria exceeded 7 log cfu/g on d 46 of storage, whereas LAB exceeded 7 log cfu/g on d 48. Consequently, storage life of chops, regardless of packaging technology in accordance with APB, expired after 45 d of storage.


View Full Table | Close Full ViewTable 3.

Least square means (LSM) of bacterial counts (log cfu/g) for pork chops stored in different packaging types during storage time (day) at 1°C1

 
APB2
LAB2
Day Control FreshCase Average Control FreshCase Average
0 1.33 1.74 1.53n 1.49 1.63 1.56l
5 1.25 1.41 1.33n 1.15 1.35 1.25l
10 1.86 1.26 1.56n 1.29 1.16 1.22l
15 2.59 2.23 2.41n 2.42 2.39 2.41k
20 3.63 3.04 3.33m 3.49 3.70 3.6j
25 5.13 4.46 4.79k 5.29 4.66 4.97i
28 5.05 4.38 4.71k 5.14 4.75 4.94i
30 5.53 4.50 5.01j,k 5.63 4.91 5.27h,i
32 5.04 5.83 5.44h,i,j 4.87 6.03 5.45h,i
34 5.12 5.36 5.24i,j,k 5.15 5.46 5.31h,i
36 5.80 6.14 5.97e,f,g,h 6.30 6.34 6.32e,f
37 5.81 5.73 5.77g,h,i 5.97 5.44 5.7g,h
38 6.29 5.80 6.05e,f,g 6.31 5.96 6.13f,g
39 6.40 5.71 6.05e,f,g 6.84 6.13 6.49d,e,f
40 6.81 6.04 6.52c,d,e 6.87 6.33 6.6c,d,e,f
41 6.45 6.59 6.42c,d,e,f 6.90 6.52 6.71b,c,d,e
42 6.37 6.39 6.38c,d,e,f,g 6.63 6.93 6.78b,c,d,e
43 6.06 6.46 6.26d,e,f 6.19 6.69 6.44d,e,f
44 6.32 6.78 6.55c,d,e 6.36 6.88 6.62c,d,e,f
45 6.50 6.54 6.52c,d,e 6.61 6.55 6.58d,e,f
46 7.12 6.67 6.9b,c 7.20 6.74 6.97b,c,d
47 6.86 7.07 6.97a,b,c 6.98 7.30 7.14a,b,c
48 7.14 6.53 6.83b,c,d 7.23 6.68 6.95b,c,d
49 7.30 7.15 7.23a,b 7.43 7.12 7.27a,b
50 7.40 7.61 7.5a 7.51 7.66 7.58a
SEM 0.27 0.34 0.23 0.26 0.30 0.21
a–nLSM with different superscript letters within columns differ (P < 0.05).
1Since 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.
2Aerobic psychrotrophic bacteria (APB) grew on tryptic soy agar plates (Acumedia, Neogen Corp, Lansing, MI) that were incubated at 7°C for 10 d; lactic acid bacteria (LAB) grew on de Man, Rogosa, and Sharpe agar plates (Lactobacilli MRS Agar; Difco Laboratories, Inc.,Detroit, MI) that were incubated at 25°C for 5 d.

Odor Panel Score.

The main effect of packaging treatment did not (P > 0.05) influence raw or cooked chop sensory scores, indicating that the use of nitrite did not accelerate development of off-odors (data not shown). The main effect of storage time (phase) affected (P < 0.05) panel scores of all off-odors for raw chops (Table 4). As storage time increased, intensity of putrid, acid, sour, and rancid odors increased, whereas meaty odor remained prevalent for raw pork chops. Despite the notable increase (P < 0.05) in intensity of putrid, acid, sour, and rancid odors in cooked pork chops (Table 4), the intensity remained low for all these attributes (off-odor panel scores ranged from 0 to 2.49 cm on a 15-cm scale) over time. Therefore, in reference to product odor, indications of spoilage remained low throughout storage. However, APB and LAB counts grew beyond the recognized level of bacterial spoilage (7 log cfu/g) in phase 3, and there was very little indication of spoilage via product odor. Additionally, throughout storage, color of FreshCase samples remained bright red and acceptable in appearance.


View Full Table | Close Full ViewTable 4.

Least squares means (LSM) of odor panel scores by storage time (phase) effect for raw and cooked pork chops stored at 1°C1

 
Raw
Cooked
Phase2 Putrid Acidic Sour Rancid Meaty Putrid Acidic Sour Rancid Meaty
Phase 1 0.1b (0.05) 0c (0.00) 0.06b (0.02) 0.08c (0.05) 4.56 (0.12) 0.07c (0.04) 0.18b (0.11) 0.02c (0.01) 0.07c (0.04) 8.93a (0.24)
Phase 2 1.63a (0.17) 0.43b (0.07) 1.55a (0.12) 1.14b (0.14) 4.31 (0.15) 0.53b (0.10) 0.51a (0.10) 0.39b (0.08) 1.30b (0.23) 7.26c (0.22)
Phase 3 1.68a (0.14) 0.81a (0.09) 2.03a (0.12) 1.83a (0.13) 4.27 (0.10) 1.04a (0.14) 0.53a (0.10) 0.66a (0.08) 2.49a (0.15) 7.95b (0.14)
a–cLSM with different superscripts within columns are different at P < 0.05.
1Panel scores were measured as the distance of a marked vertical line from the extreme left end of a 15-cm scale. The extreme left indicated no presence, and the extreme right indicated a very strong presence. SE are given in parentheses.
2Phases are grouped on the basis of aerobic psychrotrophic bacteria plate count cutoff (log cfu/g). Phase 1: d 0 to 10 (<2 log cfu/g); phase 2: d 15 to 37 (2 to 6 log cfu/g); phase 3: d 38 to 50 (>6 log cfu/g).

TBARS Values.

The TBARS values for chops stored in FreshCase packages were slightly higher (P < 0.05) than those for Control packages (Table 1). However, averaging storage time, the difference was only 0.08 mg MDA/kg. The main effect of storage time did not (P > 0.05) influence TBARS value for chops.

Ground Pork Sausage

Objective Color.

The main effects of packaging treatment on objective color, microbial counts, and pH for ground pork sausage are presented in Table 1. There was no (P > 0.05) package treatment effect for pork sausage on lightness (L*) and yellowness (b*), whereas FreshCase sausage had higher (P < 0.05) a* values, translating to a much redder appearance. The main effect of storage time (day) was significant on sausage L*, a*, and b* readings (Table 5). However, there were no discernible trends identified from these values.


View Full Table | Close Full ViewTable 5.

The effect of storage time on instrumental color (least squares means; CIE L*, a*, b*) of ground pork sausages stored at 1°C1

 
Day L* a* b*
0 44.62e 5.39g 13.24d
5 45.89d,e 6.66b,c,d 13.50d
10 46.59d 5.62f,g 12.19e
13 44.82d,e 6.09e,f 14.51c
15 58.70a 6.53c,d,e 16.64a
17 46.57d 7.28a 14.84b,c
19 49.25c 6.26de 15.32b
20 44.99d,e 7.17ab 14.48c
21 52.99b 6.95a,b,c 16.55a
22 45.51d,e 6.03e,f 14.95b,c
23 44.17e 6.10e,f 14.66b,c
SEM 0.64 0.18 0.28
a–gLeast squares means with different superscripts within a column are different at P < 0.05.
1L* reflects the lightness of meat color, a* reflects the redness, and b* reflects the yellowness.

Bacteria and pH.

As shown in Table 1, the main effect of packaging treatment did not (P > 0.05) affect APB and LAB counts. Average pH throughout storage for FreshCase sausage was slightly higher (P = 0.005; Table 1) than for Control sausage. However, this 0.03 unit difference is of little practical importance. The pH of sausage ranged from 6.19 to 6.35 and was influenced (P < 0.05) by storage time. However, no discernible trends were identified from these values (data not shown), and the 0.16 unit differences in pH values are not practically significant.

Storage time (day) influenced counts of APB and LAB (P < 0.05; Table 6). Initially, levels of APB and LAB were high compared to those of whole-muscle pork, with counts of 3.42 and 2.48 log cfu/g, respectively. Both APB and LAB counts for sausage exceeded 2 logs of growth by 13 d of storage. After 2 logs of bacterial growth were observed, sampling became more frequent while plate APB and LAB counts were steady and seemingly linear. Aerobic psychrotrophic bacteria exceeded 7 log cfu/g on d 20 of storage, whereas LAB exceeded 7 log cfu/g on d 19. Consequently, storage life of sausage, regardless of packaging type in accordance with APB, expired after 19 d of storage.


View Full Table | Close Full ViewTable 6.

Least squares means (LSM) of bacterial counts (log cfu/g) for ground pork sausages stored in different packaging types during storage time (day) at 1°C

 
APB1
LAB1
Day Control FreshCase Average2 Control FreshCase Average2
0 2.47 2.48 3.42h 3.41 3.43 2.48i
5 3.24 3.08 3.36i 3.42 3.29 3.16h
10 4.57 4.72 4.63h 4.51 4.75 4.65g
13 5.48 5.31 5.39g 5.46 5.32 5.40f
15 6.29 5.87 6.01f 6.20 5.81 6.08e
17 6.62 6.65 6.57e 6.56 6.57 6.63d
19 7.07 7.02 6.84d 6.87 6.82 7.04c
20 7.22 7.16 7.14c 7.15 7.13 7.19c
21 7.35 7.63 7.37b 7.32 7.42 7.49b
22 7.69 7.59 7.62a 7.66 7.59 7.64a,b
23 7.80 7.80 7.69a 7.74 7.63 7.80a
SEM 0.09 0.08 0.06 0.08 0.1 0.06
a–iLSM with different superscript letters within columns differ (P < 0.05).
1Aerobic psychrotrophic bacteria (APB) grew on tryptic soy agar plates (Acumedia, Neogen Corp, Lansing, MI) that were incubated at 7°C for 10 d; lactic acid bacteria (LAB) grew on de Man, Rogosa, and Sharpe agar plates (Lactobacilli MRS Agar; Difco Laboratories, Inc.,Detroit, MI) that were incubated at 25°C for 5 d.
2Since 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.

Odor Panel Scores.

There was no interactive effect of packaging treatment and storage time observed on odor panel scores for both raw and cooked sausages. Sensory odor scores for both raw and cooked sausage samples were not (P > 0.05) affected by packaging treatment (data not shown). However, storage time (phase) influenced (P < 0.05) odor panel scores for all attributes of ground pork sausage (Table 7). As storage time increased, intensity of putrid, acid, sour, and rancid odors increased, and meaty odor decreased, followed by a small increase over time for both raw and cooked sausage. Use of spice mix blending in sausage might affect panelists’ ability to detect weak intensity of off-odors of cooked sausage since spices had a very offensive odor after cooking. Intensity ratings for all attributes, excluding meaty odors, remained very low (off-odor panel scores ranged from 0 to 1.27 for raw and cooked sausage). Therefore, indications of spoilage due to odor remained low throughout storage. Additionally, even though APB and LAB counts grew beyond the recognized level of bacterial spoilage (7 log CFU/g) in phase 3, there was very little indication of spoilage odors. Throughout storage, color of FreshCase samples remained bright red and acceptable in appearance.


View Full Table | Close Full ViewTable 7.

Least squares means of odor panel scores by storage time (phase) for raw and cooked pork sausages stored at 1°C1

 
Raw
Cooked
Phase2 Putrid Acidic Sour Rancid Meaty Putrid Acidic Sour Rancid Meaty
Phase 1 0c (0.0) 0.08c (0.04) 0c (0.00) 0.09b (0.06) 6.61a,b (0.80) 0b (0.00) 0b (0.00) 0.03b (0.03) 0b (0.00) 7.84b (0.34)
Phase 2 0.09b (0.04) 0.51b (0.12) 0.43b (0.12) 0.54a (0.08) 7.17a (0.21) 0.11a (0.05) 0.15a,b (0.07) 0.28a (0.09) 0.54a (0.12) 9.13a (0.26)
Phase 3 0.40a (0.11) 1.12a (0.10) 1.31a (0.10) 0.73a (0.08) 5.87b (0.17) 0.16a,b (0.08) 0.22a (0.09) 0.20a,b (0.09) 0.71a (0.10) 8.66a,b (0.26)
a–cMeans with different superscript within columns are different at P < 0.05.
1Panel scores were measured as the distance of a marked vertical line from the extreme left end of a 15-cm scale. The extreme left indicated no presence, and the extreme right indicated a very strong presence of the odor attributes. SE are given in parentheses.
2Phases are grouped on the basis of aerobic psychrotrophic bacteria plate count cutoff (log cfu/g). Phase 1: d 0 to 5 (<3 log cfu/g); phase 2: day 10 to 19 (2 to 7 log cfu/g); phase 3: d 20 to 23 (>7 log cfu/g).

TBARS Values.

Statistically, the degree of lipid oxidation was affected (P < 0.05) by the interaction of packaging treatment by storage (day) for pork sausage (Table 8). However, the level of oxidative rancidity, indicated by TBARS values, remained very low for all samples over all time periods and treatments. The maximum tested TBARS value for Control sausage was 0.35 mg MDA/kg, and the maximum TBARS value for FreshCase samples was 0.55 mg MDA/kg.


View Full Table | Close Full ViewTable 8.

Least squares means (LSM) of thiobarbituric acid reactive substances (TBARS) values for pork sausage affected by packaging × storage time (day) stored at 1°C1

 
Day
Packaging 0 5 10 13 15 17 19 20
Control 0.34b,c,d 0.21e,f,g 0.33b,c,d,e 0.20e,f,g 0.23d,e,fg 0.18f,g 0.35b,c 0.32b,c,d,e
FreshCase 0.27c,d,e,f,g 0.24c,d,e,f,g 0.25c,d,e,f,g 0.29b,c,d,e,f,g 0.30b,c,d,e,f 0.17g 0.36b,c 0.55a
a–gLSM with the different superscript are different at P < 0.05
1The SEM for the test is 0.04.


DISCUSSION

For several years, sodium nitrite (NaNO2) combined with sodium chloride has been used in processed meat as a preservative to inhibit growth of Clostridium botulinum (Pierson and Smoot, 1982; Christiansen et al., 1974). However, the amount of nitrite in FreshCase packages utilized in this study was relatively low and does not provide any preservative antimicrobial purpose. Additionally, nitrite can inhibit growth of some spoilage bacteria, like Enterobacteriaceae and thermosphacta, but not LAB (Nielsen, 1983). Lactic acid bacteria are commonly found growing on vacuum-packaged meat at chilled temperatures (Blickstad et al., 1981; Shaw and Harding, 1989; von Holy et al., 1991). Results from this study support these facts, showing no packaging effect on microbial growth.

As expected, both chops and sausage displayed redder color (greater a* values) using FreshCase packages. This is confirmed by other studies showing nitrite as a common curing agent used in meat to maintain fresh red color (Pourazrang et al., 2002; Zarringhalami et al., 2009). The formation of NO myoglobin under vacuum conditions produces a red meat color (Siegel, 2010). Other studies (Claus and Du, 2013; Song et al., 2015) showed that use of either nitrite-embedded packaging film or nitrite as a spray could extend stability of red color for beef products.

Additionally, a florescent green color was observed on chops in Control packages on d 30 of storage. Sulphmyoglobin is responsible for the green color in meat and is highly undesirable to consumers. This sulfa compound is produced from cysteine by Lactobacillus sake when glucose and oxygen are limited (Egan et al., 1989). Meat with high pH has a higher incidence of greening; however, normal-pH meat can also develop a green pigment (Borch et al., 1996).

The internal color of cooked sausage using the FreshCase packages was pink. Generally speaking, after cooking, meat color turns gray or brown because oxymyoglobin is not heat stable. However, the red NO porphyrin ring system (usually called nitrosomyochromogen) can still exist even when NO myoglobin is heated under 120°C and the protein is denatured (Honikel, 2008). It was not expected for cooked sausage to maintain a pink color after cooking, which could mislead consumers regarding doneness of sausage, resulting in overcooking and possibly a negative effect on palatability.

Although pork chops using FreshCase packaging technology did have a higher TBARS value, overall, it was lower than the human threshold for detection of rancidity of 1 mg MDA/kg (Tarladgis et al., 1964). Likewise, all TBARS values for pork sausages were also lower than 1 mg MDA/kg. These findings support the low intensity levels of putrid and rancid odors in the sensory portion of this study. Additionally, low TBARS values of chops and sausage stored in vacuum packages confirmed results showing that vacuum packages can minimize lipid oxidation effectively (Cayuela et al., 2004; John et al., 2004, 2005). A study conducted by Krause et al. (2003) found pork chops stored in vacuum packages and modified-atmosphere packages (MAP) with 0.5% CO, 70% CO2, and 29.5% N2 have the lowest TBA values compared with chops stored in overwrap packages and MAP with 20% CO2 and 80% N2. However, Cornforth and Hunt (2008) also stated that “CO MAP has a negative image among consumers because CO is a potentially hazardous gas,” although the level of CO employed in MAP was not hazardous to consumers. Therefore, the use of FreshCase technology can maintain the fresh red color of meat and low oxidation levels without use of CO during the packaging process.

Conclusion

The results of this study prove that FreshCase packaging technology can be used to maintain a bright red color in a vacuum-sealed package and to prolong the storage life of fresh pork in comparison to other methods of packaging that allow for meat to remain bright red such as MAP and traditional overwrap packaging. Compared to MAP technology, FreshCase Packaging Technology does not require any additional equipment to modify the atmosphere during packaging. FreshCase packages can be used with existing vacuum packaging equipment but still provide the same bright red color in meat as MAP with low CO concentration. Further research may be conducted to test the residual nitrite on the meat surface to prove that the residue of nitrite used in FreshCase is nondetectable after packages are opened.

 

References

Footnotes


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