Y. Chiang and T. P. Ringkob
University of Nevada, Reno

ABSTRACT:

The objective of this study was to compare the impact of 2 retail display temperatures, 3 processing procedures, and 2 vitamin E levels on shelf life, bacterial count, and discoloration of retail beefsteaks. Vacuum packed (boxed) strip loins were purchased at Scolari's Food and Drug of Sparks, Nevada which included 12 packer A USDA Choice, 12 packer A USDA Select, and 12 packer B no-roll boneless strip loins (IMPS #180). A significant difference in vitamin E level was found between packer A and B strip loins (P < .05). Two retail display temperatures were compared (1 ± 0.3° C and 5 ± 0.3° C). Three cutting methods, sanitized knife cut, store knife cut, and store saw cut, were used for processing procedures. The steak images were imported into an image analysis program (Macintosh IPLab) to map lean surface darkening and discoloration. Sanitized knife cutting helped beefsteaks keep fresh color longer (P < .05). Processing procedures also affected the bacterial counts on the day 0 steaks (P < .05), but no difference (P > .05) was found on the discard day. Saw-cut steaks showed a higher (P < .05) percentage of both dark and brown discoloration, but there was no difference (P > .05) between sanitized and store knife cut. Low temperature (1° C) display extended shelf life (P < .05). The percentage of dark and brown discoloration was decreased (P < .05) on day 4 under lower display temperature. No difference (P > .05) in bacterial counts was found on the discard day due to temperature. No difference (P > .05) in shelf life or bacterial counts was found between vitamin E (packer A) and non-vitamin E (packer B) containing steaks. There was no difference (P > .05) between vitamin E and non-vitamin E steaks on day 4, however, both dietary treatments (E and non-E) showed more (P < .05) darkening and discoloration at the higher temperature (5° C). This study demonstrates that sanitation and temperature control are very important in retail beefsteak discoloration.

Introduction

Two problems cited by supermarket meat managers, which cause beef retail meat packages to be discounted or discarded, are poor workmanship and discoloration. Poor workmanship which displays too much fat or bone and therefore lowers the perceived value of the retail beef cut can be remedied through better procurement specifications, management and training. However, discoloration of fresh beef can be a much more complex problem also leading to lower sales and therefore negatively affects profitability. Any improvement in sanitation and temperature control usually lowers bacterial count and lengthens retail shelf life. If the retail packaged beef maintains a desirable bright red color for a longer period, more inventory can be displayed which leads to increased sales.

Fresh bright red meat is limited by surface accumulation of brown colored pigment, metmyoglobin. There are many factors that affect surface metmyoglobin accumulation. These factors include bacterial load, display temperature, oxygen consumption, and dietary vitamin E supplementation (Renerre, 1990). Madhavi et al. (1993) indicated that the progress of discoloration of fresh beef is a direct response to the impact of processing method on color stability. With regard to the method, the progress of discoloration was in the following order: knife-cut steaks < saw-cut steaks < ground muscle. Dietary vitamin E supplementation increased the color shelf life of beef muscle (Chan et al. 1996), but no differences in bacterial load were found between different vitamin E treatments during storage (Chan et al. 1995). The objective of this study was to compare the impact of 2 retail display temperatures, 3 processing procedures and 2 vitamin E levels on discoloration, bacterial count and shelf life of retail beefsteaks.

Sampling

Vacuum packed (boxed) strip loins were purchased at Scolari’s Food and Drug of Sparks, Nevada which included 12 packer A USDA Choice, 12 packer A USDA Select, and 12 packer B no-roll strip loins. One thick (5 cm) knife cut, four regular (2.5 cm) knife cut, and four regular (2.5 cm) saw cut steaks were cut from each vacuum packaged strip loin at one of 11 Scolari’s supermarkets, on a random basis, in Reno and Sparks, Nevada. Steaks were cut from the anterior end of the loin (13^th rib section). Degrees of marbling ranged from slight to moderate when compared to USDA color marbling standards.

Each thick (5-cm) loin steak was bisected into 2 thinner steaks using a sterilized butcher knife at the University Meats Laboratory. The bacterial samples were taken from the "store" bottom or anterior face of the strip loin and the "fresh" cut (sterilized knife) surfaces by sponging for total aerobic plate count (APC). The resulting steaks were repackaged supermarket style in Styrofoam trays with oxygen permeable film overwrap. The two steaks were packaged such that the original displayed "store" surface was visible in one steak and the "fresh" cut surface in the second steak. The 4 store-knife-cut and 4 saw-cut loin steaks were displayed in the original supermarket trays.

From each strip loin, one fresh-cut, one store-face, two store-knife-cut, and two saw-cut steaks were displayed at 5 ± 0.3° C and two store-knife-cut and two saw-cut steaks were displayed at 1 ± 0.3° C. The display temperatures were recorded daily. Steaks were pulled when meat department personnel would notice any discoloration or darkening. Steaks were discarded when meat department personnel would consider the steak no longer salable due to discoloration.

Bacterial Counts

The bacterial samples were taken from the fresh-cut, store-face, and one of store-knife-cut and saw-cut steaks on the "discard" day. For the other store-knife-cut and saw-cut steaks, the bacterial samples were taken on the "pull" day. The sponge bags, 25 ml of sterile Butterfield’s Phosphate buffer (BP), gloves, and 10 cm ´ 5 cm templates were purchased from Biotech Co. for sampling. The sponges were hydrated by adding 25 ml of BP buffer and well massaged. The bacterial samples were taken by sponging the steak surfaces 10 times horizontally and 10 times vertically within the template followed by agitating each sponge in the sample bag at 8 bumps per second by using a stomacher (IUL USA, Inc). The samples were diluted (a range of 10^-1 to 10 ^–6) depending on the bacterial load.

The total aerobic petrifilm plates were purchased from 3M Microbiology Products (St. Paul, MN) and were used for enumeration. One ml of the diluted sample was added to the petrifilm plate and incubated at 35 ± 1° C for 48 ± 3 hours. The numbers of colony forming units were counted and the total number of bacteria was calculated as cells per square centimeter of lean steak surface (APC/cm²).

Vitamin E Verification

A small piece (~3 g) of beef muscle was cut from each strip loin for vitamin E verification. One g of fresh muscle was weighted and put into a 25 ml test tube followed by adding 250 mg of ascorbic acid and 7.3 ml of 11% KOH (55% ETOH and 45% deionized distilled water) digestion solution. The test tubes were incubated at 80° C (water bath) for 15 min. After cooling the tubes on ice for 1 min, 4 ml of isooctane was added into the samples followed by 2 min of vortex mixing. After phase separation, the upper layer phase was transferred into an autosampler vial for HPLC analysis (a 10-min run, mobile phase: 96% isooctane : 4% THF [vol/vol] prepared fresh daily). The units of vitamin E were calculated as micrograms per gram of fresh beef muscle (Liu et al., 1996).

Image Analyses

The steaks were photographed with 160T Kodak slide film under 3000 K lighting conditions on a copy stand using an 18% gray card to adjust the F stop. The steaks were photographed everyday post purchase from day 0 until the pull or discard day. An HP ScanJet 3c scanner with a slide scanner top was set at 1.8 gamma and 300 dpi to scan TIF images (ca. 325K) from slides to a Zip disk. The images were imported into IPLab, (Signal Analytics Corp. Vienna, VA, USA) on a Macintosh Power PC platform.

The color images were displayed on the computer screen. A region of interest (ROI) was displayed on the computer screen by using a free-hand tool to trace the steak outline and the ROI was saved. The procedure in IPLab is to place it on a black background. The images were converted from the RGB format to the CMY format. After comparison to the actual image, it was found that segmentation of the cyan image could very closely approximate the lean and discolored areas by adjusting the width of the gate by using the histogram function. The lean area (red pixels) could be approximated very closely on the cyan split image by using a minimum between 45 and 85 and a maximum of 195. The steak surface that started to darken slightly was represented by yellow pixels with a setting of 115 minimum and 195 maximum. The discolored (brown color) meat surface area was matched by a setting of 125 minimum and the same 195 maximum and mapped with green pixels. The pixel color must be added to the IPLab image in the order of the largest number of pixels to the least, i.e. lean (red), slightly dark (yellow) and discolored (green). The settings are different from the first report (Ringkob, 1996) due to a gamma of 1.8 for the scanning versus no gamma setting for the first scanning process. Ringkob (1997) found that segmentation minimums and maximums must be calibrated each time due to slight differences in lighting conditions and other instrumentation variables.

Statistical Analyses

Results were analyzed by analysis of variance using the GLM procedure of SAS (1985). MXANOVA, SAS macro was used for analyzing mixed factor ANOVA and checking for the violations of assumptions (Fernandez, G. C. J., 1997).

Results and Discussion

Sanitized cutting helped beefsteaks keep fresh color longer (P < .05) as shown in Table 1. Fresh-cut steaks in the retail display case maintained desirable color longer than store-knife-cut steaks followed by saw-cut steaks. Processing procedures also affected the bacterial counts on the day 0 steaks (P < .05). The effect of cutting methods on bacteria load on day 0 was sanitized-knife-cut steaks < store-knife-cut steaks < saw-cut steaks < bottom steaks. No difference (P > .05) was found on the discard day. Saw-cut steaks showed a higher (P < .05) percentage of both dark and brown discoloration on day 4, but there was no difference (P > .05) between sanitized and store knife cuts (Table 1).

Low display temperature (1° C) extended shelf life (P < .05) for both pull and discard steaks (Table 2). No difference (P > .05) in bacterial counts was found on the pull and discard days due to temperature. The percentage of dark and brown discoloration was decreased (P < .05) on day 4 due to lower display temperature.

Implications

This study demonstrates the importance of sanitation and temperature control on retail beefsteak shelf life and discoloration. The supermarket meat department can increase beef sales and profits by following recommended sanitation procedures and maintaining strict temperature controls.

REFERENCES

3M Petrifilm Plates: Helping You Manage Lab Resources More Effectively. 3M Microbiology Products. St. Paul, MN 55144.

Chan, WKM., K Hakkarainen, C Faustman, DM Schaefer, KK. Scheller, & Q Liu. 1996. Dietary vitamin E effect on color stability and sensory assessment of spoilage in three beef muscles. Meat Sci. 42: 387-399.

Fernandez, GCJ. 1997. MXANOVA, SAS macro for analyzing mixed factor ANOVA and checking for the Violations of assumptions. APST 663: Design and Analysis of Economic and Statistics. University of Nevada-Reno, Reno, NV 89557.

Liu, Q, K. K Scheller, and DM Schaefer. 1996. Technical note: a simplified procedure for vitamin E determination in beef muscle. J. Anim. Sci. 74: 2406-2410.

Madhavi, DL and CE Carpenter. 1993. Aging and processing affect color, metmyoglobin reductase and oxygen consumption of beef muscles. J. Food Sci. 58: 939-942.

Renerre, M. 1990. Review: Factors involved in the discoloration of beef meat. Int. J. Food Sci. Technol. 25: 613-630.

Ringkob, TP. 1996. Image analysis to measure color changes in fresh retail beef steaks. Proceedings of 42^nd International Congress of Meat Science and Technology, Lillehammer, Norway. pp. 264-265.

Note: