Lactic acid enhancement can improve the fresh

Published December 4, 2014

Lactic acid enhancement can improve the fresh and cooked color of dark-cutting beef1,2 J. K. Apple,*3 J. T. Sawyer,*4 J.-F. Meullenet,† J. W. S. Yancey,* and M. D. Wharton* *Department of Animal Science, and †Department of Food Science, Division of Agriculture, University of Arkansas, Fayetteville 72701

ABSTRACT: Two experiments were conducted to compare the effects of enhancing dark-cutting (DC) strip loins with lactic acid (LAC) on fresh and cooked beef color, as well as sensory attributes, with nonenhanced, normal pH strip loins (CH). Strip loins, with an average ultimate pH of 6.70 ± 0.11 (Exp. 1) and 6.78 ± 0.11 (Exp. 2), were cut into 2 equal-length sections, and DC sections were randomly assigned as either nonenhanced DC or DC enhanced with 0.15 (Exp. 1), 0.35 (Exp. 1 and 2), or 0.50% (Exp. 2) LAC at a target of either 105 (Exp. 1) or 112% (Exp. 2) of the raw product weight. Enhancement with 0.15 and 0.35% LAC did not (P > 0.05) affect postenhancement pH of DC strip loins when enhanced at a target of 105% (Exp. 1); however, postenhancement pH was reduced (P < 0.05) substantially by LAC enhancement at 115% of raw product weight, with pH values of DC sections enhanced with 0.50% LAC being similar (P > 0.05) to those of CH strip loin sections (Exp. 2). In Exp. 1, raw steaks from CH strip loins had greater (P < 0.05) a* and b* values as well as Japanese beef color scores compared with steaks from nonenhanced and LAC-enhanced DC strip loins across the first 3 d of simulated retail display (LAC enhancement × retail display duration; P < 0.01). Again in Exp. 2, raw steaks from CH

sections had greater (P < 0.05) L*, a*, and b* values and Japanese color scores than did steaks from DC sections, regardless of LAC enhancement; however, mean Japanese color scores of CH steaks were only 0.7 and 0.4 units greater (P < 0.05) than the color scores of DC steaks enhanced with 0.35 and 0.50% LAC, respectively. In Exp. 1, CH steaks received the highest (P < 0.05) cooked color and degree of doneness scores, yet scores for CH steaks and steaks from DC sections enhanced with 0.50% LAC did not (P > 0.05) differ when cooked to 71°C in Exp. 2. Fresh and cooked color of DC beef was only minimally altered when enhanced with 0.35% LAC at 105% of the fresh product weight; however, when DC beef was enhanced with 0.35 and 0.50% LAC at a target of 112%, fresh and cooked color were improved close to that of CH beef. Because the persistent red or pink cooked color of DC was virtually eliminated by 0.50% LAC enhancement, LAC-enhanced DC beef may be suitable for food-service markets; however, the raw or fresh color results of Exp. 2 suggested that the fresh color of DC beef can be improved to the color of normal pH beef by postmortem acidification, leading to the possible recoupment of most, if not all, of the lost value associated with DC beef.

Key words: cooked color, dark-cutting beef, fresh color, lactic acid, pH, postmortem enhancement ©2011 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2011. 89:4207–4220 doi:10.2527/jas.2011-4147 1 This research was funded by the Arkansas Beef Council (Little Rock) and Arkansas beef cattle producers through their $1.00 per animal check-off program. 2 The authors wish to express their appreciation to R. T. Baublits and Tyson Foods Inc. (Springdale, AR) for assistance with strip loin procurement; M. Lee and J. Powell (Department of Animal Science, University of Arkansas Division of Agriculture, Fayetteville) for service on the trained visual color panels; and T. Tokar (Department of Food Science, University of Arkansas Division of Agriculture, Fayetteville) for scheduling and conducting sensory descriptive-attribute panels. 3 Corresponding author: [email protected] 4 Present address: Tarleton State University, Stephenville, TX 76402. Received April 6, 2011. Accepted July 30, 2011.

INTRODUCTION Dark-cutting (DC) beef is a quality defect resulting from the depletion of muscle glycogen reserves before slaughter, which curtails normal postmortem muscle metabolism and pH decline. The resultant DC beef is characterized by an ultimate muscle pH in excess of 6.0, a very dark red to almost black lean color, and a dry, firm and “sticky” lean surface texture. Even though fewer than 2% of the fed steers and heifers slaughtered annually produce DC beef (McKenna et al., 2002; Garcia et al., 2008), DC beef is considerably devalued by reductions of one-third to a full beef quality grade (USDA, 1997) and an additional discount of approxi-

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mately $70/100 kg on a carcass weight basis (USDA, 2010). Most of the previously published research on DC meat has focused on the preslaughter factors that may play a key role in excessive antemortem muscle glycogenolysis and the development of DC meat (Voisinet et al., 1997; Kreikemeier et al., 1998; Scanga et al., 1998). However, recent research has shown that enhancing postrigor DC beef with 0.25 to 0.50% lactic acid (LAC) could reduce muscle pH, thereby eliminating the persistent red-pink color typically observed in cooked DC beef and producing an internal cooked color similar to that of normal pH beef (Sawyer et al., 2008, 2009). Thus, LAC enhancement has the potential to add value to DC beef in the food-service industry, where consumers are concerned more with cooked rather than fresh beef color. Additionally, Sawyer et al. (2009) noted that LAC enhancement produced a positive change in the fresh color attributes of DC beef. Therefore, 2 experiments were conducted to test the effects of LAC enhancement of DC beef on fresh color during 5 d of simulated retail display, cooked beef color, and cooked steak palatability.

MATERIALS AND METHODS Institutional Animal Care and Use Committee approval was not obtained for this experiment because no live animals were used.

Strip Loin Selection and Enhancement Treatments Normal pH, low Choice (CH; n = 5/experiment) and DC (n = 23/experiment) beef strip loins (Institutional Meat Purchase Specification #180) were selected based on ultimate (48-h) muscle pH of the LM (IQ 400 pH meter with stainless steel puncture probe, IQ Scientific Instruments Inc., Carlsbad, CA), identified, and collected during fabrication at a large commercial slaughter facility (Tyson Foods Inc., Emporia, KS). The average pH of CH and DC strip loins was 5.37 ± 0.08 and 6.70 ± 0.11, respectively, in Exp. 1 and 5.58 ± 0.08 and 6.78 ± 0.11, respectively, in Exp. 2. Vacuum-packaged strip loins were transported to the University of Arkansas Red Meat Abattoir and allowed to age an additional week at 2°C. After the 7-d aging period, strip loins were removed from their vacuumsealed bags, and all subcutaneous fat, the gluteus medius and other accessory muscles, and heavy connective tissue were removed from the LM. Each LM was then transversely sectioned into 2 equal-length sections, and a 1.27-cm-thick slice was removed from each section to measure preenhancement LM pH. The DC sections (n = 46) were subsequently assigned at random to either a nonenhanced, negative control (DC; n = 9/experiment) or enhancement with 0.15 (n = 18; Exp. 1), 0.35

(n = 18/experiment; Exp. 1 and 2), or 0.50% (n = 18; Exp. 2) LAC (Birko Corp., Henderson, CO) at a target of 105 (Exp. 1) or 112% (Exp. 2) of the raw section weight. The CH sections (n = 9/experiment) served as a nonenhanced, positive control. The LAC solutions used in both experiments were prepared in 4°C tap water and agitated continuously with a Rotosolver high-speed mixer (Admix Inc., Manchester, NH) until enhancement. Each strip loin was weighed, and DC sections were enhanced to either 105 (Exp. 1) or 112% (Exp. 2) of the specific section weight with the randomly assigned LAC solution via a multineedle injector (Fomaco 20/40, Reiser Inc., Canton, MA). The average pH of the 0.15 and 0.35% LAC solutions used in Exp. 1 were 2.83 and 2.70, respectively, whereas the average pH of the 0.35 and 0.50% enhancement solutions used in Exp. 2 were 2.75 and 1.97, respectively. Enhanced DC sections were placed into a vacuum tumbler (model TM-300, Promarks Inc., Claremont, CA) immediately after injection, tumbled at 35 rpm under 100 kPa of vacuum for 10 min, removed from the tumbler, and allowed to drip on racks for 1 h before reweighing to calculate postenhancement yield (difference between pre- and postenhancement weights divided by the preenhancement weight multiplied by 100).

Steak Fabrication and Simulated Retail Display All sections were cut into a single 1.27-cm-thick slice and five 2.54-cm-thick steaks. The LM slice was used to measure postenhancement pH and water-holding capacity, whereas 2 steaks were vacuum packaged and immediately frozen at −20°C, one for descriptive-attribute panels and the other for cooked color and WarnerBratzler shear force (WBSF) determinations. The 3 remaining steaks from each section were placed into rigid 5.1-cm-deep plastic trays with an absorbent pad (Tray No. CS978, Cryovac Sealed Air Corp., Duncan, SC), flushed with an 80% O2/20% CO2 gas mixture (Airgas Inc., Springdale, AR), and hermetically sealed with an oxygen-barrier film (model LID 1050, oxygen transmission rate: 0.05) between CH and nonenhanced DC strip loin sections (Figure 1). Even though enhancement yields failed to meet the targets of 105 and 115% of the raw section weight, DC sections enhanced with 0.35 (Exp. 1) and 0.50% LAC (Exp. 2) had 0.8 and 1.9% greater (P < 0.05) mean postenhancement yields than those enhanced with 0.15 (Exp. 1) and 0.35% LAC (Exp. 2), respectively. In Exp. 1, CH strip loin sections had lower (P < 0.05) pre- and postenhancement pH values than did nonenhanced DC sections, and enhancement with 0.15 and 0.35% LAC did not (P > 0.05) alter postenhancement pH of the DC sections when enhanced at a target of 105% in Exp. 1 (Table 1). Again, preenhancement pH was less (P < 0.05) in CH than in DC strip loins in Exp. 2; however, postenhancement pH of DC beef was markedly decreased (P < 0.05) by LAC enhancement at 115% of raw product weight, with postenhancement pH values similar (P > 0.05) between CH sections and DC sections enhanced with 0.50% LAC. Treating normal pH beef with organic acids can reduce postenhancement muscle pH values (Oreskovich et al., 1992; Seuss and Martin, 1993; Aktaş et al., 2003). More specifically, Medyński et al. (2000) reported that pH values of normal pH beef and pork decreased to values of ≤4.3 as the LAC concentration in the marinade increased to ≥1.0%. Furthermore, Sawyer et al. (2008) found that when DC strip loins were enhanced at 110% of the raw weight, postenhancement pH values decreased from 6.37 to 4.10 as the LAC concentration of the enhancement solution increased from 0 to 2%. More recently, pH of DC strip loins was reduced by 0.37 and 1.77 pH units by 0.25 and 0.50% LAC enhancement at 110% of the raw weight, with additional reductions in postenhancement pH of 1.82 and 2.14 units when enhanced with 0.75 and 1.00% LAC (Sawyer et al., 2009). The latter results were the basis for the LAC amounts of the enhancement treatments used in the present study; however, the lack of change in postenhancement pH in Exp. 1 was believed to be a response to the enhancement rate (105%) and actual enhancement solution uptake rather than the LAC concentration, pH of the enhancement solution, or both. Although DC LM sections enhanced with 0.35% LAC had greater (P < 0.05) total moisture than DC sections enhanced with 0.15% LAC in Exp. 1, DC sections, re-

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Table 1. Effects of lactic acid enhancement on pH and water-holding capacity of dark-cutting beef steaks (Exp. 1 and 2) Lactic acid solution, % Normal-pH control

Characteristic Exp. 1 No. of sections Preenhancement pH1 Posttreatment pH2 Total moisture, % Bound moisture, % Free moisture, % Exp. 2 No. of sections Preenhancement pH1 Posttreatment pH2 Total moisture, % Bound moisture, % Free moisture, %

 

Dark-cutting control  

9 5.37b 5.33b 69.5c 76.20b 23.80a   9 5.58b 5.56c 68.7c 76.32c 23.68a

0.15  

9 6.70a 6.54a 73.2ab 86.25a 13.75b   9 6.79a 6.90a 73.32b 89.54a 10.46c

0.35  

18 6.69a 6.59a 73.0b 85.78a 14.22b     — — — — —

0.50  

18 6.70a 6.49a 74.5a 82.91a 17.09b   18 6.77a 5.99b 75.0ab 79.49b 20.51b

SEM  

  — — — — —   18 6.77a 5.79bc 76.3a 76.42c 23.58a

  0.030 0.055 0.56 1.490 1.490     0.030 0.107 0.92 1.179 1.179

a–c

Within a row, least squares means lacking common superscripts differ, P < 0.05. Measured after removal from vacuum pouches and within 1 h of treatment. 2 Measured after enhancement, vacuum tumbling, and a 1-h drip/equilibration period. 1

gardless of LAC enhancement, had greater (P < 0.05) percentages of total and bound moisture and lower (P < 0.05) percentages of free moisture than did CH sections (Table 1). In Exp. 2, total moisture percentages were greater (P < 0.05) in DC sections enhanced with 0.50% LAC than in nonenhanced DC and CH sections, whereas nonenhanced DC sections had more (P < 0.05) moisture than did CH sections. As expected, untreated DC sections had the most (P < 0.05) bound moisture and the least (P < 0.05) free moisture percentages in Exp. 2. However, in Exp. 2, LAC enhancement reduced (P < 0.05) the proportions of bound moisture and in-

Figure 1. Effect of lactic acid (LAC) enhancement on product yields measured after enhancement, vacuum tumbling, and a 1-h drip period (Exp. 1). Within each experiment, bars for nonenhanced, normal pH, low Choice, positive controls (CH); nonenhanced, darkcutting negative controls (DC); DC strip loin sections enhanced with 0.15% LAC (Exp. 1); DC strip loin sections enhanced with 0.35% LAC (Exp. 1 and 2); and DC strip loin sections enhanced with 0.50% LAC (Exp. 2) represent the mean of 9, 9, 18, 18, and 18 strip loin sections, respectively. Error bars lacking common letters (a–c) differ, P < 0.05.

creased (P < 0.05) the proportions of free moisture when compared with nonenhanced DC sections. More important, the percentages of bound and free moisture of DC sections enhanced with 0.50% LAC were not (P < 0.05) different from those of CH sections. Normal ultimate muscle pH of meat (5.4 to 5.7) is slightly greater than the isoelectric point (pI) of myofibrillar proteins (5.0 to 5.3; Wismer Pedersen, 1971; Hamm, 1986), and the number of reactive groups available to bind water will increase when muscle pH values are greater than 6.0 or below 4.0 (Gault, 1985). There are more reactive protein side-chains in the DC beef; therefore, the nonenhanced DC beef, with mean pH values in excess of 6.5, had the greatest proportion of bound moisture and the least proportion of free moisture (Table 1). Even though neither postenhancement pH values nor water-holding capacity of DC beef were affected by LAC enhancement in Exp. 1, the reduction in postenhancement LM pH by enhancement with 0.50% LAC resulted in percentages of bound and free moisture similar to those of CH beef. Sawyer et al. (2008, 2009) observed similar results when postenhancement pH of DC beef was reduced to values near the pI with LAC. It should be noted that the proportion of bound water was increased to that of nonenhanced DC beef when the pH of DC beef was reduced to 4.1 by enhancement with 2.0% LAC (Sawyer et al., 2008), which is consistent with the work of Rao and Gault (1989) and Rao et al. (1989), who demonstrated that acidification of normal pH meat below the pI increased moisture retention.

Instrumentally Evaluated Fresh Beef Color There were no (P ≥ 0.63) interactive effects of LAC enhancement and retail display duration, nor were there main effects (P ≥ 0.45) of retail display dura-

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Table 2. Effects of lactic acid enhancement on fresh beef color of dark-cutting strip steaks (Exp. 1 and 2) Lactic acid solution, % Normal-pH control

Characteristic1 Exp. 1 No. of steaks L* Hue angle Exp. 2 No. of steaks L* a* b* Hue angle C* Japanese color scores2

 


9 47.03a 36.89a   9 47.07a 30.76a 22.80a 36.54b 38.29a 3.5d

0.15  

9 35.01c 33.22c   9 37.12c 26.59bc 18.28c 34.35c 32.27bc 6.6a

0.35  

18 36.48bc 33.97bc     — — — — — —

0.50  

18 37.75b 34.17b   18 44.24b 27.71b 20.54b 36.57b 34.50b 4.2b

SEM  

  — —   18 44.43b 24.43c 18.77c 38.08a 30.84c 3.9c

  0.806 0.266     0.656 0.945 0.609 0.486 1.102 0.11

a–d

Within a row, least squares means lacking common superscripts differ, P < 0.05. L* = measure of darkness to lightness (larger value indicates a lighter color); a* = measure of redness (larger value indicates a more intense red color); and b* = measure of yellowness (larger value indicates a more yellow color). Hue angle represents the change from the true red axis (larger value indicates a shift from red to yellow). Chroma (C*) represents the total color of the sample (larger value indicates a more vivid color). 2 Plastic disks with meat-like appearance, with 1 = light red to 7 = very dark red (National Institute of Animal Industry, Ibaraki, Japan). 1

tion on L* values or hue angle in Exp. 1 (Table 2). The instrumental color of steaks from nonenhanced and LAC-enhanced DC sections was darker (lesser L* values; P < 0.05) and closer to the true red axis (smaller hue angles; P < 0.05) than was the instrumental color of steaks from CH sections, and steaks from DC sections enhanced with 0.35% LAC were lighter (greater L* values; P < 0.05) and had decreased (P < 0.05) hue angles compared with those of nonenhanced DC steaks. In Exp. 1, steaks from CH strip loin sections were redder (greater a* values; P < 0.05) and more (P < 0.05) yellow (greater b* values) than nonenhanced and LAC-enhanced DC steaks after 1 and 3 d of simulated retail display (LAC enhancement × retail display duration, P ≤ 0.001; Figure 2). Moreover, even though steaks from CH sections had more (P < 0.05) total color (greater C* values) on d 1 than on d 3 and 5 of display, C* values of CH steaks were still greater (P < 0.05) than those of steaks from DC sections, regardless of LAC enhancement, on d 1, 3, and 5 of display (LAC enhancement × retail display duration, P < 0.001; Figure 3). On d 3 of display, steaks from DC sections enhanced with 0.15 and 0.35% LAC had greater (P < 0.05) a*, b*, and C* values than did nonenhanced DC sections, but total color (C*), including redness (a*) and yellowness (b*) values, did not (P > 0.05) differ among nonenhanced and enhanced DC sections after 5 d of display. Conversely, steaks from 0.35% LAC-enhanced DC sections had a* values similar (P > 0.05) to those of nonenhanced CH sections on d 5 of display. In Exp. 2, there were no (P ≥ 0.28) 2-way interactive effects or main effects (P ≥ 0.10) of retail display duration on any instrumental color measure; therefore, only the main effects of LAC enhancement are presented in Table 2. Steaks from CH sections had greater (P < 0.05) L*, a*, and b* values than steaks from DC sections, regardless of LAC enhancement. Moreover, steaks from LAC-enhanced DC sections were lighter (P

< 0.05) than steaks from nonenhanced DC sections, whereas steaks from DC sections enhanced with 0.35% LAC were redder (P < 0.05) than steaks from 0.50% LAC-enhanced sections and were more yellow (P < 0.05) than steaks from nonenhanced and 0.50% LACenhanced DC sections. Again, CH steaks had greater (P < 0.05) total color (greater C* values) than DC steaks, and C* values were greater (P < 0.05) in steaks from DC sections enhanced with 0.35% LAC than in those from DC sections enhanced with 0.50% LAC. Steaks from untreated DC sections had the least (P < 0.05) hue angles, evidence of a color nearest the true red color axis, whereas steaks from DC sections enhanced with 0.50% LAC had the greatest (P < 0.05) hue angles; however, hue angles were virtually identical (P > 0.05) between steaks from CH strip loin sections and steaks from 0.35% LAC-enhanced DC sections.

Visually Appraised Fresh Beef Color Japanese color scores for steaks from CH strip loin sections in Exp. 1 were substantially less (P < 0.05) than those of non- and LAC-enhanced DC steaks each day of simulated retail display (LAC enhancement × retail display duration, P < 0.001; Figure 4). Even though fresh color scores were similar (P > 0.05) among enhanced and nonenhanced DC steaks on the first day of display, steaks from DC sections received greater (P < 0.05) Japanese color scores than did steaks from LAC-enhanced sections on the second day of display, whereas steaks from DC sections enhanced with 0.35% LAC received substantially lower (P < 0.05) Japanese color scores than did steaks from either nonenhanced or 0.15% LAC-enhanced DC sections over the last 3 d of retail display. Although there were no 2-way interactions (P = 0.28) or retail display duration (P = 0.10) effects on Japanese color scores in Exp. 2, nonenhanced DC steaks


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Figure 3. Interactive effects of lactic acid (LAC) enhancement and duration of simulated retail display (P < 0.001) on chroma (C*) values (Exp. 1). Bars for nonenhanced, normal pH, low Choice, positive controls (CH); nonenhanced, dark-cutting negative controls (DC); DC strip loin sections enhanced with 0.15% LAC; and DC strip loin sections enhanced with 0.35% LAC represent the mean of 9, 9, 18, and 18 steaks, respectively. Error bars lacking common letters (a–g) differ, P < 0.05.

play (LAC enhancement × retail display duration, P < 0.001; Figure 5). Even though discoloration scores were similar (P > 0.05) among steaks from CH and DC sections regardless of LAC enhancement, during the first 2 d of display, steaks from CH strip loin sections were more (P < 0.05) discolored (lesser discoloration scores) than steaks from either LAC-enhanced or nonenhanced DC sections on d 3, 4, and 5 of display.

Figure 2. Interactive effects of lactic acid (LAC) enhancement and duration of simulated retail display (P < 0.001) on A) redness (a*) values and B) yellowness (b*) values (Exp. 1). Bars for nonenhanced, normal pH, low Choice, positive controls (CH); nonenhanced, darkcutting negative controls (DC); DC strip loin sections enhanced with 0.15% LAC; and DC strip loin sections enhanced with 0.35% LAC represent the mean of 9, 9, 18, and 18 steaks, respectively. Error bars lacking common letters (a–h) differ, P < 0.05.

received the greatest (P < 0.05) Japanese color scores, whereas CH steaks received the least (P < 0.05) Japanese color scores (Table 2). Moreover, steaks from DC sections enhanced with 0.35% LAC received greater (P < 0.05) color scores than did steaks from DC sections enhanced with 0.50% LAC; however, mean Japanese color scores were only 0.7 and 0.4 units greater (P < 0.05) in DC steaks enhanced with 0.35 and 0.50% LAC than in CH steaks. In Exp. 1, discoloration scores did not (P > 0.05) change across the 5-d display period among steaks from nonenhanced and LAC-enhanced DC sections, whereas discoloration scores decreased (P < 0.05) in steaks from CH strip loin sections during the last 3 d of retail dis-

Figure 4. Interactive effects of lactic acid (LAC) enhancement and duration of simulated retail display (P < 0.001) on Japanese color scores (Exp. 1). Lines for nonenhanced, normal pH, low Choice, positive controls (CH); nonenhanced, dark-cutting negative controls (DC); DC strip loin sections enhanced with 0.15% LAC; and DC strip loin sections enhanced with 0.35% LAC represent the mean of 9, 9, 18, and 18 steaks, respectively. Error bars lacking common letters (a–h) differ, P < 0.05.

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Figure 5. Interactive effects of lactic acid (LAC) enhancement and duration of simulated retail display (P < 0.001) on discoloration scores [4 = modest (40 to 59%) discoloration; 5 = small (20 to 39%) discoloration; 6 = slight (1 to 19%) discoloration; and 7 = no (0%) discoloration; Pohlman et al., 2002] in Exp. 1. Lines for nonenhanced, normal pH, low Choice, positive controls (CH); nonenhanced, darkcutting negative controls (DC); DC strip loin sections enhanced with 0.15% LAC; and DC strip loin sections enhanced with 0.35% LAC represent the mean of 9, 9, 18, and 18 steaks, respectively. Error bars lacking common letters (a–g) differ, P < 0.05.

Steaks from nonenhanced DC strip loin sections received greater (P < 0.05) discoloration scores than did steaks from CH sections only on d 2 and 4 of simulated retail display in Exp. 2 (LAC enhancement × retail display duration, P = 0.050; Figure 6). Even though discoloration scores remained relatively unchanged (P > 0.05) across the 5-d display period, steaks from DC sections enhanced with 0.35% LAC were more (P < 0.05) discolored than steaks from CH and nonenhanced DC sections every day during display. Moreover, steaks from 0.50% LAC-enhanced sections were the most (P < 0.05) discolored during display, especially on d 1, and steak discoloration increased (lower discoloration scores; P < 0.05) as retail display extended to d 4 and 5 in steaks from 0.50% LAC-enhanced DC sections. The color of fresh beef is determined by the proportion of deoxymyoglobin that is oxygenated into oxymyoglobin upon exposure to air (Seideman et al., 1984). However, the color of DC beef is typically darker and less red and yellow than normal pH beef (Wulf et al., 2002; Apple et al., 2005). The reason DC meat does not develop the characteristic bright red color when exposed to air (Egbert and Cornforth, 1986; Gašperlin et al., 2000) is that the high muscle pH preserves the functionality of the mitochondria (Ashmore et al., 1972) and lengthens the activity of oxygen-consuming enzymes (Zhu and Brewer, 1998). In fact, Cornforth and Egbert (1985) demonstrated that the color of DC beef could be changed to that of normal pH beef by inhibiting mitochondrial respiration with rotenone. Moreover, Echevarne et al. (1990) reported that metmyoglobin reductase activity was increased in meat as muscle pH increased from 5.0 to 7.3.

It has been shown that LAC has a greater affinity for deoxymyoglobin than oxymyoglobin of normal-pH meat, which leads to decreased oxygen affinity by myoglobin and the promotion of a stable, unbloomed color (Giardina et al., 1996). Additionally, a* values of fresh beef strip loin steaks enhanced with a combination of potassium lactate and sodium acetate (and subsequently packaged in a high-oxygen modified atmosphere; Knock et al., 2006) and buffalo steaks enhanced with LAC (Naveena et al., 2006) were greater than the a* values of their nonenhanced counterparts. Moreover, Kim et al. (2006) demonstrated that injecting normal-pH beef strip loins with LAC caused regeneration of NADH via increased lactate dehydrogenase activity, and the greater NADH production caused the reduction of metmyoglobin. More recently, Sawyer et al. (2009) noted positive effects of LAC enhancement on instrumental and subjective measures of the fresh color of DC beef, and it was reported that LAC enhancement decreased metmyoglobin formation in beef at pH values of 6.5 (Giardina et al., 1996) and 7.4 (Mancini and Ramanathan, 2008). Thus, it is plausible that the improvements in fresh color noted by enhancing DC beef with 0.50% LAC in Exp. 2 may be due to a reduction in oxygen consumption by mitochondrial enzymes, a reduction in metmyoglobin reductase activity, or both.

Cooked Beef Color In Exp. 1, steaks from CH strip loin sections received the greatest (P < 0.05) cooked color and degree of doneness scores, whereas steaks from DC sections enhanced with 0.15% LAC received greater (P < 0.05) cooked

Figure 6. Interactive effects of lactic acid (LAC) enhancement and duration of simulated retail display (P = 0.050) on discoloration scores [4 = modest (40 to 59%) discoloration; 5 = small (20 to 39%) discoloration; 6 = slight (1 to 19%) discoloration; and 7 = no (0%) discoloration; Pohlman et al., 2002] in Exp. 2. Lines for nonenhanced, normal pH, low Choice, positive controls (CH); nonenhanced, darkcutting negative controls (DC); DC strip loin sections enhanced with 0.35% LAC; and DC strip loin sections enhanced with 0.50% LAC represent the mean of 9, 9, 18, and 18 steaks, respectively. Error bars lacking common letters (a–i) differ, P < 0.05.

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Table 3. Effects of lactic acid enhancement on cooked beef color of dark-cutting strip steaks (Exp. 1 and 2) Lactic acid solution, % Normal-pH control

Characteristic1 Exp. 1 No. of steaks Cooked color scores2 Degree of doneness3 L* a* b* C* Hue angle Red-to-brown ratio4 Exp. 2 No. of steaks Cooked color scores2 Degree of doneness3 L* a* b* C* Hue angle Red-to-brown ratio4

 


9 5.4a 5.1a 59.52 15.96b 17.32 23.55 47.38a 1.88b   9 5.2a 4.9a 58.32 16.32ab 17.26 23.75ab 46.87b 1.93bc

0.15  

9 3.7c 3.8c 57.36 18.08a 17.25 25.03 43.72b 2.23a   9 3.2c 3.5c 59.20 18.51a 17.13 25.15a 42.71c 2.34a

0.35  

18 4.3b 4.3b 58.03 17.20ab 16.89 24.10 44.50b 2.11a     — — — — — — — —

0.50  

18 3.8c 4.0c 58.25 17.66a 17.10 24.56 44.09b 2.16a   18 3.8b 3.9b 58.33 17.01a 17.42 24.40a 45.90b 2.15ab

SEM  

  — — — — — — — —   18 5.2a 4.9a 55.94 14.35b 16.65 22.05b 49.54a 1.80c

  0.18 0.13 0.680 0.425 0.212 0.734 0.364 0.074     0.17 0.15 0.968 0.611 0.333 0.633 0.719 0.084

a–c

Within a row, least squares means lacking common superscripts differ, P < 0.05. L* = measure of darkness to lightness (larger value indicates a lighter color); a* = measure of redness (larger value indicates a more intense red color); and b* = measure of yellowness (larger value indicates a more yellow color). Chroma (C*) represents the total color of the sample (larger value indicates a more vivid color). Hue angle represents the change from the true red axis (larger value indicates a greater shift from red to yellow). 2 Score: 1 = very red; 2 = red; 3 = pink; 4 = slightly pink; 5 = pinkish gray; 6 = gray brown; and 7 = brown (AMSA, 1991). 3 Score: 1 = very rare; 2 = rare; 3 = medium rare; 4 = medium; 5 = medium well; 6 = well done; and 7 = very well done. 4 The spectral ratio of 630/580 nm is an estimate of cooked color change from red to brown (larger value indicates a redder color; AMSA, 1991). 1

color and degree of doneness scores than steaks from nonenhanced or 0.35% LAC-enhanced DC sections (Table 3). On the other hand, cooked color and degree of doneness scores for CH steaks and steaks from DC sections enhanced with 0.50% LAC did not (P > 0.05) differ in Exp. 2, but scores were substantially greater (P < 0.05) than those for steaks from DC sections enhanced with 0.35% LAC, with nonenhanced DC steaks rated the lowest (P < 0.05) for both cooked color and degree of doneness. Neither L* (P ≥ 0.16) nor b* (P ≥ 0.35) values of cooked steaks differed among the treatment groups in Exp. 1 and 2 (Table 3). In Exp. 1, regardless of LAC enhancement, the internal color of steaks from DC sections was redder (greater a* values and red-to-brown reflectance ratios, as well as lesser hue angles; P < 0.05) than the internal color of CH steaks. In Exp. 2, a* and C* values for the internal appearance of cooked steaks from nonenhanced and 0.35% LAC-enhanced DC sections were greater (P < 0.05) than a* and C* values of cooked steaks from DC sections enhanced with 0.50% LAC. Hue angles were greatest (P < 0.05) in cooked steaks from 0.50% LAC-enhanced DC sections and were least (P < 0.05) in cooked steaks originating from nonenhanced DC sections, but CH steaks and 0.35% LAC-enhanced DC steaks had similar (P > 0.05) hue angles. Although the internal color of nonenhanced DC steaks was redder (greater red-to-brown ratio; P < 0.05) than either CH steaks or steaks from 0.50% LAC-

enhanced DC sections, reflectance ratios were similar (P > 0.05) among steaks from CH and LAC-enhanced DC strip loin sections. Cooking normal-pH meat causes the color to change from red pigment forms (deoxy-, oxy-, and metmyoglobin) into the gray pigment (globin ferrihemochrome) typically observed in cooked meats (Mendenhall, 1989). However, when high-pH (>6.0) beef is cooked to the same internal end-point temperature as normal-pH beef, the internal cooked color is much redder and appears undercooked because myoglobin is protected from heat denaturation (Trout, 1989). In fact, when cooked DC beef is exposed to air, the internal cooked color may become oxygenated and develop a bright red color similar to that of fresh, normal-pH beef (see Gašperlin et al., 2000). Moiseev and Cornforth (1999) reported that when ground beef patties manufactured from DC beef were treated with LAC, the increased myoglobin denaturation during the cooking process and development of cooked beef color were similar to those of ground beef patties made from normal-pH beef. Moreover, Sawyer et al. (2008) observed that DC steaks enhanced with 0.5% LAC had similar proportions of denatured myoglobin as normal-pH steaks, and degree of doneness scores as well as instrumental cooked color were similar between normal-pH steaks and DC steaks enhanced with 1.0% LAC. More recently, Sawyer et al. (2009) indicated that cooked color scores and the percentage of denatured myoglobin did not differ between

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normal-pH steaks and DC steaks enhanced with 0.25% LAC. Thus, it was not surprising to find that subjective scores for cooked color were similar between CH and DC steaks enhanced with 0.5% LAC in Exp. 2 of the present study.

Cooking Characteristics and Sensory Attributes In both Exp. 1 and 2, cooking times were similar (P > 0.05) among steaks from CH and DC strip loin sections, regardless of LAC enhancement (Tables 4 and 5). No evidence exists that enhancement of subprimal beef cuts with organic acids, particularly LAC, affects cooking times. However, Mendenhall (1989) and van Laack et al. (1997) reported that ground beef patties manufactured from high-pH beef took longer to cook than patties manufactured from normal-pH beef, but cooking times were not different between ground beef patties made from DC trimmings, DC trimmings treated with encapsulated LAC (Moiseev and Cornforth, 1999), or normal-pH trimmings (Berry, 1998; Moiseev and Cornforth, 1999). Cooking yields were greatest (P < 0.05) in nonenhanced DC steaks in both experiments; however, in Exp. 1, steaks from CH and 0.15% LAC-enhanced DC sections had greater (P < 0.05) cooking yields than steaks from 0.35% LAC-enhanced DC sections when the enhancement target was 105% (Table 4). In Exp. 2, cooking yields were greater (P < 0.05) in steaks from CH and 0.35% LAC-enhanced DC sections than were those from DC sections enhanced with 0.50% LAC when the enhancement target was 115% (Table 5).

Postcooking yields have been shown to be improved by reducing the pH of beef with LAC (Aktaş and Kaya, 2001; Aktaş et al., 2003; Önenç, et al., 2004). Furthermore, cook yields of normal-pH top round roasts were increased between 6.2 and 14.1% as the proportion of sodium lactate increased from 1 to 4% in an enhancement solution (Papadopoulos et al., 1991; Maca et al., 1999). Obviously, nonenhanced DC sections had the greatest cooking yields in previous studies from this laboratory (Sawyer et al., 2008, 2009); however, Sawyer et al. (2009) reported that DC sections enhanced with 0.50 or 0.75% LAC had smaller cooking yields than nonenhanced, normal-pH strip loin sections and DC sections enhanced with 0.25% LAC. Moreover, Sawyer et al. (2008) demonstrated that cooking yields were actually decreased between 3.3 to 4.2% when compared with the nonenhanced, normal-pH loin sections and between 7.5 to 8.4% when compared with the nonenhanced DC LM sections. Similarly, cooking yields of DC strip loin sections were reduced by LAC enhancement in both experiments, with values of DC sections enhanced with 0.35% LAC being similar to those of the normal-pH controls, regardless of the enhancement percentage (Tables 4 and 5). In Exp. 1, WBSF values did not (P > 0.05) differ between untreated CH and DC sections, nor did LAC enhancement treatments alter (P > 0.05) WBSF values; however, descriptive-attribute panelists noted that first-bite hardness and hardness of the mass were more (P < 0.05) intense (greater scores) for steaks from CH strip loin sections than for steaks from DC sections, regardless of LAC enhancement (Table 4). In Exp. 2, however, WBSF values, as well as scores of the panel-

Table 4. Effects of lactic acid enhancement on sensory attributes1 of dark-cutting strip steaks (Exp. 1) Lactic acid solution, % Characteristic No. of steaks Cooking time, s Cooking yield,2 % Shear force, kg Texture profile First-bite hardness Moisture release Hardness of mass Flavor profile Salt Sour Bitter Cooked beef Beef fat Roasted/caramelized Blood serumy/metallic Livery/organy Soapy a–c

Normal-pH control

Dark-cutting control

0.15

0.35

SEM

9 895.1 72.2b 2.71   8.3a 1.1 7.5a   3.7a 1.7a 0.2b 5.2a 1.5 3.4a 2.8 2.0 0.7c

9 879.0 81.4a 2.30   7.6b 1.2 6.7b   3.4b 1.1b 0.3a 5.0b 1.7 3.2b 3.0 1.9 1.4a

18 917.4 79.3b 2.31   7.4b 1.3 6.6b   3.4b 1.1b 0.3a 4.9b 1.6 3.1b 3.1 1.8 1.6a

18 1,004.2 75.6c 2.51   7.5b 1.3 6.8b   3.5ab 1.1b 0.3a 5.0b 1.7 3.2b 3.1 1.8 1.3b

  35.72 0.67 0.114   0.14 0.11 0.13   0.09 0.13 0.05 0.08 0.22 0.12 0.16 0.23 0.22

Within a row, least squares means lacking common superscripts differ, P < 0.05. Score: 0 = least intense to 15 = most intense. 2 Cooking yield = 100 × (postcooked steak weight/precooked steak weight). 1

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Lactic acid enhancement of dark-cutting beef 1

Table 5. Effects of lactic acid enhancement on sensory attributes of dark-cutting strip steaks (Exp. 2) Lactic acid solution, % Characteristic No. of steaks Cooking time, s Cooking yield,2 % Shear force, kg Texture profile First-bite hardness Moisture release Hardness of mass Flavor profile Salt Sour Bitter Cooked beef Beef fat Roasted/caramelized Blood serumy/metallic Livery/organy Soapy

Normal-pH control

Dark-cutting control

0.35

0.50

SEM

9 1,137.6 70.6b 2.96b   9.2a 1.3a 8.2b   4.4a 1.4a 0.1b 5.5a 1.1a 3.6a 3.4a 0.9 0.2c

9 1,173.0 80.4a 2.10c   8.3b 1.5a 7.4c   3.9c 0.9b 0.2a 5.0b 1.0ab 3.1b 3.3ab 1.2 1.4a

18 1,166.3 70.3b 3.82a   9.4a 1.1b 8.7a   3.9c 1.3a 0.1b 5.1b 0.8bc 3.1b 3.1b 1.3 0.6b

18 1,076.9 66.5c 3.77a   9.1a 1.1b 8.4b   4.1b 1.4a 0.1b 5.1b 0.7c 3.2b 3.0b 1.1 0.6b

  38.19 0.81 0.219   0.14 0.09 0.15   0.17 0.08 0.04 0.09 0.19 0.10 0.13 0.20 0.15

a–c

Within a row, least squares means lacking common superscripts differ, P < 0.05. Score: 0 = least intense to 15 = most intense. 2 Cooking yield = 100 × (postcooked steak weight/precooked steak weight). 1

ists for first-bite hardness and hardness of the mass, were lowest (P < 0.05) in steaks from nonenhanced DC sections (Table 5). It is interesting that CH steaks had reduced (P < 0.05) WBSF values compared with steaks from DC sections enhanced with 0.35 and 0.50% LAC, and steaks from DC sections enhanced with 0.35% LAC received greater (P < 0.05) hardness of mass scores than steaks from CH and 0.50% LAC-enhanced DC sections in Exp. 2. Beef tenderness has been shown to improve in muscle with ultimate pH values in excess of 6.0 (Marsh et al., 1980–1981) to 6.3 (Yu and Lee, 1986). Furthermore, several studies have shown that enhancement with organic acids reduces shear force values and improves sensory panel tenderness ratings of cooked beef (Arganosa and Marriott, 1989; Eilers et al., 1994; Aktaş et al., 2003). In particular, Berge et al. (2001) found that LAC enhancement reduced WBSF values of beef brisket between 34 and 39%, and they attributed the tenderization to a weakening of the myofibrillar structure and the connective tissue matrix by LAC. Obviously, the lack of a change in postenhancement pH can explain the similar WBSF values among untreated DC sections and DC sections enhanced with 0.15 and 0.35% LAC in Exp. 1. It is interesting that both Purchas (1990) and Watanabe et al. (1996) demonstrated a curvilinear relationship between ultimate pH and beef tenderness, with maximal toughness occurring between 5.8 and 6.0. Thus, the observation that steaks from DC sections enhanced with 0.35 and 0.50% LAC had greater WBSF values than did untreated CH steaks (Exp. 2) may be because the postenhancement pH values (5.99 and 5.79 for steaks from DC sections enhanced with 0.35 and 0.50% LAC, respectively; Ta-

ble 1) were within this range of maximal toughness. Ertbjerg et al. (1995) also showed that even though enhancement with low concentrations of LAC reduced ultimate muscle pH, no appreciable effects on beef tenderness were observed until pH had been decreased to approximately 4.6 with high concentrations of LAC. Additionally, there is evidence that enhancement with high amounts of sodium lactate can lead to increased WBSF values of top round roasts (Papadopoulos et al., 1991) and elevated hardness and cohesiveness intensities of ground beef patties (Eckert et al., 1997). In Exp. 1, panelists were unable to detect a difference (P = 0.56) in moisture release among the treatment groups, but cooked steaks from CH sections were rated higher (P < 0.05) than those from DC sections, regardless of LAC enhancement, for the sour, cooked beef, and roasted/caramelized flavors (Table 4). Moreover, panelists perceived steaks from CH sections as having a more (P < 0.05) intense salt flavor than steaks from nonenhanced and 0.15% LAC-enhanced strip loin sections, whereas panelists noted that nonenhanced DC steaks and 0.15% LAC-enhanced steaks had a more (P < 0.05) intense soapy flavor than did either CH or 0.35% LAC-enhanced steaks, even though the values were relatively small. Bitter flavor scores may have been statistically greater (P < 0.05) in steaks from nonand LAC-enhanced DC sections than in steaks from CH sections but the values were small, whereas panelists failed to note differences among treatments for beef fat (P = 0.21), blood serumy/metallic (P = 0.26), and livery/organy flavors (P = 0.89). In Exp. 2, steaks from nonenhanced CH and DC strip loin sections received greater (P < 0.05) moisture release scores than steaks from LAC-enhanced DC

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sections (Table 5). Panelists noted more (P < 0.05) intense cooked beef and roasted/caramelized flavors for CH steaks than for DC steaks, regardless of LAC enhancement, whereas steaks from CH strip loin sections were rated the highest (P < 0.05) for salt flavor, and steaks from DC sections enhanced with 0.50% LAC had a more (P < 0.05) intense salt flavor than did steaks from nonenhanced and 0.35% LAC-enhanced sections. Steaks from CH strip loin sections had a more (P < 0.05) intense beef fat flavor than did LAC-enhanced DC steaks, and steaks from nonenhanced DC sections had a more (P < 0.05) intense beef fat flavor than did steaks from DC sections enhanced with 0.50% LAC. Moreover, nonenhanced DC steaks received lesser (P < 0.05) sour flavor scores, and greater (P < 0.05) bitter flavor scores when compared with CH steaks and steaks from LAC-enhanced strip loin sections. Blood serum/metallic flavor scores were greater (P < 0.05) in CH steaks than in LAC-enhanced DC steaks, although the panelists failed to detect a difference (P = 0.52) in livery/organy flavor among the treatment groups. Last, panelists noted a more (P < 0.05) intense soapy flavor in steaks from nonenhanced DC sections, and LACenhanced DC steaks received greater (P < 0.05) soapy flavor scores than steaks from CH strip loin sections. Little is known about the differences in other palatability attributes between high- and low-pH beef, and there are some contradictions among the limited number of studies. Dransfield (1981) reported that DC steaks had less beef flavor than normal-pH steaks, and English consumers rated normal steaks higher in beef flavor acceptability because they preferred the stronger beef flavor. On the other hand, Viljoen et al. (2002) found that only female consumers rated normal-pH steaks as having a more meaty flavor than DC steaks. Trained sensory panelists rated LM and gluteus medius steaks from normal-pH carcasses higher for beef flavor desirability than they did steaks from high-pH carcasses (Wulf and Page, 2000; Wulf et al., 2002). In addition, Wulf et al. (2002) recorded more off-flavors in DC steaks compared with normal-pH steaks, with DC steaks receiving more peanutty, sour, bitter, and burnt off-flavor comments. Miller (2001) indicated that DC beef had greater musty/moldy, cowy/grassy, and bloody/serumy aromatic flavors than did normal-pH beef. More in line with results from the present experiments, Yancey et al. (2005) observed that normal-pH beef top blade, top sirloin, and tenderloin steaks had a greater beef flavor identity and a greater brown-roasted flavor than did DC steaks, but DC beef had greater rancid, metallic, and bloody/serumy flavors than did normal-pH beef.

Conclusions For the most part, a significant proportion of research to date has concluded that the most effective method of reducing the incidence of DC beef is by reducing

Figure 7. Fresh beef color of normal pH, low Choice, positive controls (CH); nonenhanced, dark-cutting negative controls (DC); and DC strip loin sections enhanced with 0.15 (Exp. 1), 35 (Exp. 1 and 2), and 0.50% (Exp. 2) lactic acid (LAC) at 105 (Exp. 1) or 112% (Exp. 2) of the fresh section weight. Color version available in the online PDF.

antemortem stress through improved animal handling and management. However, results of the present study indicate that postrigor enhancement of whole muscle DC beef with LAC can eliminate the persistent redpink cooked color and reduce the intensity of flavors typically associated with cooked DC beef. Even though additional research is warranted, LAC enhancement appears to be a promising method by which to alter the fresh color of DC beef from an undesirable dark red to a more appealing bright red color similar to that of normal-pH beef (Figure 7).

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