J. Anim. Sci. 2004. 82:3034-3037
© 2004 American Society of Animal Science
The effects of the antioxidant lipoic acid on beef longissimus bloom time
G. Rentfrow,
M. L. Linville,
C. A. Stahl,
K. C. Olson and
E. P. Berg1
Department of Animal Science, University of Missouri, Columbia 65211
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Abstract
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The objective of this study was to evaluate the influence of lipoic acid (LA) on beef LM steak bloom time, as well as to characterize bloom time in the CIE L*, a*, and b* color space over a 93-min period. Thirty-two Simmental steers were supplemented with LA for 21 d immediately before slaughter at levels of 0, 8, 16, or 24 mg of LA/kg BW (eight steers per treatment). Lipoic acid was mixed with liquid paraffin, allowed to solidify, prilled, and top-dressed over a standard finishing diet. Steers were slaughtered at the University of Missouri abattoir in four groups of eight (two steers per treatment) over a 2-wk period. After a 24-h chill at 4°C, the right LM was removed from each carcass. One 2.54-cm steak was removed from the anterior portion of the LM, and its color characteristics (CIE L*, a*, and b*) were measured immediately with a standardized spectrocolorimeter. Color measurements were taken every 3 min thereafter for a total of 93-min. Hue angle (true red) and chroma (color saturation) were calculated from the color measurements. Addition of LA to the diet had no effect on bloom time (P = 0.67). When treatment means were analyzed, the addition of 24 mg of LA/kg BW to the diet resulted in higher (lighter) L* values (P < 0.05) compared with other treatments, whereas the addition of 16 mg of LA/kg BW to the diet caused lower hue angles (more true red; P < 0.05) when compared with other treatments. Addition of LA to the diet did not affect a* (P = 0.13) and b* (P = 0.18) values or chroma (P = 0.62). In the absence of treatment effects, bloom times for all treatments were pooled, and L* values did not change (P > 0.05) during the 93-min bloom time; however, a* and chroma values increased for 9 min and plateaued after 12 min (P < 0.01). Similarly, b* values increased (P < 0.01) for the first 6 min, and after 9 min, no further increase in yellowness was detected. Bloom time had little effect on hue angle, which stabilized after 3 min. Supplementing steers with the antioxidant LA for 21 d had no effect on the bloom time of beef LM; however, higher levels of supplemental LA affected L* values and hue angles of beef.
Key Words: Beef • Bloom Time • Color • Lipoic Acid • Longissimus Muscle
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Introduction
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Lipoic acid (LA) is a naturally occurring compound present in all tissues of the body, with muscle containing the highest concentrations. Byrd (1995)
described LA as a universal antioxidant that is both water and fat soluble, which has the ability to regenerate the effectiveness of fat- and water-soluble vitamins (E and C). In addition, LA increases circulating levels of glutathione, the principal endogenous antioxidant responsible for free radical scavenging in all cell types (Byrd, 1995).
Color is the main quality measurement that consumers use to gauge desirability when buying beef products (Faustman et al., 1989a; Faustman and Cassens, 1991; Liu et al., 1995). Past research on beef color has used the antioxidant vitamin E to prolong the cherry-red color of beef that consumers associate with freshness (Faustman et al., 1989a; Arnold et al., 1992; Roeber et al., 2001). Research has shown that LA, like vitamin E, can combat the free radicals that can cause pigment and lipid oxidation, thereby prolonging the desirable color of beef (our unpublished data).
Bloom time refers to the amount of time needed to oxygenate deoxymyoglobin to oxymyoglobin—the process by which beef takes on a cherry-red color. Wulf and Wise (1999) used color measurements (CIE L*, a*, and b*) to characterize bloom time; however, they did not use hue angle or chroma calculations in their analysis. In addition, the affects of novel antioxidants, such as LA, on bloom time have not been characterized. Consequently, the objectives of this research were to determine whether supplementing LA to market steers during the late finishing phase would influence bloom time, and to characterize the effect of bloom time on CIE L*, a*, and b* measurements, hue angle, and chroma.
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Materials and Methods
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Animals and Diet
All procedures and protocols were approved by the University of Missouri Animal Care and Use Committee. Simmental steers (n = 32) were housed in eight pens (four steers per pen) and fed a common finishing diet (Table 1) for 200 d. Lipoic acid was added to the diet for 21 d immediately before slaughter at levels of 0, 8, 16, or 24 mg LA/kg BW (eight steers per treatment; four steers per pen). The structure of LA contains two sulfur atoms, which cause the compound to have an undesirable taste. To mask the undesirable taste, paraffin was used as a carrier. The paraffin was melted inside a double boiler and LA (powder form) was added to the liquid paraffin and thoroughly mixed (Hobart, Troy, OH). Lipoic acid has a melting point of 60°C, so it was added to the paraffin at temperatures below the melting point. The LA–paraffin mixture was poured into cookie sheets and allowed to solidify. The solidified mixture was prilled (Black and Decker Quick and Easy Food Processor, Shelton, CT), and top-dressed over the feed at approximately 0700 daily. Finally, it should be noted that vitamin E was fed at recommended levels, and not at supranutritional levels.
Bloom Time Measurements
The steers were slaughtered over a 2-wk period at the University of Missouri abattoir in four groups (eight steers per group). The two heaviest steers in each treatment group at each slaughter date were killed according to humane slaughter practices. Following a 24-h chill at 4°C, the right strip loin was removed from each carcass, and one 2.54-cm-thick LM steak was removed from the anterior portion of the strip loin and placed on a white styrofoam tray. Objective color was measured using a Miniscan XE Plus spectrocolorimeter (Hunter Associates Laboratory, Inc., Reston, VA) with illuminant D-65, and calibrated against a white and a black tile immediately before measurements were made. Spectral reflectance was determined every 10 nm over the 400- to 700-nm range. Color measurements (CIE L*, a*, and b*) were taken immediately after each steak was cut and then repeated every 3 min over a 93-min period as described by Wulf and Wise (1999). Three measurements for each color parameter were taken at different locations across the steaks and averaged, with care to avoid areas with large deposits of marbling. Hue angle (HA = tan–1 [b*/a*]) and chroma 
were calculated according to standard equations (Minolta, 1994). The hue angle is a measure of true red (0° = true red to 90° = true yellow). Chroma, or color saturation, is a measurement of the vividness of color (higher values indicate a more vivid color).
Statistics
Performance data on the steers were not collected during this trial. Bloom time data were analyzed as a completely randomized design, with a split-plot in time (Steel and Torrie, 1980) using individual steer as the experimental unit. The mixed model procedure of SAS (SAS Inst., Inc, Cary, NC) was used to analyze effects on L*, a*, and b* x time. When the F-test was significant (P < 0.05), treatment means were separated using a Bonferonni adjustment (Snedecor and Cochran, 1989).
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Results and Discussion
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There was no treatment x bloom time interaction (P = 0.67) observed over the 93-min bloom time period. Wulf and Wise (1999), as well as results from the current study, indicated that CIE L*, a*, and b* values did not change (P > 0.05) after 12 min. Therefore, the treatment x bloom time data were further analyzed using only values collected from 0 to 18 min, but there were still no treatment differences (P > 0.05) that occurred over the first 18 min of bloom for any color measurement. Dietary supplementation of 24 mg of LA/kg BW had higher (P < 0.05) L* values compared with all other treatments. Furthermore, supplementing 16 mg of LA/kg BW resulted in lower (P < 0.05) hue angle calculations (Table 2), indicating that these steaks were closer to true red than those from all other treatments. Conversely, addition of LA to the diet did not affect a* (P = 0.13) or b* values (P = 0.18) or chroma (P = 0.62) calculations.
Data were pooled to characterize the effects of bloom time on objective color measurements (values represent all four treatments combined; Table 3). Bloom time had no effect (P = 0.44) on L* values over the 93-min period, which concurs with the results of Wulf and Wise (1999), who reported that L* values did not change during bloom time. Furthermore, Brewer et al. (2001) reported a similar trend upon analysis of bloom time in pork loin chops.
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Table 3. The CIE L*, a* and b* values, hue angles, and chroma calculations for beef longissimus muscle steaks over a 93-min bloom time
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The freshly cut surface of the steaks had a mean a* value of 14.76, which increased (P < 0.01) after being allowed to bloom for 3, 6, 9, and 12 min (Table 3
). Nonetheless, after 12 min, no further increase in a* values occurred (P > 0.05). At 0 min (freshly cut), the mean b* value was 12.18, and increased after 3, 6, and 9 min of bloom time (P < 0.001); however, b* values remained constant thereafter (P > 0.05). Wulf and Wise (1999) indicated that bloom time had a greater effect on a* and b* values than on L* values, which is in agreement with results of the current study. Moreover, Wulf and Wise (1999) indicated that relative differences between treatments did not change between 3 to 12 min. In the current study, there were no differences (P > 0.05) in CIE a* and b* values after 9 min. Brewer et al. (2001) found a similar trend in pork, in which a* and b* values did not change after 10 min of bloom time.
Bloom time had limited effects on the hue angle calculation (Table 3). The freshly cut surface of steaks had a mean hue angle calculation of 39.52°, which increased (P < 0.01) to 40.27°after 3 min; however, no changes (P > 0.05) occurred past that time point. To our knowledge, there have been no reports on beef bloom time that used the hue angle to measure color. In pork, Brewer et al. (2001) indicated the hue angle calculations did not change after 5 min of bloom time; however, the numerical value of the hue angle decreased after that point. In contrast, the numerical value of hue angle increased nonsignificantly (P > 0.05) throughout the 93-min bloom time period. Price and Schweigert (1987) indicated that pork from 1- to 2-yr-old pigs contained one-fifth less myoglobin than beef from steers of the same age, which might explain the increase in hue angle in beef through the bloom time period.
The greatest increase (P < 0.01) in chroma occurred between 0 and 3 min (22.9), chroma values increased after 3, 6, 9, and 12 min before stabilizing (P >0.05; Table 3). The authors are not aware of any research that has used chroma values to characterize beef bloom time; however, chroma calculation in pork increased for 20 min before stabilizing (Brewer et al., 2001).
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Implications
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These results suggest that bloom times in excess of 12 min are necessary to obtain the most stable and repeatable color measurement on fresh cut beef. Because hue angle provides the best indication of redness, and chroma provides an objective indication of color intensity, it is suggested that hue angle and chroma calculations could be use to further describe beef color in an objective manner.
1 Correspondence: S138 ASRC 920 E. Campus Dr. (phone: 573-882-3176; fax: 573-884-4606, e-mail: BergEP{at}missouri.edu).
Received for publication February 5, 2004.
Accepted for publication June 17, 2004.
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Abstract
Introduction
