The Influence of Paylean (Ractopamine Hydrochloride) on Pork Quality
Reviewed June 2020
Introduction
Marketed under the trade-name Paylean™ (Elanco Animal Health, Greenfield, IN), ractopamine hydrochloride (RAC) is a phenethanolamine β-adrenergic agonist used as a feed supplement to redirect nutrients to improve live pig performance (daily gain and feed conversion efficiency) and fat-free lean yields in pork carcasses [1]. Research was initiated in the 1980’s and RAC was FDA-approved for inclusion in swine finishing diets in December 1999. Initial approval included an inclusion range of 4.5 to 18 g/ton and fed from 150 to 240 lb. In 2006, the label changed to include an inclusion range from 4.5 to 9 g/ton of feed and to be fed for the last 50 to 90 lbs of body weight gain prior to market. This overview summarizes all levels of Paylean feeding; however, as producers consider the current, approved feeding level, more emphasis should be placed on the 4.5 to 9 g/ton data. The specific focus of the factsheet is an overview of the effects of RAC on fresh pork quality and cooked pork palatability.
Objectives
- Discuss the effects of Paylean on fresh pork quality
- Discuss the effects of Paylean on consumer acceptance of pork
Background
Muscle pH
Muscle pH is used to determine the level of acidity or alkalinity, and muscle pH is associated with many fresh pork quality attributes, including color, firmness, and water-holding capacity. In the conversion of muscle to meat, muscle becomes more acidic, with pH declining from a pH of 7.0 – 7.1 at death to an ultimate pH value of 5.40 to 6.00 at 24 hours postmortem. Although research has reported that pH measured at 45 minutes postmortem was reduced by the addition of 9 and 18 g/ton of RAC [2], the majority of research studies have failed to detect an effect of RAC on muscle pH measured at 45 minutes postmortem [3, 4]. When pigs were fed 9 [3, 5] or 18 g/ton of RAC [3], loin muscle pH values measured at 0.75, 1.5, 3.0, 4.5, 6.0, 8.0, and 24 hours postmortem were similar to those of pigs fed diets devoid of RAC (Figure 1). Research has indicated that feeding 4.5 g/ton of RAC for the last 28 days prior to slaughter effectively elevated muscle pH measured at 24 hours and 7 days postmortem [6], and an additional report indicates that including 9 g/ton of RAC for the final 35 days prior to slaughter increased muscle pH measured 48 hours postmortem [7]. However, in contrast, most research indicates that neither 4.5 [4, 8 – 12], nor 18 g/ton of RAC [11, 13] altered ultimate (24- or 48-hour) muscle pH.
Figure 1. Effect of RAC™ on pH decline in the ribeye muscle of pork carcasses (adapted from Carr et al., 2005a, b). Open squares (□) represent the muscle pH of pigs fed control (0 g/ton RAC™), whereas closed circles ( ) and closed triangles ( ) represent the muscle pH of pigs fed 9 and 18 g/ton RAC™, respectively.
Fresh Pork Color
The color of fresh pork is one of the most important quality characteristics affecting consumers’ purchasing decisions [14], as well as exportability of fresh pork products [15]. Armstrong et al. (2004) [16] reported that pork from pigs fed 9 g/ton RAC received higher NPPC and Japanese color scores than pork from pigs fed 18 g/ton RAC, and subjective color scores for pork from pigs fed 0 or 4.5 g/ton RAC were intermediate to the pigs fed 9 or 18 g/ton (Table 1). Moreover, across 5 days of retail display, Apple et al. (2008) [7] observed that loin chops from pigs fed 9 g/ton RAC received greater NPPC and Japanese color scores than chops from control-fed pigs. Yet, for the most part, feeding pigs finishing diets formulated with 4.5 [6, 8, 9, 10], 9 [3, 5, 12] or 18 g/ton RAC [3, 11, 17] had no detrimental effects on visually-evaluated fresh pork color.
Table 1 Effects of ractopamine hydrochloride on visually-assessed color scores
| Ractopamine, g/ton | 0 | 4.5 | 9.0 | 18.0 |
|---|---|---|---|---|
| Carr et al. 20091 | 2.58 | 2.60 | 2.45 | 2.82 |
| Patience et al. 20091 | 2.9 | 3.0 | — | — |
| Patience et al. 20092 | 2.8 | 2.8 | — | — |
| Rincker et al. 20091 | 3.16 | 3.24 | — | — |
| Apple et al. 20081 | 3.6y | — | 3.8x | — |
| Apple et al. 20082 | 3.2y | — | 3.4x | — |
| Fernándex-Dueñas et al. 20081 | 3.13 | 3.06 | — | — |
| Fernándex-Dueñas et al. 20082 | 3.17 | 3.12 | — | — |
| Stahl et al. 20072 | 2.80 | 2.61 | — | — |
| Weber et al. 20061 | 2.74 | — | 2.76 | — |
| Carr et al. 2005a2 | 2.76 | — | 2.77 | 2.73 |
| Carr et al. 2005b1 | 3.31 | — | 3.17 | — |
| Carr et al. 2005b2 | 3.21 | — | 3.09 | — |
| Armstrong et al. 20041 | 3.8xy | 3.6xy | 3.9x | 3.3y |
| Armstrong et al. 20042 | 3.9xy | 3.8xy | 4.0x | 3.5y |
| Stoller et al. 20031 | 3.24 | — | 3.19 | — |
| Herr et al. 20011 | 2.93 | 2.80 | 2.73 | 2.76 |
1National Pork Producers Council color scale (1 = pale pinkish gray to 6 = dark purplish red).
2Japanese fresh pork color scale (1 = pale gray to 6 = dark purple).
xyWithin a row, means lacking a common superscript letter differ (P < 0.05).
Most packers measure and sort pork based on instrumentally-measured color, in particular lightness (L*), redness (a*), and yellowness (b*) values. Even though Rincker et al. (2009) [6] and Apple et al. (2008) [7] noted that pork loin chops from pigs fed 4.5 and 9 g/ton RAC, respectively, were darker (lower L* values) than chops from control-fed pigs (Table 2), the consensus of available research indicates that L* values are not affected by feeding 4.5 [8, 9, 10], 9 [3, 5, 17] or 18 g/ton RAC [3, 16, 17].
Table 2 Effects of ractopamine hydrochloride on instrumental measures of pork color
| Ractopamine, g/ton | L*1 | a*2 | b*3 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 4.5 | 9.0 | 18.0 | 0 | 4.5 | 9.0 | 18.0 | 0 | 4.5 | 9.0 | 18.0 | |
| Patience et al. 2009 | 54.47 | 54.13 | — | — | 8.19x | 7.43y | — | — | 13.93x | 13.10y | — | — |
| Rincker et al. 2009 | 47.52x | 46.86y | — | — | 7.52x | 6.85y | — | — | 3.87x | 3.46y | — | — |
| Apple et al. 2008 | 54.12x | — | 53.23y | — | 7.47x | — | 6.81y | — | 14.45x | — | 13.71y | — |
| Fernándex-Dueñas et al. 2008 | 47.04 | 46.61 | — | — | 7.32 | 7.01 | — | — | 2.98x | 2.54y | — | — |
| Stahl et al. 2007 | 49.09 | 50.22 | — | — | 5.86 | 5.20 | — | — | 3.76 | 3.66 | — | — |
| Carr et al. 2005a | 48.73 | — | 48.11 | 48.93 | 9.23x | — | 7.96y | 7.55y | 5.10x | — | 3.85y | 3.69y |
| Carr et al 2005b | 50.62 | — | 50.86 | — | 8.63x | — | 7.53y | — | 5.85x | — | 4.99y | — |
| Armstrong et al. 2004 | 51.9xy | 50.9y | 50.7y | 53.2x | 8.3x | 7.4xy | 8.2x | 7.1y | 15.7 | 14.9 | 15.5 | 14.9 |
| Stoller et al. 2003 | 54.20 | — | 54.50 | — | — | — | — | — | — | — | — | — |
| Herr et al. 2001 | 45.48y | 46.06xy | 46.61x | 46.31xy | — | — | — | — | 5.29x | 4.82xy | 4.72y | 4.48y |
1L* = a measure of darkness to lightness (greater L* values indicate a lighter color).
2a* = a measure of redness (greater a* values indicate a redder color).
3b* = a measure of yellowness (greater b* values indicate a more yellow color).
xyWithin an objective color measure and row, means lacking a common superscript letter differ (P < 0.05).
Even though Fernándex-Dueñas et al. (2008) [9] reported that a* (redness) values of fresh loin chops and ham did not differ between pigs fed 0 and 4.5 g/ton RAC, the literature indicates that pork from pigs fed diets devoid of RAC is redder (greater a* values) and more yellow (greater b* values) than pork from pigs fed 4.5 [6, 8, 10], 9 [3, 5, 7] or 18 g/ton [3, 16] RAC. It should be noted, however, that the subtle changes in instrumental color measures of redness and yellowness, albeit statistically significant, are not always noticed by today’s pork consumers, especially considering the lack of differences in subjective color scores mentioned previously.
Firmness and Water-Holding Capacity
Firmness is the subjective measure of pork’s ability to hold its shape and is an indirect indicator of the water-holding capacity of pork. Typically, firmness and wetness are evaluated simultaneously, and, although Herr et al. (2001) [11] observed that loin chops from pigs fed 18 g/ton RAC were firmer than chops from control-fed pigs (Table 3), most research has failed to detect a difference in firmness/wetness between pork from pigs fed 4.5 [6, 9], 9 [3, 5, 17] or 18 g/ton RAC [3,17].
Table 3 Effects of ractopamine hydrochloride on muscle firmness scores and drip loss percentage
| Ractopamine, g/ton | Firmness scores | Drip loss, % | ||||||
|---|---|---|---|---|---|---|---|---|
| 0 | 4.5 | 9.0 | 18.0 | 0 | 4.5 | 9.0 | 18.0 | |
| Carr et al 20091 | 2.20 | 2.33 | 2.08 | 2.10 | — | — | — | — |
| Patience et al. 2009 | — | — | — | — | 6.73 | 6.21 | — | — |
| Rincker et al. 20091 | 2.33 | 2.41 | — | — | — | — | — | — |
| Apple et al. 2008 | — | — | — | — | 2.89 | — | 2.44 | — |
| Fernándex-Dueñas et al. 20081 | 2.70 | 2.76 | — | — | — | — | — | — |
| Weber et al. 20061 | 2.65 | — | 2.74 | — | 2.84 | — | 2.76 | — |
| Carr et al. 2005a1 | 2.62 | — | 2.58 | 2.65 | 4.79x | — | 4.04xy | 3.82y |
| Carr et al. 2005b1 | 3.25 | — | 3.05 | — | 4.11 | — | 4.53 | — |
| Stoller et al. 20032 | 2.37 | — | 2.37 | — | 2.47 | — | 2.31 | — |
| Herr et al. 20011 | 1.71y | 1.75xy | 1.81xy | 1.87x | — | — | — | — |
1National Pork Producers Council (1991) firmness scale (1 = very soft/very wet to 5 = very firm/very dry).
2National Pork Producers Council (2000) firmness scale (1 = soft, cut surface distorts easily to 3 = very firm, cut surface very smooth and no distortion of shape.
xyWithin a pork quality trait and row, means lacking a common superscript letter differ (P < 0.05).
The ability of pork to retain water after cutting, storage, and/or the application of a force is generally referred to as water-holding capacity (WHC). Typical measures of WHC include purge loss – moisture lost during vacuum-packaged storage – and drip loss – moisture loss from pork cuts or pork samples during a 24- to 48-hour storage period. Research has indicated that purge loss decreased linearly as the dietary inclusion level of RAC increased from 4.5 to 18 g/ton when compared with pork from pigs fed the control-diet [3]. However, a meta-analysis of available research indicated that RAC, regardless of dietary inclusion level, had no detrimental effect on the WHC of fresh pork [18].
Marbling
High amounts of marbling or intramuscular fat (IMF) can have beneficial effects on cooked pork palatability, especially flavor intensity and tenderness. The vast majority of the available research has not detected a difference in marbling scores between RAC- and control-fed pigs [5, 6, 9, 10, 12], and meta-analysis of the available literature also indicated that dietary RAC does not impact marbling scores [1]. Interestingly, marbling scores were actually increased by including 4.5 [19], 9 [7, 19], and 18 g/ton of RAC [19] in the finishing diet when compared to control diets.
Neither Carr et al. (2005b) [5] nor Rincker et al. (2009) [6] observed an effect of dietary RAC on the IMF of the loin eye muscle. Interestingly, Aalhus et al. (1990) [2] reported that feeding pigs 18 g/ton of RAC reduced visual marbling scores of the loineye muscle by 7.2%, but the IMF content of the same muscle samples was actually increased over 10% when compared to that of untreated controls. It is evident from the available literature that RAC has little to no effects on marbling or IMF.
Table 4 Effects of ractopamine hydrochloride on marbling scores and intramuscular fat content
| Ractopamine, g/ton | Marbling Scores1 | Intramuscular fat content, % | ||||||
|---|---|---|---|---|---|---|---|---|
| 0 | 4.5 | 9.0 | 18.0 | |||||
| Carr et al. 20091 | 2.15x | 1.90xy | 1.78y | 2.08xy | — | — | — | — |
| Patience et al. 2009 | 1.8 | 1.8 | — | — | — | — | — | — |
| Rincker et al. 20091 | 1.71 | 1.70 | — | — | 2.90 | 2.76 | — | — |
| Apple et al. 2008 | 1.9y | — | 2.2x | — | — | — | — | — |
| Fernándex-Dueñas et al. 20081 | 1.89 | 1.79 | — | — | — | — | — | — |
| Stahl et al. 2007 | — | — | — | — | 2.43x | 2.17y | — | — |
| Weber et al. 20061 | 1.03 | — | 1.03 | — | 2.44x | — | 1.92y | — |
| Carr et al. 2005a1 | 1.5 | — | 1.63 | 1.60 | 2.07xy | — | 1.98y | 2.29x |
| Carr et al. 2005b1 | 2.27 | — | 2.35 | — | 2.39 | — | 2.03 | — |
| Armstrong et al. 2004 | 1.7xy | 1.8xy | 1.3y | 2.0x | — | — | — | — |
| Stoller et al. 20032 | 2.40 | — | 2.38 | — | 2.53 | — | 2.43 | — |
1National Pork Producers Council (1999) marbling scale (1 = 1% intramuscular fat to 10 = 10% intramuscular fat).
xyWithin a pork quality trait and row, means lacking a common superscript letter differ (P < 0.05).
Cooked Pork Palatability
Cooked pork palatability includes the perceptions of juiciness, tenderness, flavor intensity, and the presence/absence of off-flavors. Most research employs trained sensory panelists (using linear scales) to ascertain differences in these properties. Patience et al. (2009) [10] reported a tendency for pork from pigs fed 4.5 g/ton RAC to receive lower pork-flavor intensity scores than pork from control-fed pigs; however, panelists failed to note differences in juiciness, flavor desirability or overall acceptability. Trained panelists in studies conducted by Fernándex-Dueñas et al. (2008) [9] and Rincker et al. (2009) [6] could not discern, however, any differences in juiciness and pork flavor between pigs fed 0 or 4.5 g/ton RAC. Moreover, when comparing pork from pigs fed 9 [3, 5] or 18 g/ton [3] RAC to that of control fed pigs, panelists were unable to detect differences in juiciness or flavor intensity ratings. On the other hand, several studies had demonstrated that pork loin chops from pigs fed 4.5 [10], 9 [3, 5], and 18 g/ton [3] of RAC received less desirable tenderness scores than chops from pigs finished on diets devoid of RAC.
The effect of RAC on Warner-Bratzler shear force (WBSF) values, the standard objective measurement of meat tenderness, remains a controversial topic. Several studies failed to observe an effect of feeding 4.5 [6, 19], 9 [7, 6, 12, 19] or 18 g/ton [19] of RAC on WBSF values of cooked pork. However, cooked pork chop WBSF values were increased between 8 and 12% by feeding 9 g/ton of RAC [2, 5] and between 9 and 18% by feeding 18 g/ton RAC [2, 3]. More recently, research has shown that feeding only 4.5 g/ton of RAC increased shear force values of cooked pork over 10% [8, 9], and Patience et al. (2009) [10] noted that only pork loin chops from gilts fed 4.5 g/ton RAC had higher WBSF values than control-fed gilts; however, no differences in shear force values were found between chops of barrows fed 0 or 4.5 g/ton of RAC.
It is generally accepted that to optimize the growth performance and efficiency of RAC-fed pigs that the dietary lysine content of the finishing diet must be increased between 0.73 [20] to 1.08% [21]. And, there is consideration information indicating that WBSF values increase, and sensory panel tenderness scores decrease, in response to increased dietary protein [22], dietary lysine [23], or increased lysine-to-energy ratio [24, 25]. In fact, Apple et al. (2004) [26] noted that the WBSF values of pigs fed 9 g/ton RAC increased linearly as the lysine-to-energy ratio increased from 1.7 to 3.1 g lysine/ Mcal of ME; thus, reductions in cooked pork tenderness appear to be a result of increased dietary protein/lysine content and not a response to RAC per se. In addition, Xiong et al. (2006) [27] found that the pork from RAC-fed pigs had greater WBSF values after 2, 4 and 7 days of aging than pork from control pigs; however, there was no difference in WBSF values between chops from RAC- and control-fed pigs when chops were allowed to age 10, 14 or 21 days postmortem (Figure 2); thus, extending postmortem storage 10 days, or greater, may diminish any pork toughening associated with feeding RAC.
Fat and Fresh Pork Belly Quality
Soft pork fat and bellies are an economic concern for today’s pork processors, resulting in carcass handling/processing difficulties, reduced bacon yields, unattractive products, reduced shelf-life, and consumer discrimination. The increased incidence of soft fat has resulted from the adoption of leaner, faster-growing genetics and increased use of polyunsaturated dietary fats/oils as cost-effective energy sources. Aalhus et al. (1990) [2] found that fat hardness was decreased in pigs fed RAC, and they attributed this diminishing fat hardness to reductions in fat accumulation in RAC-fed pigs. More- over, Perkins et al. (1992) [28] reported that the proportion of saturated fatty acids (SFA) in backfat was reduced, whereas the proportion of polyunsaturated fatty acids (PUFA) in backfat was increased, by including RAC in the finishing diet. Xi et al. (2005) [29] showed that fatty acid profiles of backfat from control-fed pigs and pigs fed 4.5 g/ton RAC were similar, but the PUFA content was increased between 6.9 and 9.9% in the backfat from pigs fed 9 g/ton RAC [4, 5, 7]. The increased unsaturation of pork backfat of RAC-fed pigs is the result of much greater deposition of linoleic acid [5, 7, 28] and linolenic acid [7] when compared with backfat from control-fed pigs. Mills et al. (1990) [30] reported that RAC depressed the bio- synthesis of fatty acids from glucose in porcine fat; so, the fatty acid content of pork backfat would be a greater reflection of the fatty acids absorbed from the digestion of the fats and/or oils included in the finishing diet [7, 31]. The increase in unsaturated fatty acids due to feeding RAC is significantly less than the increase observed when feeding highly unsaturated lipids from plant sources [30].
Because of the noticeable increase in thin/soft pork bellies, many pork processors are placing the blame on the inclusion of RAC in swine finishing diets and the noted increases in pork fat unsaturation associated with feeding RAC. However, neither Stites et al. (1991) [19] nor Uttaro et al. (1993) [32] noted an effect of feeding RAC on fresh belly thickness. And, although Carr et al. (2005b) [5] noted that feeding 9 g/ton RAC reduced belly firmness, the available research indicates that belly firmness does not differ between pigs fed RAC or a control diet [3, 31, 33]. Moreover, Scramlin et al. (2008) [33] reported that pickle uptake was actually greater in bellies from pigs fed 4.5 g/ton RAC than control-fed pigs, and the total slice area, slice length, and slice lean area were also greater in bacon from RAC-fed pigs. Lastly, trained sensory panelists were unable to detect differences in the texture and flavor profiles of bacon between control- and RAC-fed pigs [34, 35].
Based on the most recent literature, including RAC in the late-finishing diet has no detrimental effects on muscle pH, fresh pork color, firmness/wetness, water-holding capacity, or marbling/IMF content. Feeding RAC may result in greater deposition of polyunsaturated fats, but there is no evidence that RAC compromises pork fat or fresh belly quality. Lastly, although several studies have reported that feeding RAC reduced cooked pork tenderness, extending the postmortem aging time to at least 10 days will diminish the negative effect of RAC on pork tenderness.
Summary
Ractopamine hydrochloride (RAC), known by its trademarked name Paylean, is a phenethanolamine β-adrenergic agonist used as a feed supplement to redirect nutrients to improve live pig performance (daily gain and feed conversion efficiency) and fat-free lean yields in pork carcasses.
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