Assessing boar taint in Portuguese pork: A small-scale study of prevalence and classification via established detection thresholds

Introduction

The castration of male piglets, a longstanding and widespread practice in most countries, aims to prevent the occurrence of boar taint in the meat of certain male pigs (Bonneau & Weiler, 2019BonneauM, WeilerU, 2019. Pros and cons of alternatives to piglet castration: welfare, boar taint, and other meat quality traits. Animals9(11): 884. 10.3390/ani9110884). However, the practice has attracted criticism and has been identified as an animal welfare issue (Sodring et al., 2020SodringM, NafstadO, HasethTT, 2020. Change in Norwegian consumer attitudes towards piglet castration: increased emphasis on animal welfare. Acta Vet Scand62(1): 22-22. 10.1186/s13028-020-00522-6). Boar taint is an unpleasant odour found in the carcasses of entire males (EFSA, 2004EFSA, 2004. Welfare aspects of the castration of piglets. The EFSA Journal91.; Fredriksen et al., 2011FredriksenB, JohnsenAMS, SkuterudE, 2011. Consumer attitudes towards castration of piglets and alternatives to surgical castration. Res Vet Sci90(2): 352-357. 10.1016/j.rvsc.2010.06.018) caused mainly by the accumulation of androstenone and skatole (Claus et al., 1994ClausR, WeilerU, HerzogA, 1994. Physiological-aspects of androstenone and skatole formation in the boar - a review with experimental-data. Meat Sci38(2): 289-305. 10.1016/0309-1740(94)90118-X), and commonly found in the meat of approximately 5 to 10% of entire male pigs (Baek et al., 1997BaekC, Hansen-MollerJ, FriisC, CornettC, HansenSH, 1997. Identification of selected metabolites of skatole in plasma and urine from pigs. J Agr Food Chem45(6): 2332-2340. 10.1021/jf9605862; Aluwe et al., 2020AluweM, Heyrman, E, AlmeidaJM, BabolJ, BattaconeG, CitekJ, et al., 2020. Exploratory survey on European consumer and stakeholder attitudes towards alternatives for surgical castration of piglets. Animals10(10): 1758. 10.3390/ani10101758). The accumulation of these compounds in the adipose tissue during pubertal development of growing animals leads to off-odours and off-flavours in pork, creating a negative perception of pork quality among consumers (Bonneau & Weiler, 2019BonneauM, WeilerU, 2019. Pros and cons of alternatives to piglet castration: welfare, boar taint, and other meat quality traits. Animals9(11): 884. 10.3390/ani9110884).

In prominent pig-producing nations like Germany, France, and Denmark, approximately 75% to 93% of commercial male piglets undergo surgical castration (Van Ferneij, 2022Van FerneijJP, 2022. The pig castration situation in the European Union. pig333com - Professional Pigs Community Webpage. https://wwwpig333com/articles/the-pig-castration-situation-in-the-european-union_18100/ [March 11, 2022].). In other countries, most of the male pigs are raised without undergoing castration (Spain, 80%; Portugal, 85%; Ireland, 100%; United Kingdom, 98%), and are slaughtered before reaching puberty, with around five months of age and 100 kg of body weight. (De Briyne et al., 2016De BriyneN, BergC, BlahaT, TempleD, 2016. Pig castration: will the EU manage to ban pig castration by 2018?Porc Health Manag2: 29. 10.1186/s40813-016-0046-x). This practice is seen as the most sustainable in reducing androstenone levels, by feeding rapid-growth diets allowing entire males to reach market weight before becoming sexually mature (Squires et al., 2020SquiresEJ, BoneC, CameronJ, 2020. Pork production with entire males: directions for control of boar taint. Animals10(9): 1665. 10.3390/ani10091665). However, there is the risk of some animals reaching puberty earlier and tainting pork in consequence.

The concentrations of skatole and androstenone vary between individuals, with a dispersion caused by several factors such as sex, age, feed, and genotype, among others (Bonneau & Weiler, 2019BonneauM, WeilerU, 2019. Pros and cons of alternatives to piglet castration: welfare, boar taint, and other meat quality traits. Animals9(11): 884. 10.3390/ani9110884; Squires et al., 2020SquiresEJ, BoneC, CameronJ, 2020. Pork production with entire males: directions for control of boar taint. Animals10(9): 1665. 10.3390/ani10091665). If the concentrations of these compounds are small, the average consumer will not detect the off-odour. But this aspect is still under debate in the literature, with authors proposing different limit values for consumers not being able to detect boar taint (Lundstrom et al., 2009LundstromK, MatthewsKR, HaugenJE, 2009. Pig meat quality from entire males. Animal3(11): 1497-1507. 10.1017/S1751731109990693; Prusa et al., 2011PrusaK, NederveldH, RunnelsPL, LiR, KingVL, CraneJP, 2011. Prevalence and relationships of sensory taint, 5 alpha-androstenone and skatole in fat and lean tissue from the loin (Longissimus dorsi) of barrows, gilts, sows, and boars from selected abattoirs in the United States. Meat Sci88(1): 96-101. 10.1016/j.meatsci.2010.12.008; Bonneau & Chevillon, 2012BonneauM, ChevillonP, 2012. Acceptability of entire male pork with various levels of androstenone and skatole by consumers according to their sensitivity to androstenone. Meat Sci90(2): 330-337. 10.1016/j.meatsci.2011.07.019; Borrisser-Pairo et al., 2016Borrisser-PairoF, Panella-RieraN, ZammeriniD, OlivaresA, GarridoMD, MartinezB, et al., 2016. Prevalence of boar taint in commercial pigs from Spanish farms. Meat Sci111: 177-182. 10.1016/j.meatsci.2015.10.001; Verplanken et al., 2017VerplankenK, WautersJ, VercruysseV, AluweM, VanhaeckeL, 2017. Sensory evaluation of boar-taint-containing minced meat, dry-cured ham and dry fermented sausage by a trained expert panel and consumersFood Chem233: 247-255. 10.1016/j.foodchem.2017.04.105; Aluwe et al., 2018AluweM, AaslyngM, BackusG, BonneauM, ChevillonP, HaugenJE, et al., 2018. Consumer acceptance of minced meat patties from boars in four European countries. Meat Sci137: 235-243. 10.1016/j.meatsci.2017.11.034; Christensen et al., 2019ChristensenRH, NielsenDB, AaslyngMD, 2019. Estimating the risk of dislike: An industry tool for setting sorting limits for boar taint compounds. Food Qual Prefer71: 209-216. 10.1016/j.foodqual.2018.07.008). These limits can be defined by the sensory detection thresholds. The detection threshold is the lowest concentration of a substance in a medium relating to the lowest perception at which a stimulus is detected (ASTM:E679-04, 2011ASTM:E679-04, 2011. Standard practice for determination of odor and taste thresholds by a forced-choice ascending concentration series method of limits. ASTM International.); however, sensory thresholds may not be generalised to cover different groups of people over extended periods of time (Annor-Frempong et al., 1997Annor-FrempongIE, NuteGR, WhittingtonFW, WoodJD, 1997. The problem of taint in pork 1. Detection thresholds and odour profiles of androstenone and skatole in a model systemMeat Sci46(1): 45-55. 10.1016/S0309-1740(97)00003-X).

The objectives of this study were: a) to gain insights into the occurrence of boar taint within the Portuguese pork production industry by analysing levels of skatole and androstenone in the fat; b) to estimate thresholds for skatole and androstenone among Portuguese consumers. With these results, it was also intended to determine if a significant portion of samples exhibit off-odours by cross linking collected boar taint data with determined perception thresholds.

Material and methods

Results

The skatole and androstenone levels in fat are shown in Table 1. A total of 140 samples were assessed and categorised based on the sampling location (abattoirs A, B, and C) and gender. In this survey, 140 pigs (100%) had measurements of skatole above the limit of detection (LoD), and 72 pigs (51.4%) had androstenone below the LoD. The peak concentrations detected were 169 ng/g for skatole and 1215 ng/g for androstenone, respectively.

Mean and confidence interval (95%) for skatole concentration for all samples was 36.0 ± 4.7 ng per gram of liquid fat. The average concentration of androstenone in all the 140 samples was 64.5 ± 21.3 ng per gram of liquid fat.

Skatole levels were significantly different (p<0.05) between males and females (40.3 ± 5.9 ng/g and 24.7 ± 5.4 ng/g respectively). As expected, there was a substantial discrepancy in the androstenone values obtained between males and females (84.1 ± 28.4 ng/g and 11.7 ± 0.7 ng/g respectively). In fact, the median value for females aligns with the calculated value for cases falling below the detection limit (Fig. 1).

Figure 1 Boxplot representing skatole and androstenone content distribution according to gender (M, male; F, female). 

Discrepancies were observed in individual odour thresholds, with detection limits ranging from 17.7 to 141 ng/g for skatole (Table 2) and 106.1 to 3394.1 ng/g for androstenone (Table 3). The group’s BET for skatole was determined to be 35.4 ng/g, while for androstenone, it was 566.3 ng/g.

Considering the 140 samples under study and using the determined BET group values, it was found that the determined skatole content exceeded the BET values in 46 samples (28.8%), while only one sample (0.7%) exceeded the BET value for androstenone (Fig. 2).

Figure 2 Distribution of skatole and androstenone levels (nanogram per gram of liquid fat) in 140 pigs from Portuguese abattoirs and odour thresholds determined in this study. 

Discussion

This study is grounded in an observational study approach, utilising various carcasses sourced from the slaughterhouse. Its primary objective is to establish the prevalence of boar taint, although with a limited number of samples, without controlling for prior feeding programs, production systems during the growing-finishing period, or the specific crossbreeds included in the sample. Very low concentrations were not possible to measure due to limitations in chemical analysis techniques, and are typically referred to as being below the LoD. These data points are frequently censored in statistical assessments and replaced with a fixed value. According to Croghan & Egeghy (2003CroghanW, EgeghyPP, 2003. Methods of dealing with values below the limit of detection using SAS Carry. Proc 2003 SouthEast SAS Users Group Conf; Sept 22-24; St. Petersburg, FL. Cary, NC: SAS Users Group, 1-4.), opting to replace zero or LoD values with LoD divided by the square root of 2 (LoD/) stands out as the most appropriate choice when addressing measurements that fall below the LoD. This approach is favoured due to its tendency to yield a diminished bias. Given that the values acquired for skatole and androstenone do not conform to a normal distribution supplementary to the mean and standard deviation, this study also presented median values and interquartile ranges. The low sample size (140 adipose tissue samples collected from 140 animals) can also be addressed, representing a limitation of this study and indicating its small-scale nature. A study conducted by Prusa et al. (2011PrusaK, NederveldH, RunnelsPL, LiR, KingVL, CraneJP, 2011. Prevalence and relationships of sensory taint, 5 alpha-androstenone and skatole in fat and lean tissue from the loin (Longissimus dorsi) of barrows, gilts, sows, and boars from selected abattoirs in the United States. Meat Sci88(1): 96-101. 10.1016/j.meatsci.2010.12.008), aimed at defining the prevalence of skatole and androstenone in the fat of pigs within the United States. The findings revealed an average of 197.3 ng/g of skatole and 2363 ng/g in entire males, while female pigs exhibited levels of 34.1 ng/g for skatole and 120 ng/g for androstenone. When comparing these results to the ones obtained in the current study, significantly higher levels of boar taint were observed in the male pigs. The pigs processed in the Iberian market are usually slaughtered between five and six months old, which is insufficient time to reach sexual maturity. In contrast, the pigs examined in the United States were sourced from farms and had attained full maturity, hence the expected presence of elevated quantities of skatole and androstenone. Concerning the skatole values observed in female pigs, they seem to be closely aligned with the results from our study. However, it is noteworthy that the androstenone levels in the females appear unusually elevated. In a study by Walstra et al. (1999WalstraP, Claudi-MagnussenC, ChevillonP, Von SethG, DiestreA, MatthewsKR, et al., 1999. An international study on the importance of androstenone and skatole for boar taint: levels of androstenone and skatole by country and season. Livest Prod Sci62(1): 15-28. 10.1016/S0301-6226(99)00054-8), skatole and androstenone levels were assessed in male and female pigs across six European countries (Spain, France, Netherlands, United Kingdom, Denmark and Sweden). The results from this study indicated higher values when compared to the results obtained in our study. In average skatole and androstenone values were reported to be 70 ng/g and 30 ng/g, respectively. For entire males, the skatole averages ranged from 100 ng/g to 170 ng/g, and androstenone levels varied between 800 ng/g and 1270 ng/g. Borrisser-Pairo et al. (2016Borrisser-PairoF, Panella-RieraN, ZammeriniD, OlivaresA, GarridoMD, MartinezB, et al., 2016. Prevalence of boar taint in commercial pigs from Spanish farms. Meat Sci111: 177-182. 10.1016/j.meatsci.2015.10.001) published a study examining the occurrence of boar taint in commercial pigs from Spain. They specifically included entire males with comparable ages and weights to those in our study sample. In the study, involving 903 animals, the average skatole level in the fat was 40 ng/g, identical to the values found in the males analysed in our study. However, concerning androstenone, the overall values reported by this author were 200 ng/g, higher than those detected in 102 males examined in this study. Assessing boar taint in adipose tissue, melted fat, or pure fat may yield disparate values (with lower values typically in adipose tissue, attributed to the presence of additional constituents). This disparity complicates direct comparison of values found in literature and underscores the importance of harmonising boar taint detection methods, since additional validation of current methods and standardisation of methodologies are required to accurately quantify boar taint compounds (Haugen et al., 2012HaugenJE, BruniusC, ZamaratskaiaG, 2012. Review of analytical methods to measure boar taint compounds in porcine adipose tissue: The need for harmonised methods. Meat Sci90(1): 9-19. 10.1016/j.meatsci.2011.07.005). The presence of androstenone doesn’t seem to be limited exclusively to entire males. It is expected that, androstenone should only be present in males, but there are reports suggesting its presence in females as well, as noted by van Oeckel et al. (1996van OeckelMJ, CasteelsM, WarnantsN, De BoeverJL, van RenterghemR, BoucqueCV, 1996. Production of entire males with Belgian Landrace and hybrid pigs: The incidence of sensory aberrations. J Anim Physiol Anim Nutr76(2-3): 111-121. 10.1111/j.1439-0396.1996.tb00681.x) and Prusa et al. (2011PrusaK, NederveldH, RunnelsPL, LiR, KingVL, CraneJP, 2011. Prevalence and relationships of sensory taint, 5 alpha-androstenone and skatole in fat and lean tissue from the loin (Longissimus dorsi) of barrows, gilts, sows, and boars from selected abattoirs in the United States. Meat Sci88(1): 96-101. 10.1016/j.meatsci.2010.12.008). This phenomenon may be attributed to the conversion of progesterone into androstadienone and subsequently into androstenone (Robic et al., 2014RobicA, FarautT, PrunierA, 2014. Pathways and genes involved in steroid hormone metabolism in male pigs: A review and update. J Steroid Biochem Mol Bio140: 44-55. 10.1016/j.jsbmb.2013.11.001). Also, while skatole levels are typically higher in intact male pigs, it’s worth noting that skatole can also be found in barrows and females, albeit in smaller quantities (Aldal et al., 2005AldalI, AndresenO, EgeliAK, HaugenJE, GrodumA, FjetlandO, et al., 2005Levels of androstenone and skatole and the occurrence of boar taint in fat from young boars. Livest Prod Sci95(1-2): 121-129. 10.1016/j.livprodsci.2004.12.010). The primary reason for the elevated skatole levels in intact male pigs compared to barrows or gilts is the reduced hepatic degradation of skatole. This reduction is attributed to the inhibition of hepatic metabolism by androstenone, testosterone, or 17β-estradiol (Zamaratskaia & Squires, 2009ZamaratskaiaG, SquiresEJ, 2009. Biochemical, nutritional and genetic effects on boar taint in entire male pigs. Animal3(11): 1508-1521. 10.1017/S1751731108003674; Bonneau & Weiler, 2019BonneauM, WeilerU, 2019. Pros and cons of alternatives to piglet castration: welfare, boar taint, and other meat quality traits. Animals9(11): 884. 10.3390/ani9110884). Additionally, environmental conditions and housing facilities can play a role in skatole levels, since it can be absorbed through the skin via contact with faeces or through the lungs by inhalation (Thomsen et al., 2015ThomsenR, EdwardsSA, JensenBB, RousingT, SorensenJT, 2015. Effect of faecal soiling on skatole and androstenone occurrence in organic entire male pigs. Animal9(9): 1587-1596. 10.1017/S1751731115000798). Moreover, the dietary composition plays a crucial role in regulating intestinal skatole synthesis. Adding fermentable carbohydrates can reduce skatole levels by changing gut microflora activity and composition, leading to less L-tryptophan availability in the colon and decreased intestinal lumen apoptosis (Bee et al., 2020BeeG, QuiniouN, MariboH, ZamaratskaiaG, LawlorPG, 2020. Strategies to meet nutritional requirements and reduce boar taint in meat from entire male pigs and immunocastrates. Animals10(11): 1950. 10.3390/ani10111950; Squires et al., 2020SquiresEJ, BoneC, CameronJ, 2020. Pork production with entire males: directions for control of boar taint. Animals10(9): 1665. 10.3390/ani10091665). In this study, it was also possible to observe a positive correlation between androstenone and skatole concentrations (r=0.5382, p<0.01). This correlation has also been reported by Walstra et al. (1999WalstraP, Claudi-MagnussenC, ChevillonP, Von SethG, DiestreA, MatthewsKR, et al., 1999. An international study on the importance of androstenone and skatole for boar taint: levels of androstenone and skatole by country and season. Livest Prod Sci62(1): 15-28. 10.1016/S0301-6226(99)00054-8) and Borrisser-Pairo et al. (2016Borrisser-PairoF, Panella-RieraN, ZammeriniD, OlivaresA, GarridoMD, MartinezB, et al., 2016. Prevalence of boar taint in commercial pigs from Spanish farms. Meat Sci111: 177-182. 10.1016/j.meatsci.2015.10.001). Certain studies have reached the conclusion that the existence of androstenone hampers the metabolism of skatole (Doran et al., 2004DoranE, WhittingtonFA, WoodJD, McGivanJD, 2004. Characterisation of androstenone metabolism in pig liver microsomes. Chem Biol Interact147(2): 141-149. 10.1016/j.cbi.2003.12.002; Panella-Riera et al., 2008Panella-RieraN, MoeM, GrindflekE, OliverMA, WoodJD, DoranO, 2008. Effect of sex steroids on expression of sulfotransferase 2B1 immunoreactive protein in primary cultured porcine hepatocytes. Livest Sci118(3): 223-230. 10.1016/j.livsci.2008.01.021), potentially elucidating the observed positive correlation between these two compounds responsible for boar taint.

With the purpose of comparing and classifying the values obtained in the study of the prevalence of boar taint, the olfactory thresholds of skatole and androstenone were determined using Portuguese consumers. Sensory thresholds cannot be universally applied to diverse groups of people over extended periods, as their success in detecting specific substances in threshold tests depends on momentary individual sensitivity, which has been shown to change over time (Annor-Frempong et al., 1997Annor-FrempongIE, NuteGR, WhittingtonFW, WoodJD, 1997. The problem of taint in pork 1. Detection thresholds and odour profiles of androstenone and skatole in a model systemMeat Sci46(1): 45-55. 10.1016/S0309-1740(97)00003-X). It is important to highlight that the optimal approach for establishing boar taint sensitivity thresholds would involve utilising pork fat free of androstenone and skatole initially instead of liquid vaseline, in order to imitate the meat odour as closely as possible, taking into consideration any potential interference it may introduce. Comparing this study group BET with a publication by Annor Frempong et al. (1997Annor-FrempongIE, NuteGR, WhittingtonFW, WoodJD, 1997. The problem of taint in pork 1. Detection thresholds and odour profiles of androstenone and skatole in a model systemMeat Sci46(1): 45-55. 10.1016/S0309-1740(97)00003-X), the calculated BET values were slightly lower, being 26 ng/g for skatole and 426 ng/g for androstenone. The lowest individual odour thresholds of this study were obtained by women. Worth notice is that females seem to exhibit a higher sensitivity to androstenone: a study carried out in Spain and Germany determined that 31% of the Spanish and 18% of German respondents to a survey revealed higher sensitivity to androstenone, and among these sensitive individuals, a notably larger proportion were women (Weiler et al., 2000WeilerU, FurnolsMFI, FischerK, KemmerH, OliverMA, GispertM, et al., 2000. Influence of differences in sensitivity of Spanish and German consumers to perceive androstenone on the acceptance of boar meat differing in skatole and androstenone concentrations. Meat Sci54(3): 297-304. 10.1016/S0309-1740(99)00106-0). Roughly 50% of the adult human population cannot detect the characteristic scent when they inhale androstenone (Wysocki et al., 1989WysockiCJ, DorriesKM, BeauchampGK, 1989. Ability to perceive androstenone can be acquired by ostensibly anosmic people. P Nat Acad Sci USA86(20): 7976-7978. 10.1073/pnas.86.20.7976). This finding is corroborated by a recent investigation by Klyuchnikova et al. (2022KlyuchnikovaMA, KvashaI, LaktionovaT, VoznessenskayaVV, 2022. Olfactory perception of 5 alpha-androst-16-en-3-one: Data obtained in the residents of central Russia. Data Br45: 108704. 10.1016/j.dib.2022.108704), which evaluated the ability of 807 individuals residing in central Russia to perceive the odour of androstenone; it was found that 49% of these participants could be classified as potentially having a specific inability to detect this substance through smell. On the other hand, skatole is perceived by 99% of consumers (Weiler et al., 2000WeilerU, FurnolsMFI, FischerK, KemmerH, OliverMA, GispertM, et al., 2000. Influence of differences in sensitivity of Spanish and German consumers to perceive androstenone on the acceptance of boar meat differing in skatole and androstenone concentrations. Meat Sci54(3): 297-304. 10.1016/S0309-1740(99)00106-0), thus explaining why panellists exhibit a higher level of proficiency in detecting odour.

Industrial procedures for quality control concerning meat classification according to the level of boar taint are usually based on consumer’s perception threshold values. Thus, it is essential to set threshold values for androstenone, skatole, or boar taint levels, determining whether these carcasses should be categorised as having boar taint or not. This threshold should be determined considering consumer sensitivity, acceptability, and the prevalence of boar taint in the swine population (Aluwe et al., 2018AluweM, AaslyngM, BackusG, BonneauM, ChevillonP, HaugenJE, et al., 2018. Consumer acceptance of minced meat patties from boars in four European countries. Meat Sci137: 235-243. 10.1016/j.meatsci.2017.11.034; Font-i-Furnols et al., 2020Font-i-FurnolsM, Martin-BernalR, AluweM, BonneauM, HaugenJE, MoerleinD, et al., 2020. Feasibility of on/at line methods to determine boar taint and boar taint compounds: an overview. Animals10(10): 1886. 10.3390/ani10101886). From the results, given the lowest BET, it can be inferred that panellists with higher olfactory sensitivity would be able to detect the odour of skatole in 114 of the tested samples (constituting 81.4%), while they would detect the odour of androstenone in 19 samples (equivalent to 13.6%). Nonetheless, it’s important to note that factors such as panel training can significantly influence the odour detection thresholds by a substantial margin. Additionally, test conditions, such as the size of sniff bottles employed, can be relevant to the results and some how justifies the variability found on the published data (Annor-Frempong et al., 1997Annor-FrempongIE, NuteGR, WhittingtonFW, WoodJD, 1997. The problem of taint in pork 1. Detection thresholds and odour profiles of androstenone and skatole in a model systemMeat Sci46(1): 45-55. 10.1016/S0309-1740(97)00003-X). The thresholds for evaluating boar taint, frequently discussed in the literature, exhibit variability. This divergence might arise from the fact that the current acceptability standards are mostly based on the concentrations of these odour compounds in uncooked meat (Annor-Frempong et al., 1997Annor-FrempongIE, NuteGR, WhittingtonFW, WoodJD, 1997. The problem of taint in pork 1. Detection thresholds and odour profiles of androstenone and skatole in a model systemMeat Sci46(1): 45-55. 10.1016/S0309-1740(97)00003-X). Researchers have suggested a range between 500 and 1000 ng/g for androstenone as a potential limit (Prusa et al., 2011PrusaK, NederveldH, RunnelsPL, LiR, KingVL, CraneJP, 2011. Prevalence and relationships of sensory taint, 5 alpha-androstenone and skatole in fat and lean tissue from the loin (Longissimus dorsi) of barrows, gilts, sows, and boars from selected abattoirs in the United States. Meat Sci88(1): 96-101. 10.1016/j.meatsci.2010.12.008; Borrisser-Pairo et al., 2016Borrisser-PairoF, Panella-RieraN, ZammeriniD, OlivaresA, GarridoMD, MartinezB, et al., 2016. Prevalence of boar taint in commercial pigs from Spanish farms. Meat Sci111: 177-182. 10.1016/j.meatsci.2015.10.001). In cases where skatole is absent, some studies propose even higher limits, falling within the range of 2000 to 3000 ng/g (Bonneau & Chevillon, 2012BonneauM, ChevillonP, 2012. Acceptability of entire male pork with various levels of androstenone and skatole by consumers according to their sensitivity to androstenone. Meat Sci90(2): 330-337. 10.1016/j.meatsci.2011.07.019). As for skatole, the acceptable limits can differ, with some sources suggesting a range of 100 to 200 ng/g (Prusa et al., 2011PrusaK, NederveldH, RunnelsPL, LiR, KingVL, CraneJP, 2011. Prevalence and relationships of sensory taint, 5 alpha-androstenone and skatole in fat and lean tissue from the loin (Longissimus dorsi) of barrows, gilts, sows, and boars from selected abattoirs in the United States. Meat Sci88(1): 96-101. 10.1016/j.meatsci.2010.12.008; Borrisser-Pairo et al., 2016Borrisser-PairoF, Panella-RieraN, ZammeriniD, OlivaresA, GarridoMD, MartinezB, et al., 2016. Prevalence of boar taint in commercial pigs from Spanish farms. Meat Sci111: 177-182. 10.1016/j.meatsci.2015.10.001). However, Aluwe et al. (2018AluweM, AaslyngM, BackusG, BonneauM, ChevillonP, HaugenJE, et al., 2018. Consumer acceptance of minced meat patties from boars in four European countries. Meat Sci137: 235-243. 10.1016/j.meatsci.2017.11.034) has reported that skatole values exceeding 100 ng/g are not considered acceptable, regardless of the androstenone level, probably caused by the synergistic relationship between androstenone and skatole when it comes to defining the intensity of odours (Annor-Frempong et al., 1997Annor-FrempongIE, NuteGR, WhittingtonFW, WoodJD, 1997. The problem of taint in pork 1. Detection thresholds and odour profiles of androstenone and skatole in a model systemMeat Sci46(1): 45-55. 10.1016/S0309-1740(97)00003-X). Furthermore, Bonneau & Chevillon (2012BonneauM, ChevillonP, 2012. Acceptability of entire male pork with various levels of androstenone and skatole by consumers according to their sensitivity to androstenone. Meat Sci90(2): 330-337. 10.1016/j.meatsci.2011.07.019) deems skatole values in the 200 to 250 ng/g range to be excessively high. The determination of any sorting threshold is contingent upon the tolerance for adverse consumer responses that stakeholders are prepared to accept. Hence, Aluwe et al. (2018AluweM, AaslyngM, BackusG, BonneauM, ChevillonP, HaugenJE, et al., 2018. Consumer acceptance of minced meat patties from boars in four European countries. Meat Sci137: 235-243. 10.1016/j.meatsci.2017.11.034) undertook a study to illustrate the decline in preference for boar meat patties as the levels of androstenone and skatole increased. The preference for boar meat patties diminished with higher skatole content. Additionally, for consumers sensitive to androstenone, preference decreased as androstenone levels increased, particularly when skatole levels were low. Moreover, Christensen et al. (2019ChristensenRH, NielsenDB, AaslyngMD, 2019. Estimating the risk of dislike: An industry tool for setting sorting limits for boar taint compounds. Food Qual Prefer71: 209-216. 10.1016/j.foodqual.2018.07.008) stated that the anticipated risks of aversion among an average consumer, a discerning consumer, and the general consumer population aligned with sorting thresholds averaging 250 ng/g of skatole and 4000 ng/g of androstenone.

In conclusion, a low level of boar taint was found in this study aiming at investigating the prevalence of skatole and androstenone in pork entering the food chain in Portugal. There were little worth notice number of samples classified as having high levels of boar taint (4.2% exceeded the threshold value of 100 ng/g for skatole, and 0.7% surpassed the value of 500 ng/g of androstenone), however 28.8% of the samples exceeded the estimated BET values for skatole, which underscores that the practice of slaughtering immature males alone may not be sufficient to resolve this issue. Additionally, high skatole levels in females may indicate the possibility of skatole resorption, possibly stemming from inadequate hygiene management. An inherent limitation of this study lies in its observational study design, lacking control over preceding factors such as diet, production system, or genetic crossbreeding. Nonetheless, and despite the limitation of a small sample size in this study, the knowledge about the percentage of carcasses with elevated levels of androstenone and skatole offers valuable and objective insights to the sector regarding boar taint, which directly impacts the sensory quality of pork. Nevertheless, it's essential to tailor the acceptable limits of these compounds to the particular sensitivity of a given population or culture. This adaptation can be achieved through sensory tests like the best-estimated threshold.