Marinating as a technology to shift sensory thresholds in ready-to-eat entire male pork meat

This study investigated the effect of marinades in improving the eating quality in ready-to-eat boar meat. Neck chops with fat content below 18.9%, skatole 1.1 ppm (range 0.03–1.1) and androstenone 5.6 ppm (range 0.01–5.6) were used. In a screening experiment different marinades were tested for their ability to mask boar taint (defined as manure and urine odour and flavour). Liquid smoke and oregano extracts appeared to have the best potential for masking, and were studied in detail. Results from the study indicated that marinated chops with skatole content of approximately 0.4 ppm appeared similar to castrates in boar taint. Chops with skatole contents above 0.7 ppm remained unmasked despite the use of strongly flavoured marinades. Unmarinated chops served at 60 °C were more tainted than those served at 15 °C, but scored lower for boar taint when reheated, although the concentrations of androstenone and skatole remained the same. The fat content of the chops was not well correlated to the perception of boar taint. The attributes manure and urine were correlated with the level of skatole, but urine attribute was not a good indicator of the androstenone level.     

Predicting the likelihood of developing boar taint: Early physical indicators in entire male pigs

Three potential early-age predictors of which boars are likely to develop boar taint (testes volume, skin lesions and dirtiness) were measured on 102 boars every fortnight from 10 weeks of age until slaughter. These predictors were correlated with the level of boar taint according to the hot iron method and the concentrations of skatole and androstenone as determined by chemical analysis. The chance of no/low boar taint according to the hot iron method decreased with higher testes volume (weeks 22 and 24) and increased with skin lesion score (weeks 12, 16 and 18). For the concentrations of androstenone and skatole, the strongest correlation was found with testes volume in week 12. Skin lesions in week 16 were negatively correlated with skatole levels. Dirtiness was negatively correlated with skatole concentrations (week 18) but positively correlated with androstenone concentrations (weeks 20 and 22). Testes volume has the greatest potential for predicting the likelihood of developing boar taint.     

Effects of context and repeated exposure on food liking: The case of boar taint

This study investigated whether consumer acceptance of boar meat is overestimated by standardised situational testing and whether repeated exposure decreases liking. Thus, a home use test (HUT) followed by a central location test (CLT) was conducted to assess the acceptance of minced boar meat with approximately 14% fat either HIGH or LOW in androstenone (2.0 vs. 0.30 ppm) and skatole (0.30 vs. 0.06 ppm) in comparison to meat from castrates and gilts (CONTROL). In HUT, no significant difference (p > .05) in dislike frequency was observed between CONTROL and LOW. For HIGH, liking was strongly impaired during frying. The results indicated a masking effect of the ready-made sauce on the odour but not on the flavour. In CLT, dissatisfaction was generally higher than in HUT. Similar to HUT, HIGH boar meat was more often disliked (p < .001) compared to LOW and CONTROL in the CLT. To conclude, standardised testing did not underestimate acceptance. In contrast to anticipations, a single previous exposure to boar meat with high levels of androstenone and skatole did not affect (p > .05) liking in the follow-up CLT.     

A single nucleotide polymorphism in the CYP2E1 gene promoter affects skatole content in backfat of boars of two commercial Duroc-sired crossbred populations

The prevention of unpleasant boar taint is the main reason for castration of male piglets. This study aimed to investigate how the malodorous compound skatole is affected by a single nucleotide polymorphism (g.2412 C>T at − 586 ATG) in the porcine cytochrome p450 II E1 (CYP2E1) gene. 119 boars of two commercial Duroc-sired crossbred populations raised at different farms were investigated. Skatole and androstenone in backfat averaged 114 ± 125 ng/g and 1206 ± 895 ng/g melted fat, respectively. The frequency of the genotypes CC, CT, and TT was 25, 52, and 23%, respectively. CC boars had the highest average skatole levels (175 ng/g) compared to CT (92 ng/g) and TT (93 ng/g). Applying suggested sensory threshold levels for skatole (> 150 ng/g) and androstenone (> 2000 ng/g), 30% of the carcasses may be unacceptably tainted while the proportion of tainted carcasses is significantly higher within genotype CC (56.7%) compared to genotypes CT (24.3%) and TT (14.8%). Effective reduction of tainted carcasses appears feasible applying marker assisted selection.     

Effect of feeding fermentable fibre-rich feedstuffs on meat quality with emphasis on chemical and sensory boar taint in entire male and female pigs

Skatole, androstenone and other compounds such as indole cause boar taint in entire male pork. However, female pigs also produce skatole and indole. The purpose of this experiment was to minimise boar taint and increase overall impression of sensory quality by feeding entire male and female pigs with fibre-rich feedstuffs. The pigs have been fed three organic diets for either 1 or 2 weeks prior to slaughter of which two diets contained different fermentable fibre-rich feedstuffs – 10–13.3% dried chicory roots or 25% blue lupines. These two treatments were compared with pigs fed with an organic control diet for either 1 or 2 weeks prior to slaughter. Lupines significantly reduced skatole in blood and backfat for both genders after 1 week. Moreover, lupines showed negative impact on growth rate and feed conversion whilst chicory showed no significant differences in this respect. However, the indole concentration was significantly lower in chicory than lupine fed pigs. From a sensory perspective, chicory and lupine feeding reduced boar taint since odour and flavour of manure related to skatole and urine associated to androstenone were minimised. The level of boar taint in the entire male pigs was most effectively reduced after 14 days by both fibre-rich feeds while lupine had the largest influence on “boar” taint reduction in female pigs.     

The effects of method of castration,rearing condition and diet on sensory quality of pork assessed by a trained panel

Beside surgical castration possible alternatives helping to reduce the incidence of boar taint in cooked pork are rearing conditions, immunocastration and feeding strategies for entire males known to lower the skatole levels. The goal of this study was to assess the effects of these alternatives on the sensory acceptability of pork. In experiment 1, carcasses from barrows, entire males (EM) and entire males fed raw potato starch (EM+) 7 d before slaughter were selected based on the androstenone (≤ 2 µg/g) and skatole (≤ 0.32 µg/g) levels. In experiment 2, carcasses from barrows, immunocastrates (IC), entire males either group-penned (EMG) or individually penned (EMP) were selected based on the aforementioned criteria. Boar odour and boar flavour intensities of longissimus dorsi (LD) and neck chops were evaluated by trained panellists. Boar odour and flavour scores were higher (P < 0.01) in neck than LD chops. Although skatole tissue levels in barrows and EM+ were similar (P > 0.05), boar odour and flavour scores were greater (P < 0.05) in EM+ than barrows. In experiment 2, scores for boar odour and flavour were lower (P < 0.05) in pork from barrows and IC than EMP, with intermediate values for EMG. In conclusion, we observed a discrepancy between the known boar taint compounds androstenone and skatole and sensory acceptability, which indicates that other factors influenced the perception of boar taint. Thus, surgical castration with or without anesthesia or immunocastration are still the safest methods to avoid boar taint.     

Quantification of myosin heavy chain isoform in porcine muscle using an enzyme-linked immunosorbent assay

The aim of the present study (part of an EU AIR programme on boar taint) was to make objective the perception of boar taint in entire male pork, and to relate the perception to skatole and androstenone levels. Trained analytical sensory panels in seven European countries assessed pig meat with known levels of androstenone and skatole. The panels performed a sensory profiling using the attributes pig, urine, manure/stable, naphthalene/mothballs, rancid, sweet, sweat and abnormal, both for odour and flavour in separate sessions. It turned out to be difficult to harmonise sensory methodology for seven sensory panels throughout the EU, especially with respect to the exact level of training the panellists received. Sensory panels in general were able to differentiate between the two compounds and between different levels of the compounds, though substantial differences between the panels in the different countries existed. Androstenone was found to relate mostly to the urine attribute, while skatole related mostly to manure and, to a lesser extent, to naphthalene.     

Effect of feeding fermentable fibre-rich feedstuffs on meat quality with emphasis on chemical and sensory boar taint in entire male and female pigs

Skatole, androstenone and other compounds such as indole cause boar taint in entire male pork. However, female pigs also produce skatole and indole. The purpose of this experiment was to minimise boar taint and increase overall impression of sensory quality by feeding entire male and female pigs with fibre-rich feedstuffs. The pigs have been fed three organic diets for either 1 or 2 weeks prior to slaughter of which two diets contained different fermentable fibre-rich feedstuffs – 10–13.3% dried chicory roots or 25% blue lupines. These two treatments were compared with pigs fed with an organic control diet for either 1 or 2 weeks prior to slaughter. Lupines significantly reduced skatole in blood and backfat for both genders after 1 week. Moreover, lupines showed negative impact on growth rate and feed conversion whilst chicory showed no significant differences in this respect. However, the indole concentration was significantly lower in chicory than lupine fed pigs. From a sensory perspective, chicory and lupine feeding reduced boar taint since odour and flavour of manure related to skatole and urine associated to androstenone were minimised. The level of boar taint in the entire male pigs was most effectively reduced after 14 days by both fibre-rich feeds while lupine had the largest influence on “boar” taint reduction in female pigs.     

Sensory characterization of meat from pigs vaccinated against gonadotropin releasing factor compared to meat from surgically castrated,entire male and female pigs

Boar taint is a sensory defect mainly due to androstenone and skatole. The most common method to control boar taint is surgical castration at an early age. Vaccination against gonadotropin releasing factor (also known as immunocastration) is an alternative to surgical castration to reduce androstenone content. In this experiment, loins from 24 female (FE), 24 entire male (EM), 24 vaccinated males (IM) and 23 surgically castrated males (CM) were evaluated by eight trained panellists in 24 sessions. Loins were cooked in an oven at 180 °C for 10 min. Furthermore loins were evaluated by consumers and its androstenone and skatole content were also chemically determined. Meat from EM had higher androstenone and skatole odour and flavour than meat from FE, IM and CM and lower sweetness odour scores. High correlations were found between androstenone and skatole levels assessed by trained panelists, chemical analysis and consumers’ acceptability. Moreover meat from EM is mainly related to androstenone and skatole attributes.     

Consumers’ sensory acceptability of pork from immunocastrated male pigs

Boar taint is the off-odour or off flavour of cooked pork. Currently, the most common method of controlling boar taint is surgical castration. However, immunocastration has been used in some parts of the world as an alternative to surgical castration. The aim of this study was to evaluate the sensory acceptability of meat from immunocastrated pigs (IM) compared with meat from females (FE), surgically castrated (CM) and entire males (EM). Twenty animals of each type were evaluated by 201 consumers in 20 sessions. Longissimus thoracis muscle of the different animals was cooked in an oven at 180 °C for 10 min. Consumers scored the odour and the flavour of the meat in a 9-point category scale without an intermediate level. There were no significant differences in consumer’s evaluation of meat from IM, CM, and FE. In contrast, EM meat presented a higher percentage of dissatisfied scores and was significantly (P < 0.05) less accepted than meat from CM, IM and FE. Consumers’ acceptability of EM meat was always lower, independently of its androstenone levels. However meat with low levels of androstenone was more accepted that meat with medium or high levels of this substance. It can be concluded that immunocastration produced pork that was accepted by the consumers, and was indistinguishable from pork from CM or FE.     

Supercritical Carbon Dioxide Extraction of Androstenone and Skatole from Pork Fat

Boar taint, an unpleasant odor observed in pork from some mature intact male pigs, is attributed primarily to the presence of two compounds in boar fat, androstenone (Sα-androst-16-ene-3-one) and skatole (3-methyl indole). A rapid extraction method for the preparation of fat samples for androstenone/skatole screening assays would lead to more efficient use of boar carcasses for pork production. Supercritical carbon dioxide removed 97 ± 2% of the androstenone (extraction at 40°C; 5 min) and 65 ± 3% of the skatole (extraction at 40°C; 20 min) from 0.5 g of boar backfat. Supercritical CO₂ provides the basis for a fairly rapid extraction method to remove compounds associated with boar taint.     

Predicting the likelihood of developing boar taint: Early physical indicators in entire male pigs

Three potential early-age predictors of which boars are likely to develop boar taint (testes volume, skin lesions and dirtiness) were measured on 102 boars every fortnight from 10weeks of age until slaughter. These predictors were correlated with the level of boar taint according to the hot iron method and the concentrations of skatole and androstenone as determined by chemical analysis. The chance of no/low boar taint according to the hot iron method decreased with higher testes volume (weeks 22 and 24) and increased with skin lesion score (weeks 12, 16 and 18). For the concentrations of androstenone and skatole, the strongest correlation was found with testes volume in week 12. Skin lesions in week 16 were negatively correlated with skatole levels. Dirtiness was negatively correlated with skatole concentrations (week 18) but positively correlated with androstenone concentrations (weeks 20 and 22). Testes volume has the greatest potential for predicting the likelihood of developing boar taint.     

An international study on the importance of androstenone and skatole for boar taint: I. Presentation of the programme and measurement of boar taint compounds with different analytical procedures

An international study, involving 11 participants in 7 European countries, was conducted to provide scientific evidence for an objective measurement of boar taint in entire male pigs and its possible variation between countries. The specific objectives were to determine the respective contributions of androstenone and skatole to boar taint and their possible variations according to production systems and consumer populations. Over 4000 entire male pigs and 200 gilts were raised and slaughtered in 6 countries. Meat samples were taken from the loin and backfat samples were used for the rapid measurement of androstenone and skatole. A sub-population of 377 entire males and 42 gilts was then selected in such a way as to represent all combinations of skatole and androstenone levels. Androstenone and skatole levels in the selected samples were checked, using established reference methods. Meat samples from the selected animals were used for sensory evaluation by trained panels and for consumer surveys in 7 European countries. The present paper gives a general presentation of the programme and reports the main characteristics of the samples. Three companion papers present the results of the evaluation by trained sensory panels [Dijksterhuis, G., Engel, B., Walstra, P., Font i Furnols, M., Agerhem, H., Fisher, K., Oliver, M. A., Claudi-Magnussen, C., Siret, F., Béague, M. P., Homer, D. B., & Bonneau, M. (2000). An international study on the importance of androstenone and skatole for boar taint: II. Sensory evaluation by trained panels in seven European countries. Meat Science54, 261-269], the results of the consumer surveys [Matthews, K. R., Homer, D. B., Punter, P., Béague, M. P., Gispert, M., Kemspter, A. J., Agerhem, H., Claudi-Magnussen, C., Fischer, K., Siret, F., Leask, H., Font i Furnols, M., & Bonneau, M. (2000). An international study on the importance of androstenone and skatole for boar taint: III. Consumer survey in seven European countries. Meat Science, 54, 271-283] and the main conclusions and recommendations [Bonneau, M., Walstra, P., Claudi-Magnussen, C., Kempster, A. J., Tornberg, E., Fischer, K., Diestre, A., Siret, F., Chevillon, P., Claus, R., Dijksterhuis, G., Punter, P., Matthews, K. R., Agerhem, H., Béague, M. P., Oliver, M. A., Gispert, M., Weiler, U., von Seth, G., Leask, H., Font i Furnols, M., Homer, D. B., & Cook, G. L. (2000). An international study on the importance of androstenone and skatole for boar taint: IV. Simulation studies on consumer dissatisfaction with entire male pork and the effect of sorting out carcasses on the slaughter line, main conclusions and recommendations. Meat Science, 54, 285-295]. Seasonal effects and differences between countries in skatole and androstenone levels are presented elsewhere [Walstra, P., Claudi-Magnussen, C., Chevillon, P., von-Seth, G., Diestre, A., Matthews, K. R., Homer, D. B., & Bonneau, M. (in press). An international study on the importance of androstenone and skatole for boar taint: Levels of androstenone and skatole according to country and season. Livestock Production Science]. A supplementary paper considers the effects of human sensitivity to androstenone and skatole on the consumer acceptance of entire male pork [Weiler, U., Font i Furnols, M., Fischer, K., Kemmer, H., Oliver, M. A., Gispert, M., Dobrowolski, A., & Claus, R. (in press). 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 Science]. A study of possible other compounds contributing to boar taint was also carried out within this programme.     

Boar taint detection using parasitoid biosensors

The off-flavor boar taint associated with the substances skatole, androstenone, and possibly indole represents a significant problem in the pig husbandry industry. Boar taint may occur in meat from uncastrated sexually mature male pigs; consumers commonly show a strong aversion to tainted meat. Consequently, there is a need for rapid methods to sort out and remove tainted carcasses at the slaughterline. We tested the ability of wasps, Microplitis croceipes to perceive and learn the 3 boar taint compounds both individually and in combination using classical conditioning paradigms. We also established the effectiveness and reliability of boar taint odor detection when wasps were used as biosensors in a contained system called the "wasp hound" using a cohort of trained wasps. We found that the wasps are able to successfully learn indole, skatole and to also detect them when presented a 1:1:1 mixture of all 3 compounds. This was shown for both a single hand-manipulated wasp bioassay and when using the "wasp hound" detector device. In contrast, the wasps showed a weak conditioned response to androstenone at the concentration tested. The estimated gas phase concentrations that the wasps perceived during training were in the range of 10 ± 0.4 pg/s for skatole and indole, and 2 ± 0.5 pg/s for androstenone. We conclude that use of these wasps as biosensors presents a promising method for boar taint detection and discuss future training paradigms that may improve their responses to compounds such as androstenone. Practical Application: The development of a perceptive, inexpensive, and reliable means of detecting boar taint before the product is presented to sensitive consumers.     

Comparison of heating methods and the use of different tissues for sensory assessment of abnormal odours (boar taint) in pig meat

Five heating methods (microwave, hotwire, boiling at 25 °C and 75 °C and melting) were used to generate cooking odours from backfat of entire male pigs and a 'composite' sample consisting of fat and muscle from the head along with salivary glands. The methods elicited significantly different scores for odours from 4 groups of 10 samples differing in their concentrations and ratios of skatole and androstenone. The odours (pork odour, abnormal odour, skatole odour and androstenone odour) were assessed by 3 experienced assessors. Correlations between skatole and androstenone concentrations and abnormal odour score in backfat were higher for skatole, suggesting it is the more important boar taint compound. In the composite sample, androstenone concentration was much higher than in backfat and androstenone was a more important contributor to boar taint. The microwave, hotwire and boiling (75 °C) methods produced the clearest separation between samples and the microwave method was considered the most suitable for on-line use.     

Threshold Detection of Boar Taint Chemicals Using Parasitic Wasps

Abstract: Surgical castration has been long used to prevent consumers from experiencing taint in meat from male pigs, which is a large problem in the pig husbandry industry. Due to obvious animal welfare issues, the EU now wants an alternative for castration, suggesting an urgent need for novel methods of boar taint detection. As boar taint is only a problem when taint chemicals exceed a well‐defined threshold, detection methods should be concentration‐specific. The wasp, Microplitis croceipes’ ability to learn and respond to particular concentrations of the boar taint compounds, skatole, androstenone, and indole was tested. Also tested was the wasps’ ability to discriminate between known concentrations of indole, skatole, and androstenone in real boar fat samples at room temperature. Wasps were trained using associative learning by providing food‐deprived wasps with sucrose–water in the presence of specific odor concentrations. Trained wasps’ responses were tested to a range of concentrations of 3 compounds. Wasps showed unidirectional generalization of learned concentration responses, whereby the direction of concentration generalization was shown to be chemical‐dependent. Through both positive (sucrose) and negative feeding experiences (water only) with varying compound concentrations, the wasps can also be conditioned to respond to concentrations exceeding a defined threshold, and they were successful in reporting low, medium, and high concentrations of indole, skatole, and androstenone in boar fat at room temperature. The need for threshold detection rather than simple detection of absence/presence applies to many food quality issues, including the detection of spoilage or pest damage in crops or stored foods. Practical Application: An inexpensive and reliable means of detecting boar tainted pork at slaughter to avoid tainted meat on the market and dissatisfied consumers.     

Expected effects on carcass and pork quality when surgical castration is omitted — Results of a meta-analysis study

Alternatives to the common castration (C) practice of piglets are surgical castration under anaesthesia and rearing entire males (EM) or immunocastrates (IC). It is well established that boar taint hinders the breakthrough of these options. Less is known how avoiding surgical castration would affect carcass characteristics and pork quality. The objective of this meta-analysis was to estimate the impact of lack of castration on quality traits besides boar taint. The most marked effect of castration method and gender was found in lean meat and intramuscular fat percentage. Compared to EM, carcass leanness was estimated to be greater (P < 0.05) and intramuscular fat level lower (P < 0.05) than in C, IC and females. Regarding pork quality traits only the difference in shear force between IC and EM was of relevant magnitude. This meta-analysis revealed that the implementation of EM production should not be hindered by pork quality concerns.     

Quantitative determination of the boar taint compounds androstenone,skatole, indole, 3α-androstenol and 3β-androstenol in wild boars (Sus scrofa) reveals extremely low levels of the tryptophan-related degradation products

The major boar taint compounds androstenone and skatole as well as the minor compounds indole, 3α-androstenol and 3β-androstenol were determined in back fat samples of 23 male wild boars by applying a recently published SIDA–HS-SPME–GC/MS method. The boar pheromones androstenone, 3α-androstenol and 3β-androstenol were found in extraordinary high concentrations, resulting in mean values of 3329 ng/g androstenone, 1273 ng/g 3α-androstenol and 545 ng/g 3β-androstenol. Interestingly, skatole was not detectable in about 50% of the boars and negligibly low in all other samples as expressed by a mean skatole value of only 14 ng/g. Indole was also found in every sample, but again in low concentrations with a mean value of 40 ng/g. Possible factors explaining this remarkably low skatole deposition in wild boars such as intestinal flora and anatomy, dietary composition, housing or genetic predisposition are discussed in this paper.