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.     

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.     

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.     

Boar taint in pigs selected for components of efficient lean growth rate

Genetic and nutritional effects on the boar taint traits of androstenone, skatole and indole and the eating quality traits associated with boar taint were examined by testing animals from four selection lines and a control line on isoenergetic diets, which differed in ileal digestible lysine: digestible energy (0.40, 0.76 and 1.12 g lysine/MJ DE). The selected lines resulted from seven generations of selection for high daily food intake, lean food conversion ratio (LFC) and lean growth rate on ad libitum (LGA) or restricted (LGS) feeding regimes in a Large White population. During performance test, from 30 to 90 kg, boars were fed on either ad libitum or restricted (0.75 g/g ad libitum daily food intake) feeding regimes. A sensory panel assessed heated fat samples for androstenone odour, skatole odour and abnormal odour. There were no significant differences between the selection and control lines or diets for log transformed fat content of androstenone, skatole, indole. The significant diet with feeding regime interaction for log transformed fat content of skatole and indole were essentially due to significantly higher log transformed fat contents with ad libitum feeding of the high lysine diet compared to restricted feeding (skatole: -1.94 vs -3.06, s.e.d. 0.43; indole: -3.44 vs -4.22, s.e.d. 0.28), as differences between feeding regimes on diets A and C were not significantly different from zero. There were no significant differences between selection and control lines for sensory panel score for abnormal odour or androstenone odour, but the LFC and LGA selection lines had a significantly higher skatole odour score than the LGS selection line. Neither diet nor feeding regime had any significant effect on sensory panel assessment of odour. Log transformed fat content of androstenone and skatole were significantly correlated with sensory panel score for skatole odour (0.37 and 0.46, s.e. 0.12), but not with sensory panel score for androstenone odour (0.06 and 0.09), such that they would not be useful predictors of androstenone odour.     

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.     

The effects of castration on the eating quality of dry-cured ham

The influence of the castration of entire male pigs on the eating quality of dry-cured ham was evaluated. Forty-eight dry-cured hams (435-day aged) were studied from entire and castrated males of two different crossbreeds. The proximate composition of the meat and the androstenone, indole and skatole fat content were determined. The entire hams were classified according to the androstenone and skatole content. Sensory analysis was carried out by a trained panel, evaluating marbling, juiciness, saltiness, graininess, toughness, overall flavour, boar odour and boar flavour. Also carried out was a preference and acceptability paired test by consumers. Castration increased meat fattening and reduced the androstenone and skatole levels of the fat. Significant differences (P<0.05) were found between entires and castrates for the average values given in all the sensory attributes studied. The dry-cured ham from castrates was scored as more flavoured, more marbled and softer. It was also perceived as less grainy, less salty and having less boar odour and flavour. The sensory perception of boar odour was more intense than that of flavour in dry-cured ham and appears to be related to the level of androstenone and skatole in fat. Dry-cured ham from castrated males was also more accepted and more preferred by consumers, especially women and habitual consumers. Castration of male pigs contributes to improve the quality of dry-cured ham. The rejection caused by boar odour and flavour is reduced, improving the overall flavour, texture and juiciness. In addition, the saltiness is less pronounced in ham from castrates. For this reason, the production of high quality dry-cured ham will have to shoulder the extra costs associated with processing castrated pigs.     

Different scalding techniques do not affect boar taint

The prevention of unpleasant boar taint is the main reason for castration of male piglets. For animal welfare reasons, castration is announced to be banned in the European Community. This study aimed to investigate whether androstenone, skatole and indole in backfat of boars may be reduced by different scalding technologies. To discriminate ante and post mortem effects, carcasses were sampled before and after scalding in two abattoirs using either horizontal (TANK) or vertical (TUNNEL) scalding. Backfat samples were analysed using gas chromatography (androstenone) and liquid chromatography (skatole, indole). Neither TANK nor TUNNEL scalding did significantly reduce malodorous compounds. Skatole and androstenone in backfat obtained after scalding averaged 112 ± 123 ng/g and 1196 ± 885 ng/g melted fat, respectively; significant differences between abattoirs were observed for skatole. Increased skatole levels were tentatively assigned to longer transport duration. Concluding from recent consumer research and subsequent application of suggested sensory rejection thresholds for androstenone (2000 ng/g) and skatole (150 ng/g), nearly 30% of the carcasses may be unacceptably tainted.     

Temporal aspects related to the perception of skatole and androstenone, the major boar odour compounds

Pork fat samples from 50 boars slaughtered at a commercial abattoir were analysed for skatole and androstenone concentrations and grouped within a 3×3 matrix representing low, medium and high levels of the odour compounds. A 10 member sensory panel, screened and trained to recognise and quantify skatole and androstenone odour intensities, was used to verify the human perception of boar odour in these pork fat samples immediately after heating (±65°C) and following a cooling period of ten minutes (±25°C). Principal component analysis revealed that the sensory panel differentiated the pork fat samples first and foremost on the basis of the presence or absence of androstenone and/or skatole odours and secondly on the character of the androstenone or skatole odour. Evidence of adaptation towards the odour of skatole was shown by a decreased sensitivity over replicates. Sensory perception of boar odour seems to have a temporal character which can be explained by differences in volatilisation (involving both odourant release and retention) of skatole and androstenone, odour synergism and possibly differences in the properties of the fat matrix of different samples. The results suggest that factors influencing volatilisation of skatole and androstenone should also be considered when predicting sensory responses of boar odour.     

Relationships between skatole and androstenone accumulation, and cytochrome P4502E1 expression in Meishan×Large White pigs

The effects of age, castration and diet on accumulation of skatole and androstenone in the backfat of 50% Meishan male pigs, was studied in relation to boar taint. Skatole and androstenone deposition in backfat of entire males was increased with age (114, 144 and 174 days). Castration significantly decreased skatole and androstenone levels in all age groups. The level of cytochrome P4502E1, the initial enzyme involved in hepatic skatole metabolism, was increased by castration at all ages. These results suggest that the decrease in androstenone levels following castration affects the regulation of cytochrome P4502E1 expression, and as a consequence, results in a decrease in skatole levels. The use of sugar beet feed in the diet decreased the level of skatole and increased that of cytochrome P4502E1 expression, but did not affect androstenone levels. It is suggested that skatole accumulation is reduced both by castration and by diet via induction of cytochrome P4502E1. However, the mechanism of induction of cytochrome P4502E1 by diet is different from that involved in its induction by castration.     

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.     

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 carcasses on the slaughter line, main conclusions and recommendations

An international study has been conducted in order to determine the respective contributions of androstenone and skatole to boar taint and their possible variations according to production systems and consumer populations. The presentation of the study and the main results concerning skatole and androstenone levels and data from sensory evaluation or consumer surveys are reported in companion papers. The present paper summarises the main conclusions of the study and gives tentative recommendations. A simulation study was conducted, based on the skatole and androstenone levels currently observed in European populations of entire male pigs and on the results of the consumer surveys. The first part of the simulation study demonstrated that, overall, 6.5% (odour) and 3.0% (flavour) more consumers were dissatisfied with entire male than with gilt pork. The differences were, however, very variable according to countries. Consumer dissatisfaction for the odour of entire male pork was mostly associated with high skatole levels, while androstenone had little influence on it. On the other hand, androstenone and skatole had similar contributions to the level of dissatisfaction for flavour. From the present study it is not possible to determine clear cut-off levels for androstenone/skatole. The regression equations presented in [Matthews, K. R., Homer, D. B., Punter, P., Béague, M. P., Gispert, M., Siret, F., Leask, H., Fonti i Furnols, M., & Bonneau, M. (2000). An international study on the importance of androstenone, skatole for boar taint: III. Consumer survey in seven European countries. Meat Science, 54, 271-283] provide a basis for decision making. However, due to methodological limitations, the results may underestimate consumer reaction to entire male pork. The second part of the simulation study demonstrated that sorting carcasses on the basis of androstenone/skatole would reduce, but not eliminate, differences in consumer dissatisfaction between entire male and gilt pork. For odour, taking androstenone into account did not improve the efficiency obtained from sorting using skatole only. For flavour, sorting using both compounds was more efficient than sorting using skatole only. Sorting out 15% of the entire males, on the basis of skatole only, would result in a difference in the proportion of dissatisfied consumers of 4.2% (odour) or 2.0% (flavour) between entire male and gilt pork. The results of the last part of the simulation study demonstrated that decreasing skatole in entire male pig populations, to levels as low as 0.10 ppm, would still result in a difference in the proportion of dissatisfied consumers of 3.2% (odour) or 1.6% (flavour). To reduce this difference further, the levels of both compounds would have to be reduced still further. The lowest difference that can be achieved is 2.3% (odour) or 0.4% (flavour). The conclusions of the present study may differ according to whether immediate commercial applications or long-term goals are considered. On the basis of the skatole and androstenone levels currently observed in entire male pig populations, sorting out procedures based on skatole is the easiest way to rapidly achieve a significant decrease in consumer dissatisfaction with entire male pork. In most countries, however, this will not be sufficient to obtain the same level of acceptability as with gilts. In the long term, a sharp reduction in both skatole and androstenone would have to be achieved in entire male pig populations to obtain low differences in acceptability between entire male and gilt pork.     

An international study on the importance of androstenone and skatole for boar taint: III. Consumer survey in seven European countries

There has long been debate over the relative importance for consumer acceptability of androstenone and skatole. The objective of this study was to investigate consumer reaction to pig meat of varying levels of androstenone and skatole in seven member states of the European Union. Over 4000 entire male pigs (and 233 gilts as a control) were produced in six European countries, and a sub-sample of 420 were selected to represent a range of androstenone and skatole levels. Loin samples from these pigs were distributed to the seven participating countries. Samples were prepared and cooked according to standardised procedures in each of the countries and presented to pork consumers. Each consumer rated samples from five pigs for liking of flavour and liking of odour. Although there were significant differences between country panels in their liking of meat from entire males generally, there was a greater degree of dislike as both androstenone and skatole increased. This reaction was stronger for skatole than androstenone and consumers reacted more negatively in terms of odour than flavour.     

Effects of raw potato starch and live weight on fat and plasma skatole,indole and androstenone levels measured by different methods in entire male pigs

A total of 96 entire male pigs were used to evaluate the effects of feeding raw potato starch (RPS) and live weight (LW; 90, 100 or 115 kg) on skatole, indole and androstenone levels in fat and plasma. Different methods to analyse the compounds were compared. Fat levels of skatole analysed by HPLC and colorimetric methods, and androstenone analysed by HPLC and ELISA, were highly correlated. However, androstenone values obtained by ELISA were overestimated. Feeding RPS reduced skatole levels in plasma and fat but did not affect indole levels. Androstenone levels in plasma measured by direct ELISA were not altered by diet, whereas the levels measured by ELISA with extraction were lower in the pigs fed RPS. Feeding RPS did not reduce androstenone levels in fat. Androstenone levels in fat were higher at 115 than at 90 kg, whereas skatole and indole levels were not affected by LW.     

The effect of supplementation of a white clover or perennial ryegrass diet with grape seed extract on indole and skatole metabolism and the sensory characteristics of lamb

Condensed tannin in the form of a grape seed extract (GSE) was dosed to weaned wether lambs fed white clover (WC) or perennial ryegrass (PRG) over a 9‐week period to determine whether the ‘pastoral’ flavour and odour of meat could be altered. The concentrations of the pastoral flavour compounds indole and skatole were determined in the rumen fluid, blood plasma and intermuscular fat. The odour and flavour of fat and meat from the slaughtered lambs was assessed by a trained panel. The rumen fluid and blood plasma concentrations of indole and skatole were higher in those lambs fed WC compared to PRG (P < 0.05) and the overall meat flavour intensity was greater when feeding WC (P < 0.01). The observed concentration of indole and skatole in the fat between WC and PRG feeding treatments was not statistically different. Power analysis indicated that increasing the number of lambs per treatment group from 20 to 65 would result in a higher fat skatole concentration (P < 0.05) being detected in lambs fed WC compared to PRG. Dosing with GSE gave a small reduction in skatole concentration in the rumen fluid and reduced plasma concentration of indole and skatole (P < 0.001). Odour and flavour scores of the fat and meat samples were not particularly high however, dosing with GSE lowered the overall and sweet odour and the sheepy, camphor, faecal and barnyard flavour (P < 0.05). Although the plasma concentration of indole and skatole suggests that GSE reduced indole and skatole formation, the intermittent supply of the GSE to the rumen environment was not sufficient to reduce their concentration in the fat. Hence, the small difference in the scores for pastoral odour and flavour attributes associated with GSE treatment may arise from other unknown factors. From a primary investigation, there was no difference in the concentration of indole and skatole in fat samples collected from carcasses before and after chilling. Further investigations into meat pastoral flavour are warranted through feeding condensed tannin‐containing forages. Copyright © 2007 Society of Chemical Industry     

The problem of taint in pork-II. The influence of skatole, androstenone and indole, Presented individually and in combination in a model lipid base, on odour perception

Responses to varying concentrations of androstenone and skatole in a neutral lipid base were studied using a trained 10-member panel. Concentrations for skatole and androstenone ranged between 0-1.32 and 0-6.0 μg g(-1), respectively. Odour, androstenone and skatole intensities were assessed by the line scaling method. Triangular tests showed that the panel significantly distinguished indole from androstenone, p ≤ 0.01, but not from skatole nor mixtures of androstenone and skatole. Regression analyses showed linear relationships between skatole and androstenone concentrations and odour intensity but with a significant (p ≤ 0.01) androstenone-assessor interaction. Correlation coefficients with odour intensity were 0.64 and 0.63 for androstenone and skatole concentrations, respectively. Response surface curves showed that odour intensity depended on the linear terms of skatole, androstenone and on the quadratic term of androstenone. Androstenone and skatole intensity ratings revealed that the effect of skatole was enhanced by the presence of androstenone, but not the reverse. It was concluded that whilst both androstenone and skatole may be important for the sorting (classification) of pork, the importance of androstenone lies in its detection threshold whilst for skatole, the acceptability threshold may be a suitable criterion for quality control purposes.