Sensory evaluation of boar loins: Trained assessors' olfactory acuity affects the perception of boar taint compounds

Meat Science 94 (2013) 19–26

Contents lists available at SciVerse ScienceDirect

Meat Science journal homepage: www.elsevier.com/locate/meatsci

Sensory evaluation of boar loins: Trained assessors' olfactory acuity affects the perception of boar taint compounds Lisa Meier-Dinkel a, Ahmad Reza Sharifi a, Ernst Tholen b, Luc Frieden b, Mark Bücking c, Michael Wicke a, Daniel Mörlein a,⁎ a b c

Department of Animal Sciences, University of Göttingen, D-37075 Göttingen, Germany Institute of Animal Science, Animal Breeding and Husbandry Group, University of Bonn, D-53115 Bonn, Germany Fraunhofer Institute for Molecular Biology and Applied Ecology IME, D-57392 Schmallenberg, Germany

a r t i c l e

i n f o

Article history: Received 20 July 2012 Received in revised form 3 December 2012 Accepted 10 December 2012 Keywords: Sensory analysis Triangle test Androstenone sensitivity Detection threshold Entire male production

a b s t r a c t This study investigated the impact of assessors' varying olfactory acuity on the perceived intensity of androstenone and skatole odour and flavour in boar loins. To discriminate sensitive (SENS) and highly sensitive (SENSHIGH) panellists, two levels of androstenone were used on smell strips. Sensitivity was defined as the correct identification of the androstenone strip in three replicate triangle tests. Judges then assessed loins from boars, castrated pigs and gilts. SENSHIGH assessors scored low-fat boar loins with 1.5 to 2.0 μg of androstenone per gram of melted back fat which is significantly different from castrate and gilt loins for androstenone odour and flavour whereas SENS assessors were less discriminating. Panellists' olfactory acuity should thus be considered for selection and training. The presented paper strip system is suggested for objective screening and training purposes and to be used as quantitative references in descriptive analysis. © 2012 Elsevier Ltd. All rights reserved.

1. Introduction The surgical castration of male piglets without the use of pain reducing means must be discontinued by 2012 and castration should be banned by 2018 (European Declaration on Alternatives to Surgical Castration of Pigs, 2010). Raising intact boars instead requires the control of the so-called boar taint mainly caused by androstenone and skatole (Lundström, Matthews, & Haugen, 2009; Patterson, 1968; Vold, 1970; Zamaratskaia & Squires, 2009). Consumer rejection thresholds for androstenone and skatole were reported to be 0.5 to 1 μg/g of fat and 0.20 to 0.25 μg/g of fat, respectively (Walstra et al., 1999). Due to the lipophilic properties of androstenone and skatole these thresholds are usually related to carcass backfat (Claus, Weiler, & Herzog, 1994). Recent interlaboratory comparisons, however, revealed considerable protocol differences and how these values are reported, i.e. whether related to native tissue weight, melted fat or pure fat (Ampuero Kragten et al., 2011). Accordingly, recent consumer studies indicated that androstenone levels exceeding 1 μg/g of melted backfat are still tolerated in loins (Bonneau & Chevillon, 2012; Meier-Dinkel et al., 2013). With respect to off-odour and off-flavour, boar loins that are not perceived to be different from gilt or castrate loins by trained judges ⁎ Corresponding author at: University of Göttingen, Department of Animal Sciences, Albrecht-Thaer-Weg 3, D-37075 Göttingen, Germany. Tel.: +49 551 39 5611; fax: +49 551 39 5587. E-mail address: [email protected] (D. Mörlein). 0309-1740/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.meatsci.2012.12.009

are considered safe with regard to consumer acceptance. Selection and training of sensory assessors, however, appear to be crucial as detection thresholds and perceived odour quality of androstenone greatly vary among individuals (Havlicek, Murray, & Saxton, 2010). This has also been observed for skatole (Fischer, 1999; Meier-Dinkel et al., 2013). Annor-Frempong, Nute, Whittington, and Wood (1997a) reported trained panellists' individual detection thresholds for androstenone and skatole to vary around a factor of 5 to 10. There is, however, only little known about how assessors' olfactory acuity affects the objective evaluation of boar meat. The aims of this study were i) to evaluate boar loins with various levels of androstenone and skatole compared to loins from gilts and castrated male pigs, ii) to determine trained panellists' olfactory acuity to androstenone, and iii) to relate assessors' sensitivity to their sensory evaluation results. A model system based on paper strips and discrimination tasks is introduced for assessing the olfactory acuity at two androstenone concentrations. References that are recommended for descriptive sensory analysis (Lawless & Heymann, 2010) but whose application for the evaluation of boar taint is only rarely described (Font i Furnols, Guerrero, Serra, Àngels Rius, & Àngels Oliver, 2000; Lunde et al., 2010) were developed and applied for odour attributes. 2. Material and methods Table 1 outlines the study procedure and scopes of the experiments. Initially, 87 potential assessors were invited to screening

20

L. Meier-Dinkel et al. / Meat Science 94 (2013) 19–26

Table 1 Scope of experiments and application of paper smell strips.

A

B

C

a b c d

Scope of the experiment

Purpose

Method

Amount of odorantc

Selection of analytical assessors, 87 potential assessors

Determination of androstenone sensitivity

Triangle testa, 2 replicates

Androstenone ~ 150 ng

Skatole identification

Odour identification

Skatole ~ 30 ng

Determination of sensory abilities after training, 16 assessors

Sensory profiling of boar meat loins, 16 assessors

a

Perception of androstenone in different concentrations

Triangle test , 3 replicates

Perception of skatole

Triangle testa, 3 replicates

Intensity rating, skatole and androstenone odour and flavour

Profiling testb

Androstenone ~15 ng (SENSHIGH) ~150 ng (SENS) Skatole ~ 40 ng References for odour: Skatole50: ~40 ngd Skatole90: ~80 ngd Androstenone50: ~150 ngd Androstenone90: ~300 ngd

Sensory analysis — Methodology — Triangle test (DIN EN ISO 4120:2004). Sensory analysis — Methodology — General guidance for establishing a sensory profile (ISO 13299:2003). Given is the absolute amount of odorant presented on paper strips. All solutions in propylene glycol (PG). Subscripted numbers, i.e., 50 and 90, refer to scale intensity.

tests (A). Thereafter 21 of them were selected and further trained for the assessment of boar taint, 16 thereof accomplished the training. Their sensory acuity to androstenone was tested at two concentrations after a training period of 11 weeks (B) to ascertain individual differences. Skatole was tested at a single concentration. Trained assessors then evaluated boar and control loins with regard to the intensity of the androstenone and skatole odour and flavour in a sensory profiling test (C). All experiments were conducted in the Laboratory for Sensory Analysis and Consumer Research at the University of Göttingen equipped with 10 individual booths (according to ISO 8589:2010, sensory analysis: general guidance for the design of test rooms). The ventilation system allowed an air exchange at a rate of 6 times per hour. All experiments were conducted under fluorescent day light tubes. 2.1. Preparation of smell strips For the preparation of smell strips, stock solutions of skatole (3-methylindole, M 131.17 g/mol; Aldrich-Chemie GmbH, Steinheim, Germany; 10 mg diluted in 10 ml methanole) and androstenone (16, (5α)-Androsten-3-one, M 272.43 g/mol, Steraloids Inc., Newport, USA; 10 mg diluted in 2 ml methanole) were prepared in methanol and further dissolved in propylene glycol (PG; 1, 2-propanediol, M 76.10 g/mol; Carl Roth, Karlsruhe) to achieve the amounts as summed up in Table 1. The solutions (30 μl) were dispersed on filter paper strips (240 g/m 2; ssp ident, Einbeck) with a 100 μl-pipette. The strips were placed in polystyrene test tubes (Carl Roth, Karlsruhe, 16 mm diameter, 150 mm long), dried for approximately 24 h under a fume hood until visual dryness, and the tubes were then closed before further use. In the following the total amount of androstenone transferred onto the strips (in ng) is referred to. The tubes were encoded with random three-digit numbers and the strips were presented to the assessors at room temperature. The participants were instructed to remove the strips from the test tubes, and to sniff at the marked area. The strips for smell tests and odour reference samples (C) were replaced every week. 2.2. Assessor selection (A), training, and documentation of final olfactory abilities (B) In total, 87 potential assessors were recruited via advertisements and tested for their ability to perceive androstenone and skatole and for their general sensory acuity (A). General sensitivity to androstenone odour was determined by duplicate triangle tests (ISO, 2004) using smell strips. The odd sample contained approximately 150 ng of androstenone while the identical sample of smell

strips were prepared using the solvent (PG) only, i.e. 30 μl was transferred onto the strips and they were allowed to dry for approximately 24 h. The position of the odd sample within a triangle was random. To avoid olfactory adaptation, androstenone was always presented as odd sample while equal samples were always prepared using PG only. The correct identification of 150 ng of androstenone on paper smell strips compared to strips prepared with the solvent only was chosen due to previous experiments where approximately 50% of participants repeatedly identified this amount in triangle tests (data not shown). According to this definition 54 out of 87 participants (62%) were androstenone-sensitive, i.e. correctly identified the androstenone sample in both triangle tests. The probability of correctly detecting the odd sample by chance is 11% which was considered sufficient for screening. Perception of skatole (30 ng dissolved in 30 μl PG transferred on smell strip; dried for 24 h) was assessed with an odour identification test (A). Eight encoded samples (skatole, 1-Octen-3-ol, thyme, rosemary, cloves, anethole, oregano, butyric acid) had to be assigned to eight terms given on a protocol. Participants who assigned the skatole sample to the terms “stable, manure-like” were considered to be skatole-sensitive. All participants (n = 87) correctly assigned the terms “stable, manure-like” when 30 ng skatole were presented. Furthermore, general sensory abilities were evaluated by identification of basic taste modalities and discrimination tests to detect sweetness intensity differences (DIN, 1996). Finally, the respondents were asked to describe two samples of commercial sausages to test their verbalization abilities (results not shown). All tests were conducted by self-administration without time constraint. For further training 16 androstenone- and skatole-sensitive assessors that performed best in the other tests were selected. The assessors (n = 16) were trained with regard to the identification and differentiation of androstenone and skatole odour in two 90-minute sessions per week for 11 weeks. In total, 22 training sessions were held. Triangle (ISO, 2004), paired comparison (ISO, 2005) and ranking tests (ISO, 1988) were conducted to train the detection and differentiation of androstenone, skatole, and the mixtures thereof. At a later stage of training, melted pork fat was used instead of propylene glycol for preparing the smell strips to increase the complexity and thus the difficulty of the smell tests. The training also included the evaluation of boar loins and backfat odour and flavour with known amounts of skatole and androstenone. Reference samples that were free of malodourous compounds were also provided to acquaint the assessors to the odour and flavour of cooked but unseasoned pork. After 11 weeks of training (B) the assessors were again tested for their ability to perceive androstenone (~150 ng) and skatole (~40 ng).

L. Meier-Dinkel et al. / Meat Science 94 (2013) 19–26

For each odorant and amount, triplicate triangle tests that each consisted of two identical samples (solvent only) and one odd sample, i.e. either androstenone or skatole diluted in the solvent, were performed. The probability of correctly detecting the odd sample in triplicate by chance is 3.7%. All assessors correctly identified the lower amount of ~150 ng androstenone and were thus confirmed to be generally sensitive to androstenone. To determine the highly sensitive assessors a ten-fold lower amount of androstenone was presented in triplicate (~15 ng on smell strips). Based on this test, 9 out of 16 panellists were classified to be highly sensitive (SENSHIGH) assessors while 7 were regarded as generally sensitive (SENS) assessors. 2.3. Animals and selection of meat samples Meat samples were derived from a breeding experiment as described in Meier-Dinkel et al. (2013). Briefly, entire males, castrates and gilts (Pietrain × F1 (Large White × German Landrace)) were raised on performance testing stations and slaughtered at an average hot carcass weight of 91 kg. Meat samples (12 to 16 cm length) were taken 24 h post mortem from the M. longissimus (13./14. rib, cranial), vacuum-packed and kept frozen at − 18 °C until assessment. Average intramuscular fat content of boar loins was 1.25%. Boar loins for objective sensory evaluation were selected with regard to androstenone and skatole levels (low, medium, and high) in melted backfat (determination described in Mörlein, Grave, Sharifi, Bücking, & Wicke (2012)); four to six boar loins were assigned to seven product categories (meat type; see Tables 2 and 3), respectively. Additionally, loins from gilts and castrates were included to allow for a comparison to German standard pork. In total, nine meat types were evaluated. 2.4. Preparation and evaluation of meat samples (C) Loins were thawed at 4 °C for 48 h before assessment. About 1.5 h before the sensory assessment sessions, the samples were cut into cubes (1.5 × 2 × 2 cm; approximately 8 g) and stored at 4 °C in 50 ml beaker glasses covered with watch glasses. Subcutaneous fat

21

was removed to ensure comparable fat contents in all samples. No seasonings were added to avoid masking of boar taint as reported by Lunde et al. (2008). Loin samples were cooked in the covered beaker glasses in a convection oven (Hans Dampf Junior Professional, MKN, Germany) at 170 °C (hot steam, 20% relative humidity) for 8 min to a core temperature of approximately 68 °C. This helped to avoid the development of roast. The samples were kept for 3 min at room temperature and were then served in a monadic manner following a balanced design to avoid sample order effects (Meilgaard, Civille, & Carr, 2007). A similarly prepared loin sample of castrate or gilt was evaluated by the assessors before each session to avoid first-sample effects and to acquaint the assessors with the German standard pork odour and flavour. Due to the different odour quality of skatole and androstenone, e.g. reported by Annor-Frempong et al. (1997a), it was decided with the panellists during panel training not to use the term “boar taint” but to separately evaluate the odour and flavour intensity of androstenone and skatole, respectively following descriptive sensory analysis (ISO, 2003). The aim of the sensory profiling test is to determine the intensity of distinct attributes and, thereby, identify differences between the products. The samples were encoded with three-digit random numbers. Six replicates per meat type were assessed by each panellist. In total, nine sessions were held where six samples were evaluated by each panellist. Assessors were instructed to remove the watch glass from the beaker and rate the intensity of the odour attributes directly after the first sniff. Flavour attributes had to be evaluated after 15 to 20 times of chewing the whole meat sample; this approach was chosen by the assessors within a group discussion. To neutralize senses of taste and smell, wheat bread, tap water and a coffee bean (only for sense of smell) were provided. The assessors were instructed to rinse the mouth after each sample. The participants reported their ratings using EyeQuestion software (Logic8 BV, Elst, The Netherlands). Intensity of all attributes (odour and then flavour) were rated on a 100 mm line-marking scale with labelled endpoints (0 = “not perceivable”; 100 = “extremely perceivable”) (Lawless & Heymann,

Table 2 Effect of product and androstenone sensitivity on androstenone odour and flavour intensity, ANOVA table. Sensory attributesA

Androstenone odour

Factors

p-values

p-values

Product (meat types) Androstenone sensitivity Product × androstenone sensitivity

b0.0001 0.8185 0.3874 All assessors, n = 16

b0.0001 0.8143 0.0075 Highly-sensitive assessors (SENSHIGH)D, n = 9

Meat types

Skatole [μg/g]B

Boar (LL) Boar (LM) Boar (LH) Boar (ML) Boar (HL) Boar (HH) Gilt Castrate Boar (NN)

Sensitive assessors (SENS)C, n= 7

Androstenone [μg/g]B Range (mean)

E

Androstenone flavour

b0.10 (0.06) b0.10 (0.08) b0.10 (0.06) 0.15–0.20 (0.17) 0.25–0.28 (0.25) 0.25–0.40 (0.30) b0.10 (0.06) b0.10 (0.07) b0.10 (0.04)

Least square means (standard errors) b0.6 (0.50) 0.8–1.0 (0.93) 1.5–2.0 (1.87) b0.5 (0.33) b0.5 (0.37) 1.5–2.0 (1.68) – – b0.2 (0.1)

19 24 32 22 21 33 14 16 21

c

(3.0) (3.0)abc (3.0)ab (3.0)bc (3.0)c (3.0)a (3.0)c (3.0)c (3.0)c

20 (4.1)ab 20 (4.1)ab 24 (4.1)ab/x 18 (4.1)ab 22 (4.1)ab 27 (4.1)a 9 (4.1)b 15 (4.1)ab 20 (4.1)ab

17 (3.6)b 20 (3.6)b 37 (3.6)a/y 17 (3.6)b 17 (3.6)b 36 (3.6)a⁎ 9 (3.6)b 11 (3.6)b 19 (3.6)b

a,b,c Least square means with the same letter are not significantly different within the same column (lsd test with Bonferroni adjustment, p b 0.05). Significant differences were extracted within SENS and within SENSHIGH assessors; significant differences were calculated with the whole dataset. x,y Least square means with the same letter are not significantly different within the same row for androstenone flavour (LSD test, pairwise t-test, p b 0.05). Significant differences were extracted within meat types; significant differences were calculated with the whole dataset. A Scores are defined as 0 = not perceivable to 100 = extremely perceivable. B Related to melted backfat of assessed animals. C,D SENS [SENSHIGH] assessors: correct differentiation between 150 ng [15 ng] androstenone in propylene glycol (PG) and PG in triangle test (3 replicates). E First letter in parentheses indicates the skatole and the second letter the androstenone concentration in backfat (L = low, H = high, M = medium, N = very low). 4 to 6 animals per product (meat type). ⁎ p = 0.09 (within row, pairwise t-test).

22

L. Meier-Dinkel et al. / Meat Science 94 (2013) 19–26

Table 3 Effect of product and androstenone sensitivity on skatole odour and flavour intensity, ANOVA table. Sensory attributesA

Skatole odour

Factors

p-values

p-values

Product (Meat types) Androstenone sensitivity Product × androstenone sensitivity

b0.0001 0.9997 0.0644 All assessors, n= 16

b0.0001 0.5990 0.0468 Highly-sensitive assessors (SENSHIGH)D, n = 9

Meat types

Skatole [μg/g]B

Boar (LL)E Boar (LM) Boar (LH) Boar (ML) Boar (HL) Boar (HH) Gilt Castrate Boar (NN)

b0.10 (0.06) b0.10 (0.08) b0.10 (0.06) 0.15–0.20 (0.17) 0.25–0.28 (0.25) 0.25–0.40 (0.30) b0.10 (0.06) b0.10 (0.07) b0.10 (0.04)

Skatole flavour

Sensitive assessors (SENS)C, n = 7

Androstenone [μg/g]B Range (mean)

Least square means (standard errors) b0.6 (0.50) 0.8–1.0 (0.93) 1.5–2.0 (1.87) b0.5 (0.33) b0.5 (0.37) 1.5–2.0 (1.68) – – b0.2 (0.1)

20 (3.3)cd 21 (3.3)bcd 24 (3.3)bcd 31 (3.3)abc 32 (3.3)ab 35 (3.3)a 20 (3.3)cd 20 (3.3)cd 17 (3.3)d

15 18 17 31 29 35 16 13 12

(4.9)bc (4.9)abc (4.9)abc (4.9)ab (4.9)abc (4.9)a (4.9)bc (4.9)c (4.9)c

26 23 27 25 32 26 19 16 17

(4.4)ab (4.4)ab (4.4)ab (4.4)ab (4.4)a (4.4)ab (4.4)ab (4.4)b (4.4)ab

a,b,c,d Least square means with the same letter are not significantly different within the same column (lsd test with Bonferroni adjustment, p b 0.05). Significant differences were extracted within SENS and within SENSHIGH assessors; significant differences were calculated with the whole dataset. A Scores are defined as 0 = not perceivable to 100 = extremely perceivable. B Related to melted backfat of assessed animals. C,D SENS [SENSHIGH] assessors: correct differentiation between 150 ng [15 ng] androstenone in propylene glycol (PG) and PG in triangle test (3 replicates). E First letter in parentheses indicates the skatole and the second letter the androstenone concentration in backfat (L = low, H = high, M = medium, N = very low). 4 to 6 animals per product (meat type).

2010). For a comparable grading of the intensity of the skatole and androstenone odour in boar meat and backfat, physical reference standards were developed during training with the panellists as recommended by Lawless and Heymann (2010). For each odour attribute two smell strips were made available for each session, i.e. for 50 and 90 scale intensity that were also marked with anchor points at the scales for skatole odour: skatole50 (~ 40 ng) and skatole90 (~ 80 ng), and androstenone odour: androstenone50 (~ 150 ng) and androstenone90 (~ 300 ng). 2.5. Statistical analysis To investigate whether the varying ability to perceive androstenone (SENS vs. SENSHIGH) affected the sensory evaluation of loins, analysis of variance was conducted (MIXED procedure, SAS version 9.2, SAS Institute Inc., Cary, US) by applying the following model: yijkr ¼ μþpi þ sj þ pi  sj þ Ak þ pi  Ak þ eijkr

ð1Þ

where yijkr is the intensity of the sensory attribute; μ is the general mean; Pi is the fixed effect of product (meat type: 1 to 9); Sj is the fixed effect of androstenone sensitivity (SENS and SENSHIGH); Pi × Sj is the meat type × sensitivity interaction effect; ak is the random effect of assessor; Pi × ak is the random effect of the assessor × product interaction; and eijkr is the residual error. The evaluation day (session) did not significantly affect the evaluation and was not included in the model. Least square means and pairwise least square mean differences were estimated using LSMEANS and PDIFF (with Bonferroni adjustment) statement of SAS. Significant differences between LSMEANS were extracted separately for SENS and SENSHIGH assessors only when the interaction (product ∗ androstenone sensitivity) was significant for an attribute and displayed with small letters (a,b,c,d) within each column (Tables 2 and 3). When the interaction was not significant the significant differences of LSMEANS were displayed for the main factor product. Small letters (x,y) within a row (Table 2) indicate significantly different LSMEANS between SENS and SENSHIGH assessors for a certain product (meat type).

3. Results 3.1. Analysis of variance: effect of olfactory acuity to androstenone The main effect of product (meat type) was significant for all sensory attributes but the main effect of olfactory acuity to androstenone (androstenone sensitivity) was not. Significant interaction effects between androstenone sensitivity and product were observed for androstenone flavour (p-value: 0.0075) and skatole flavour (p-value: 0.0468); it was close to significance for skatole odour (p-value: 0.064) and not significant for androstenone odour. 3.2. Perception of androstenone odour and flavour in boar loins with respect to assessors' olfactory acuity to androstenone A significantly higher androstenone odour was perceived in LH and HH boar loins, i.e. from carcasses with 1.5 to 2.0 μg/g of androstenone in melted backfat, compared to reference loins and LL, HL and NN boar (Table 2). Highly-sensitive assessors (SENSHIGH) detected a significantly higher intensity of the androstenone flavour in LH and HH boar loins, i.e. from carcasses with 1.5 to 2.0 μg/g of androstenone in melted backfat, compared to gilt, castrate as well as LL, LM, ML, HL and NN boar loins. SENS assessors perceived a significantly higher androstenone flavour in HH boar loins compared to gilt but not to castrate loins. They perceived, however, no significant difference between LL, LM, LH, ML, HL, HH and NN boar loins, i.e. they were less discriminative. SENSHIGH assessors scored LH loins, i.e. from carcasses with 1.5 to 2.0 μg/g of androstenone in melted backfat, significantly higher in androstenone flavour compared to SENS assessors. By trend, HH loins were also rated higher for androstenone flavour by SENSHIGH assessors compared to SENS assessors (p=0.09). 3.3. Perception of skatole odour and flavour in boar loins The product (meat type) effect was significant for the intensity of skatole odour and flavour (Table 3). Compared to the reference loins, skatole odour was significantly higher in HL and HH boar loins, i.e. when skatole values exceeded 0.25 μg/g of skatole in melted backfat. The difference between ML loins, i.e. from carcasses with

L. Meier-Dinkel et al. / Meat Science 94 (2013) 19–26

0.15 to 0.2 μg/g of skatole in melted backfat, and reference loins was close to significance (p= 0.07). SENS assessors did also rate skatole flavour intensity of ML and HH loins to be significantly higher compared to castrate loins. HH loins were perceived as significantly different from LL and NN loins. Assessors being highly sensitive to androstenone (SENSHIGH) were less discriminative for skatole related attributes compared to SENS assessors. HL loins, i.e. from carcasses with 0.25 to 0.4 μg/g of skatole melted fat, received significantly higher skatole flavour scores compared to castrate loins. SENSHIGH assessors, however, perceived no significant differences between NN, LL, LM and LH (very low in skatole) compared to ML, HL and HH (higher in skatole) with regard to the skatole flavour intensity. By trend SENS assessors scored ML, HL and HH loins, i.e. with skatole levels of 0.15 to 0.4 μg/g of melted backfat, to have a stronger skatole flavour compared to reference and other boar loins, i.e. with less than 0.1 μg/g of melted backfat. Compared to the smell strips used as reference standards mean intensity of the odour attributes per meat type were scored below 50% scale intensity (androstenone50 and skatole50).

4. Discussion 4.1. Impact of assessors' olfactory acuity to androstenone on sensory evaluation of boar meat Olfactory acuity for the androstenone odour was determined at two levels and assessors were grouped into so-called sensitive assessors (SENS) and highly sensitive assessors (SENSHIGH). Main effect of olfactory acuity to androstenone was not significant for any attribute. Significant meat type ∗ androstenone sensitivity interaction effects were, however, observed for flavour attributes which indicated that certain products were evaluated differently by SENS (n = 7) compared to SENSHIGH (n = 9) assessors. SENSHIGH assessors gave significantly higher values for androstenone flavour in lean boar loins when androstenone levels exceeded 1.5 to 2.0 μg/g of melted backfat and skatole was below 0.1 μg/g of melted backfat. SENS assessors were less discriminative with regard to androstenone flavour. Although we did not define absolute detection thresholds for the individual assessors, clearly there is a variance among individuals with regard to olfactory acuity, i.e. SENSHIGH subjects detected at least a ten-fold lower amount of androstenone (15 ng) on smell strips compared to SENS subjects (150 ng). These results support the findings by Annor-Frempong et al. (1997a) reporting that individual detection thresholds vary considerably, e.g. around a factor of 5 for androstenone (0.2 to 1.0 μg/g) and a factor of 10 for skatole (0.008 to 0.06 μg/g) in a 20 ml neutral lipid base. Detection thresholds for skatole were shown to be lower compared to androstenone which is in line with our results. Also indicating the higher odour strength of skatole, in the present study panellists detected at least about 40 ng skatole (about 0.3 nmol) on paper strips compared to about 150 ng androstenone (about 0.55 nmol). Font i Furnols et al. (2000) reported lower detection thresholds of 0.05 to 0.2 ppm skatole and 0.1 to 0.5 ppm androstenone. These values refer, however, to a 10 ml oil base, i.e. the absolute amount presented is much higher compared to our model system using paper strips. To compare thresholds, the partition coefficient of the odorant in the respective model system also needs to be considered (Amoore & Buttery, 1978). With regard to skatole flavour intensity highly androstenone sensitive assessors (SENSHIGH) were less discriminative compared to SENS assessors that significantly separated loins (HH and ML) from carcasses with 0.15 to 0.4 μg/g of melted fat from (boar) loins with skatole levels below b0.1 μg/g of melted fat, i.e. NN and castrate loins. For skatole odour the interaction effect of product and androstenone sensitivity was close to significance (p = 0.06). Lunde et al. (2010) found the panellist recruitment method, namely the use of pure crystals vs. androstenone diluted in water,

23

to affect the perceived intensity of androstenone odour and flavour in minced meat spiked with androstenone. It remains open whether the differences in sensory perception between SENS and SENSHIGH assessors had biological or psychophysical reasons. To our knowledge there is no study reporting whether skatole detection is negatively related to androstenone detection. The question persists whether certain volatiles show antagonistic behaviour, i.e. compete at receptor binding proteins. Laing, Eddy, and Best (1994) reported that individual odorants in complex mixtures affect the perception of each other with regard to pleasantness, strength and quality characteristics. Thereby individual components of a mixture can interact with each other in different manners that are often not predictable. The greater the number of individual constituents in a mixture the more difficult it became to identify individual components and the greater was the degree of suppression of the individual components (Laing et al., 1994). Likewise Bell, Laing, and Panhuber (1987) found evidence that odorants can mask or suppress each other at the peripheral epithelium which is probably caused by their different chemical polarities. Several studies have shown that the capacity of humans to identify and discriminate individual components from odour mixtures is limited to a small number of two to four compounds (Livermore & Laing, 1998; Marshall, Laing, Jinks, & Hutchinson, 2006). It has also been observed that with extensive training odours previously experienced together as a mixture were less discriminable than controls presented individually (Stevenson, 2001). In the case of boar taint Annor-Frempong et al. (1997b) also observed, that some assessors who were sensitive to both androstenone and skatole when presented individually, became completely odour blind to one of these compounds when presented with a mixture thereof in a neutral fat base. Dijksterhuis et al. (2000) reported the confusion between androstenone and skatole for several European panels assessing boar meat; the attributes “urine” and “manure” were for instance related to both androstenone and skatole. Compared to the present study, Bañón, Costa, Gil, and Garrido (2003) reported lower androstenone (0.5 μg/g fat) and skatole (0.1 μg/g fat) contents to be perceived as boar taint in cooked loin. They only included assessors with an unpleasant sensation of both skatole and androstenone in the sensory panel and did not evaluate androstenone and skatole separately during sensory assessment. Byrne, Thamsborg, and Hansen (2008) and Font i Furnols et al. (2000) also included only assessors who described the odour of androstenone and skatole as unpleasant. They, however, provided no information about the total amount of androstenone used to define sensitivity (compare 4.4). Furthermore, the perceived quality of a given odorant may change with its concentration (Gross-Isseroff & Lancet, 1988; Livermore & Laing, 1998). 4.2. Descriptive analysis of boar loins and consequences for the boar taint problem Trained sensory assessors with a documented sensitivity to androstenone could significantly differentiate LH boar loins, i.e. from carcasses with 1.5 to 2.0 μg/g of androstenone in melted backfat from castrate and gilt loins with regard to androstenone odour. For androstenone flavour, only SENSHIGH assessors perceived significantly higher androstenone flavour in LH boar loins compared to standard loins. The question persists if untrained (naïve) consumers would show a lower acceptance of such boar loins. Sensory defects as detected by trained panellists can still be tolerable for naïve consumers (Lawless & Claassen, 1993). In our recent consumer study (Meier-Dinkel et al., 2013) we have shown that androstenone levels up to 2.7 μg/g of melted backfat (and skatole below 0.23 μg/g of melted backfat) did not lower the average acceptance of lean boar loins with 1 mm backfat. To evaluate how many consumers of a given population would be negatively affected by low levels of androstenone in boar meat because of an increased sensitivity,

24

L. Meier-Dinkel et al. / Meat Science 94 (2013) 19–26

olfactory acuity and odour liking need to be assessed using various androstenone levels. Reviewing recent studies, there is considerable variation of the lowest levels of androstenone or skatole in boar meat to be perceived as significantly different compared to castrate or gilt meat (“least perceivable difference”). Clearly this needs to be related to the fat content of the meat or meat product as the compounds are lipophilic. Bañón et al. (2003) reported that cooked loins with lower androstenone and skatole levels (related to backfat) than in our study were perceived to have significantly higher boar odour than castrate loins. In contrast, Lunde et al. (2010) referred that trained panellists perceived no higher androstenone odour and flavour intensity in minced meat with a considerably higher androstenone content (in fat) and a higher fat content of the product than in the present study although the opposite could be expected. Compared to lean meat, in heated backfat androstenone levels exceeding 0.5 μg/g of fat were perceived to have significantly higher androstenone intensity compared to samples with androstenone concentrations below 0.5 μg/g of fat (De Kock, Heinze, Potgieter, Dijksterhuis, & Minnaar, 2001). In addition, the perception of boar taint compounds varies also due to the impact of processing and sample temperature at presentation (Annor-Frempong et al., 1997a; Bañón et al., 2003; De Kock et al., 2001; Stolzenbach, Lindahl, Lundström, Chen, & Byrne, 2009). These factors should be taken into account when study results are compared and discussed. Furthermore, also varying the protocols for chemical analysis of androstenone and skatole need to be considered (Ampuero Kragten et al., 2011). As for skatole, its odour was scored significantly higher in boar loins from carcasses with skatole levels as low as 0.25 μg/g of melted backfat compared to castrate loins. Skatole odour scores tended (p = 0.07) to be higher in ML loins, i.e. from carcasses with 0.15 μg/g of melted backfat, compared to castrate and gilt loins. Skatole flavour was found to be significantly higher in HH and ML loins, i.e. from carcasses with 0.15 to 0.4 μg of skatole per gram of melted backfat by SENS assessors and in HL loins by SENSHIGH assessors. This is in line with the observations by Lunde et al. (2010) who found trained assessors being able to detect also 0.15 μg of skatole per gram of fat in minced meat with 20% fat. Bañón et al. (2003) found trained assessors being able to identify “boar odour” in cooked meat with slightly lower skatole content, i.e. exceeding 0.1 μg/g of backfat. Compared to trained panellists, naïve consumers were however not negatively affected by skatole from 0.01 to 0.23 μg/g of melted fat when evaluating lean loins in a central location test (Meier-Dinkel et al., 2013). Another aspect that should be taken into consideration is the improvement in olfactory acuity after regular exposure to androstenone shown earlier (Möller, Pause, & Ferstl, 1999; Pause, Rogalski, Sojka, & Ferstl, 1999; Wysocki, Dorries, & Beauchamp, 1989). For androstadienone, an odorous steroid structurally closely related to androstenone, Jacob, Wang, Jaffer, and McPhee (2006) observed a decrease in detection thresholds and changes in odour quality perception after repeated exposure. Training status of assessors should, therefore, be considered when interpreting the results of smell experiments as detection thresholds may considerably decrease with training (Dalton, Doolittle, & Breslin, 2002). With respect to consumers' sensory capabilities, it has, furthermore, to be clarified whether sensitization to androstenone could be induced by repetitive consumption of boar meat. 4.3. Use of smell strips as reference standards Physical reference standards are recommended for descriptive sensory analysis to be used for illustrating a value of a given attribute and its intensity (Lawless & Heymann, 2010). For sensory evaluation of boar taint, however, references are rarely reported. Font i Furnols et al. (2000) declared the use of chemical references for skatole and androstenone without specifying their concentration and preparation. Lunde et al. (2010) used minced meat spiked with skatole and

androstenone as references during training; the reported concentration of 9.0 μg/g of androstenone and 0.35 μg/g of skatole in fat corresponded to the endpoint of the used intensity scale. Pauly et al. (2010) suggested a boar taint intensity of five (neither weak nor strong) on a nine-point scale to correspond to a medium androstenone (1.0 μg/g) and skatole (0.16 μg/g) adipose tissue concentration. In the present study, the assessors were provided with smell strips that represent 50 and 90% scale intensity for androstenone and skatole odour, respectively. Assessors reported to feel more confident in their odour ratings due to the availability of these references. Furthermore, it allows for a comparison among studies. Intensity of the odour attributes have been on average below 40 for all loin samples. Odour references were, however, selected during training with meat and backfat samples where the latter were perceived more intensely with regard to androstenone and skatole odour. For further sensory profiling experiments it could be useful to develop references that illustrate androstenone and skatole odour intensities below 40. This is anticipated to improve the sensory discrimination of lean boar meat samples compared to backfat. Despite the provision of reference standards even castrate and gilt loins scored with a common offset of 15 to 20% of the scale for skatole and androstenone odour and flavour. Results for androstenone and skatole intensity in boar loins should, therefore, be judged in comparison to the reference loins from castrates and gilts.

4.4. Determination of olfactory acuity with smell strips Perception of androstenone is widely known to vary among individuals and according to the psychophysical assessment protocol (Havlicek et al., 2010). Screening sensory panellists' and consumers' sensitivity to the androstenone odour has thus been investigated in several studies related to boar taint, e.g., using pure androstenone crystals (Bonneau & Chevillon, 2012; Weiler et al., 2000), androstenone dissolved in oil (Bañón et al., 2003; Byrne et al., 2008; De Kock et al., 2001; Font i Furnols et al., 2000), in methanol (Pauly et al., 2010) or in water (Bekaert et al., 2011; Lunde, Skuterud, Nilsen, & Egelandsdal, 2009). Compared to Bekaert et al. (2011) and Lunde et al. (2009), who applied a total amount of 1700 μg of androstenone, we used a considerably smaller absolute amount of 15 and 150 ng androstenone on paper strips, respectively, to assess panellists' sensitivity. Boyle et al. (2006) reported a concentration-related trigeminal, i.e. nonolfactory perception of androstenone and a negative correlation between odour sensitivity and trigeminal perception of the odour. It is with such studies in mind that we decided to use a relatively low concentration of androstenone thereby minimizing the risk of an exclusive activation of the trigeminal nerve. Furthermore, considering average meat cuts and meat products even with elevated fat content 1700 μg of androstenone as used in previous studies by far exceed androstenone levels in meat. Besides, we aimed to control the exact amount of androstenone crystals dissolved. Propylene glycol was therefore used as a solvent due to the low solubility of androstenone in water. As for the psychophysical protocols, discrimination tests as applied herein and in several other studies (Bañón et al., 2003; Lunde et al., 2009) allow for a more objective evaluation of sensitivity compared to using line or category scales (Bonneau & Chevillon, 2012; Weiler et al., 2000) as the latter introduce subjectivity due to varying scale use by the respondents and subjective classification of “detectors” by the experimenter. Compared to more elaborate threshold tests (Lötsch, Lange, & Hummel, 2004), testing two androstenone concentrations (in three replicates) provides less precise information about assessors' detection thresholds but requires less administration time. In addition, bias due to decreasing attention of participants is probably lowered. Test–retest reliability has to be further approved for the smell strip method presented here. All subjects (n = 16) of the present study, however, correctly identified the screening level

L. Meier-Dinkel et al. / Meat Science 94 (2013) 19–26

of 150 ng androstenone in triplicate both at the beginning and at the end of the training period indicating a good repeatability. Finally, the low amount of odorants utilized on the smell strips presented here allow for a comparably cheap method to determine olfactory acuity. Handling and application of smell strips is quite convenient because they can be stored, transported and used at room temperature. For comparison, e.g., Annor-Frempong et al. (1997a) and Font i Furnols et al. (2000) heated their smell samples (androstenone and skatole diluted in oil). Having provided proper handling instructions, smell strips allow for large scale self-administered tests of olfactory acuity at various test surroundings.

5. Conclusions In general, trained assessors were able to detect boar taint attributes in boar loins without adjacent back fat and average intramuscular fat as low as 1.25%. Compared to German standard loins from castrates and gilts, androstenone odour intensity was significantly higher in loins from boar carcasses exceeding 1.5 μg/g of androstenone in melted backfat. The validity of these findings applies to situations in which the sensory assessors are not involved in the cooking process. Olfactory acuity of trained assessors influences perceived intensity of androstenone and skatole odour and flavour in lean boar loins and should, therefore, be considered during assessor selection and training. For androstenone flavour, assessors highly sensitive to androstenone (SENSHIGH) showed better discrimination between boar samples with varying androstenone levels. SENS assessors perceived, however, no significant difference between boar loins with low and medium androstenone levels below 1.5 μg/g of melted backfat, i.e. they were less discriminating. Assessors with very low androstenone detection thresholds should thus be used to establish “worst-case scenarios” for the detection of androstenone off-odours in boar meat. On the other hand, SENSHIGH assessors seem to be less discriminating with regard to skatole flavour compared to assessors with lower olfactory acuity to androstenone. Accordingly, studying the proportion of SENSHIGH consumers is needed to conclude on e.g. sorting thresholds for androstenone in slaughter houses. Furthermore, the selection of SENS assessors appears to be more appropriate when focusing on the detection of skatole-related off-flavours in meat. For comparison of studies, assessors' detection thresholds should be reported together with the results of their sensory evaluation of boar meat. It is, moreover, worthy to investigate how olfactory acuity to skatole affects perceived intensity of boar taint compounds in boar meat and fat. The presented paper strip system is suggested for assessing the olfactory acuity of panellists and to be used as attribute and scale intensity references in descriptive sensory analysis of boar meat. Psychophysical evaluation of subjects' olfactory acuity using discrimination tests in consumer and trained panel studies is suggested.

Acknowledgements We thank all persons who helped with the experiments at Göttingen University, especially all sensory panellists and Christian Wagner, Johanna Trautmann, Ricarda Hoberg and Ruth Wigger. We gratefully acknowledge the financial support provided by the Federal Office for Agriculture and Food (BLE) and the QS Qualität und Sicherheit GmbH. The authors greatly acknowlegde the helpful comments of the two anonymous reviewers. Authors' contributions Conceived the study: DM LMD. Performed the sensory experiments: LMD. Organized sample collection: ET LF. Chemical analysis: MB. Analysed the data: LMD RS DM ET. Wrote the paper: LMD DM.

25

Supervised the study: MW DM. All authors have read and approved the manuscript.

References Amoore, J. E., & Buttery, R. G. (1978). Partition coefficients and comparative olfactometry. Chemical Senses and Flavour, 3(1), 57–71. Ampuero Kragten, S., Verkuylen, B., Dahlmans, H., Hortos, M., Garcia-Regueiro, J. A., Dahl, E., Andresen, O., Feitsma, H., Mathur, P. K., & Harlizius, B. (2011). Inter-laboratory comparison of methods to measure androstenone in pork fat. Animal, 5(10), 1634–1642. Annor-Frempong, I., Nute, G., Whittington, F., & Wood, J. (1997a). The problem of taint in pork: I. Detection thresholds and odour profiles of androstenone and skatole in a model system. Meat Science, 46(1), 45–55. Annor-Frempong, I., Nute, G., Whittington, F., & Wood, J. (1997b). The problem of taint in pork: II. The influence of skatole, androstenone and indole, presented individually and in 490 combination in a model lipid base, on odour peception. Meat Science, 47(1/2), 49–61. Bañón, S., Costa, E., Gil, M., & Garrido, M. (2003). A comparative study of boar taint in cooked and dry-cured meat. Meat Science, 63(3), 381–388. Bekaert, K. M., Tuyttens, F. A. M., Duchateau, L., De Brabander, H. F., Aluwé, M., Millet, S., Vandendriessche, F., & Vanhaecke, L. (2011). The sensitivity of Flemish citizens to androstenone: Influence of gender, age, location and smoking habits. Meat Science, 88(3), 548–552. Bell, G. a, Laing, D. G., & Panhuber, H. (1987). Odour mixture suppression: Evidence for a peripheral mechanism in human and rat. Brain Research, 426(1), 8–18. Bonneau, M., & Chevillon, P. (2012). Acceptability of entire male pork with various levels of androstenone and skatole by consumers according to their sensitivity to androstenone. Meat Science, 90(2), 330–337. Boyle, J. A., Lundström, J. N., Knecht, M., Jones-Gotman, M., Schaal, B., & Hummel, T. (2006). On the trigeminal percept of androstenone and its implications on the rate of specific anosmia. Journal of Neurobiology, 66(13), 1501–1510. Byrne, D. V., Thamsborg, S. M., & Hansen, L. L. (2008). A sensory description of boar taint and the effects of crude and dried chicory roots (Cichorium intybus L.) and inulin feeding in male and female pork. Meat Science, 79(2), 252–269. Claus, R., Weiler, U., & Herzog, A. (1994). Physiological aspects of androstenone and skatole formation in the boar — A review with experimental data. Meat Science, 38(2), 289–305. Dalton, P., Doolittle, N., & Breslin, P. A. S. (2002). Gender-specific induction of enhanced sensitivity to odors. Nature Neuroscience, 5(3), 199–200. De Kock, H. L., Heinze, P. H., Potgieter, C. M., Dijksterhuis, C. B., & Minnaar, A. (2001). Temporal aspects related to the perception of skatole and androstenone, the major boar odour compounds. Meat Science, 57(1), 61–70. Dijksterhuis, G. B., Engel, B., Walstra, P., Font I Furnols, M., Agerhem, H., Fischer, 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 Science, 54(3), 261–269. DIN (1996). DIN 10961:1996 Untersuchung von Lebensmitteln Schulung von Prüfpersonen für sensorische Prüfungen. European declaration on alternatives to surgical castration of pigs (2010). Retrieved October 26, 2011, from http://ec.europa.eu/food/animal/welfare/farm/docs/ castration_pigs_declaration_de.pdf Fischer, K. (Kulmbach) (1999). Eberfleisch - Was sagt der Verbraucher? Lohmann Information, 1–6. Font i Furnols, M., Guerrero, L., Serra, X., Àngels Rius, M., & Àngels Oliver, M. (2000). Sensory characterization of boar taint in entire male pigs. Journal of Sensory Studies, 15, 393–409. Gross-Isseroff, R., & Lancet, D. (1988). Concentration-dependent changes of perceived odor quality. Chemical Senses, 13(2), 191–204. Havlicek, J., Murray, A. K., & Saxton, T. K. (2010). Current issues in the study of androstenes in human chemosignaling. (1st ed.). Vitamins and hormones: pheromones, Vol. 83. (pp. 47–81). ISO (1988). ISO 8587:1988: Sensory analysis — Methodology — Ranking. : ISO. ISO (2003). Sensory analysis — Methodology — General guidance for establishing a sensory profile (ISO 13299:2003; German version EN ISO 13299:2010). ISO (2004). Sensory analysis — Methodology — Triangle test (ISO 4120:2004); German version EN ISO 4120:2007. ISO (2005). Sensory analysis — Methodology — Paired comparison test (ISO 5495:2005 and ISO 5495:2005/Cor 1:2006); German version EN ISO 5495:2007. Jacob, T. J. C., Wang, L., Jaffer, S., & McPhee, S. (2006). Changes in the odor quality of androstadienone during exposure-induced sensitization. Chemical Senses, 31(1), 3–8. Laing, D. G., Eddy, A., & Best, D. J. (1994). Perceptual characteristics of binary, trinary, and quaternary odor mixtures consisting of unpleasant constituents. Physiology & Behavior, 56(1), 81–93. Lawless, H. T., & Claassen, M. R. (1993). Validity of descriptive and defect-oriented terminology systems for sensory analysis of fluid milk. Journal of Food Science, 58(1), 108–112. Lawless, H. T., & Heymann, H. (2010). Sensory evaluation of food (2nd ed.). New York: Springer. Livermore, A., & Laing, D. G. (1998). The influence of chemical complexity on the perception of multicomponent odor mixtures. Perception & Psychophysics, 60(4), 650–661. Lötsch, J., Lange, C., & Hummel, T. (2004). A simple and reliable method for clinical assessment of odor thresholds. Chemical Senses, 29(4), 311–317.

26

L. Meier-Dinkel et al. / Meat Science 94 (2013) 19–26

Lunde, K., Egelandsdal, B., Choinski, J., Mielnik, M., Flatten, A., & Kubberod, E. (2008). Marinating as a technology to shift sensory thresholds in ready-to-eat entire male pork meat. Meat Science, 80(4), 1264–1272. Lunde, K., Skuterud, E., Egelandsdal, B., Font, I., Furnols, M., Nute, G. R., Bejerholm, C., Nilsen, A., Stenstrøm, Y. H., & Hersleth, M. (2010). The importance of the recruitment method for androstenone sensitivity with respect to accurate sensory evaluation of androstenone tainted meat. Food Quality and Preference, 21(6), 648–654. Lunde, K., Skuterud, E., Nilsen, A., & Egelandsdal, B. (2009). A new method for differentiating the androstenone sensitivity among consumers. Food Quality and Preference, 20(4), 304–311. Lundström, K., Matthews, K. R., & Haugen, J. -E. (2009). Pig meat quality from entire males. Animal, 3(11), 1497. Marshall, K., Laing, D. G., Jinks, A., & Hutchinson, I. (2006). The capacity of humans to identify components in complex odor–taste mixtures. Chemical Senses, 31(6), 539–545. Meier-Dinkel, L., Trautmann, J., Frieden, L., Tholen, E., Knorr, C., Sharifi, A., Bücking, M., Wicke, M., & Mörlein, D. (2013). Consumer perception of boar meat as affected by labelling information, malodorous compounds and sensitivity to androstenone. Meat Science, 93, 248–256. Meilgaard, M., Civille, G., & Carr, B. (2007). Sensory evaluation techniques (4th ed.). Boca Raton, FL, USA: CRC Press. Möller, R., Pause, B. M., & Ferstl, R. (1999). Induzierbarkeit geruchlicher Sensitivität durch Duft-Exposition bei Personen mit spezifischer Anosmie. Experimental Psychology (formerly Zeitschrift für Experimentelle Psychologie), 46(1), 53–71. Mörlein, D., Grave, A., Sharifi, A. R., Bücking, M., & Wicke, M. (2012). Different scalding techniques do not affect boar taint. Meat Science, 91(4), 435–440. Patterson, R. L. S. (1968). 5a-Androst-16-ene-3-one: Compound responsible for boar taint in boar fat. Journal of the Science of Food and Agriculture, 19, 31–38. Pauly, C., Spring-Staehli, P., O'Doherty, J. V., Ampuero Kragten, S., Dubois, S., Messadène, J., & Bee, G. (2010). The effects of method of castration, rearing condition and diet on sensory quality of pork assessed by a trained panel. Meat Science, 86(2), 498–504.

Pause, B. M., Rogalski, K. P., Sojka, B., & Ferstl, R. (1999). Sensitivity to androstenone in female subjects is associated with an altered brain response to male body odor. Physiology & Behavior, 68(1–2), 129–137. Stevenson, R. J. (2001). Perceptual learning with odors: Implications for psychological accounts of odor quality perception. Psychonomic Bulletin & Review, 8(4), 708–712. Stolzenbach, S., Lindahl, G., Lundström, K., Chen, G., & Byrne, D. V. (2009). Perceptual masking of boar taint in Swedish fermented sausages. Meat Science, 81, 580–588. Vold, E. (1970). Fleischproduktionseigenschaften bei Ebern und Kastraten. IV. Organoleptische und gaschromatographische Untersuchungen wasserdampfflüchtiger Stoffe des Rückenspeckes von Ebern. Report Nr 238 (pp. 25). : Institute of Animal Genetics and Breeding, NLH, Vollebekk, Norway. Walstra, P., Chevillon, P., Seth, G. Von, Diestre, A., Matthews, K. R., Homer, D. B., & Bonneau, M. (1999). An international study on the importance of androstenone and skatole for boar taint: Levels of androstenone and skatole by country and season. Livestock Production Science, 62, 15–28. Weiler, U., Font i Furnols, M., Fischer, K., Kemmer, H., Oliver, M. A., Gispert, M. A., Dobrowolski, A., & Claus, R. (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 Science, 54(3), 297–304. Wysocki, C. J., Dorries, K. M., & Beauchamp, G. K. (1989). Ability to perceive androstenone can be acquired by ostensibly anosmic people. Proceedings of the National Academy of Sciences of the United States of America, 86(20), 7976–7978. Zamaratskaia, G., & Squires, E. J. (2009). Biochemical, nutritional and genetic effects on boar taint in entire male pigs. Animal, 3(11), 1508–1521.