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 measurement of the responses to different odour intensities of `boar taint' using a sensory panel and an electronic nose.

This study explored the possibility of using an electronic nose (e-nose) with a 12-conducting-polymer sensor array combined with pattern recognition routines to discriminate between varying intensities of boar taint. A set of samples in a model system comprising a neutral lipid base containing varying combinations of androstenone and skatole were tested, as were pork fat samples. The e-nose responses for pork fat were calibrated against those given by a trained 10-member sensory panel for abnormal odour of the same samples from a total of 60 Large White cross-bred pigs. The e-nose responses related strongly to those of the sensory panel with a significant (p<0·01) canonical correlation of 0·78. The data set was used to develop a discriminant function for grouping pork samples into three `response classes': normal, doubtful and abnormal. Based on this, the e-nose identified all the abnormal samples correctly. However, 16% of the normal samples were also classified as abnormal. It was concluded that, in general, the electronic nose can discriminate between different levels of boar taint and that although a high specificity of sensors to androstenone and skatole may be desirable it may not be entirely important to the development and configuration of a boar taint sensor array.

The problem of taint in pork: 1. Detection thresholds and odour profiles of androstenone and skatole in a model system.

Detection thresholds of androstenone and skatole were established using a trained 10-member sensory panel. Odour profiles for these compounds were also developed using a model system comprising a lipid base spiked with synthetic androstenone and skatole. A total of 2160 presentations were used for the determination of sensory thresholds which were obtained using the Ascending Method of Limits with a 3-AFC (Alternate Forced Choice) mode of presentation. Preliminary odour profiles were obtained by three consensus-profiling sessions. Character notes developed were then validated by profiling four classes of model samples containing androstenone, skatole, a mixture of skatole plus androstenone and a mixture of skatole plus androstenone plus indole. Individual sensory thresholds for the ten panel members varied between 0.2 to 1.0 µg g(-1) for androstenone and 0.008 to 0.06 µg g(-1) for skatole, leading to group thresholds of 0.426 µg g(-1) and 0.026 µg g(-1) for androstenone and skatole, respectively. The important descriptors for the odour of androstenone included; sweaty, ammonia, dirty, parsnip, silage, nosefeel and acrid. Among these, only the sweaty note was found to be a significant (p < 0.05) basis for separating pure samples of androstenone from pure samples of skatole by the panel. The important descriptors for the odour of skatole were; mothball, musty and body reaction. Both the mothball and musty notes were a significant (p < 0.001 to p < 0.05) basis for distinguishing between either pure samples of skatole or mixtures containing skatole from pure samples of androstenone. The results show that androstenone and skatole are synergistic, but only in relation to the descriptors defining intensity of the odours, and not in those defining the character of their individual odours.

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.

The problem of taint in pork-III. Odour profile of pork fat and the interrelationships between androstenone, skatole and indole concentrations.

Samples from 100 Large White × Meishan crossbred pigs (50 males, 50 females) with androstenone, skatole and indole concentrations ranging between 0-2.68, 0.004-1.43 and 0.007-1.57 µg g(-1), respectively, were assessed by a trained 10-member sensory panel. The intensities of pork odour, abnormal odour, androstenone, skatole and odour pleasantness were assessed using line scaling. The descriptors mothball and musty associated with skatole and sweaty, dirty, silage and parsnips associated with androstenone all significantly (p < 0.05) characterised taint in pork. Regression analyses showed that pork odour depended on the linear terms of androstenone and indole, whilst abnormal odour depended on the linear terms of androstenone, skatole, indole and the quadratic terms of skatole and indole (r(2) = 0.76). Responses to different combinations of androstenone and skatole were sometimes similar. This implies that instrumentation for on-line sorting (classification) of pigs should be based on a response criterion instead of on concentrations. The equations derived in this study could be tested to form the basis for a reliable calibration system.