Pastoral and species flavour in lambs raised on pasture, lucerne or maize

Abstract Variations in diet, age and castration were employed to generate a range of flavours that were chemically analysed to find the cause of ‘pastoral’ flavour in sheepmeat and its relationship to species flavour. Lambs were raised on pasture (ram or castrate) or on a maize‐based or lucerne‐based concentrate diet (ram only). They were slaughtered at 132 and 232 days. Fat from animals raised on concentrates had lower proportions of fat‐hardening stearic acid and higher proportions of oxidation‐prone fat‐softening oleic and linoleic acids. Concentrations of species‐characterising short branched‐chain fatty acids (BCFAs), typified by 4‐methyloctanoic acid, were lower for pasture‐fed lambs, particularly at 232 days, although between‐animal variation was high. Castration did not statistically affect BCFA concentration at this age. Correlations between BCFAs and testes weight were not significant, suggesting that they were not acting as sex pheromones. Concentrations of 3‐methylindole (skatole) in perirenal fat were higher for the pasture diet at both slaughter dates. Concentrations of 4‐methylphenol in the fat were not affected by diet. However, 3‐methylphenol was more abundant in pasture treatments. A sensory panel found that the intensity of ‘sheepmeat’ flavour was higher for pasture‐raised animals, but that associations of ‘barnyard’ flavour (which has been linked to pastoral flavour) with diet were more complex. The issue was resolved by fat sniffing. Panel responses to heated subcutaneous fat were recorded as frequency of descriptive terms drawn from a limited lexicon. Volatiles from fats pooled by treatment were resolved on a gas chromatographic column whose effluent was monitored by odourport sniffing. Compounds were identified by parallel chromatographic/mass spectrometric runs. The headspace concentrations of these compounds were then measured for individual animals. These data were related to frequency data by the principal component method. ‘Mutton’ and ‘sheepmeat’ odour notes were clearly linked to indoles (skatole particularly) and, to a lesser extent, methylphenol, setting these notes apart from ‘lamb’, an odour note more associated with lucerne and maize diets through higher concentrations of BCFAs. It was concluded that 3‐methylindole was the major cause of pastoral flavour in sheepmeat, and that fat oxidation products represented a background flavour that varied quantitatively but not qualitatively with fatty acid profile. © 2002 Society of Chemical Industry