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 oxidationprone fat-softening oleic and linoleic acids. Concentrations of species-characterising short branchedchain 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.

Traceability of grass feeding in beef: terpenes, 2,3-octanedione and skatole accumulation in adipose tissue of young bulls

“…In their study, the protein/non-fibrous carbohydrate ratio was much higher in pasture than in the maize diet. Young et al (2003) reported higher levels of skatole in the perirenal fat of lambs raised on pasture compared to maize-dominated concentrate-fed lambs. In the same study, a third group of lambs fed on a lucerne-dominated concentrate diet with intermediate values of nitrogen/soluble carbohydrate ratio presented (Table 2) and the proportion forage/concentrate in the diet, the protein/soluble carbohydrate ratio would be higher in GL group followed by HL and PH groups.…”

“…In forage-based diets with highprotein/non-fibrous carbohydrate ratios, protein and therefore tryptophan degradation is enhanced, resulting in increased skatole production (Sheath et al, 2001). Differences in skatole formation and tissue accumulation have been reported not only when comparing forage vs. concentrate-based diets (Lane and Fraser, 1999;Young et al, 2003;Priolo et al, 2009), but also between forage diets (Schreurs et al, 2003 and, depending on protein solubility and degradability and on synchronisation of protein and carbohydrate degradation in the rumen.…”

Meat odour and flavour and indoles concentration in ruminal fluid and adipose tissue of lambs fed green herbage or concentrates with or without tannins

“…Formation of skatole results from degradation of tryptophan in the rumen by bacteria (Carlson and Breeze, 1984). The high protein content and the high ratio protein/readily digestible carbohydrates of herbage diets would therefore increase the free tryptophan in the rumen (Young et al, 2003) with consequent higher skatole production. In our study we have observed also an effect of dietary tannins on ruminal skatole concentration.…”

“…Skatole (3-methylindole) and indole are compounds found in the adipose tissue of different animals. In pork, skatole is responsible for the unpleasant boar taint (Annor-Frempong et al, 1997a), while in sheep, it is linked with typical species flavour (Young et al, 1997) and pastoral odour and flavour (Young et al, 2003). In ruminants, skatole is formed by ruminal microorganisms and it has been often found at higher concentrations in fat from lambs fed green herbages compared to animals given concentrates (Young et al, 1997 andPriolo et al, 2005).…”

“…The problem of pastoral flavour in sheep is mostly linked to green herbage intake while species flavour can be linked to both grass and concentrate diets (Young et al, 2003). Consumers not accustomed to meat from animals raised on pasture often find this product too strong in flavour and therefore they dislike it (Sañ udo et al, 2000).…”