Influence of nutritional regime (grain, grass, brassica) on sheep meat texture and flavour.

Summary

​Finishing feeds such as lucerne or some brassica crops may have a negative effect on lamb flavour according to some studies and anecdotal evidence. However, few well-designed experiments have been conducted to objectively ascertain to what extent (if any) different finishing feeds affect lamb quality and flavour. In this study we examined the influence of different finishing feeds and sheep genotypes on the sensory and flavour characteristics of grilled lamb. Ewes with known Australian Breeding Values (ABVs) from low IMF (Sires 1 & 6) and high IMF (Sires 3 & 8) genotypes were randomly allocated to four different finishing feeds. Lambs (n = 25 per feed treatment) were finished for 42-days in January/February 2013 on; (1) lucerne, (2) a low glucosinolate brassica cultivar - brassica napus, cv. “Titan”, (3) a high glucosinolate brassica brassica napus, cv.  “Greenland” or (4) a control regime of ryegrass supplemented with grain. Left and right striploins were obtained and cut into standardised 15 mm steaks. High ABV genotypes were initially heavier than low ABV animals; these differences persisted throughout the trial. Significant differences in growth rates were recorded at different periods throughout the trial. Negative growth was recorded in the first 12 days (adjustment period) on all feeds except the ryegrass. In subsequent periods, rapid positive growth was measured for the novel feed treatments compared to the ryegrass; this was especially true for the Titan feed in the early phase of the finishing trial. 
Descriptive sensory evaluation was carried out on grilled lamb from right striploins by a trained panel. Consumer acceptance testing using Caucasian and Chinese background Australian consumers was conducted using matching left striploins. The trained sensory panel measured animal, feed and sire related effects. Feed induced flavour differences were minimal, with no evidence of a “taint” present in any of the novel feeds compared to the control. In general, lamb from high ABV Sires had stronger flavour and better texture characteristics. Lamb from the Sire 8 genotype in particular had better sensory characteristics compared to the others. 
The consumer study clearly showed that acceptance of grilled lamb was higher for the novel finishing feeds (brassicas & lucerne) compared to the control. Both of the brassica treatments were rated highest by both consumer groups in terms of overall liking and flavour liking. The rye finished lamb was rated the lowest and lamb from sires with high ABVs were clearly preferred by both consumer groups. Further chemical analyses were conducted on samples to characterise differences in free amino acids, branched chain fatty acids, other fatty acids and aroma volatiles according to feed and genotype. Overall, the data provided no evidence that brassica derived taints were present in lamb finished on the experimental feeds. In fact, contrary to our initial hypothesis, the data strongly indicated that lambs finished on the lucerne and brassica feeds had better sensory characteristics than the ryegrass/ grain treatments.