Studies on the composition of food

Abstract

1. The nutrient content and distribution of the carcass meat in broilers (B) and free range cockerels (FR) was studied in two experiments in 1961–2. Half the birds of each type were roasted at 177°C, without additional fat, before dissection and analysis. The breast muscles and red meat were separately analysed for moisture, protein, fat and thiamine. 2. Chunky hybrids (frozen) and Light Sussex × Rhode Island Red (LS × RIR) cockerels were used in both experiments. Expt 1 (group 1) was a pilot study (using groups of six) inwhich B and FR of similar dressed weight were compared. Expt 2 (group 2) consisted of twelve ‘fresh’ (B1) and twelve frozen (B2) broiler hybrids from the same batch of birds killed at 9 weeks; twelve slightly heavier LS × RIR cockerels (FR2) were killed at 18 weeks and twelve Sykes hybrid 3 cockerels (FR1) killed at 20 weeks. The birds received various standard feeds. 3. The edible portion (skin plus meat), expressed as a percentage of the dressed weight, was greater in the free range birds than in the broiler chickens. Increased cooking losses resulting from freezing were responsible for a significantly smaller proportion of edible meat in the cooked frozen broilers. In both groups the edible portion increased with age irrespective of breed or weight. 4. In broiler and free range chickens differenccs in the mean protein content of the total edible meat were small. 5. Fat content appeared to be related to breed as well as to type of bird. In group 1, B contained slightly more fat than FR1. In group 2, B1, and B2, contained significantly more fat then FR1, but the fat content of the raw meat in FR2, was greater. 6. In both experiments the flesh of the free range chickens contained more thiamine than the broiler meat. In group 1 this difference was significant in all the cooked birds; in group 2 significant differences between free range chickens and broilers were found in the breast and red meat of the cooked birds for all comparisons except FR2 and B1. About one-third of the thiamine was lost on cooking both types of chicken in group 1; in group 2 the loss from the broilers was similar but in the FR birds between 18% (FR1) and 26% (FR2) of the thiamine was destroyed. 7. In general the meat of the broilers contained less thiamine and more fat than did that of the free range chickens. Though such differences are of no significance in a mixed diet (as chicken supplies so little thiamine) they are a useful index of differences in nutritive value which result from the different systems of management.