Effects of castration age, protein level and lysine/methionine ratio in the diet on colour, lipid oxidation and meat acceptability of intensively reared Friesian steers

A total of 64 intensively reared Friesian steers were used in a 2x2x2 design to study the effects of age of castration (15 days old v. 5 months old), dietary protein level (14.6% v. 16.8%; DM basis) and lysine/methionine (lys/met) ratio (3.0 v. 3.4) on meat quality. The lys/met ratio of 3.0 was reached with supplementation of protected methionine. Animals were slaughtered at a live weight of 443.5 +/- 26.2 kg at around 12 months of age. Colour and lipid oxidation were measured in the longissimus thoracis muscle throughout the 14 days of display under modified atmospheric and commercial display conditions. A panel of 17 consumers assessed daily the visual acceptability of the meat on display. A consumer acceptability eating test was also performed with 120 consumers in meat aged for 7 days under vacuum conditions. Lipid oxidation was not influenced by castration age and the protein level in the diet. Castration age did not affect meat colour, but meat from the low protein level diet and the low lys/met ratio showed higher redness (a*) from 3 days of display onwards. Nevertheless, from 6 days onwards, consumer visual acceptability was below the level of acceptance in all treatments, and even from 5 days onwards in those animals that underwent early castration and were fed either a high protein diet or a combination diet low in protein content and high in lys/met ratio. The best accepted treatments throughout the display period were those from late castrated animals fed a low protein diet, probably related to other visual aspects. However, the best accepted meat after consumption was that from late castrated animals fed high protein and high lys/met. The addition of protected methionine to reach lys/met levels of 3.0 did not improve beef acceptability, with the high protein diet being preferred by consumers in terms of palatability in late castrated animals.