OPTIMIZATION OF FIRMNESS TRIAL FOR FAT CARCASS APPRECIATION IN MARKET LAMBS

Optimization of firmness trial for fat carcass appreciation in market lambs. The technological qualities and the potential organoleptic value of market lamb carcasses are partly associated with the firmness and colour of subcutaneous fat. The aim of this study was to establish a scale of firmness with significant discrimination. Two hundred and twenty-two Lacaune male lambs were weaned early (4-5 weeks old) and intensively managed (ADG** = 274 g per day) in a sheep-fold till they attained a slaughter weight of 39 kg. Three different means of investigation were examined to test discriminant value based on different grading levels, repeatability and agreement. A classic grading with 5 scaled grades via a tactile approach (NTENAba) was performed on chilled carcasses in the slaughterhouse (18 h). A laboratory classification with 6 scaled grades (NTENLab) was carried out later based on the physical aspect after unthawing of ground subcutaneous fat (n = 222) cut from the dock (base of the tail). The various grades of the laboratory scale were compared for fatty acid composition (n = 6). An indirect instrumental determination of subcutaneous fatty tissue resistivity from different parts of the loin was carried out via a prototype. The slaughterhouse grading showed poor discrimination for the intermediate grades (Sorensen criterium (S < 56%), while the extreme grade corresponding to the firmest fatty tissue showed good repeatability (S > 98%). However, the laboratory grading provides a good control (r2 > 0.99). Multivariate analysis (ACP** and cluster analysis) of their characteristic fatty acid composition only allowed 3, at most 4, grades to be differentiated (P < 0.001; P < 0.01). Resistivity measurement was correlated with subcutaneous fatty tissue water content (r = -0.66; P < 0.001). However, at present this measurement cannot serve as a grading reference, as the correlations with NTENAba and NTENLab were poor (r = 0.33 and r = 0.31; P < 0.001). The AFC** analysis, based on slaughterhouse and laboratory gradings (n = 222, sets up a slaughterhouse optimal judgment criterion based on 4 grades, with the following characterisitics: NTEN 1 = very soft external carcass fat, noticeably oily consistency, markedly extensible aponeurosis over the loin (> 4 cm); NTEN 2 = soft, malleable, non oily fat, with an intermediate loosening of the aponeurosis over the loin (1-4 cm); NTEN 3 = firm slightly compressible fat, with a slight loosening of the aponeurosis over the loin (< 1 cm); NTEN 4 = very firm fat, with adherent aponeurosis.