PREDICTION OF THE CHEMICAL-COMPOSITION OF LAMB CARCASSES FROM MULTIFREQUENCY IMPEDANCE DATA

Multi-frequency bioimpedance analysis (MFBIA) was used to determine th e impedance, reactance and resistance of 103 lamb carcasses (17.1-34.2 kg) immediately after slaughter and evisceration. Carcasses were halv ed, frozen and one half subsequently homogenized and analysed for wate r, crude protein and fat content. Three measures of carcass length wer e obtained. Diagonal length between the electrodes (right side biceps femoris to left side of neck) explained a greater proportion of the va riance in water mass than did estimates of spinal length and was selec ted for use in the index L-2/Z to predict the mass of chemical compone nts in the carcass. Use of impedance (Z) measured at the characteristi c frequency (Z(c)) instead of 50 kHz (Z(50)) did not improve the power of the model to predict the mass of water, protein or fat in the carc ass. While L-2/Z(50) explained a significant proportion of variation i n the masses of body water (r(2) 0.64), protein (r(2) 0.34) and fat (r (2) 0.35), its inclusion in multi-variate indices offered small or no increases in predictive capacity when hot carcass weight (HCW) and a m easure of rib fat-depth (GR) were present in the model. Optimized equa tions were able to account for 65-90 % of the variance observed in the weight of chemical components in the carcass. It is concluded that si ngle frequency impedance data do not provide better prediction of carc ass composition than can be obtained from measures of HCW and GR. Indi ces of intracellular water mass derived from impedance at zero frequen cy and the characteristic frequency explained a similar proportion of the variance in carcass protein mass as did the index L-2/Z(50).