Visible spectroscopy on carcass fat combined with chemometrics to distinguish pasture-fed, concentrate-fed and concentrate-finished pasture-fed lambs

•Visible spectroscopy of carcass fat was used for diet authentication in lambs.•Pasture-fed, stall-fed and stall-finished pasture-fed lambs were distinguished.•Full reflectance data can reliably discriminate three production systems.•Fat carotenoid content decreased exponentially with weight gain during finishing.

We used visible spectroscopy of fat to discriminate lambs that were pasture-fed (n = 76), concentrate-fed (n = 79) or concentrate-finished after pasture-feeding (n = 69). The reflectance spectrum of perirenal and subcutaneous caudal fat was measured at slaughter and 24 h post mortem. In Method 1 (W450–510), the optical data were used at wavelengths in the range of 450–510 nm to calculate an index quantifying light absorption by carotenoids. In Method 2 (W400–700), the full set of data at wavelengths in the range of 400–700 nm was used to differentiate carcasses using PLS-DA as a classification method. W400–700 proved more reliable than W450–510 (P < 0.0001). The proportion of correctly classified lambs using W400–700 was 95.6% and 95.9% for measurements made on perirenal fat at slaughter and 24 h post mortem. The intensity of light absorption by carotenoids decreased exponentially with live weight gain during the finishing period.