In this study, the important odor impact volatiles generated in the meat of grilled beef loin muscle were characterized. Animals were finished in 4 different diet systems:T1, pasture (a mixture of Medicago sativa, Trifolium repens, and Festuca arundinacea); T2, pasture supplemented with cracked corn grain (offered at 0.6% live weight, LW); T3, pasture supplemented with cracked corn grain (offered at 1.2% LW); and T4, concentrate (pellets with 85% corn and 12.8% sunflower, on a dry-matter basis) plus alfalfa hay (both ad libitum). Aroma compounds were assessed by dynamic headspace-solid phase extraction (DHS-SPE) and gas chromatographic-olfactometric (GC-O) analysis. Most odorants were carbonyl compounds, some of them reaching high GC-O scores, especially 1-octen-3-one, (E)-2-octenal, methional, and hexanal. A specific quantitative analysis of ketones and aldehydes was conducted through their derivatization with o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride directly on the headspace trap and analyzed by GC-MS, with the purpose of studying the effect of finishing diet systems. From the 23 carbonyl compounds quantified, 2 were especially affected by the diet system; methional was higher in the treatment based on concentrates, whereas (E,E)-2,4-heptadienal was higher in the treatment based only in pastures. The results are discussed considering previous published productive and quality traits.