A cell-free translation assay was applied for the quick detection of ricin in food samples. Three economically important foods-ground beef, low-fat milk, and liquid chicken egg--were tested. The results indicated that ground beef had very little matrix effect on the assay, whereas low-fat milk and liquid chicken egg showed clear interference on the protein translation. A simple dilution in phosphate-buffered saline (PBS) effectively eliminated the translational inhibition from these foods. The concentrations inhibiting 50% of luciferase translation derived from the current study were 0.01 nM for the pure ricin A chain, 0.02 nM for pure ricin, and 0.087 nM for crude ricin in PBS. In most cases, the half inhibitory concentration values for ricin in food matrices were significantly lower than for those in PBS buffer, suggesting that some components in these food matrices might potentiate the activity of ricin. Thermal stability tests indicated that the ricin A chain was the least stable among the three forms of ricin in all matrices measured. The thermal stability of pure and crude ricins varied depending on the matrices. The specific activities of ricin in PBS buffer were confirmed by a neutralization test with ricin-specific and nonspecific antibodies. This study demonstrates that the cell-free translation assay is a rapid and sensitive method for detection of biologically active ricin toxin in ground beef, low-fat milk, and liquid chicken egg and that food matrices can greatly affect the thermal stability of ricin.