Tomato plants with delayed fruit ripening have been produced by stable insertion of the gene encoding the 1-aminocyclopropane-1-carboxylic acid deaminase (ACCd) protein into the tomato chromosome. Two approaches were used to assess the safety of the ACCd protein for human consumption. Purified Escherichia coli-produced ACCd protein, which is chemically and functionally equivalent to the ACCd protein produced in delayed ripening tomato fruit, was used in these studies. First, the ACCd protein was readily degraded under simulated mammalian digestive conditions. Second, the ACCd protein did not have any deleterious effects when administered to mice by acute gavage at a dosage of up to 602 mg/kg of bodyweight. This dosage correlates to greater than a 5000-fold safety factor relative to the average daily consumption of tomatoes, assuming that all tomatoes consumed contain the ACCd protein. These results in conjunction with previously published data, established that ingestion of tomato fruit expressing the ACCd protein does not pose any safety concerns.