Uracil as an index of lactic acid bacteria contamination of tomato products

Aim of this research was to evaluate the suitability of uracil as an hygienic quality index of tomato products. While uridine was naturally present throughout tomato berries ripening, uracil appeared only after microbial contamination. In tomato pulp inoculated with nine different microbial strains, all the five lactic acid bacteria (LAB) studied released relevant quantities of uracil (150 - 1040 mg/kg dm), with a correlated partial or total decrease of uridine. Uracil production by yeasts and moulds was very low or non existent; the starting uridine concentration (ca. 960 mg/kg dm) remained constant or increased. Uracil thermostability was also verified. Twenty six samples of tomato paste (30 °Brix) were collected from bag-in-drums produced in an industrial processing plant, some with evident swelling symptoms. All the samples with high microbial count presented uracil. Uracil was also detected in samples with microbial contamination under the detection limit and Howard Mould Count (HMC) below legislation limits, implying the reprocessing, at least partial, of altered tomato product. The results indicate that uracil presence in tomato products represents an index of LAB contamination occurred before heat treatment.