Inactivation of Salmonella enterica on tomato stem scars by antimicrobial solutions and vacuum perfusion

A study was conducted to identify sanitizing solutions effective at inactivating ca. 5 log CFU of Salmonella enterica inoculated onto the stem scar of red round tomatoes during two-minute immersion treatments. Sixty-three antimicrobial combinations were tested. Vacuum perfusion was applied to tomatoes during selected treatments to promote infiltration of sanitizer into porous tomato stem scar tissue. Red round tomatoes were inoculated to ca. 6.9 log CFU/stem scar with a four-serovar composite of Salmonella enterica, air dried, and tomatoes were immersed in circulating sanitizing solutions for 120 s at ca. 22 °C. Stem scars were aseptically excised, macerated in DE neutralizing broth, and the homogenate was spiral plated. Twenty-four washes inactivated ≥ 3.0 log CFU/stem scar. Seven treatments reduced ≥ 4.8 log (viz., 40% EtOH, sulfuric acid, and organic acid combinations). Log CFU/stem scar reductions for various sanitizers are listed in parenthesis, as follows: 90 ppm peroxyacetic acid (1.31), 200 ppm chlorine (1.53), 190 ppm chlorine + 15″ Hg vacuum perfusion (2.23), 0.2 N sodium hydroxide (NaOH) (3.78), 2% total of lactic + acetic acid (4.35), 3% total of phosphoric + lactic acids (4.51), and 40% ethanol (4.81). Solutions that achieved ≥ 4.95 log reductions were 5.1% total of lactic + acetic + levulinic acids, 49% ethanol, 6% total of lactic + acetic acids, and a 0.2 M H2SO4 (sulfuric acid) solution. The use of vacuum perfusion with 200 ppm chlorine increased inactivation by 0.7 log CFU over chlorine alone, however, P > 0.05. Results from this study provide tomato processers with some sanitization options effective at inactivating Salmonella from the stem scars of tomatoes. These results may also help processors and scientists design future decontamination studies by incorporating combinations of these chemical treatments.