Sanitizing treatments on fresh vegetables artificially contaminated with Yersinia enterocolitica and Shiga toxin-producing Escherichia coli.

MASTRODONATO, ANNA CHIARA; IRIARTE, HEBE JORGELINA; FAVIER GABRIELA ISABEL; LUCERO ESTRADA CECILIA; ESCUDERO MARÍA ESTHER

San Luis

Jornada; XXXVII Reunión Científica Anual de la Sociedad de Biología de Cuyo; 2019

Sociedad de Biología de Cuyo

Fresh vegetables constitute essential ingredients of ready-to-eat salads in a healthy diet. From orchard to table, they may become contaminated by numerous microorganisms including Yersinia enterocolitica (Ye) and Shiga toxin-producing Escherichia coli (STEC), which are known foodborne enteropathogens responsible for moderate and severe human diseases, respectively. There is great interest in developing safe and efficient sanitizing treatments avoiding to modify the organoleptic characteristics of vegetables. In this study, 2% citric acid (CA), 200 ppm sodium hypochlorite (SH), commercial vinegar with 5% acidity (V) and 0.5 g/L acidified sodium chlorite (ASC) were assayed as sanitizers on pear tomatoes (Lycopersicum esculentum Mill), fresh lettuce leaves (Lactuca sativa) and strawberries (Fragaria ananassa) artificially contaminated with Ye or STEC. Fourteen units of each vegetable were used in each experiment. They were submerged in 1 x 108 cfu/ml suspensions of each pathogen by 2 min at 22°C. Vegetables were removed and placed in sterile containers for 12 h at 4°C to facilitate bacterial adhesion. Solutions of each sanitizer were prepared the same day of each experiment. Samples were individually placed inside sterile plastic bags and agitated during 1 min in 50 ml of one of four sanitizing solutions. After washing, each sample was subjected to a 100 ml sterile distilled water rinse during 1 min to remove chemical residues and placed on sterile paper towels to dry. Vegetables were individually placed in new bags, added with 20 ml of sterile saline solution and agitated for 1 min to detach bacteria. To perform bacterial counts after sanitizing, these suspensions were serially diluted and volumes of each dilution were spread on Mac Conkey agar for Ye or Sorbitol Mac Conkey agar for STEC. In each group of vegetables, untreated/contaminated products were processed to determine the initial pathogen load on surface. Bacterial counts were reported as log10 cfu/vegetable. Bacterial reduction in each vegetable group by each sanitizing treatment was calculated as the difference between the count of untreated/contaminated group and the count of treated/ contaminated group. After sanitizing, vegetables were stored at 4°C for 7 days to assess changes in appearance. Lettuce leaves showed highest initial loads of each pathogen as compared to other vegetables. Major bacterial reductions were produced by V (4.3 log in Ye and 4.5 log in STEC, both on lettuce) and ASC (3.76 log in Ye and 4.5 log in STEC, both on lettuce), followed by SH (2.28 log in Ye on tomatoes and 2.74 log in STEC on strawberries) and CA (2.83 log in Ye on tomatoes and 2.32 log in STEC on strawberries). After 7-day storage, tomatoes treated with any sanitizer and V- and ASC-treated remaining vegetables exhibited acceptable organoleptic characteristics; meanwhile, lettuce and strawberries treated with other sanitizers showed slight changes of color and texture and fungal growth. Vinegar and ASC are proposed as the best sanitizers to control Ye and STEC on fresh vegetables.