Trisodium Phosphate and Other Alkaline Washing Agents

Trisodium phosphate (TSP) has been marketed by Rhodia Specialty Phosphates (www.rhodia-phosphates.com) as an antimicrobial rinse (AvGard®,

Assur-Rinse®) to reduce human pathogen populations on processed beef and poultry. TSP is classified as GRAS by the FDA [89].

The antimicrobial activity of TSP probably is due to its high pH (pH 12) which disrupts the cytoplasmic membrane [90,91]. Highly alkaline washes based on sodium and potassium hydroxide (pH 11 to 12) resulted in 3 log reductions in the population of a nonpathogenic E. coli on surface-inoculated oranges [92]. A 30-minute dip in 0.25% calcinated calcium suspension, another highly alkaline product derived from oyster shells (pH 10), reduced the native bacterial population on cucumbers by about 2 logs [93]. In a more recent study, Bari et al. [94] reported population reductions exceeding 5 logs on tomatoes that had been surface inoculated with E. coli O157:H7, salmonella strains, or L. monocytogenes and treated with 0.5% calcinated calcium. These exceptionally high population reductions (for a wash) may be a reflection of the brief interval (30 minutes) between inoculation and treatment used by these investigators. Sapers et al. [67] obtained population reductions approaching 3 logs when apples that had been dip-inoculated with E. coli (ATCC 25922) were washed with 5% hydrogen peroxide, followed by brushing the calyx and stem areas with a paste of calcinated calcium; the population reduction was <2 logs with only the peroxide wash. TSP solutions (12 to 15%) were highly effective in reducing S. Montevideo populations on inoculated tomato surface but failed to inactivate completely this organism in the tomato core tissue [95]. Survival in the latter tissue probably resulted from bacterial infiltration. Sapers et al. [78] reported a 2 log reduction in a nonpathogenic E. coli strain on inoculated apples washed with 4% TSP at 50°C. A 1% TSP wash reduced the population of E. coli O157:H7 and S. Montevideo on strawberries by 93 and 96%, respectively [38]. Treatment of lettuce with 2% TSP was ineffective in killing L. monocytogenes [14]. Addition of 0.3% TSP to the irrigation water was ineffective in reducing the native microflora on alfalfa sprouts [42]. TSP was reported to be highly effective in inactivating E. coli O157:H7 in biofilms but less effective against S. Typhimurium and L. monocytogenes in biofilms [96].

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