Inactivation of Salmonella in liquid egg albumen by antimicrobial bottle coatings infused with allyl isothiocyanate, nisin and zinc oxide nanoparticles.

AIMS: To develop an antimicrobial bottle coating effective at inhibiting the growth of Salmonella in liquid egg albumen (egg white) and reduce the risk of human Salmonellosis. METHODS AND RESULTS: Four-ounce glass jars were coated with a mixture of polylactic acid (PLA) polymer and antimicrobial compounds containing 100-500 µl allyl isothiocyanate (AIT), 250 mg nisin, 250 mg zinc oxide nanoparticles per jar or their combinations. The coated jars contained 100 ml of liquid egg white (LEW) inoculated with a three-strain Salmonella enterica ssp. enterica cocktail at populations of 10(3) or 10(7) CFU ml(-1) and stored at 10°C for 28 days. The PLA coating with 500 µl AIT completely inactivated 3 and 7 log CFU ml(-1) of Salmonella after 7 and 21 days of storage, respectively. The PLA coating with 200 µl AIT in combination with 250 mg nisin reduced Salmonella populations to an undetectable level (<10 CFU ml(-1) ) after 21 days of storage. CONCLUSIONS: PLA coatings containing AIT alone or in combination with nisin effectively inactivated salmonellae in LEW. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated the commercial potential of applying the antimicrobial bottle coating method to liquid eggs and possibly other fluid food products.

Comparison of supplements to enhance recovery of heat-injured Salmonella from egg albumen.

AIMS: The purpose of this study was to determine the proficiency of supplements to enhance the recovery of Salmonella from heat-treated liquid egg albumen on solid agar media. METHODS AND RESULTS: Salmonella-inoculated albumen, heated at 53.3 degrees C for 4 min, was plated on 39 combinations of solid media with or without the addition of 12 supplements. Greater numbers of Salmonella (P < 0.05) recovered with the addition of 1.0 g l(-1) ferrous sulfate (FeSO(4)) than with any other supplements, except for 0.5 or 1.0 g l(-1) 3'3'-thiodipropionic acid (TDP), which recovered equivalent populations. Addition of 1.0 g l(-1) sodium pyruvate or 6.0 g l(-1) yeast extract plus 1.0 g l(-1) sodium pyruvate supported greater resuscitation than unsupplemented tryptic soy agar (TSA) or supplementing with 0.01 or 0.1 g l(-1) N-propyl gallate, 10 g l(-1) activated charcoal, 0.1 g l(-1) KMnO(4) or 50 mg l(-1) ethoxyquin. The remaining supplements supported recovery of equivalent numbers of Salmonella, which were fewer cells than recovered with 1.0 g l(-1) FeSO(4), yet greater populations than recovered with 50 mg l(-1) ethoxyquin. CONCLUSION: Supplementation of plating media with FeSO(4), TDP or sodium pyruvate enhanced recovery of sublethally injured Salmonella from albumen. SIGNIFICANCE AND IMPACT OF THE STUDY: Pasteurizing albumen impedes recovery of pathogens. These results suggest that the addition of supplements to plating media may assist resuscitation and colony development of heat-injured salmonellae.

Inactivation of salmonella on tomato stem scars by edible chitosan and organic Acid coatings.

This study was conducted to investigate the efficacy of antimicrobial coatings for inactivation of Salmonella on the surface of tomato stem scars. Scars were inoculated with a four-strain cocktail of Salmonella (serovars Montevideo, Newport, Saintpaul, and Typhimurium) and coated with acid-chitosan solutions. The chitosan coating with three acids (3A plus chitosan), the chitosan coating with one acid, and the three-acid solution without chitosan reduced the populations of Salmonella by 6.0, 3.6, and 5.3 log CFU per stem scar, respectively. Addition of allyl isothiocyanate (10 µl/ml) to the 3A plus chitosan coating did not significantly increase (P > 0.05) the antimicrobial efficacy. Although the populations of Salmonella in the controls (ca. 7.5 log CFU per stem scar) did not change significantly throughout the 14-day storage period at 10° C, Salmonella cells were reduced to undetectable levels (< 0.7 log CFU per stem scar) in the samples treated with 3A plus chitosan coating after two days of storage, and no growth was observed for the remaining storage period. Results from this study demonstrate that coatings of acid plus chitosan provide an alternative antimicrobial intervention for decontamination of tomatoes.

Performance of media for recovering stressed cells of Enterobacter sakazakii as determined using spiral plating and ecometric techniques.

A study was done to determine the performance of differential, selective media for supporting resuscitation and colony development by stressed cells of Enterobacter sakazakii. Cells of four strains of E. sakazakii isolated from powdered infant formula were exposed to five stress conditions: heat (55 degrees C for 5 min), freezing (-20 degrees C for 24 h, thawed, frozen again at -20 degrees C for 2 h, thawed), acidic pH (3.54), alkaline pH (11.25), and desiccation in powdered infant formula (water activity, 0.25; 21 degrees C for 31 days). Control and stressed cells were spiral plated on tryptic soy agar supplemented with 0.1% pyruvate (TSAP, a nonselective control medium); Leuschner, Baird, Donald, and Cox (LBDC) agar (a differential, nonselective medium); Oh and Kang agar (OK); fecal coliform agar (FCA); Druggan-Forsythe-Iversen (DFI) medium; violet red bile glucose (VRBG) agar; and Enterobacteriaceae enrichment (EE) agar. With the exception of desiccation-stressed cells, suspensions of stressed cells were also plated on these media and on R&F Enterobacter sakazakii chromogenic plating (RF) medium using the ecometric technique. The order of performance of media for recovering control and heat-, freeze-, acid-, and alkaline-stressed cells by spiral plating was TSAP > LBDC > FCA > OK, VRBG > DFI > EE; the general order for recovering desiccated cells was TSAP, LBDC, FCA, OK > DFI, VRBG, EE. Using the ecometric technique, the general order of growth indices of stressed cells was TSAP, LBDC > FCA > RF, VRBG, OK > DFI, EE. The results indicate that differential, selective media vary greatly in their abilities to support resuscitation and colony formation by stressed cells of E. sakazakii. The orders of performance of media for recovering stressed cells were similar using spiral plating and ecometric techniques, but results from spiral plating should be considered more conclusive.

Survival and growth of Enterobacter sakazakii in infant rice cereal reconstituted with water, milk, liquid infant formula, or apple juice.

AIMS: To determine survival and growth characteristics of Enterobacter sakazakii in infant rice cereal as affected by type of liquid used for reconstitution and storage temperature after reconstitution. METHODS AND RESULTS: A commercially manufactured dry infant rice cereal was reconstituted with water, apple juice, milk, or liquid infant formula, inoculated with a 10-strain mixture of E. sakazakii at populations of 0.27, 0.93, and 9.3 CFU ml(-1), and incubated at 4, 12, 21 or 30 degrees C for up to 72 h. Growth did not occur in cereal reconstituted with apple juice, regardless of storage temperature, or in cereal reconstituted with water, milk, or formula and stored at 4 degrees C. The lag time for growth in cereal reconstituted with water, milk, or formula was decreased as the incubation temperature (12, 21 and 30 degrees C) was increased. Upon reaching maximum populations of 7-8 log10 CFU ml(-1), in some instances populations decreased to nondetectable levels during subsequent storage which was concurrent with decreases in pH. CONCLUSIONS: Enterobacter sakazakii initially at very low populations can rapidly grow in infant rice cereal reconstituted with water, milk, or infant formula. SIGNIFICANCE AND IMPACT OF THE STUDY: Reconstituted infant rice cereal can support luxuriant growth of E. sakazakii. Reconstituted cereal that is not immediately consumed should be discarded or stored at a temperature at which E. sakazakii and other food-borne pathogens cannot grow.