Masters Theses

Date of Award

5-2003

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

David A. Golden

Committee Members

P. Michael Davidson, John R. Mount

Abstract

This study was conducted to evaluate the effect of various sanitizing treatments applied to cantaloupe rinds on survival of Salmonella. A five-strain cocktail of nalidixic acid resistant Salmonella was inoculated (~ 6 log cfu/cm2) onto the rinds of whole cantaloupes, which were then treated with tap water (control), chlorine dioxide solution (100 and 200 ppm for 30, 60 and 90 sec), peroxyacetic acid solution (40 and 80 ppm for 45, 90 and 150 sec), dimethyl dicarbonate solution (1000, 5000, and 10,000 ppm for 3 min), ozonated water (~1.66 ppm for 1, 2, 3, and 4 hours), steam pasteurization (85°C for 2, 4, 6 and 8 min), and a combination of steam pasteurization/ozonated water (30 sec/20 or 40 min and 60 sec/20 min or 40 min). Excised pieces of cantaloupe rinds (25 cm2) were pummeled in 50 ml DE broth, serially diluted in 0.1M phosphate buffer, and surface plated onto tryptic soy agar containing 50 ppm nalidixic acid (TSAN) or bismuth sulfite agar containing 50 ppm nalidixic acid (BSAN). Survival of the pathogen was reduced by all treatments (P < 0.05) as compared to initial and control populations. Substantial portions of the surviving Salmonella population were sublethally injured by treatments as indicated by reduced recovery on BSAN. Therefore, survival data that follow represent recoveries on TSAN. Chlorine dioxide (90 sec at 200 ppm) reduced Salmonella populations from 6.22 to 3.72 log cfu/cm2 . However, use of 100 ppm chlorine dioxide (up to 90 sec) was not significantly better than tap water (P < 0.05). After just 45 sec at 40 ppm, peroxyacetic acid reduced the Salmonella population from 6.99 to 4.43 log cfu/cm2, while longer treatment times and higher concentration (80 ppm) of peroxyacetic acid were no more effective. Treatment of cantaloupes for three minutes with 10,000 ppm dimethyl dicarbonate reduced the population of Salmonella from 5.01 log cfu/cm2 to undetectable levels. Populations of Salmonella on cantaloupes treated with ozonated water (~1.66 ppm ozone) were reduced by only 3.12 log cfu/cm2 after one hour of treatment. Slightly greater reduction occurred after ozone treatment for up to four hours, the differences were not significantly greater. Surprisingly, reductions caused by ozone and air were not significantly different, suggesting that active aeration has a substantial oxidative, destructive effect on viable Salmonella. Despite the relatively poor overall reduction in Salmonella populations by ozone after four hours, the treatment did cause substantial sublethal injury as indicated by the inability to detect the organism recovery on BSAN after ozone treatment for three hours. Steam pasteurization of cantaloupes significantly reduced Salmonella populations, from 5.36 to 1.70 log cfu/cm2, after only two minutes of treatment. Steam treatments did not result in an increase in the internal temperature of cantaloupes. The combination of steam pasteurization and ozone treatment was quite effective at reducing Salmonella populations on cantaloupes. Treatment of cantaloupes with steam for 30 sec followed by ozone treatment for 20 minutes reduced Salmonella populations from 5.50 log cfu/cm2 to undetectable levels. The observation that the steam/ozone combination effectively reduced Salmonella populations suggests that additional hurdles may provide a complete elimination of Salmonella populations on cantaloupes, while allowing for reduced intensity of individual treatments.

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