Title page for ETD etd-08062003-173925

Type of Document Master's Thesis
Author Ramasamy, Thilahavathy
Author's Email Address tramasam@vt.edu
URN etd-08062003-173925
Title Fate of Foodborne Pathogens During Osmotic Dehydration and Subsequent Storage of Apples.
Degree Master of Science
Department Food Science and Technology
Advisory Committee
Advisor Name Title
Williams, Robert C. Committee Chair
Eifert, Joseph D. Committee Member
Sumner, Susan S. Committee Member
  • E. coli O157:H7
  • osmotic dehydration
  • apple
  • calcium chloride
  • Salmonella
Date of Defense 2003-07-24
Availability unrestricted

The fate of E. coli O157:H7 and Salmonella spp. during osmotic dehydration of apples was determined at different processing temperatures, times and calcium chloride (CaCl2) concentrations. Apple slices were inoculated to achieve an 8 log CFU/ apple slice concentration of a five strain mixture of E. coli O157:H7 or Salmonella spp. and were soaked in sucrose solutions (60% w/w). In the first study, apple slices were subjected to osmotic dehydration at three different temperatures: 20°C, 45°C and 60°C. In a second study, CaCl2 was added in the sucrose solution at concentrations of 2%, 4% and 8% to determine its efficacy as an antimicrobial agent. The storage effect of osmotic dehydrated apples on pathogen survival was also tested for seven days at 4°C.

Samples were withdrawn at appropriate time intervals, diluted with 0.1% peptone water and surface plated onto recovery media. Recovery of E. coli O157:H7 was compared on Tryptic Soy Agar + 50 ppm nalidixic acid (TSAN) and MacConkey Sorbitol agar (MCS). Recovery of Salmonella was compared on TSAN and XLD agar.

There was lower microbial reduction at the lower temperatures tested with approximately 1.0 and 3.0 log CFU/apple slice reduction at 20°C and 45°C, respectively. The population reduction of cells was highest at 60°C, with an approximate five log reduction for both microorganisms (P<0.001). CaCl2 used as an additive in the osmotic solution, was associated with slightly higher reduction of both E. coli O157:H7 and Salmonella spp. Greater than a 5 log reduction was observed when the combination of CaCl2 (8%) and 60°C processing temperature was used. During refrigerated storage E. coli O157:H7 and Salmonella decreased by approximately 4.5 log CFU/apple slice, but were still recoverable via direct plating at Day seven.

The results of this study show that the survival of E. coli O157:H7 and Salmonella in osmotically dehydrated fruit is influenced by the osmotic processing method used and the level of additive (i.e., CaCl2) utilized. Parameters associated with decreased survival of pathogens, and therefore, improve product safety, include increasing temperature and time of processing and increasing concentration of CaCl2. However, E. coli O157:H7 and Salmonella in artificially contaminated apple slices, survived osmotic dehydration processing and subsequent storage under processing and storage parameters of this study. Therefore, processors who produce osmotically dehydrated fruit must consider the potential food safety impact of the osmotic dehydration processes they choose.

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