Examination of the microbial load of a sample of sandwiches following incubation at 20C for 4 hours'

1
Examination of the microbial load of a sample of
sandwiches following incubation at 20C for 4
hours. Potential food safety issues for
childrens pack lunches. Lesley Brown
Fig. 2

• 2. Method
• 4 sandwich types, egg cress, ham, tuna . S.
  corn and meatspread cucumber underwent
  microbial analysis pre and post 4 hours
  incubation at 20C. Repeated on 4 independent
  occasions.
• Sandwiches were examined for aerobic colony
  count, S. aureus and Listeria spp.
• Guidelines for retail food by Gilbert et al.
  (2000) were used to assess microbiological
  quality pre and post incubation.
• A paired sample t test (CI 95) to test
  hypothesis of no difference in aerobic colony
  counts following incubation for 4 hours at 20C.

• Fig.1 Pre incubation, 94 of sandwiches were
  satisfactory for aerobic colony count (lt106
  CFU/g). 88 satisfactory post incubation. The
  remainder were acceptable (106-lt107 CFU/g).
• Fig.2 18.75 increase in numbers of sandwiches
  unsatisfactory for Listeria spp. and/or S. aureus
  following incubation at 20C for 4 hours.
• Paired sample t test Result t(15)
  1.325pgt0.05.
• 4. Conclusion
• There is no significant difference in aerobic
  colony count following incubation at 20C for 4
  hours (Pgt0.05) However, all sandwich types are
  vulnerable to contamination from Listeria spp.
  and/or S. aureus due to ingredients, handling and
  time/ temperature abuse. Reference. Gilbert et
  al. (2000) Guidelines for the microbiological
  quality of some ready to eat foods sampled at the
  point of sale. Communicable disease Public
  health 3(3)163-167.

3. Results

• 1. Introduction
• Sandwiches predominate as the popular food
  choice within the pack lunch box.
• Previous studies have recorded temperatures
  within lunchboxes in excess of 27C. On average
  sandwiches are prepared 4 -5 hours prior to
  consumption,
• There is a risk of contamination during
  preparation, from ingredients, handling and
  time/temperature abuse.
• Sources of contamination include Listeria spp.
  and S. aureus
• Listeria spp. is common in the environment and
  may indicate presence of pathogenic L.
  monocytogenes.
• S. aureus is one of the commonest organisms to
  contaminate food due to inhabitation of , nose,
  throat and skin.

Fig 1.