Microbiological Quality of Unrefrigerated Desserts - 1999

April - June 1999

Report prepared by Geoff Millard

Objective

This survey was designed to determine the microbiological status of Unrefrigerated Desserts eg tarts, cream buns, custard croissants available in the ACT. A previous survey conducted in 1997 identified microbiological problems with certain dessert products.

Background

Unrefrigerated Desserts are stored at room temperature and widely available in the ACT. A previous survey of Unrefrigerated Desserts conducted between January and March 1997 highlighted some problems with handling, storage and/or cross contamination. A comparison with the previous survey will be made, however the 1997 survey design differed from the 1999 survey in that sampling in 1997 included an investigation into an unsatisfactory dessert product.

Standards

The Australia New Zealand Food Authority (ANZFA) Food Standards Code has no standards for these products.

Survey

Between April and June 1999, the ACT Government Analytical Laboratory (ACTGAL) collected seventy-two samples from thirty-nine different establishments. Samples were purchased as consumer items over the counter by ACTGAL staff and analysed by the Microbiology Unit. The samples (51 types) covered the available range of Unrefrigerated Desserts available from supermarkets, food-halls, delicatessens, bakers and other food outlets. Establishments were only visited once with a number of different deserts being collected at the time. All of the samples were assessed for overall hygiene quality by a Standard Plate Count (SPC) and Escherichia coli (E. coli) and for the specific pathogens Coagulase-positive Staphylococcus (Coag+staph), Bacillus cereus (B. cereus) Listeria monocytogenes (L. monocytogenes) and Salmonella sp.

Table of acceptability criteria for the 1997 survey prepared by Microbiology Unit.

Table 1 Acceptability criteria

 

Test Criteria

Good

Poor

Unacceptable

SPC #

<50 – 10,000

10,001 – 1,000,000

>1,000,000

E. coli #

<3

2 –1000

>1000

Coag+staph #

<50

50 –1000

>1000

B. cereus #

<50

50 – 1000

>1000

Salmonella sp.*

Not detected

Not detected

Detected

 

# Results expressed in terms of Colony forming units (cfu) per gram.

* in 25 grams of sample

These criteria will be used to compare the results of the current survey with the results of the 1997 survey.

Results

Standard Plate Count

Counts were obtained for 70 of 72 samples collected. Counts were not obtained from two of the samples due to spreading organisms.

Graph 1

 

SPC distrubution graph

The median value was determined as 5000 cfu/g. Eleven (15.7%) samples had an SPC greater than 1,000,000 cfu/g, seven (10.0%) had an SPC greater than 10,000,000 cfu/g. One (1.4%) sample had an SPC greater than 100,000,000 cfu/g. (See Graph 1).

Escherichia coli

E. coli was not detected in any of the 72 samples tested.

Coagulase Positive Staphylococcus

Coagulase-positive Staphylococcus was detected in five (6.9%) of 72 samples tested, with a range of 200 cfu/g to 30,000 cfu/g and a median of 550 cfu/g.

B. cereus

B. cereus was detected in five (6.9%) of the 72 samples with a range of 100 cfu/g to 100,000 cfu/g and a median of 1700 cfu/g.

Listeria monocytogenes

Listeria monocytogenes was isolated from one (1.4%) of the 72 samples tested for this organism.

Salmonella

Salmonella was not detected in any of the 72 samples tested.

Discussion

Table 2: Comparison of 1997 and 1999 results

 

Test Criteria

Good %

Poor %

Unacceptable %

YEAR

1997

1999

1997

1999

1997

1999

SPC

34

61.4

37

22.9

29

15.7

E. coli

90

100

9

0

1

0

Coag+staph

97.1

93

2.9

5.6

0

1.4

B. cereus

78

93

10.3

2.8

11.7

4.2

Salmonella sp

100

100

0

0

0

0

 

The SPC and B. cereus counts in the 1997 survey were skewed because of the repeat sampling of a specific food type (vanilla slice) from a number of retail outlets. This repeat sampling was due to previous unsatisfactory results. In the 1997 survey 38.2% of the samples consisted of vanilla slice, whereas in the 1999 survey this particular food type represented only 8.3% of the samples tested. If the percentage of vanilla slices in the 1997 survey were adjusted to the 1999 level by the random removal of 22 samples, the data for SPC and B cereus results would read as illustrated in table 3 which are similar to the 1999 results for these organisms.

Table 3 Adjusted 1997 data

 

Test Criteria

Good %

Poor %

Unacceptable %

SPC

40

24.5

35.5

B. cereus

86.6

6.7

6.7

 

From a comparison of Tables 2 and 3;

  • The SPC showed significant improvement particularly in the "Good" category having a 53.5% improvement.

The 1999 E. coli results were a 10% improvement over the 1997 survey and all samples were rated as "Good".

  • The pathogen Coagulase positive Staphylococcus deteriorated slightly from 97% to 93% for the "Good" category.
  • The pathogen L. monocytogenes was not looked for in the 1997 survey. It was however detected in one sample in 1999. While this is a low isolation rate it is of some Public Health concern that this pathogen was isolated from this food type.

Anecdotal evidence suggests that restaurants are changing their storage practices for these products with a move to storing them under refrigeration. On the other hand bakeries are not following this trend. The move to storing cream, custard based desserts under refrigeration would improve their microbiological quality and shelf life.

Conclusion

This survey has identified that while the microbial quality of unrefrigerated desserts in the ACT has improved they still have the potential to be a risk to the publics health.

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Microbiological Quality of Unrefrigerated Desserts