Microbial Quality of Refrigerated Pre-cooked Products

July September 1996

Report prepared by Simon Rockliff, Geoff Millard

Samples collected and analysed by the staff at ACTGAL

1. OBJECTIVE

1.1 Survey was designed to determine microbiological status of a range of refrigerated pre-cooked products available on the ACT market.

2. Background

2.1 This product type has gained popularity over the past 5 years and because their primary preservation strategy is refrigeration they are considered high risk products which have the potential to cause foodborne illness. There are no Australia New Zealand Food Authority (ANZFA) Food Standard Code (FSC) for this non-frozen type of product.

2.2 During the period July to September 1996, 72 samples were purchased from eleven different establishments. Samples were purchased as consumer items over the counter by the ACT Government Analytical Laboratory (ACTGAL) staff and analysed by the ACTGAL Microbiology Unit.

2.3 The samples were assessed for indication of overall hygiene quality by the Standard Plate Count (SPC), Escherichia coli (E. coli) and coagulase-positive Staphylococcus (Coag+staph) analyses and for specific food pathogens such as, Clostridium perfringens (C. perfringens), Bacillus cereus (B. cereus), Listeria monocytogenes (L. monocytogenes) and Campylobacter spp.

2.4 24 samples collected before 6th August 1996 were not tested for B. cereus and Cl. perfringens. The unit decided to add these parameters to the survey after this date.

2.5 Table 1 gives the surveys acceptability criteria.

Table 1

 

Test Organism

Good

Poor

Unacceptable

SPC

<50–100,000

100,001–1,000,000

>1,000,000

E. coli

<2#

2–1000

>1000

Coag+Staph

<50#

50–1000

>1000

B.cereus

<50#

50–1000

>1000

C. perfringens

<50#

50–1000

>1000

L. monocytogenes

Not detected*

Detected

Campylobacter spp

Not detected*

Detected

 

# Units expressed in terms of Colony forming units (cfu) per gram. * Organism not detected in 25 gms.

3. Results

3.1 The samples consisted of lasagne, pasta, pasta sauces and other food products that are preserved by refrigeration and require minimal or no cooking prior to consumption i.e. dips. Table 2 shows the range of results for the organisms tested except SPC which are given by Table 3.

4 Discussion

4.1 From Table 2 it can be seen that no E. coli, Coag+staph, C. perfringens, L. monocytogenes or Campylobacter spp. were detected in any sample. B. cereus was detected in one sample at the level of 50 cfu/g. This level was not regarded as being significant.

Table 2

 

Test Organism

Range

L. monocytogenes

All samples <3#

E. coli

All samples <2#

Campylobacter spp

Not Detected in all samples*

B. cereus

<50–50#

Coag+Staph

All samples <50#

Cl. perfringens

All samples <50#

 

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

* Units expressed in terms of isolated/not isolated in 25 gms

Table 3

 

Standard Plate Count Range#

Number of samples in range

<50–100

25 (34.7%)

101–1000

6 (8.3%)

1001–10,000

10 (13.9)

10,001–100,000

4 (5.6%)

100,001–1,000,000

8 (11.1%)

1,000,001–10,000,000

6 (8.3%)

>10,000,000

13 (18.1%)

 

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

4.1 Samples with SPC counts greater than 1,000,000 cfu/g were regarded as being unacceptable. 19 (26.4%) samples fell into this category.

4.2 SPC levels of less than 1,000,000 cfu/g are not generally of concern as these products undergo some form of reheating prior to consumption. The following SPC trends could be noted from an analysis of the raw data:

  • curried dishes had in general low SPCs
  • no single manufacturer consistently had high SPC counts across all their products.

4.3 Apart from some samples having unacceptable SPC levels, the majority of the surveyed products were found to be of acceptable quality with few pathogens. No trend for certain products having unacceptable SPC levels could be determined from the raw results. The unacceptable SPCs could have arisen for a multitude of reasons including improper handling, storage at incorrect temperature, post processing contamination and inadequate cooking to name a few.

5. Conclusion

5.1 The results of this is survey indicate that most of the sampled Refrigerated pre-cooked products are microbiologically acceptable.