Pre-Packaged vs. Unpackaged Food Microbial Quality

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The main goal of the research was to examine the various types of microbial load on diverse samples of ready-to-eat food. It examined the microbial burden of fresh with canned and pre-packaged foods on the day of purchase and a week later. Fresh baby spinach, sliced salami, and sliced black olives were the three food items that were randomly selected and examined on days 0 and 7. Depending on the type of agar utilized, the concentration of the microbial load in these samples was determined to be variable. Also, gram staining technique was employed whereby on day 0, there was an observable yeast on olive (U) sample, on day 7 there was high amount of gram-positive rods in singles or cluster in spinach samples (U+P), gram-positive cocci in clusters on salami samples (U+P) and olive samples (U). Also, the gram-positive cocci in chains were seen in samples of spinach (P). Results from previous reviews showed that a microbial contamination was the primary factor leading to food borne outbreaks and recalls in Australia. Thus, it was vital to implement correct measures to ensure that packaging of the processed foods was at right calibre.

Key words: Microbial load, ready to eat food, samples, food borne, Australia, Unpackaged (U), Pre-packaged (P)


In recent years, many parts of the world, including Australia, have resorted to consuming ready to eat food (Vital, et al., 2014). It is attributed to consumption of minimal processed vegetables due to increased change in human lifestyle and other reasons that can be seen as laziness in human. However, it should be noted that contrary to their healthy and nutritional habits, there has been an increase in outbreak of human infections that are associated with eating of this food as many pathogens are easily being transmitted to human beings (Western Australian Food Monitoring Program, 2005). The primary sources of contamination are packaging containers. In addition, vegetables and fruits are more likely to be contaminated since slicing and cutting damages the natural barriers used to protect their intact, leading to the release of nutrients that are used in facilitating microorganisms' growth (Workneh, et al., 2012).

Literature reviews

The outbreak of diseases related to consumption of readymade food has shown an overwhelming increase in the past years. For instance, the Centre for Science, due to public demand, provided a report as shown by data obtained from CDC (Centre for Disease Control and Prevention), indicating that green vegetables were responsible for more than 363 outbreaks in addition to 13, 569 incidences of illness. For instance, in September 2006, 26 US states reported an outbreak of E. coli, leading to more than 20 cases of illness, besides causing three deaths. From the data, fresh spinach grown in California was the major cause of contamination (Jeddi, et al., 2014). Other reviews have indicated that Salmonella is a major cause of food borne diseases across the world. Its outbreak has also been linked to taking fresh fruits and vegetables (WHO, 2017).

Some of the driving forces for this study are built on the ground that microbial contamination is regarded as the main reason for the outbreak of food borne in Australia and this has been costing many factories lots of money. These effects have been studied on the ground that many consumers never take initiative to re-cook meals or take other measures that are aimed at killing or reducing the load of microbes. In this issue, it is clear that other measures as shown by other studies have taken place to ensure the safety of processed meals. For instance, packaging is the main means of controlling food borne pathogens by preventing the growth of microbes through prevention against moisture and atmospheric oxygen and protection of food against microbial contamination (Hanning, et al., 2009). Thus, the study will determine if the packaged meals are safer than unpackaged meals. It will aim at providing measures that need to be increased and others, if already, exist to be improved. It is noticeable that this case is not only affecting Australia, but also other countries.

Material and method

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A total of three ready to eat meals that were put into two different conditions, that is, pre-packaged and unpackaged, namely Spinach (U+P), Salami(U+P) and Olive (U+P) from both open markets and supermarket were analysed for the presence of microbial load using culture techniques in day 0 from purchase and day 7 after purchase. From the analyses, in day 0, Salami (U) had a high level of microbe's contamination that was analyzed by PCA, having cfu/g of 3.50E+04. The second highest level of microbe's contamination was seen in Olive (U) under the same agar with 3.20E+04 cfu/g. Salami (P) had 1.40E+05 cfu/g followed by Spinach (U) with 1.20E+05 cfu/g and lastly Spinach (P) with 9.00+04 cfu/g. The level of microbes exposed in Olive (P) was minimal, thus not able to detect. On the same 0 day, the analysis done via McConkey reveals that, the highest level of microbes were detected in Salami (U), having a cfu/g of 6.40E+05, followed by Salami (P) with cfu/g of 9.70E+04. The other microbial loads were detectable in Spinach (U) with a cfu/g of 5.40+04 and Spinach (P), having a cfu/g of 5.30E+04. Both Olive (U+P) had no detectable microbes under this agar. When the same samples were treated under OGYE agar, the level of microbes was only detectable in Olive (U) with a cfu/g of 3.10E+04. On the same day, under a negative controlled experiment, there were no colonies.

The table above shows the microbial load collected on day 0

The graph above is a representation of different loads of microbes on day 0.

On day 7, when the analyses was done with similar samples that were preserved in a fridge, the results were as follows; under PCA agar, Salami had a high cfu/g of 2.25E+06, followed by Salami (U) with a cfu/g of 2.21E+06. Spinach (P) had a cfu/g of 1.05E+06 and Spinach (U) had a cfu/g of 1.48E+05. Both Olive had low load of microbes with (P) having 1.00E+05 and (U) having 5.00E+03. When the sample were treated with McConkey agar, Spinach (P) had cfu/g of 2.28E+06, Salami (P) had a cfu/g of 1.60E+06, Salami (U) 1.11E+06, Spinach (U) had 4.50E+05, Olive (P) had a cfu/g of 1.00E+04 and Olive (U) had a cfu/g of 0.00E+00. When the samples were treated under the OGYE agar, it had minimal loads. For instance, (P) had a cfu/g of 1.44E+05, Salami (U) had 1.00E+05, Olive (U) had a cfu/g of 2.90E+04, and then the Spinach (U), Olive (P) and Salami (P) had minimal value of microbes, thus, not detectable.

The table above shows the quality of loads collected on day 7

The graph above is a representative of microbes load collected on day 7.

Further study using gram staining technique indicated other characters that can be used for further profiling as culturing alone cannot be sufficient to tell which bacteria were present in the samples. For instance, from gram staining, on day 0, olive (U) had yeast. Both spinach samples (U+P) had gram-positive rods either in singles or in clusters. Both samples of salami (U+P) and olive (U) samples had gram-positive cocci in clusters. In addition, spinach (P) had gram-positive cocci in chains.

The photos above are representative of gram staining technique


The high rate of consuming ready to eat produce has led to rapid growth of industry. However, this sector is facing emerging challenges that are calling for attention and action, for instance, consumer protection against food borne microbes. Vegetable and fruit contamination is series that can occur due to complex and mixed factors such as processing, harvesting or during growth. Predisposing factors that are responsible for entry of microbes might include, but not limited to; cuts, stem scar, punctures and split. In many countries across the globe, there is an increasing alarm in regard to food borne disease, linking fruits and vegetables (Chen, et al., 2012).

From this study, it can be deduced from the first day that unpackaged salami had a high amount of pathogens than other ready to eat meals studied here. These factors can be attributed to the fact that at first it was open, allowing microbes to penetrate. Also, pathogens can be from contaminated hands of the seller. Salami being a fermented food, it has meats that can provide a conducive environment of growth for microbes ( Ministry for Primary Industries , 2015).

After preservation and further analysis on day 7, the results indicated across the agar that pre-packaged meals were more contaminated than unpackaged ones. Thus, the study can be interpreted to mean that high temperature increase contamination of pre-packaged meals as compared to unpackaged ones.

On day 0, samples analysis revealed that gram positive bacteria were more. However, after preservation, day 7 indicated high growth of gram-negative bacteria. It is depicted more by the high loads of microbe's inMcConkey agar, which has the ability to inhibit growth of gram positive and encourage rapid growth of gram negative. In this case, it can be seen that yeast and Enterobacteriacea were present in the samples.

Over the entire study, the level of microbes in olives maintained low loads due to the fact that as microbes underwent their normal excretion, they accumulated high levels of lactic acid, leading to low pH. From the study, it is clear that there is a consistent growth of loads in pre-packaged meals than unpackaged ones. Therefore, it is worth to say that contamination of food is more rampant when packing. However, this is a mixed situation that leads to such an occurrence.


Since the sample of study in this survey was minimal, the report cannot conclude that the cause of food contamination comes from packaging of meals, more so vegetables. It is vital to note that these meals are subjected to many conditions that can lead to contamination. The treatment and preservatives used cannot assure the consumer that the meals are okay and fit for consumption.


The researcher recommends that more techniques be employed in future studies, for instance, the use of real time PCR to facilitate profiling and identification of specific organisms in the sample. The experiment was limited to only two techniques that do not guarantee reality of contamination. Also, the test of pathogen should be timely. Thus, the study should commence once the meals are supplied to the markets and supermarkets. There is a need to test the loads of pre-packaged meals verses unpackaged meals throughout their shelf-life. Lastly, future studies should be in a position to test the produce from the farmer and food brought to the market to determine the various load concentrations.


Ministry for Primary Industries , 2015. Microbiological survey of pre-packaged leafy salads available at retail in New Zealand, WELLINGTON 6140 : Ministry for Primary Industries .

Chen, J. H. et al., 2012. Intervention Technologies for Ensuring Microbiological Safety of Meat: Current and Future Trends. Comprehensive reviews in food science and food safety, 11(2), p. 119-132.

Hanning, I., Nutt, J. & Ricke, S., 2009. Salmonellosis outbreaks in the United States due to fresh produce: sources and potential intervention measures. Journal of foodborne pathogen and disease, 6(6), pp. 635-48..

Jeddi, M. Z. et al., 2014. Microbial Evaluation of Fresh, Minimally-processed Vegetables and Bagged Sprouts from Chain Supermarkets. Journal of Health Population and Nutrition, 32(3), p. pp 391-399.

Vital, P. G., Dimasuay, K. G. B., Widmer, K. W. & Rivera, W. L., 2014. Microbiological Quality of Fresh Produce from Open Air Markets and Supermarkets in the Philippines. The Scientific World Journal, 2014(219534), pp. pp 1-7.

Western Australian Food Monitoring Program, 2005. Microbiological Quality of Fruit And Vegetables Inwestern Australian Retail Outlets. [Online]

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[Accessed 11 Oct 2017].

WHO, 2017. Salmonella (non-typhoidal). [Online]

Available at:

[Accessed 11 Oct 2017].

Workneh, T. S., Osthoff, G. & Steyn, M., 2012. Effects of preharvest treatment, disinfections, packaging and storage environment on quality of tomato. Journal of food scince and technology, 49(6), p. 685-694.

April 13, 2023

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