A practical procedure for the determination of safe shelf life of chilled, ready to eat cooked meat products

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Project acronym: GVOP-3.1.1.-2004-05-0152/3.0
Duration: Jan 2005 - Oct 2006
Funded by: National project (Hungary)
Website: www.campden.hu/projekt

Coordinator: Campden BRI Magyarország Nonprofit Kft. Hungary

Contact: Dr. András Sebők, Dr. Erika Horváth, Csaba Baár Campden BRI Magyarország Non-profit Kft, Budapest, 1096 Haller utca 2. Email: (a.sebok@campdenkht.com), Phone: +3614331470; Fax: +3614331480

1. Context and problematic

By the regulation (EC) 2073/2005 food business operators are responsible for the determination of safe shelf life at the reasonably foreseeable conditions of distribution, storage and consumer use. At ready-to-eat products supporting the growth of Listeria monocytogenes the critical limit of 100 cfu/g must not be exceeded during the shelf life. In many cases companies establish the safe shelf life of their ready- to-eat products on the basis of testing the changes of the microbiological and sensory properties of samples taken from the production stored at relatively low (+ 5-8°C), constant temperatures and don’t consider the temperature deviations during the steps of distribution till the consumption. This method provides information on the change of the spoilage organisms but it is not appropriate for evaluation of the growth of the pathogens which may be present only incidentally, can grow at low (3-8°C) temperatures and their growth is not associated with the change of the sensory properties. Shelf life is usually designed for proper food chain and consumer practices. However false practices are frequent and consumers’ decision about the safety is generally based on visual observation of the spoilage free or discoloration free status of the products. Although there are sophisticated methods based on challenge tests at variable storage temperature regimes, but the majority of the companies, particularly SMEs find difficult to carry out such tests. A simple method was developed for screening the products for safe shelf life by comparing the results of predictive microbiological modelling to shelf-life gained from traditional storage tests and limit the use of the more sophisticated methods for those cases where the simpler method shows a significant uncertainty. This new method can be used for chilled ready-to-eat cooked meat products and other chilled ready-to-eat foods and for assessment of risk of pathogens and quality changes at realistic cold chain conditions.

2. Results and Applications

A procedure was developed for establishing the safe shelf life of ready to eat (RTE) cooked meat products. It was established that variations in the water activity, salt, pH and nitrate content can result in 30-50 % reduction of safe shelf life calculated by the Growth Predictor predictive model at the worst case scenario compared to the standard average composition. The product temperatures in retail cabinets and domestic refrigerators may be relatively high. The highest average product temperature measured in the domestic refrigerators during summer was: 7.2°C ± 3.1ºC. In more than 74% of the cases the temperature was higher than 5ºC; in 33% of the cases the temperature was higher than 8ºC. The average temperature of retail cabinets was 6.6°C ± 2.4ºC. In 60% of the cases the temperature was higher than 5ºC and in 15% of the cases the temperature was higher than 8ºC. The typical temperature profile for a cold chain in Hungary was established as follows.

Wiki tabl.JPG

Temperature has a large impact on safe shelf-life. Challenge tests showed significant reduction of safe shelf-life when the samples were stored at 8°C compared to 5°C: for turkey ham 26% for vacuum packed and 22% for modified atmosphere packaging (MAP), at turkey rolled ham 40% for vacuum packed, for wieners 0- 3% for vacuum packed, and for Bologna sausages 73% for vacuum packed and 74% for MAP and 67% for vacuum packed and 53% for MAP products when the samples were stored at the fluctuating temperatures of the typical cold chain.

MAP (30% CO2: 70% N2) showed an inhibition effect compared to vacuum packing at Bologna sausages and ham in challenge tests. Based on the result of risk profiling and Monte-Carlo simulation handling/ storage in retail cabinets and household refrigerators had the largest impact on safe shelf life. False consumer practices (top shelf of refrigerators, where the temperature was the highest, is preferred by consumers for storage of meat products; 50-60% of consumers are neglecting the use by date on the packaging) are frequent partly because of the low awareness of potential growth of pathogens.

How the new solution works

The procedure for establishing of safe shelf life of RTE cooked meat products is the following:

1. Define the variation of the intrinsic properties of a product.
2. Carry out predictive modelling for the worst case scenario for composition at constant temperature, which has an equivalent impact to the real cold chain on the growth of L.monocytogenes (at 8.5°C for Hungary for cooked cold meat) and calculate the predicted safe shelf-life (TS).
3. Carry out a traditional shelf life test at the typical times- temperatures of the cold chain. This gives quality based shelf-life (TQ).
4. If TQ < TS accept. If TQ > TS challenge tests have to be carried out.

For its application only a freely available, industry user friendly predictive microbiology software and a domestic refrigerator with adjustable temperatures is necessary in addition to the usual storage test facilities.

3. Novelties, benefits and added value

By the use of this simple procedure it can be established whether the result of traditional storage testing of a regular ready-to-eat cooked meat product can be accepted as the safe shelf life or further challenge testing is necessary. The impact of the fluctuating temperatures of a realistic cold chain and false consumer practices are also taken into consideration. With the new stepwise screening approach the number of necessary challenge tests can be reduced. This will save efforts and costs.

4. Successful applications, success stories

The method has been applied by a large cooked meat manufacturer in Hungary. The method was further developed for application for naturally fermented air-dried non-heat- treated traditional meat products.

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