vacuum packaging of meat products

4
504 Table 1. Vacuum packaging of fresh meat. Antonie van Leeuwenhoek 48 (1982) Application in the Netherlands Beef about 25~ Pork less than 5~ Advantages Stable colour of myoglobine (blue meat) No drying loss Increased ripening-tenderness (beef) Keepability about 4 weeks (beef) as a result of: a) absence of oxygen b) accumulation of carbon dioxide Disadvantages Relative dark colour of myoglobin Some purge formation in the pack High-graded expensive packing material Short keepability of pork For packing of retail meat at present gas mixtures are applied consisting of carbon dioxide to retard the growth of gram-negative bacteria and oxygen to stabilize the meat colour. On the meat in these packs gram-positive bacteria, especially Brochothrix thermosphacta, grow most rapidly and, thus, dominate the microfiora. The keepability of gas-packed meat is about 5-6 days against 2-3 days for retail meat that is normally packed in PVC stretch film. In practice, the costs of gas are negligible, whereas the costs of the packaging materials are rather high. Moreover, there are some objections to the new method on the part of the consumers. For these reasons gas packing of fresh meat is as yet not applied on a large scale in the Netherlands. Vacuum packaging of meat products H, LABOTS Institute CIVO-Technology TNO, Department Netherlands Centre for Meat Technology, Utrechtseweg 48, 3704 HE Zeist, The Netherlands The most important processing factors for the preservation of meat are salt and heat treatment. The keeping quality and safety of the raw/ripened products depend mainly on the salt content, while that of the heat-treated products depends on both heating and salt content. Besides these factors nitrite plays an important role and sometimes a lowered pH. Raw or ripened meat products such as fermented sausages and raw ham have a decreased water activity and/or pH and are only susceptible to mould growth. Since moulds cannot develop in a vacuum pack, raw or ripened vacuum-packed products possess a good microbiological stability.

Upload: h-labots

Post on 10-Jul-2016

220 views

Category:

Documents


4 download

TRANSCRIPT

Page 1: Vacuum packaging of meat products

504

Table 1. Vacuum packaging of fresh meat.

Antonie van Leeuwenhoek 48 (1982)

Application in the Netherlands Beef about 25~ Pork less than 5~

Advantages Stable colour of myoglobine (blue meat) No drying loss Increased ripening-tenderness (beef) Keepability about 4 weeks (beef) as a result of:

a) absence of oxygen b) accumulation of carbon dioxide

Disadvantages Relative dark colour of myoglobin Some purge formation in the pack High-graded expensive packing material Short keepability of pork

For packing of retail meat at present gas mixtures are applied consisting of carbon dioxide to retard the growth of gram-negative bacteria and oxygen to stabilize the meat colour. On the meat in these packs gram-positive bacteria, especially Brochothrix thermosphacta, grow most rapidly and, thus, dominate the microfiora. The keepability of gas-packed meat is about 5-6 days against 2-3 days for retail meat that is normally packed in PVC stretch film.

In practice, the costs of gas are negligible, whereas the costs of the packaging materials are rather high. Moreover, there are some objections to the new method on the part of the consumers. For these reasons gas packing of fresh meat is as yet not applied on a large scale in the Netherlands.

V a c u u m p a c k a g i n g o f m e a t p r o d u c t s

H, LABOTS

Institute CIVO-Technology TNO, Department Netherlands Centre for Meat Technology, Utrechtseweg 48, 3704 HE Zeist, The Netherlands

The most important processing factors for the preservation of meat are salt and heat treatment. The keeping quality and safety of the raw/ripened products depend mainly on the salt content, while that of the heat-treated products depends on both heating and salt content. Besides these factors nitrite plays an important role and sometimes a lowered pH.

Raw or ripened meat products such as fermented sausages and raw ham have a decreased water activity and/or pH and are only susceptible to mould growth. Since moulds cannot develop in a vacuum pack, raw or ripened vacuum-packed products possess a good microbiological stability.

Page 2: Vacuum packaging of meat products

Antonie van Leeuwenhoek 48 (1982) 505

Cooked products, e.g. cooked ham, liver sausages and luncheon-meat type products, that have been heated to an internal temperature of 65-70'~C in closed containers or impermeable synthetic casings, have a fairly good microbiological stability as long as the impermeable packing is not opened or removed. Many cooked meat products, however, are processed in re-usable containers and re- packed in vacuum bags. These products are contaminated during handling and bacterial develop- ment between packaging material and meat-product surface will occur during storage. The results of a limited survey of vacuum-packed, cooked meat products are presented in Fig. 1.

The microflora on the surface of these products mainly consists of lactic acid bacteria and, to a somewhat lesser degree, of Brochothrix thermosphacta. The same microflora is present on sliced, vacuum-packed, cooked meat products (Fig. 2) (Labots and Mulder, 1977; Egan et al., 1980). When a fermentable carbohydrate is used as an ingredient this flora might cause a significant pH-drop during storage, even at low temperatures (Labots and M ulder, 1977; Stiles and Ng, 1979). Sometimes heterofermentative lactic acid bacteria become dominant, causing the package to be blown. The presence of very active H2Oz-producing strains results in greening of the surface after the package has been opened. However, in general, products are still organoleptieally acceptable, even when the lactic acid bacteria have reached levels of 10 ~ bacteria per cm 2 or g (Egan et al., 1980).

Development of Enterobacteriaceae (Akerstrand and Norberg, 1980) does not occur unless the brine content (% salt in the water phase of the product) is low (Fig 3). When these products are not kept under refrigeration, Enterobacteriaceae may reach the 106-level in a few days.

For repression of Enterobacteriaceae the salt level is very important, while nitrite is active too. Air leaks in vacuum-packed products promote the development of Enterobacteriaceae as well

as of yeasts. The synthetic films used for vacuum-packaging should have a very low oxygen perme- ability.

Freshly sliced, cooked meat products sold in retail shops prepared from cooked sausages or vacu- um-packed meat products contain high numbers of lactic acid bacteria and B. thermosphacta, some- times high numbers of Enterobacteriaceae and yeasts (Akerstrand and N orberg, 1980). The presence of these groups can be explained by the use of vacuum-packed pieces of meat products, partly with low salt contents, and cross-infection during slicing. The presence of large numbers of yeasts might be an indication of insufficient cleaning of tables and slicing machines.

Vacuum-packed cooked meat products with a normal salt content (about 2%) and a normal nitrite content, prepared according to good manufacturing and distribution practice, have a good safety record (Stiles and Ng, 1979).

N

40-

30 ]

20- , J

10- J

r ! O- f

01~1 212 3~3 4~4 5'5 6~6 7 ~78~8_9 log ( standard plate count/cm 2 )

Fig. 1. Distribution of the standard plate count per cm 2 of the surface of vacuum-packed, cooked meat products.

Page 3: Vacuum packaging of meat products

506 Antonie van Leeuwenhoek 48 (1982)

IogN

9-

8- e / o

6-

5-

4-

3-

2-

1- X .-----'=x'~-x

o ~ e standard plate count ll~m B.lhermosphacta

X ~ X Enterobacteriaceae

6 1~ 2~ days

Fig. 2. Average bacterial numbers (log N) of vacuum-packed, sliced, cooked meat products from 5 industrial meat packers, stored at 7 ~

log N

9-7

6-

7 ~

6-

5-

4-

3-

2-

I -

Roasted minced meat ( brine percentage 4.3]

m ~ u

X 'X

I I

Cooked shoulder ( brine percentage 2.8 )

log N

' X X /

I I I f

weeks weeks

I I ultimate freshness date s,---,,,e standard plate count

I - - I B. thermosphacto X - - X Enterobocterioceae

Fig. 3. Bacterial numbers per g of vacuum-packed, sliced meat products during storage at 7 ~

AKERSXRAr~O, K. and NORBER6, P. 1980. F6r l~nga h~.llbarhetstider f6r f6rpackad sm6rghsmat. - - V~tr F6da 32: 402408.

EGAN, A. F., FaRo, A. L. and Sr~nY, B. J. 1980. A comparison of Microbaeterium thermosphaetum and lactobaci]li as spoilage organisms of vacuum-packaged sliced luncheon meats. - - J. Food Sci. 45: 1745-1748.

Page 4: Vacuum packaging of meat products

Antonie van Leeuwenhoek 48 (1982) 507

LABOTS, H. en MULDER, S. J. 1977. Vacuiim verpakte gesneden vleeswaren. - - Vleesdistributie Vlees- technol. 13: (l) 28-31; (2) 6-8.

STILES~ M. E. and NG, L. K. 1979. Fate of pathogens inoculated onto vacuum-packaged sliced hams to simulate contamination during packaging. - - J. Food Prot. 42: 464-469.

Factors affecting the shelf life of chilled poultry: packaging and storage temperature

R. W. A. W. MULDER

Spelderholt Institute for Poultry Research, Ministry of Agriculture and Fisheries,

Spelderhoh 9, 7361 DA Beekbergen, The Netherlands

The change-over from the production of deep-frozen eviscerated poultry to chilled eviscerated poultry has renewed people's interest in factors affecting the shelf life of these products. In this paper, shelf life is only defined by microbiological criteria. Recent literature data on effects of pack- aging are lacking, only some very specific applications being mentioned.

Chilled eviscerated poultry is that slaughtered poultry, which is stored and sold at temperatures not below - 1 ~ The scalding temperature during the slaughtering process is mostly below + 55 ~ With this temperature the epidermis of the carcasses remains unimpaired after the plucking process and protects the carcasses against untimely spoilage and drying-out.

Shelf life of chilled eviscerated poultry is of interest to processors, retailers and consumers. Many data on shelf life in general are known (Erdtsieck, 1975; Mulder, 1975; Ito and Bee, 1980). For comparison, however, it should be known which microbiological criteria were used in the various

i ~i 20

14 ~:�9

8 ": . : :

6 �9 e e ~ ~ e �9

2 �9

0 -'1 ~ ~ 1~ 1'~ Temperature (~

Fig. 1. Shelf life of chilled poultry (from Erdtsieck, 1975).

2'o