PACKAGING TECHNOLOGY AND SCIENCE VOL 7 61-63 (1994)

Course Report-Meat Packaging Research and Development in the UK

The Department of Animal Science (DMAS) and the Meat Technology Service (MTS) are the succes- sors to the AFRC Institute of Food Research, Bristol Laboratory. Langford continues to be the UK centre for meat research.

The Meat Technology Service (MTS) conducts research for individual companies or organisa- tions in the meat/food industry. It also provides a consultancy service, drawing on the expertise of the Department of Meat Animal Science (DMAS) in all areas of meat science and technology from the slaughter process, through carcass and meat processing, carcass classification, meat quality and analysis to sensory testing.

The facilities of DMAS, which are available to MTS members, include a red meat abattoir, poultry processing plant, meat cutting rooms, processing area, analytical laboratory and an experimental kitchen and computer-linked taste panel.

On 9-10 September 1993, the DMAS held a course on ‘Development in Meat Packaging’. This was organized under the auspices of the European Consortium for Continuing Education in Advanced Meat Science and Technology. The full programme included papers on: spoilage, vacuum, gas, sous vide, modified atmosphere packaging and retort pouches, as well as aspects on legislation and possible future developments. The introductory paper is reproduced in full below. Further informa- tion on meat packaging can be obtained from the course organiser, Mr Sandy Taylor, University of Bristol, Department of Meat Animal Science, Langford, Bristol BS18 7DY, UK.

BASIC CONSIDERATIONS IN MEAT PACKAGING

The development of packaging in the meat industry has brought about fundamental changes in the way meat is stored, distributed and retailed. Most modern meat factories have highly efficient cutting

and packing operations, which distribute partly butchered carcasses or fully prepared retail cuts to retail outlets. The supplier is generally respon- sible for final product quality. Supermarkets are the major customers and they rely entirely on the correct use of packaging. In the UK, supermarkets account for more than half of all meat sales, with the five major companies responsible for 40%.

Meat properties

The performance of a meat package is determined by the properties of the meat and the way that they are influenced by the package. The important properties are water content, microbiology, tissue respiration and colour, and packaging must take these into consideration.

Water content

Fresh meat is 75% water and some of this can be lost by evaporation and by exudate or drip from cut surfaces.

Microbiology

Before packing, carcasses and joints carry a wide range of surface bacteria, some of which can grow between 0°C and 5°C. The most important are pseudomonads, which are eventually respon- sible for spoilage of chilled meat stored in air.

Tissue respiration

Muscle tissue contains respiratory enzymes that continue to function after death, consuming oxygen and producing carbon dioxide. Consumption rate varies with species and between muscles and is

6 1994 by John Wiley & Sons, Ltd.

62 COURSE REPORT

limited to the surface layer, which is penetrated by oxygen. The depth of penetration increases as oxy- gen pressure of the surface increases; in air it may be around 6mm deep, although 80% oxygen may drive it in 12 mm. Because of oxygen consumption by the muscle tissue, a concentration gradient develops from the surface inwards, reducing to zero at the limit of oxygen penetration.

Colour

The colour of meat is of primary importance in marketing, and the consumer has come to regard bright red colour as an indication of freshness and quality. The colour of meat is determined by reactions between oxygen and the muscle pig- ment, myoglobin. Where oxygen concentration is high, there is a quick oxygenation to bright red oxymyoglobin, the colour the consumer prefers; at low concentrations of oxygen the pigment slowly oxidizes to brown-grey metmyoglobin, a colour which the consumer rejects. Low tempera- ture increases the solubility of oxygen in the meat surface and decreases muscle tissue respiration rate, so that the depth of oxygen penetration is increased. This improves colour stability. Colour is also affected by pigment concentration, which varies with species and between muscles of the same species. The order of pigment concentration is: beef > lamb > pork > chicken. Highly active muscles tend to have higher pigment concentra- tion than muscles that have a supporting role in the animal. Enzymes in muscle may have the ability to reduce oxidized metmyoglobin back to myoglo- bin. The activity of these enzymes can differ between muscles in the same carcass and cause some muscle to remain red longer than others. This difference between muscles is particularly noticeable in lamb cuts. Anything that reduces the depth of oxygen penetration into a piece of meat reduces colour stability.

Processing meat by curing destroys tissue respira- tion and preserves against microorganisms responsi- ble for spoiling fresh meat. Cured meat colour is derived from the reaction between nitrite and myo- globin and is stable if kept away from oxygen.

Influence of packaging

Packaging functions by creating a new environment for the meat, the most important feature being the

gaseous atmosphere. The active gases are O2 and C02. Packaging changes oxygen availability to the meat and determines colour, and also storage life by deciding the type of bacteria that will grow. The composition of the gas atmosphere is governed by initial concentrations, tissue respira- tion and gas permeability of the package. Carbon dioxide suppresses the growth of aerobic spoilage bacteria and has been used with meat for many years at concentrations of 10% and more, to extend storage life. In this context, it must be rea- lized that C 0 2 is very soluble in meat ( 1 kg meat can dissolve 11 C 0 2 at OOC).

A wide range of plastics are used in meat packag- ing, chosen on the basis of properties such as strength, clarity, sealability and permeability to moisture and gases. If repaired properties cannot be satisfied by a single film, several can be com- bined to give composite laminates or co-extrusions which provide all the requirements.

Packaging can be used in storage and distribu- tion, generally long duration and away from the consumer, or it can be used in retailing, where it may be shorter term and in direct contact with the consumer.

Storage and distribution

The principal use of packaging in this area is in the distribution of vacuum packed boneless beef joints from centralized cutting factories. These large joints are vacuum packed by sealing in plastic bags from which the air has been removed. The bags have very low gas permeabilities and there- fore exclude oxygen from the meat. Any residual O2 is quickly consumed by tissue respiration and C02 accumulates. The combination of low oxygen concentration and carbon dioxide concentration > 30% gives a storage life of 2 months at 1°C. The C 0 2 encourages the growth of lactic acid bacteria, which suppress the growth of the pseudo- monads that are normally responsible for spoilage. In absence of O2 the meat pigment is in the purple- red state but on exposure to air it oxygenates to the attractive bright-red colour. Vacuum packing is not so appropriate for bone-in cuts, such as pork and lamb, because of the danger of puncturing the bags, and therefore, this type of meat is frequently packed in large barrier bags, where the air has been replaced with CO2 or a mixture of C 0 2 and N2. Spoilage in the absence of O2 is similar to that in a vacuum pack.

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Retail packing

During the last 10 years or so, the most active and innovative area of meat packaging has been in retailing. Most of the developments have been in response to increasing demands by large super- markets for attractive appearance, longer display life and consistent quality. The simplest and most widely used retail package is the tray, over- wrapped with a plastic film chosen to be moisture proof but freely permeable to 02. This keeps the meat in the bright red oxygenated state, but only for 1 or 2 days under typical display conditions, before the surface oxidizes to the unattractive grey-brown colour.

Centralized preparation and packing of retail meat

Centrally located factories now prepare and pack retail meat for distribution directly to retail out- lets. Such meat requires a useful selling life of about a week from packing. Simple overwrapping of trays cannot satisfy this, but improved pack- aging is now available which can accomplish this, generally by sealing the meat in barrier trays filled with a gas atmosphere designed to prolong the attractive red colour while at the same time restrict- ing microbiological growth.

Sandy Taylor Division of Food Animal Science,

University of Bristol, UK