Module 1: Hazards, issues and their control

There are many reasons why a food business might decide to use vacuum packing and modified atmosphere packing technology. Some of the potential advantages will be identified at the end of this section.

One of the main commercial reasons to pack food under a vacuum or a modified atmosphere is to extend the shelf-life of the product. For a business, this has important financial benefits.

Vacuum packing involves removing air from the packaging that surrounds the food and preventing its return by an airtight seal. In a typical vacuum pack, the packaging material is moulded closely around the food.

Modified atmosphere packing is a process or condition where the gaseous mixture within a food pack is different from that of the atmosphere. This can involve removing the air and replacing it with an inert mixture of gases. The combination and mixture of the gases used will vary according to the product.

Some products that are packed in a modified atmosphere will have the appearance of an extended pillow, such as prepared salads. Products in a formed pack will look normal, but the fact that the product has been packed in a modified atmosphere will be identified in the labelling of the food.

Removing air from product packaging changes the micro-environment surrounding the food, inhibiting the growth of the majority of spoilage organisms and pathogens that grow in the presence of oxygen.

Concerns about vacuum packing and modified atmosphere packing have existed for some time. In 1990, the Government established a new committee to advise it on microbiological food safety issues. To reflect its role it was given the title of Advisory Committee on the Microbiological Safety of Food, commonly referred to as the ACMSF. It continues to meet and advise the FSA.

See the ACMSF website.

One of the first issues considered by the ACMSF was the safety of vacuum and modified packed chilled foods. The committee published its report in 1992 and the science and public health concerns are still valid today. The contents of the report are considered in this module and Module 3. The ACMSF advice to businesses and enforcers has been summarised by the Food Standards Agency in the guidance at the link below, and this is reflected in the content of this online training course.

See the Guidance on the safety and shelf-life of vacuum and modified atmosphere packed chilled foods with respect to non-proteolytic Clostridium botulinum.

Removing air (including oxygen) surrounding the food creates conditions suitable for the growth of anaerobic organisms. The most significant of these, from a public health perspective, is Clostridium botulinum.

The potential hazard, in relation to Clostridium botulinum, is the consumption of chilled foods in which the growth and toxin production by non-proteolytic strains of Clostridium botulinum may have occurred before the food is perceived to be spoiled. The foods most at risk are those in which the spoilage microflora are eliminated or inhibited, while non-proteolytic Clostridium botulinum may survive and grow.

Clostridium botulinum can result in serious illness. Deaths have been recorded following outbreaks in other countries.

For further information about non-proteolytic Clostridium botulinum, see Module 2.

Non-proteolytic strains of Clostridium botulinum can grow and produce toxin at low temperatures. Growth can still take place at 3ºC – albeit very slowly. This is a temperature below which chilled foods are required to be stored and displayed according to the temperature control regulations.

Hence, organism growth and toxin production are possible at chilled temperatures.

In 1992, the ACMSF said:

'Changes in food processing and preservation such as extended life cook-chill, sous vide catering, vacuum packing, reductions in nitrite levels in cured meats, and the tendency to use lower cooking temperatures to reduce loss yield and improved colour and texture of products, all have the potential to cause problems in the future.'

The committee’s key findings were detailed in chapter 2 of its report. For example:

• ‘Given the widespread occurrence in the environment of the organism, it is not surprising that non-proteolytic Clostridium botulinum has been found in many foods and it is not possible to be certain that an unprocessed food will not contain spores of non-proteolytic Clostridium botulinum.'

ACMSF 1992 report, Chapter 2.

In the light of these findings, the committee concluded that:

• ‘All chilled food manufacturers must address the control of non-proteolytic Clostridium botulinum through composition and formulation’.

This conclusion links with a need to observe good manufacturing practice (GMP). The importance of observing good hygiene practice will be considered in Module 4.

The only exception to this control is for those foods that have both been sterilised and then aseptically packaged or have received a sporicidal heat treatment within a hermetically sealed container.

The main commercial benefit of using vacuum packing and modified atmosphere packing is the extension of a product’s shelf-life due to its inhibiting effects on spoilage organisms.

Other claimed advantages include:

• freshness and flavour is maintained for three to five times longer than conventional storage materials
• texture and appearance is improved
• moist foods do not dry out
• rancidity of foods with high fat is delayed
• meat and fish marinate quickly
• wastage is reduced