Modified atmospheres and vacuum packaging

Abstract

The ability of modified-atmosphere packaging (MAP) to extend the shelf-life of foods has been known for a long time. First, the delaying effects of MAP or controlled-atmosphere storage (CAP) on the ripening of fruits and vegetables were discovered. In the 1920s, studies at the Low Temperature Research Station in Cambridge, UK, demonstrated that the shelf-life of apples could be increased by storing them in atmospheres containing reduced levels of oxygen and increased levels of carbon dioxide (Davies, 1995) whilst by the late 1930s the antimicrobial effects of carbon dioxide were being exploited industrially. Most of the beef (60%) and some of the lamb (26%) shipped from Australia and New Zealand to the United Kingdom was stored in an atmosphere enriched with carbon dioxide. In 1979, the retail chain Marks & Spencer launched a range of gas-flushed packs of fresh meat products in the United Kingdom, which created renewed interest in the use of MAP. Until recently, meat and, to a lesser extent, fish, dominated both the market place and the scientific literature on MAP, and this was reflected in the discussion of this topic in the first edition of this book. Since then, there has been a significant increase in the range of products packaged in modified atmospheres and, today, foods marketed in modified atmosphere include vegetables, fruit, pasta, cheese, bakery products, potato crisps, prepared foods, coffee, and tea as well as an increased range of raw and cooked meats and fish. This increase is partly a result of the growing consumer demand for fresh and chilled convenience food containing fewer preservatives. The result of this is that, whilst modified-atmosphere and vacuum-packed foods are not highly visible in world food marketing and technology, they constitute a substantial and growing proportion of North American and European food supplies — albeit it normally in distribution packaging (Brody, 1998). Together with this increase in the range of products marketed in MAP, recent studies/developments have largely focused on intelligent packaging (predominantly oxygen scavengers), mathematical modelling of the influences of MAP on microbial growth, especially of food-poisoning microorganisms (Bennick et al., 1995; Garcia de Fernando et al., 1995), and the safety of MAP (Hintlian and Hotchkiss, 1986), together with technical developments in the packaging film and associated equipment area. Several of these aspects are discussed below.