Evaluation of oxygen content in commercial modified atmosphere packs (MAP) of processed cooked meats Mary Smiddy a , Dmitri Papkovsky b , Joe Kerry a, * a Department of Food Science, Food Technology and Nutrition, University College Cork, National University of Ireland, Cork, Ireland b Department of Biochemistry, University College Cork- National University of Ireland, Cork, Ireland Received 14 June 2001; accepted 11 October 2001 Abstract Twenty-five packs of each of 13 processed cooked meats products, produced by three manufacturers, were analysed. Analysis was performed 1, 7, 14 and 21 days after obtaining samples at the point of manufacture. Although all products were packaged in modified atmospheres of 70% N 2 and 30% CO 2 , oxygen was present in 88% of packs 24 h after packaging. Overall percentages of packs containing 0.0, 0.01–0.5, 0.51–1.2 and > 1.2% oxygen were 11.7, 38.4, 29.4 and 20.4%, respectively on day 1 and 0.0, 15.5, 5.3 and 79.3%, respectively, on day 21. Three comparable pork products produced by three different manufacturers contained different levels of oxygen on day 1. The high proportion of packages containing rejectably high levels of oxygen may pose a potential risk of product quality deterioration and reduced shelf-life of muscle-based foods. Results emphasize the necessity to monitor oxygen levels within packs of oxygen-sensitive foods, including processed, cooked muscle foods. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Oxygen; Retail processed meats; MAP 1. Introduction Modern trends toward convenience foods have led to an increase in the production of precooked and restruc- tured meat products. Modified atmospheres are widely used for packaging these foods. Residual oxygen is an important determinant of quality and shelf-life (Tewari, Jayas, & Holley, 1999). Although oxygen-sensitive foods may be packaged using modified atmosphere packaging (MAP), oxygen is not always completely removed and may also permeate through the packaging material (Vermieren, Devlie- ghere, van Beest, de Kruijf, & Debevere, 1999). Knowl- edge of actual oxygen levels in each pack provides useful information about package integrity, efficiency of the packaging equipment and an indication of product quality changes (Fitzgerald et al., 2001). Removal of oxygen is particularly important with cooked MAP muscle foods. MAP involves holding perishable foods in a modified environment, to inhibit spoilage, thereby maintaining higher quality and/or extending the shelf- life (Church & Parsons, 1995). Cooking promotes lipid oxidation, partially due to the release of iron, which acts as a pro-oxidant. The presence of small amounts of oxygen accelerates oxidation of cooked MAP meat even further. Development of warmed-over flavour is very slow in cooked cured meats compared with uncured meats due to the inhibitory affect of a number of nitrite- derived compounds on lipid oxidation (Varnam & Sutherland, 1995). The presence of oxygen in the pack atmosphere is the most important factor influencing lipid oxida- tion, since oxygen (in small quantities) is necessary for oxidation reactions to proceed. In many cases, deterioration of meat is caused by oxidation of meat components or spoilage by aerobic microorgan- isms, both of which are accelerated by the presence of oxygen. The objective was to assess the levels of oxygen in a variety of commercial modified atmosphere packs (MAP) of processed and cooked meat products, pro- duced by three manufacturers and sampled from the point of manufacture to the end of retail display. 0963-9969/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0963-9969(01)00159-4 Food Research International 35 (2002) 571–575 www.elsevier.com/locate/foodres * Corresponding author. Tel.: +353-21-4903798; fax: +353-21- 4276318. E-mail address: joe.kerry@ucc.ie (J. Kerry).