Technology-induced selection towards the spoilage microbiota of artisan-type cooked ham packed under modified atmosphere Charalampos Vasilopoulos a , Hannelore De Maere b , Eveline De Mey b , Hubert Paelinck b , Luc De Vuyst a , Fre ´ de ´ ric Leroy a, * a Research Group of Industrial Microbiology and Food Biotechnology (IMDO), Faculty of Sciences and Bio-engineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium b Research Group for Technology and Quality of Animal Products, Department of Industrial Engineering, KaHo Sint-Lieven, Gebroeders Desmetstraat 1, B-9000 Ghent, Belgium article info Article history: Received 3 July 2009 Received in revised form 26 August 2009 Accepted 28 August 2009 Available online 4 September 2009 Keywords: Cooked ham Spoilage Lactic acid bacteria Brochothrix thermosphacta Enterobacteriaceae abstract The microbiota associated with a highly-perishable Belgian artisan-type cooked ham was analyzed through plating and (GTG) 5 -fingerprinting of isolates throughout its processing chain. The raw tumbled meat was characterized by the presence of a versatile microbiota around 4.8 log(cfu g 1 ), consisting of lactic acid bacteria, staphylococci, Brochothrix thermosphacta, Gram-negative bacteria, and yeasts. Pas- teurisation of the ham logs reduced bacterial counts below 2 log(cfu g 1 ) and subsequent manipulations selected for leuconostocs and carnobacteria. Also, B. thermosphacta and several Enterobacteriaceae were found at this stage. During storage in an intermediate high-care area for 2 days, a selection towards certain Enterobacteriaceae (Hafnia alvei, Enterobacter spp., and Pantoea agglomerans) and lactic acid bacteria (mainly vagococci and Streptococcus parauberis) was observed. B. thermosphacta, Leuconostoc carnosum and carnobacteria were also detected, but only after allowing bacterial outgrowth by incu- bating the meat logs at 7  C for four weeks. After a mild post-pasteurisation process and subsequent handling, incubation of the meat logs at 7  C for four weeks led to outgrowth of Enterobacteriaceae (mainly Enterobacter spp. and Serratia spp.). B. thermosphacta, and lactic acid bacteria (Enterococcus faecalis, Leuc. carnosum, and Carnobacterium maltaromaticum) were also found. After slicing and pack- aging under modified atmosphere, the microbiota of the refrigerated end-product consisted of leuco- nostocs, carnobacteria, and B. thermosphacta. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Microbial growth and metabolism contribute to the limitation of the shelf-life of cooked meat products. The manifestation of the metabolic action is perceived by the consumer as spoilage, resulting from the combined effect of off-flavours, discolouration, and/or slime formation on the surface of the product (Gram et al., 2002; Bruhn et al., 2004; Holley et al., 2004). Modified-atmosphere- packaging (MAP), in combination with chilling, is one of the most widespread methods to delay spoilage in cooked meat products. Not only does packaging act as a barrier against contaminants, it also plays a crucial role in the selection of spoilage microorganisms due to its effect on oxygen availability (Labadie, 1999; McMillin, 2008; Nychas et al., 2008). From the large group of microorganisms that initially colonise the raw meat ecosystem, lactic acid bacteria and Brochothrix thermosphacta mostly prevail in the cooked end- product, thereby outcompeting most Gram-negative bacteria such as Pseudomonadaceae and Enterobacteriaceae (Borch et al., 1996; Rattanasomboon et al., 1999; Blixt and Borch, 2002; Gram et al., 2002). Lactic acid bacteria that are most commonly encountered are Lactobacillus spp., Carnobacterium spp., Leuconostoc spp., and Enterococcus spp. (Bjo ¨rkroth and Korkeala, 1997; Metaxopoulos et al., 2002; Peirson et al., 2003b; Vasilopoulos et al., 2008). Despite the available knowledge on the nature of the microbial spoilage of MAP cooked meat products, little is reported on the source of the spoilage bacteria and the effect of the processing chain on the selection towards the final microbiota (Ma ¨ kela ¨ and Korkeala, 1987; Bjo ¨rkroth and Korkeala, 1997; Borch et al., 1988; Dykes et al., 1991). Studies that deal with the processing chain focus mainly on food pathogens rather than on spoilage microorganisms (Berends et al., 1998; Chasseignaux et al., 2002; Aslam et al., 2004; Byrne et al., 2008). It is not fully clear to what extent microorgan- isms that are present in meat products originate from the meat itself or rather from handling-related operations in the processing * Corresponding author. Tel.: þ32 2 6293612; fax: þ32 2 6292720. E-mail address: fleroy@vub.ac.be (F. Leroy). Contents lists available at ScienceDirect Food Microbiology journal homepage: www.elsevier.com/locate/fm 0740-0020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fm.2009.08.008 Food Microbiology 27 (2010) 77–84