Occurrence and growth of yeasts in processed meat products - Implications for potential spoilage

Spoilage of meat products is in general attributed to bacteria but new processing and storage techniques inhibiting growth of bacteria may provide opportunities for yeasts to dominate the microflora and cause spoilage of the product. With the aim of obtaining a deeper understanding of the potential role of yeast in spoilage of five different processed meat products (bacon, ham, salami and two different liver pates), yeasts were isolated, enumerated and identified during processing, in the final product and in the final product at the end of shelf life. Yeasts were isolated along the bacon production line in numbers up to 4.2 log (CFU/g). Smoking of the bacon reduced the yeast counts to lower than 1.0 log (CFU/g) or non-detectable levels. In general, yeasts were only isolated in low numbers during the production of salami, cooked ham and liver pate. In the final products yeasts were detected in low numbers in a few samples (3 out of 30) samples, 1.0-1.3 log (CFU/g). By the end of storage, yeasts were only detected in 1 out of 25 investigated samples 1.8 log (CFU/g). A combination of phenotypic and genotypic methods was used to identify the yeast microflora present during production of the processed meat products. The yeast microflora was complex with 4-12 different species isolated from the different production sites. In general, Candida zeylanoides, Debaryomyces hansenii and the newly described Candida alimentaria were found to be the dominant yeast species. In addition, three putatively previously undescribed yeast species were isolated. Fourteen isolates, representing seven different species isolated during the production of the processed meat products and one species isolated from spoiled, modified atmosphere packed, sliced ham, were screened for their ability to grow in a meat model substrate under a low oxygen/high carbon-dioxide atmosphere (0.5% 02, 20% CO2, 79.5% N-2) at two different temperatures (5 and 8 degrees C). Eleven out of the tested 14 strains were able to grow in the meat model substrate with C zeylanoides, D. hansenii, Pichia guilliermondii and Candida sake reaching levels of 10(5)-5 x 10(6) log (CFU/g), where sensoryical changes appear. (C) 2008 Elsevier Ltd. All rights reserved.