Microbiological criteria and ecology of commercially available processed cheeses according to the product specification and physicochemical characteristics

Highlights

• A variety of processed cheese products were released and traded in the global market.

• Legal definitions and standards/regulations of major cheese traders were summarized.

• A total 800 commercially processed cheese products were microbiologically analyzed.

• None of the tested samples contained coliforms or foodborne pathogens.

• No relation was observed with salinity, water activity, pH, and heating conditions.

Abstract

Although global cheese manufacturers release a variety of products onto the market, research on the microbiological quality and safety of cheese has focused mainly on conventional cheeses made from milk. Here, this study aimed to investigate commercially processed cheese products produced by mixing conventional cheeses after melting. Two approaches were used: a summary and comparison of legal definitions and standards/regulations regarding the microbiological criteria used by major cheese traders in the global market (Australia/New Zealand, China, European Union, Japan, Mexico, Republic of Korea, and the United States) and a comprehensive microbiological analysis of commercial products (n = 800), along with an assessment of salinity, pH, water activity, and heating conditions. The results of the literature search showed that major importing countries (China, Japan, Mexico, and the Republic of Korea) have stricter microbiological criteria for commercially available cheese products than major exporters (Australia/New Zealand, EU, and the USA). The former set limits with respect to the number of total coliforms in the product. Microbiological analyses were designed according to global standards and recommendations. No test sample contained detectable levels of Clostridium perfringens, enterohemorrhagic Escherichia coli, Listeria monocytogenes, Salmonella, or Staphylococcus aureus. In addition, no coliform bacteria (including E. coli) were detected. Overall, 79.9% of the samples contained detectable aerobic plate counts (1.0–7.8 log CFU/g); these levels varied significantly according to product type (grated cheese > chunks; cream cheese > portions or sliced) (p < .05). There was no significant association between microbe levels and salinity, water activity, pH, and heating conditions. The results can be used to develop a comprehensive database about commercially processed cheese products available in the global market and, as such, may be helpful for both national authorities and cheese manufacturers when considering novel strategic management plans for microbiological quality and safety.

Introduction

Cheese is a dairy product that is generally considered ‘safe’ as one of the preserved foods; however, many outbreaks of foodborne diseases have been linked to cheese, and pathogens are frequently isolated from the raw materials, semi-finished products, and the final products (Heiman et al., 2016; Johler et al., 2015; Kousta, Mataragas, Skandamis, & Drosinos, 2010; Schoder, Stessl, Szakmary-Brändle, Rossmanith, & Wagner, 2014). A number of studies isolated several species of pathogenic bacteria (e.g., enteropathogenic Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus) or spore-forming bacteria from various cheese products worldwide (Barancelli et al., 2014; Brooks et al., 2012; Little et al., 2008; Oliveira et al., 2016; Oliveira et al., 2018; Oliveira et al., 2018; Rosengren, Fabricius, Guss, Sylvén, & Lindqvist, 2010).

Although conventional cheeses are generally known to be made from milk by microbial fermentation, a processed cheese is commercially manufactured in general by blending or mixing several types of cheeses (with different specification such as color, flavor, maturity, texture, etc.) in the presence or absence of heating and/or food additives such as emulsifying agents (Guinee, Caric, & Kalab, 2004; Kapoor & Metzger, 2008). Walter ad Geber first produced processed cheese in Switzerland in 1911, with the aim of extending the shelf-life of cheese products (Meyer, 1973); since then, many manufacturers have used various processing techniques (mostly heating) to produce commercial processed cheese products and sought several strategies to meet new market demands, for suggesting better options for consumers with higher nutritional quality of processes cheeses products (Dantas et al., 2016; Ferrão et al., 2016).

The raw materials (raw milk) used to make cheese and the environments (on dairy farms) are potential sources of microbial contamination, as is the cheese manufacturing/processing line itself (Kousta et al., 2010). Among the various pathogens, those that are highly resistant to high salt concentrations and a dry environment (e.g., L. monocytogenes and S. aureus) (Taormina, 2010) pose the greatest risk (Kousta et al., 2010; Verraes et al., 2015). These pathogens have been detected in brine, cheese cloth, cheese vats, cold rooms, and production rooms, and on curd cutting knives, floors, food handlers, and packaging materials (Brito et al., 2008; Callon, Gilbert, De Cremoux, & Montel, 2008; Temelli, Anar, Sen, & Akyuva, 2006). However, to the best of our knowledge, few microbiological analyses have been performed to examine contaminants in processed cheese products sold worldwide; this is because most microbiologists have focused on microbial contamination of conventional cheeses, which have higher potent to be contaminated and contain greater numbers of microorganisms than the commercially processed ones.

However, there are hundreds of commercially processed cheese products on the global food market: chunk cheese (also called ‘loaf’ cheese), cream cheese (‘spread’), ground cheese (‘shredded or grated’), cheese portions (‘cubed or pieced’), and cheese slices (Kapoor & Metzger, 2008). Although the national food safety authorities of each country legally define processed cheese in their own way and have established national standards and regulations regarding quality and safety, no previous studies have pulled these together for analysis.

Therefore, the objectives of this study were to examine legal definitions and standards/regulations regarding microbiological criteria for commercially processed cheeses from a global perspective and to perform a comprehensive examination of product characteristics (salinity, pH, and water activity) and microbiological quality.