Jackin N. Nanua and John U. McGregor
Cheese is one of the most ancient forms of manufactured food. It is the product of enzymatic action and lactic fermentation of milk using various bacterial cultures. These enzymatic actions and fermentations lead to the coagulation of milk and production of typical cheese characteristics.
Fermented milk products originated in the Near East and then spread to southern and eastern Europe. Nomadic tribes who carried milk in storage pouches made from the stomachs of cows, sheep, camels or goats accidentally developed the earliest forms of cheese. Under warm storage conditions, the milk coagulated or clabbered because of the action of proteolytic enzymes naturally present in the storage containers and the production of acid end products by lactic bacteria. Fortunately, the predominant bacteria were lactic types (acid producers) and, therefore, helped to preserve the product by suppressing spoilage and pathogenic bacteria. People evidently enjoyed the refreshing, tart taste of this discovery and began to handle milk so that this preserving action would be encouraged.
Milk and curdled milk products are mentioned throughout history dating back as far as 4000 BC: “He asked for water, and she gave him milk; in a bowl fit for nobles she brought him curdled milk” (Old Testament, Judges 5:25). There is also remarkable pictorial evidence that the custom of keeping milk in containers for later consumption was already a craft systematically practiced by the Sumerians around 2900 BC. Through scientific principles and advances in manufacturing technology, these early products have developed into a highly diversified group of foods popular throughout the world.
Different varieties of cheese are created by varying coagulation agents,processing methods and ripening agents.Cheeses can be classified by moisture content as hard, semi-hard and soft.During the ripening of cheese, lactic acid bacteria use lactose to produce acid and other flavor compounds, some of which inhibit undesirable contaminating microorganisms.
Mold-ripened soft cheeses such as Camembert and Brie are inoculated with the mold Penicillium camemberti, which produce proteolytic enzymes leading to protein hydrolysis. The amines and ammonia produced during protein hydrolysis raise the pH of the cheese to levels that can allow growth of undesirable microorganisms. Spices are sometimes added to these cheeses, and these could introduce undesirable microorganisms into the cheese. It has been demonstrated that pathogens such as Listeria monocytogenes can grow during the ripening of Camembert cheese but decrease during the ripening of Cheddar cheese.
A number of disease outbreaks have been traced to consumption of soft cheese. This has raised safety concerns, especially for vulnerable consumers such as pregnant women and immune compromised individuals. The Food and Drug Administration (FDA) recommends that pregnant women avoid consumption of soft cheeses such as Camembert, Brie, Roquefort, feta and Mexican-style cheeses because of the risk of listeriosis. Stringent hygienic standards should be maintained during the manufacture and subsequent handling of soft-ripened cheese to minimize chances of contamination.
Researchers in the LSU Agricultural Center’s Department of Dairy Science conducted a study to assess the microbiological quality of imported and domestic soft-ripened, French-style cheese in the retail market. Cheese samples—three imported French Brie varieties, one German Camembert variety and one U.S. Camembert—were collected from three supermarkets located in the greater Baton Rouge area. Samples were analyzed in the Dairy Science Department. The cheeses were aseptically sliced to obtain surface, intermediate and center samples.
Analyses were performed immediately. Age of the cheese could not be determined, but they were within the “sell by” date. The sampling was replicated three times.
The pH and proteolysis decreased from the surface to the center. This could be attributed to the activity of the ripening molds. Molds produce proteases and other enzymes that break down proteins leading to the formation of amino acids, peptides and ammonia. They also degrade lactic acid, milk fat and produce carbon dioxide. Protein breakdown causes an increase in soluble citrate and short-chain peptides. The net effect is an increase of pH. The average moisture content was 43 percent for Brie and 48 percent for Camembert. The high pH and moisture contents observed in these cheeses could encourage the growth of microorganisms including pathogens. Many common pathogens grow within a pH range of 4.5 to 10. Surface mold-ripened cheeses with a pH of about 6 can support the growth of pathogens. Listeria monocytogenes, Enterobacter aerogenes and Escherichia coli have been reported to grow in Camembert cheese. L. monocytogenes grow at pH 5.5 to 5.3.
Plain Brie and Brie with herbs had higher coliform counts than U.S. Camembert and Brie with peppercorns (Table 1). In addition, Brie with herbs had high coliforms in the interior while all the other cheeses had very few coliform counts in their interiors. The higher internal contamination of Brie with herbs might be caused by mixing herbs into the cheese. The herbs are mixed into the cheese interior, and peppercorns are applied only to the surface.
Brie and Camembert
Brie had a higher incidence of microbiological contamination than Camembert. Brie is typically sliced into wedges in the retail shop, and Camembert is presented as whole wheels. Contamination may have occurred during the cutting in the supermarkets. Four Brie wheels were collected from the supermarkets before cutting into wedges and analyzed for coliforms to determine whether contamination was at the cutting stage. Only one wheel had detectable coliform bacteria, confirming that cutting in the supermarket is probably responsible for most of the contamination with coliforms. No E. coli were detected in any of the cheese samples examined. Canned Camembert, which is normally pasteurized by dipping in hot water, had no viable microorganisms.
The soft-ripened cheeses examined in this study had viable coliforms. This indicates conditions that could have exposed the products to microbial contamination. This is a cause of concern, especially for high-risk consumers such as pregnant women, the young, the elderly and immune-compromised individuals. High-risk consumers should consume cheeses like Cheddar and mozzarella instead.
The higher coliform count on the surface suggests post-process contamination, most likely during cutting and the adding of spices for Brie. This could be reduced by using high quality spices and by following good sanitary procedures during the cutting step carried out at retail supermarkets.
Another means for potentially improving the microbiological quality of cheese at the retail level is to buy cheese cut and wrapped at the cheese manufacturing plant. The sanitary procedures used in dairy processing plants are typically strict and carried out by highly trained food industry professionals.
The FDA recommends that pregnant women and immune-compromised people avoid consumption of soft cheeses such as Camembert, Brie, Roquefort, feta and Mexican-style cheeses because of the risk of listeriosis.
(This article was published in the spring 2000 issue of Louisiana Agriculture.)