Location: Dairy and Functional Foods
2011 Annual Report
The fate of LM will also be determined on low-salt Cheddar Cheese of various salt contents for comparison to Queso Fresco and the study expanded to monitor growth of other pathogens.
Improving the quality and safety of Queso Fresco cheese. Queso Fresco is one of the most popular of the Hispanic-style cheeses in the U.S. but, because of its high moisture content and pH, has been implicated as the source of several food borne illness outbreaks. A high-pressure post packaging treatment was developed to determine if Listeria monocytogenes, a bacterium implicated in most of these illnesses, would be killed while preserving the expected quality traits of the cheese. Listeria cultures were added prior to treatment at various pressures, temperatures, and lengths of time, and combinations were found that initially killed the bacteria (see project 1935-41000-087-00D). QF were then treated at the optimum conditions and aged to determine long term effects. Listeria proved to be resistant to high pressure and enough bacteria survived the treatment and recovered after a 7-28 day lag time to begin growing again. In parallel studies conducted with pathogen-free QF (see project 1935-41000-091-00D), the extreme conditions negatively affected the quality of the cheese; most noted was the accumulation of whey in the packaging and increased hardness of the cheese; flavor and mouth feel were different but not objectionable. High pressure processing is a very promising deterrent to pathogen growth but needs to be paired with other interventions to ensure the safety of the cheese. Results from this study help in developing new options for cheese manufacturers to make safe Queso Fresco cheeses.
Pathogen growth on reduced-salt, low-fat Cheddar cheese. Health conscious American consumers are demanding lower salt levels in all foods, including a favorite in the U.S., Cheddar cheese. Because salt is critical in limiting the growth of bacteria in cheese, it is essential to determine if altering the salt level will alter the growth of bacteria responsible for food borne illnesses. Low-fat Cheddar cheese made with four different levels of salt by collaborators at the Western Dairy Center, Utah State University, Logan, Utah, were received at the ERRC Center of Excellence in Process Validation (CEPV), Wyndmoor, Pennsylvania, and exposed to three pathogens most often implicated in food borne illness from dairy products (see project 1935-41420-015-00D). After aging the cheese for six months, cell counts of two of the three pathogens (E. coli O157:H7 and Staph aureus) had decreased significantly in cheeses at all salt levels, while the third pathogen (Listeria monocytogenes) showed reduced numbers only at the two higher salt levels. The results from this study confirmed that salt level in Cheddar will be a significant factor in maintaining the safety and quality of the cheese and provided guidance in developing safe low-fat low-salt cheese that meets the demands of the health conscious American consumer.