2010 Annual Report
1a.Objectives (from AD-416)
The objectives of this research are to: (1) characterize and quantify the chemical and physical properties of Hispanic-style cheeses, (2) determine the cheesemaking steps or parameters that are responsible for developing these characteristics, and develop cheesemaking methods to produce pasteurized Hispanic-style cheeses that meet U.S. regulations and retain the desirable flavors and functional and textural properties of the traditional raw milk cheeses, and (3) develop sensory terminology to characterize the flavors of cheeses made with raw and pasteurized milk and relate flavor development to microflora present in the cheeses and the degree of proteolysis in the cheese.
1b.Approach (from AD-416)
This research will focus on understanding the factors that give Hispanic-style cheeses their distinctive flavors and functional and textural properties. The first step is to determine the properties of the most popular cheeses available on the market today by characterizing and quantifying the chemical, physical, functional, rheological, and textural properties of three types of Hispanic-style cheeses (Mennonite-style, Queso Fresco, and Queso Blanco); both the traditional raw milk cheeses from Mexico and the pasteurized milk cheeses from the United States and Mexico. At the same time, the cheese making steps or parameters that are key elements in developing the desired characteristics in Hispanic-style cheeses will be identified. The sensory characteristics of the cheeses will be defined, the impact of the microflora will be evaluated and compared in the raw milk and the pasteurized milk cheeses, and the proteolysis of the cheeses will be measured and correlated to sensory and physical properties. Once the specifications for the cheeses have been developed, the processing steps to produce pasteurized Hispanic-style cheeses that meet U.S. regulations and retain the targeted properties of the traditional cheeses will be adapted or modified from current procedures.
Queso Fresco (QF) is one of the most popular high-moisture Hispanic-style cheeses made and consumed in the U.S., but relatively little is known about its quality traits and the impact of storage on these traits. Multiple batches of Queso Fresco were manufactured from pasteurized milk without starter cultures using industry protocol and stored at either 4 degrees C (warehouse storage) or 10 degrees C (retail dairy case or home refrigerator) for up to 8 weeks. Samples of the cheeses were used to test different chemical and biological interventions in preventing the growth of Listeria monocytogenes (see associated -01R project). In other studies, modifications were made to the manufacturing protocol (such as altering added salt levels, or testing different curd milling techniques) to determine how the quality traits changed over 8 weeks of storage. The results from these studies will expand our knowledge of the quality traits of QF, extend its shelf life and safety, and increase the utilization of this cheese.
Low salt Hispanic-style cheese. Health conscious Americans want to reduce their dietary sodium and are carefully analyzing their favorite foods, such as Queso Fresco (QF), a popular high-moisture, fresh Hispanic-style cheese that can contain up to 2.5% salt. As a first step in keeping this nutrient-dense food in the American diet, ARS scientists at Wyndmoor, PA made QF with reduced levels of added salt. It was found that the salt could be reduced to about 1.5% without substantially altering the functionality, texture, and structure of the cheese. This study establishes baseline salt levels for QF from which future studies on flavor and salt replacements will be based. This information should lead to the development of low-salt versions of Queso Fresco.
Improving the quality and safety of Queso Fresco cheese. Approximately 2% of all the cheeses manufactured in the U.S. are Hispanic-style cheeses. Of these, Queso Fresco (QF) is one of the most popular fresh, high-moisture cheeses. Cheesemakers and retailers require information about making and storing QF to ensure that its quality is maintained over the entire shelf-life of the cheese. ARS scientists at Wyndmoor, PA conducted studies to characterize the manufacturing protocols and quality traits of this cheese and then carried out extensive in-house cheese trials to examine how modifications to manufacturing parameters and the use of different chemical and biological interventions impact the quality traits and safety of QF. Results show that the composition, functionality, and texture of QF remained fairly constant when stored at either 4 or 10°C for 8 weeks. The cheese protein showed minimal breakdown during storage, which supports longer shelf life. Manufacturing modifications shows that homogenization of the cheese milk ensures the non-melt functional property expected of this type of cheese, and that the fine milling of the curd using different size blades has minimal impact on cheese texture. The chemical and biological interventions tested have mixed results in slowing, but not inhibiting, the growth of selected food pathogens. Results will help U.S. manufacturers produce high-quality Hispanic-style cheeses with longer shelf life that meets the expectations of the American consumer.
5.Significant Activities that Support Special Target Populations
Improving the availability of U.S.-made goat milk cheeses with reduced fat. The manufacture of goats’ milk dairy products is a growing industry in the U.S. The production of high quality cheese is a critical factor in the industry’s continued growth, especially since many dairy goat operations are small- scale, part-time, or subsistence farms. Consumers are demanding healthier cheeses and there is significant interest from small producers that serve niche markets to develop reduced-fat goats’ milk cheeses that have the same flavors and textures as the full-fat versions. In collaboration with researchers at Fort Valley State University, GA, a 1890s university, DFFRU scientists finished collecting data on a 3-year project that evaluated protein breakdown and associated textural changes of semi-hard cheeses made from goats’ milk containing 2% fat and aged for up to 6 months. This research will contribute to improving the ability of the American goats’ milk industry to provide high-quality cheeses with the nutritional benefits desired by health-conscious consumers.
Van Hekken, D.L., Wall, R.J., Somkuti, G.A., Powell, A.M., Tunick, M.H., Tomasula, P.M. 2009. Fate of lysostaphin in milk from individual cows through pasteurization and cheesemaking. Journal of Dairy Science. 92:444-457.
Tunick, M.H., Brine, C.J. 2009. One hundred years of the Division of Agricultural and Food Chemistry. Journal of Agricultural and Food Chemistry. 57:8063-8069.