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Queso Fresco is a fresh, high moisture, white, rennet-set cheese that is the most popular Hispanic-style cheese in the US and Mexico. Traditionally, Mexican Queso Fresco is made with raw milk although the use of pasteurized milk is slowly replacing this practice. In the US, the FDA mandates that cheeses, such as Queso Fresco, sold less than 60 d after manufacture must be made with pasteurized milk. Queso Fresco has not been studied extensively and it is not known if the pasteurized milk cheeses are different from the raw milk originals. In this study, the compositional (moisture, fat, protein, and salt) and physical properties (whiteness value, water activity, and pH) of Queso Fresco from 6 commercial cheese plants in Sonora, Mexico (4 using raw milk and 2 using pasteurized milk) were characterized and compared to 8 commercial US-made cheeses. In composition, raw milk cheeses were higher in moisture (58-60%), and lower in fat (20-24%) and protein (15-17%) than the pasteurized milk cheeses from Mexico and the US (47-52% moisture, 23-36% fat, and 18-24% protein); the US-made cheeses contained more salt than the Mexicanmade cheeses (1.2-1.9% and 0.7-1.2%, respectively). In physical properties, all cheeses were bright white (whiteness L* values of 92-93) whereas raw milk cheeses had higher water activities (0.980 to 0.998) than the pasteurized cheeses (clustered near 0.975). The pH values of Mexican-made cheeses ranged from 4.8 to 6.0 whereas the pH values of US-made cheeses were above 6. The differences in manufacturing techniques, the unique microflora presence in the raw milk, and the excessive acid production in some of the cheeses contributed to the differences noted in composition and physical properties of the Queso Frescos. Establishing the basic chemical and physical properties of Queso Fresco is the first step in understanding the unique quality traits of this cheese and identifies traits that need to be maintained in pasteurized versions. [ABSTRACT FROM AUTHOR]

Queso Fresco is the most popular variety of Hispanic-style cheese consumed in the United States and Mexico. It is traditionally made from raw milk without specific starter cultures and the functional and flavor properties of the cheese are determined by the native microflora present in the raw milk. In the U.S., Queso Fresco is made from pasteurized milk with non-specific starter cultures resulting in a product with different organoleptic qualities from the traditional cheese. In this ARS-CIAD study, the indigenous microflora from six commercial Queso Fresco cheeses, obtained from Sonora, Mexico, were analyzed to identify bacterial species which may function as specific starter cultures. Four of the cheeses analyzed were made from raw milk and two from pasteurized milk. Classification of bacterial species was based on growth on selective media and 16S rDNA sequencing. The highest colony counts were obtained on M17 and MRS agar used for the selection of streptococci and lactobacilli respectively. Growth on MRS agar supplemented with vancomycin suggested that Leuconostoc species were present in all six samples. A high number of coliforms, enterococci and coagulase-positive staphylococci were identified in all raw milk samples. The number of enterococci remained high in cheese samples made from pasteurized milk but a 2 log10 reduction of coliforms was observed. Coagulase-positive staphylococci were reduced by 3 log10 in one pasteurized milk sample but remained high in the other (log 6.26 CFU/g). 16S rDNA sequence analysis revealed that lactobacilli were not present in any sample. Lactococcus lactis ssp. lactis was identified in four samples and Leuconostoc mesenteriodes and Entercoccus faecium were identified in all six samples. The results suggest that these species need further study to explore their potential as starter cultures for the production of cheese made from pasteurized milk while preserving the organoleptic qualities of traditional Queso Fresco. [ABSTRACT FROM AUTHOR]