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Influence of Adjunct Use and Cheese Microenvironment on Nonstarter Bacteria in Reduced-Fat Cheddar-Type Cheese¹

J. R. Broadbent^*, K. Houck, M. E. Johnson and C. J. Oberg

^* Western Dairy Center and Department of Nutrition and Food Sciences, Utah State University, Logan, 84322-8700
Wisconsin Center for Dairy Research, University of Wisconsin, Madison, 53706
Department of Microbiology, Weber State University, Ogden, UT 84408-2506

Corresponding author: J. R. Broadbent; e-mail: broadbnt{at}cc.usu.edu.

This study investigated population dynamics of starter, adjunct, and nonstarter lactic acid bacteria (NSLAB) in reduced-fat Cheddar and Colby cheese made with or without a Lactobacillus casei adjunct. Duplicate vats of cheese were manufactured and ripened at 7°C. Bacterial populations were monitored periodically by plate counts and by DNA fingerprinting of cheese isolates with the random amplified polymorphic DNA technique. Isolates that displayed a unique DNA fingerprint were identified to the species level by partial nucleotide sequence analysis of the 16S rRNA gene. Nonstarter biota in both cheese types changed over time, but populations in the Colby cheese showed a greater degree of species heterogeneity. The addition of the L. casei adjunct to cheese milk at 10⁴ cfu/ml did not completely suppress "wild" NSLAB populations, but it did appear to reduce nonstarter species and strain diversity in Colby and young Cheddar cheese. Nonetheless, nonstarter populations in all 6-mo-old cheeses were dominated by wild L. casei. Interestingly, the dominant strains of L. casei in each 6-mo-old cheese appeared to be affected more by adjunct treatment and not cheese variety.

Key Words: Lactobacillus • nonstarter lactic acid bacteria • cheese flavor

Abbreviation key: NSLAB = nonstarter lactic acid bacteria, RAPD = randomly amplified polymorphic DNA

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