Use of Galactose-Fermenting Streptococcus thermophilus in the Manufacture of Swiss, Mozzarella, and Short-Method Cheddar Cheese

Galactose-fermenting (galactose-posirive) strains of Streptococcus tbermopbilus, alone and combined with galactosepositive and galactose-negative strains of Lactobacillus bulgaricus, were used as starter cultures in the manufacture of Swiss and Mozzarella cheese and were paired with Streptococcus lactis (also galactose-positive) in short-method Cheddar cheese manufacture. Experimental Swiss cheese made with the galactosepositive Streptococcus tbermopbilus starter alone contained a large amount of galactose (ca. 26 to 28 /amol/g of curd) 28 h after hooping compared with control Swiss (< 2/amol/g) made with a nongalactose fermenting strain of Streptococcus tbermopbilus and a galactosepositive strain of Lactobacillus bulgaricus. Mozzarella and short-method Cheddar made with only galactose-positive Streptococcus tbermopbilus also contained large amounts of galactose. Swiss cheese made with a galactose-positive strain of Streptococcus tberrnopbilus and a galacrose-negative strain of Lactobacillus bulgaricus had little galactose remaining after 28 h, indicating that the Lactobacillus had a st imulatory effect on galactose metabolism in Streptococcus tbermopbilus. These results indicate that galacrose-fermenting Streptococcus tbermopbilus may have limited potential when used as single strain starter cultures in Swiss cheese, but may be useful when combined with galactose-positive Lactobacillus in the manufacture of Mozzarella cheese. Received May 13, 1985. 1 Department of Microbiology, Boston University School of Medicine, Boston, MA 02118. 2 Kraft, Inc., Glenview, IL 60625. I N T R O D U C T I O N A number of fermented dairy products, including yogurt, Swiss, Mozzarella, and other cheese varieties, are cooked or incubated at elevated temperatures and require a thermophilic lactic starter culture. Thermophilic starter microorganisms generally include strains of Streptococcus tbermopbilus and either Lactobacillus bulgaricus or L. belveticus. These microorganisms are responsible for the conversion of lactose to lactic acid and also contr ibute to important sensory qualities in fermented dairy products (1). Associative growth of S. tberrnopbilus and L. bulgaricus in milk has been described as a symbiotic relationship [(2, 7, 26, also review 17)]. The suggested role of the Lactobacillus species is to degrade casein, providing the nonproteolyt ic S. tbermopbilus with a source of peptides and amino acids (2, 19). Production of formic acid (7) or carbon dioxide (5) by the Streptococcus has been reported to stimulate L. bulgaricus. The sugar fermentat ion pattern in milk products containing S. tbermopbilus and L. bulgaricus led Turner et al. (25) to suggest another important role of the Lactobacillus. Most strains of S. tbermopbilus, unlike other lactic streptococci, are unable to ferment galactose (Gal--) and utilize only the glucose portion of lactose, releasing free galactose into the extracellular medium (10, 13, 21, 22). In a milk fermentation, such as in Swiss cheese manufacture, rates of lactose utilization and galactose accumulation in the curd are very similar (20, 25) and reflect the initially rapid growth of S. tbermopbilus (Martley, Morris, and Gilles, unpublished data). After about 8 h of incubation, lactobacilli begin to predominate and complete the fermentat ion by utilizing the galactose and any remaining lactose (25). In Swiss cheese made without starter Lactobacillus, subsequent fermentat ion of galactose does not occur (25), at least within the immediate 24 h 1986 J Dairy Sci 69:1-8 1