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US scientists at the Utah State University have spent ten years studying Mozzarella and its unique qualities. Report by Donald McMahon and Craig Oberg from the university's Western Dairy Center [...]

An essay is presented on the world of microorganisms at the Yellowstone National Park in the United States. The author notes that in the thermal features of the park, visitors can witness a visual display of microorganisms, and even smell and taste the metabolic efforts of these creatures. The author claims that the national park not only provided a refuge for dwindling population of wildlife, but also prevented exploitation of geothermal resources, preserving a microscopic world.

Salted and unsalted nonfat mozzarella cheese was made by direct acidification and stored at 4°C over 60 d. Changes in cheese opacity were measured by using reflectance L* values while the cheese was heated from 10 to 90°C, then cooled to 10°C, and reheated to 90°C. A characteristic opacity transition temperature (TOP) was obtained for each cheese. Both salt content and storage time influenced TOP. Opacity during heating, cooling, and reheating formed a hysteresis. At d 1, the unsalted cheese became opaque when heated to 20°C, but the salted cheese required heating to 40°C. As the salted cheese was aged, its TOPincreased so that by 60 d the cheese did not become opaque until it was heated to 70°C.

AbstractOf 73 essential oils tested for antibacterial activity against Streptococcus pneumoniaeR36A (an unencapsulated strain) with a paper disk diffusion assay, three oils were highly inhibitory, fifteen moderately inhibitory and the remainder weakly or non-inhibitory. Three oils from each group were selected and tested with a broth assay in which each oil was added to growing cultures of S. pneumoniaeR36A and optical densities (OD) were measured over time. The oils with high antibacterial activity; oregano, thyme and rosewood, induced rapid lysis of R36A as indicated by a decrease in OD, and appearance of dechaining and considerable cell debris within 30 min of addition. The lytic response of R36A to the three oils with moderate activity was variable but all induced some lysis. Oils that were weak inhibitors generally caused slowing of growth but little or no lysis. Several oils were also tested against an encapsulated isolate, S. pneumoniaeIC2. Both disk assay and broth results were similar to those obtained with R36A, except that the oils were slightly less effective. Disk assay results showed some correlation with the broth assay, but were not always predictive of an oil's ability to induce bacterial lysis. Essential oils that induce lysis in S. pneumoniaemay have potential as an alternative treatment for infections caused by drug resistant pneumococci.

The aim of this study was to determine what happens to water in Mozzarella cheeses during storage and to relate those changes to cheese microstructure and functionality. A reduced fat (8% fat) Mozzarella cheese and a control cheese with 19% fat were made and evaluated over 21 d of refrigerated storage at 4°C. Fat, protein, ash, salt, and water were measured on d 1. Meltability, total water, freezable water, and expressible water were measured on d 1, 7, 14, and 21. Even though the reduced fat cheese had a higher total water content than did the control cheese, the reduced fat cheese contained less water on a fat-free basis. The amount of water expressible at 25°C was higher in the control cheese than in the reduced fat cheese and was proportional to the fat content of the cheese. During storage, the expressed serum for both cheeses decreased to zero by d 21. Based on changes observed in microstructure of a commercial Mozzarella cheese (19% fat) during storage, we concluded that the expressed water was derived from water contained in the fat-serum channels that were interspersed throughout the protein matrix. The amount of bound water was lower in the control cheese than in the reduced fat cheese and was proportional to the protein content of the cheese. Bound water levels remained constant throughout storage. During storage of the commercial Mozzarella cheese, the fat-serum channels became smaller with the protein matrix expanding into the areas between the fat globules. By d 21, the fat globules were completely encased by the protein matrix. This expansion of the protein matrix in the commercial cheese occurred over the same time span as the decrease in expressible water of the experimental cheese and indicated that the protein matrix was absorbing the water originally located in the fat-serum channels. Because no change in bound water was observed, the water that had been expressible at d 1 was being absorbed into the protein matrix as entrapped water. The meltability of both cheeses increased during storage while the percentage of entrapped water increased.

Mitomycin C was used to induce temperate bacteriophage from three strains of Pediococcus acidilactici.The new bacteriophage, designated pa97, pa40, and pa42, were characterized based on morphology, DNA homology, and major protein profiles.Morphological attributes (small isometric heads with non-contractile tails) place these bacteriophages within the B1 group of the family Siphovirdae.Restriction endonuclease digests suggested that the bacteriophage genomes were linear molecules without cohesive ends, and between 33 and 37 kilobases in length.All three bacteriophages possessed one major protein with an estimated mass of 30 to 35 kilodaltons.Bacteriophage pa42 also contained a second major protein of approximately 47 kilodaltons.DNA-DNA hybridization showed bacteriophages pa40 and pa42 were homologous to each other, but not to pa97, suggesting that Pediococcus acidilacticibacteriophage fall into at least two different species.

Increased consumer demand for yogurt and Italian cheeses, particularly Mozzarella, over the past decade has intensified production demands on thermophilic starter cultures. Dramatically elevated production rates within existing facilities have created problems analogous to those experienced years ago by the dairy industry for mesophilic lactococci when Cheddar cheese production increased dramatically. In contrast to mesophilic lactococci, however, diversity among lactic genera that contain thermophilic species has impeded the progress of microbiological research required to meet these challenges. For example, the bacteriophages that attack these cultures are becoming an important commercial problem, yet little is known about them. Another unique characteristic of thermophilic lactic cultures is the microbial interaction between lactobacilli and streptococci cultured together. Further characterization of this interaction, particularly its effects on physical characteristics of the product, would benefit the cheese industry. Diversity of proteolytic and peptidolytic enzymes exists within lactobacilli. These enzymes are important in cheese flavor and texture development, therefore, further characterization of these systems would facilitate manipulation of organoleptic and physical properties of products. Finally, utilization of other, less studied thermophilic species would facilitate manufacture of new products and improved quality or manufacturing processes.

Nonfat Mozzarella cheese curd was manufactured in 227-kg batches on 3 separate d using direct acidification. Cheeses with differing NaCl concentrations were obtained by dividing curd into separate lots that received various applications of dry NaCl (0, 0.5, and 1.0% NaCl, wt/wt) and hot brine (0, 5, and 10% NaCl, wt/vol) stretching treatments. The NaCl, Ca, ash, fat, moisture, and protein contents as well as cheese meltability and expressible serum of each cheese were determined. In addition, observations were made on cheese color and functionality over 24 d of storage at 4̊C. Transmission and scanning electron micrographs of unsalted and salted cheeses were evaluated to determine the differences in the protein matrix. The type of NaCl application and the NaCl content of the cheeses influenced the cheese moisture, meltability, expressible serum, microstructure, and ultrastructure. The moisture content was highest in cheeses in which the curd was salted before stretching. The melt was the lowest in cheeses that were unsalted. Cheeses that were stretched in either 5 or 10% brine had <1% of the amount of expressible serum observed in unsalted cheese. Unsalted cheeses had a more open structure than did salted cheeses. Pockets of free serum were distributed throughout the protein matrix of the unsalted cheese, thus producing light-scattering surfaces and making the cheese opaque. In contrast, the salted cheeses had a more homogeneous protein matrix that lacked light-scattering surfaces, resulting in a translucent cheese. Neither NaCl concentration nor method of salting affected.the Ca content of the cheeses.

Lactobacillus acidophilus, L. casei, and L. helveticusare industrially important bacteria for the manufacture of fermented dairy foods. Despite widespread commercial use, there is limited knowledge of basic physiological responses by these bacteria to dairy processing conditions. This study investigated the heat shock (HS) response in L. acidophilusNCFM, L. caseiLC301, and L. helveticusLH212. Thermotolerance experiments showed HS improved the ability of log phase L. acidophilusNCFM, L. caseiLC301, and L. helveticusLH212 cells to withstand a 20 min high temperature incubation by approximately 27-, 5- and 11-fold, respectively. Two-dimensional polyacrylamide gel electrophoresis showed HS induced synthesis of several proteins in each Lactobacillusspecies, and Western blots revealed these molecules included homologs to the universally conversed heat shock proteins DnaK, GroEL, ClpB, and GrpE. DnaJ was also detected, but expression of this protein was not stimulated by HS in any of the Lactobacillusspecies tested.

Reduced fat Mozzarella cheese was produced usingStreptococcus thermophilusandLactobacillus helveticus, and either total or partial replacement ofL. helveticuswithLactobacillus caseissp.casei. Stretch, melt and cook colour were determined at 1, 7, 14, and 28 d. All cheeses decreased in stretch during the first 7 d of storage, but there were no significant differences between culture types. Reduced fat cheese made withL. helveticusandS. thermophilusshowed the greatest stretch at both 1 and 7 d. After 14 d, all cheeses showed the same level of stretch. Storage time significantly affected stretch and melt. All reduced fat cheeses showed less melt through 14 d than the control cheese. Reduced fat cheese made with partial or total replacement ofL. helveticuswithL. caseissp.caseihad more stretch and less cook colour at day 1 than the part-skim Mozzarella. At 28 d of storage, all cheeses showed the same levels of melt and stretch with the reduced fat cheeses having less cook colour. Both scanning and transmission electron microscopy showed substantial differences between reduced fat and part-skim Mozzarella cheese during the manufacturing process. Reduced fat Mozzarella had a much more dense protein matrix with fewer small vacuoles (voids left in the cheese upon removal of fat with chloroform, particularly after stretching). TEM showed that after set, the reduced fat cheese had much larger protein strands where casein micelles had formed dense aggregates. Overall, the physical properties of reduced fat Mozzarella cheese made in this study, including those made with theL. caseiculture adjunct, compared favourably to part-skim Mozzarella cheese made with conventional thermophilic cultures.

Low fat (6%) Mozzarella cheese was made in 10-L vats using an exopolysaccharide-producing starter culture consisting of Streptococcus thermophilusand Lactobacillus delbrueckiissp. bulgaricus. A control cheese was made using strains of S. thermophilusand Lactobacillus helveticusthat did not produce exopolysaccharide. Both starter cultures were also used with the addition of a mesophilic exopolysaccharide-producing adjunct culture consisting of Lactococcus lactisssp. lactisand L. lactisssp. cremorisstrains. Moisture content of the cheese was measured at d 1, and melt was measured at 1, 7, 14, and 28 d of storage at 4°C. Analysis of variance showed significant differences in moisture and melting properties between cheeses made with or without exopolysaccharide-producing starter cultures. Cheeses made with the addition of the adjunct culture showed significant differences in moisture, but not in melting properties. The moisture content of cheeses made with both the exopolysaccharide-producing starter and the adjunct cultures increased 4%, and the use of the exopolysaccharide-producing starter cultures alone increased moisture content 3% over that of the control cheese. Melt also increased in cheeses as moisture content increased.

Exopolysaccharide-producing starter cultures, consisting of single strains of Streptococcus thermophilusMR-1C and Lactobacillus delbrueckiissp. bulgaricusMR-1R, were used to make three trials of low fat (6% fat) Mozzarella cheese. Our aim was to determine whether observations made using small [10-kg (22-lb) capacity] vats with manual stretching of curd could be replicated using pilot-scale [454-kg (1000-lb) capacity] double-O vats with mechanical stirring and stretching of the curd. A control cheese was made using S. thermophilusTA061 and Lactobacillus helveticusLH100 as starter cultures that did not produce exopolysaccharides. Cheese was measured for moisture content and meltability at d 1. Cheese made with the exopolysaccharide-producing starter cultures had 2% higher moisture contents and exhibited slightly higher meltability. Because of changes in the procedure to manufacture low fat cheese that were necessary when the mechanized vats were used, the cheeses made in the double-O vats were slightly lower in moisture than cheeses previously made in the hand-stirred laboratory-scale vats.

Low fat Mozzarella cheese was made from milks containing casein to fat ratios of 3.0, 5.0, 7.0, and 8.0. Prior to addition of rennet, milk was pasteurized at 79°C for 28s and then acidified to pH 6.0 with lactic acid. Three replicates of each cheese were made in 7-L vats and stored at 4°C. Functional properties as pizza cheese were evaluated. Cheese moisture and fat contents were evaluated at 1 d. Apparent viscosity and extent of flow of melted cheese, cook color, and proteolysis were evaluated at 1, 7, 14, and 28 d. Moisture content measured by a rapid microwave oven method underestimated the moisture content of low fat cheeses; probable moisture was calculated by component analysis. The part-skim Mozzarella control with 19% fat had a moisture content of 51%; the moisture contents of the low fat cheeses containing 2 to 5% fat were 63%. Low fat cheeses did not melt as well as did the part-skim Mozzarella cheese, although the differences between the cheeses with 2 and 5% fat were insignificant. Storage for 28 d only marginally increased the meltability of low fat cheese. Lower fat content also increased cook color. The amount of intact αs-CN decreased by at least 48% in all cheeses as a result of proteolysis during 28 d of storage.