ADSA Foundation Scholar Award: Possibilities and Challenges of Exopolysaccharide-Producing Lactic Cultures in Dairy Foods

Classification of lactic acid bacteria based on the type of exopolysaccharide (EPS) produced. Strains producing capsular but not unattached EPS and noncapsule-forming nonropy strains producing unattached EPS have not been confirmed.

Photomicrographs of capsule-forming strains of Streptococcus thermophilus S3855S (top) and Lactobacillus delbrueckii ssp. bulgaricus RR (bottom). Arrow points to bacterial capsule; bar = 10μm. Source: Hassan et al. (1995a).

Photomicrographs of microstructure development in yogurt made with encapsulated lactic cultures obtained by using confocal scanning laser microscopy in reflectance mode. Top left: pH=6.4, top right: pH=5.40, bottom right: pH=5.35, and bottom left: pH=5.0. Long arrows indicate pores occupied by bacterial cells and their capsule; short arrows indicate protein aggregates; bar = 10μm. Source: Hassan et al. (1995b).

Optical sections of yogurt made using capsule-nonforming (left) and capsule-forming (right) lactic cultures at pH 5.0 (top), pH 4.2 (bottom left), and 4.4 (bottom right). Long arrows indicate pores occupied by bacterial cells and their capsule; short arrows indicate protein aggregates; bar = 10μm. Source: Hassan et al. (1995b).

Conventional scanning electron microscopy image of milk fermented with an exopolysaccharide (EPS)-producing culture. Fine filaments indicate dehydrated EPS. Source: Anne Skriver, Chr. Hansen, Denmark.

Distribution of exopolysaccharides (EPS) in set (left) and stirred (right) yogurts made with a moderately ropy strain (top) and highly ropy strain (bottom). Light grey (green) = EPS; dark grey (red-orange) = protein network; bar = 10μm. Source: Hassan et al. (2002b). Color figure available at http://jds.fass.org/content/vol91/issue4/.

Cryo-scanning electron microscopy images of milk fermented with a moderately ropy strain (top) and a highly ropy strain (bottom). Specimens were etched for 10min. P=protein, E=exopolysaccharides, and W=casein aggregates covered with frozen water; bar (top image) = 5μm. Source: Hassan et al. (2003a). Reprinted from Int. Dairy J. vol. 13, Observation of bacterial exopolysaccharide in dairy products using cryo-scanning electron microscopy, Hassan, AN, Frank, JF, and Elsoda, M.©2003, with permission from Elsevier.

Cryo-scanning electron microscopy images of exopolysaccharides (EPS) produced by a highly ropy strain (top) and a moderately ropy strain (bottom). Specimens were etched for 10min. W = frozen water. Source: Hassan et al. (2003a). Reprinted from Int. Dairy J. vol. 13, Observation of bacterial exopolysaccharide in dairy products using cryo-scanning electron microscopy, Hassan, AN, Frank, JF, and Elsoda, M. © 2003, with permission from Elsevier.

Volume rendering of yogurt made using capsule-forming nonropy cultures to give different views compiled from 60 optical sections obtained by using confocal scanning laser microscopy in reflectance mode. The rendered image is approximately 36μm thick. Arrows indicate pores occupied by capsule-forming bacterial cells. Source: Hassan et al. (1995b).

Microstructure of reduced-fat Cheddar cheese made with a highly ropy culture of Lactococcus lactis ssp. cremoris (JFR1). Arrow indicates exopolysaccharides in a large pore. Source: Hassan and Awad (2005).

Microstructure of reduced-fat cheeses made with a highly ropy culture of Lactococcus lactis ssp. cremoris (JFR1) (top) and an exopolysaccharide-nonproducing culture (bottom). Long arrow indicates exopolysaccharide; short arrow indicates depression originally occupied by a fat globule and formed as a result of surface fracture; P = background protein network; F = fat. Source: Hassan and Awad (2005).

Microstructure of 6-mo-old reduced-fat Cheddar cheese made with a highly ropy strain of Lactococcus lactis ssp. cremoris (JFR1) (top) and an exopolysaccharide (EPS)-nonproducing culture (middle) and full-fat cheese (bottom). Long arrow indicates a large pore occupied by EPS; short arrow indicates a fracture in the protein network; P = background protein network. Source: Hassan and Awad (2005).

Photomicrographs of acid-coagulated cheese (Karish) made with an exopolysaccharide (EPS)-producing culture (top) and a nonproducing culture (bottom). Large arrows indicate masses of EPS; small arrows indicate bacterial cells. Note the dense protein network in cheese made with the nonproducing culture (bottom). Source: Hassan et al. (2003a). Reprinted from Int. Dairy J. vol. 13, Observation of bacterial exopolysaccharide in dairy products using cryo-scanning electron microscopy, Hassan, AN, Frank, JF, and Elsoda, M. © 2003, with permission from Elsevier.