D

+

+

+

+

glu, glucose; gal, galactose; lac, lactose; EMG, Embden-Meyerhof glycolytic pathway;

PKP, phosphoketolase pathway

Lc. cremoris, Lactococcus lactis subsp. cremoris

Lc. lactis, Lc. lactis subsp. lactis (citrate-)

Lc. diacetylactis, Lc. lactis subsp. lactis biovar. diacetylactis

Leuc. cremoris, Leuconosstoc mesenteroides subsp. cremoris glu, glucose; gal, galactose; lac, lactose; EMG, Embden-Meyerhof glycolytic pathway;

PKP, phosphoketolase pathway

Lc. cremoris, Lactococcus lactis subsp. cremoris

Lc. lactis, Lc. lactis subsp. lactis (citrate-)

Lc. diacetylactis, Lc. lactis subsp. lactis biovar. diacetylactis

Leuc. cremoris, Leuconosstoc mesenteroides subsp. cremoris facturing protocol for the different cheese varieties and are exemplified by comparing normal-fat Herrgard 45% with relatively high cooking temperatures and long cooking time and low-fat Danbo 20%, for which both lower temperatures and shorter time periods are used (Fig. 2). Typically the acidifiers (Lc. cremoris and Lc. lactis) grow to a higher number in cheeses with lower cooking temperatures, which are closer to the optimal temperatures for these bacteria (5). In the semihard cheeses made using the lower temperatures also, Lc. cremoris has an advantage over Lc. lactis which will be more important in those made at higher temperatures (6). In cheeses where the growth of Lc. diacetylactis is limited—for instance, because of the cooking temperature—the Leuconostoc that grow at lower pH than Lactococcus may develop to a higher number in cheese because there is more citrate left. The normal variation of milk influences the starter population—for example, less manganese in milk during winter is unfavorable to Leuconostoc (7).

The undefined DL-starters contain an unknown number of strains of bacteria. During growth, these strains react in different ways to environmental changes such as variations in milk and cheese composition, pH, and temperature. Many properties of importance for cheese manufacture vary among the bacterial strains, such as growth rate, sensitivity to temperatures and to autolysis, phage tolerance, and the proteolytic and peptidolytic activities as well as other metabolic activities. Important factors influencing the dynamics of the DL-starter population have been reviewed (6).

The number of bacteria and the ratio between the different starter strains in fresh cheese will certainly influence the ripening process. The starter bacteria do not multiply to larger numbers than they have reached already after a day or two, when the lactose is exhausted. After that, the numbers of the different bacteria decrease or are maintained at a certain level. Viable Lc. diacetylactis have been found at constant levels (107-108/g) over a period of time for several months in semihard cheese, whereas the total number of Lc. lactis and Lc. cremoris decreases rapidly to 1% or less within a couple of weeks. Leakage of enzymes, autolysis of bacterial cells, and possibility for intracellular enzymes to act directly in the cheese matrix are important parts of the ripening process. The bacteria exist in many different physiological states in cheese, and a decreasing number of starter bacteria found in cheese is no guarantee that free enzymes are active in the cheese matrix (5,8). The existence of bacterial spheroplasts in cheese have been shown by electron microscopy (9) and evidence has been given for strain dependence of enzyme release from spheroplasts (10). A large variation in autolytic behavior has been found among single strains of starter Lactococcus under conditions of starvation in phosphate buffers (11).

Figure 2 Development of mesophilic DL-starter in normal-fat (45% FDM) Herrgard and low-fat (20% FDM) Danbo cheese. Filled squares, Lc. lactis subsp. cremoris and subsp. lactis (citrate-); open squares, Lc. lactis subsp. lactis (citrate+); filled diamonds, Leutonostoc. The bacteria were analyzed using the Leesment method. (From Refs. 40 and 41).

Figure 2 Development of mesophilic DL-starter in normal-fat (45% FDM) Herrgard and low-fat (20% FDM) Danbo cheese. Filled squares, Lc. lactis subsp. cremoris and subsp. lactis (citrate-); open squares, Lc. lactis subsp. lactis (citrate+); filled diamonds, Leutonostoc. The bacteria were analyzed using the Leesment method. (From Refs. 40 and 41).

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