**7. Cholesterol uptake and release by** *Lactococcus* **in the simulated human gastrointestinal tract**

#### **7.1 Cholesterol uptake by** *Lactococcus* **under conditions of simulated gastric fluid**

Cholesterol uptake by *Lactococcus* cells in simulated gastric fluid depends on the amount of biomass [4]. Ziarno [4] carried out in vitro experiments with the use of

**87**

*Cholesterol Uptake and Survival of* Lactococcus lactis *Strains in Fluids Simulating the Human…*

industrial starter cultures of mesophilic lactic bacteria, including *Lactococcus*. The cultures were grown for 5 h at 37°C in a simulated gastric fluid containing addi-

cholesterol was bound by *Lactococcus* cells contained in mixed cultures than cells from *Lactococcus lactis* monocultures. Bacterial cells present in the mixed cultures

from *Lactococcus lactis* cultures reduced cholesterol concentration in the simulated

removed 1.4–2.3 times more cholesterol than bacterial cells with 1× cell concentration. In turn, biomasses with 0.1× bacterial cell concentration bound 2.2–4.6 less cholesterol than bacterial cultures with 1× cell concentration. This means that the conditions prevailing in the stomach may favor removal of cholesterol by bacterial cells independent of their viability. However, it remains unknown whether bacterial cells release the bound cholesterol after entering the gastrointestinal tract and whether it may penetrate to the blood. Similar studies concerning aflatoxin B bound by the cell wall of lactic bacilli suggest that such assimilation by the cell wall may be

robust [81–84]. This may indicate that cholesterol binding is also robust.

**7.2 Release of cholesterol bound by** *Lactococcus* **in the conditions of simulated** 

[4].

bacteria cells and uncovering of additional binding sites for aflatoxin B1.

**7.3 Cholesterol removal by** *Lactococcus* **in the conditions of simulated** 

As stated by Ziarno and Bartosz [113], cholesterol removal by lactic acid bacteria in intestinal fluid is less pronounced than in culture broth. This is further confirmed by the experiments of Ziarno [4] conducted under in vitro conditions with *Lactococcus* isolates originating from industrial starter cultures. The mentioned cultures were grown at 37°C for 6 h in a simulated intestinal fluid with addition of cholesterol. The tested *Lactococcus* cultures resulted in a reduction of cholesterol

In the majority of the tested cultures, the influence of biomass concentration on the degree of cholesterol removal was statistically significant; however, 10-fold concentrated biomass did not remove 10 times more cholesterol than onefold concentrated

Similar tendencies are observed in the case of studies conducted on aflatoxin B1 binding by lactic acid bacteria [81, 84]. El-Nezami et al. [81] observed that aflatoxin B1 uptake from culture medium by selected lactic acid bacteria cultures depended on their population and culture temperature. The same was demonstrated by Lee et al. [84]. Identical relationships were observed in the present study with regard to binding and release of cholesterol by lactic acid bacteria cells. Moreover, Lee et al. [84] concluded that thermal killing of bacteria resulted in a change of the surface of

The study of Ziarno [4] indicates that the binding of a portion of cholesterol by lactic acid bacteria cells is robust enough so that it is not released in the conditions of gastric fluid. The study was carried out using isolates of *Lactococcus* originating from industrial monocultures and mixed cultures. Bacterial cells present in the tested cultures released 51–84% of the removed and bound cholesterol independent of bacterial cells' viability. The biomass of dead cells released lower amount of cholesterol than the biomass with viable cells, but it also bound and removed lower amount of cholesterol from the culture medium earlier. Biomass of live *Lactococcus* 

removed cholesterol in the range from 0.012 to 0.020 g/dm3

*lactis* cells removed an average of 0.063 g cholesterol/dm3

cells removed average of 0.033 g/dm3

from the initial content of 0.543 g/dm3

of cholesterol. The study demonstrated that higher amount of

. 10× concentrated bacterial biomasses

. In turn, bacterial cells

, whereas biomass of dead

to the level between 0.011 and 0.087 g/dm3

.

*DOI: http://dx.doi.org/10.5772/intechopen.88462*

gastric fluid by an average 0.005 g/dm3

tion of 0.511 g/dm3

**gastric fluid**

**intestinal fluid**

*Cholesterol Uptake and Survival of* Lactococcus lactis *Strains in Fluids Simulating the Human… DOI: http://dx.doi.org/10.5772/intechopen.88462*

industrial starter cultures of mesophilic lactic bacteria, including *Lactococcus*. The cultures were grown for 5 h at 37°C in a simulated gastric fluid containing addition of 0.511 g/dm3 of cholesterol. The study demonstrated that higher amount of cholesterol was bound by *Lactococcus* cells contained in mixed cultures than cells from *Lactococcus lactis* monocultures. Bacterial cells present in the mixed cultures removed cholesterol in the range from 0.012 to 0.020 g/dm3 . In turn, bacterial cells from *Lactococcus lactis* cultures reduced cholesterol concentration in the simulated gastric fluid by an average 0.005 g/dm3 . 10× concentrated bacterial biomasses removed 1.4–2.3 times more cholesterol than bacterial cells with 1× cell concentration. In turn, biomasses with 0.1× bacterial cell concentration bound 2.2–4.6 less cholesterol than bacterial cultures with 1× cell concentration. This means that the conditions prevailing in the stomach may favor removal of cholesterol by bacterial cells independent of their viability. However, it remains unknown whether bacterial cells release the bound cholesterol after entering the gastrointestinal tract and whether it may penetrate to the blood. Similar studies concerning aflatoxin B bound by the cell wall of lactic bacilli suggest that such assimilation by the cell wall may be robust [81–84]. This may indicate that cholesterol binding is also robust.
