**2. Influence of lactic acid bacteria, including** *Lactococcus***, on the cholesterol level in humans**

The extensive collection of scientific publications devoted to health-promoting properties of lactic acid bacteria includes articles presenting studies on the possibility of reducing the cholesterol level in human and animal organisms through consumption of fermented milk products including traditional and probiotic strains of lactic acid bacteria.

As early as in 1974, Mann and Spoerry [5, 6] determined the reduced level of cholesterol in the blood serum of men from the African Maasai, which stemmed from the consumption of high amounts of fermented milk containing wild lactic acid bacteria strains. This research enabled researchers to look for the methods of reducing the cholesterol level in the human organism, although the first reports on the positive impact of fermented milk drinks on the reduction of the cholesterol level in live organisms were criticized due to their methodological and technical errors. However, these studies opened a new route for researchers in terms of the search of methods of cholesterol level reduction in the human organism, increasing the chances of the modern human populations in the combat with cardiovascular disorders [7–13].

**77**

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

The interpretation of study results concerning the influence of lactic acid bacteria on the cholesterol level obtained under in vivo conditions on living organisms is not easy. Organisms of animals and humans differ in terms of mechanisms of regulation of lipid metabolism, including cholesterol. It should be taken into account that introduction of lactic acid bacteria to the gastrointestinal tract does not only have a direct influence on the cholesterol metabolism but also on the entire intestinal microflora, which is capable of metabolizing cholesterol and other lipids, as indicated by the study results obtained by Hosono et al. [14]. This might be the cause for the difficulties in proving the positive influence of lactic acid bacteria on

Certain in vitro studies from this field conducted within the last dozen or so years enabled assumption that it is lactic acid bacteria that produce the effect of cholesterol level decrease in humans and animals consuming fermented milk products. Numerous study results are available in the literature concerning cholesterol level reduction under laboratory conditions in model media. Decrease of the cholesterol level in culture media has been determined for numerous species and strains of lactic acid bacteria. The majority of research concerns thermophilic bacilli of the genus *Lactobacillus* [14–22]. Other genera of bacteria exhibiting similar property include *Streptococcus*, *Enterococcus*, *Lactococcus*, and *Leuconostoc* [20, 21, 23–26]. According to these studies, the cholesterol binding capacity can be exhibited not only by strains with probiotic characters documented by research but also certain lactic acid bacteria species that are traditionally used to manufacture dairy products and included in dairy starter cultures. It should be borne in mind that despite the results of in vitro and in vivo studies on animals and humans, it is impossible to unambiguously confirm or negate the capacity of lactic acid bacteria to reduce the cholesterol level in the blood serum due to the possibility of methodological and technical errors and the lack of reproducibility [27]. The more so that the level of cholesterol in blood serum is positively correlated not only with the amount of cholesterol taken with food but also depends on the intake of saturated fatty acids and refined carbohydrates. Therefore, the definite confirmation of the manner in which lactic acid bacteria exercise a benefi-

cial influence on the level of cholesterol in humans is still missing [28–30].

**3. Mechanism of cholesterol level reduction by lactic acid bacteria** 

The assumption that lactic acid bacteria may cause reduction of the cholesterol level directly in fermented milk products or live organisms was made on the basis of numerous in vivo and in vitro studies demonstrating that certain lactic acid bacteria produced a reduction of the cholesterol level in the blood serum of experimental animals or human volunteers or in model culture media. This type of research has been conducted since the 1970s [5, 7, 8, 14, 31–36]. The majority of these studies concern the influence of consumption of fermented products or products containing lactic acid bacteria strains, including primarily probiotic strains. In that time, several scientific hypotheses were formed on the mechanisms through which the phenomenon of cholesterol level reduction performed by lactic acid bacteria may occur. Literature data lists here primarily cholesterol binding, enzymatic deconjugation of bile salts, production of exopolysaccharides, and synthesis of short-chain

Cholesterol binding by the bacterial cell wall and its incorporation into the cell wall or cytoplasmic membrane of bacterial cells are listed among the major mechanisms [9, 19, 23–25, 43]. It is known that cholesterol binding may have different paths. Certain bacteria incorporate cholesterol into the cell wall, as exhibited by

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

the cholesterol level in the human organism.

**including** *Lactococcus* **in humans**

fatty acids (SCFAs) [15, 21, 23–25, 28, 29, 36–45].

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

The interpretation of study results concerning the influence of lactic acid bacteria on the cholesterol level obtained under in vivo conditions on living organisms is not easy. Organisms of animals and humans differ in terms of mechanisms of regulation of lipid metabolism, including cholesterol. It should be taken into account that introduction of lactic acid bacteria to the gastrointestinal tract does not only have a direct influence on the cholesterol metabolism but also on the entire intestinal microflora, which is capable of metabolizing cholesterol and other lipids, as indicated by the study results obtained by Hosono et al. [14]. This might be the cause for the difficulties in proving the positive influence of lactic acid bacteria on the cholesterol level in the human organism.

Certain in vitro studies from this field conducted within the last dozen or so years enabled assumption that it is lactic acid bacteria that produce the effect of cholesterol level decrease in humans and animals consuming fermented milk products. Numerous study results are available in the literature concerning cholesterol level reduction under laboratory conditions in model media. Decrease of the cholesterol level in culture media has been determined for numerous species and strains of lactic acid bacteria. The majority of research concerns thermophilic bacilli of the genus *Lactobacillus* [14–22]. Other genera of bacteria exhibiting similar property include *Streptococcus*, *Enterococcus*, *Lactococcus*, and *Leuconostoc* [20, 21, 23–26]. According to these studies, the cholesterol binding capacity can be exhibited not only by strains with probiotic characters documented by research but also certain lactic acid bacteria species that are traditionally used to manufacture dairy products and included in dairy starter cultures.

It should be borne in mind that despite the results of in vitro and in vivo studies on animals and humans, it is impossible to unambiguously confirm or negate the capacity of lactic acid bacteria to reduce the cholesterol level in the blood serum due to the possibility of methodological and technical errors and the lack of reproducibility [27]. The more so that the level of cholesterol in blood serum is positively correlated not only with the amount of cholesterol taken with food but also depends on the intake of saturated fatty acids and refined carbohydrates. Therefore, the definite confirmation of the manner in which lactic acid bacteria exercise a beneficial influence on the level of cholesterol in humans is still missing [28–30].
