**3. Materials and methods**

*Prebiotics and Probiotics - Potential Benefits in Nutrition and Health*

values up to 9.6; however, most grow between pH of 4 and 4.5 [19].

There are many probiotic bacteria that are used for human consumption, although the most used are *Lactobacillus* spp. These lactic acid bacteria have been used for food preservation through fermentation for hundreds of years, in addition to providing flavor and texture, and they increase the nutritional value and are also found in the gastro-intestinal tract of humans [20]. In addition, they are a key factor in the processes of competitive exclusion and immunomodulation carried out by commensal organisms. *Lactobacillus acidophilus* is a Gram-positive, non-sporeforming bacterium, homofermentative anaerobic, and catalase negative, 2–10 μm in diameter, which has an optimal growth temperature of 37°C and is a typical intestinal bacterium in humans [21]. This microorganism is not part of the natural flora of milk and acts on it very slowly, which is why it is essential to avoid contamination

*Lactobacillus acidophilus* uses the glycolysis or Embden-Meyerhof-Parnas route (EMP) to ferment hexoses and produce lactic acid. Lactic acid does not contribute to the aroma because it is odorless, but it helps the sour taste of dairy products [13]. *Lactobacillus acidophilus* LA-1/LA-5 is one of the main species of microorganisms that can potentially be used as probiotic cultures in dairy products. Some examples in the market of fermented milk products that include *Lactobacillus acidophilus* are

Today, the main function of fermented milk is to prolong shelf life, improve flavor and digestibility, and manufacture a wide range of dairy products. In fermented milk products, probiotic bacteria can act in the treatment of some infectious, atopic, and tumoral diseases, among others [23]. Fermented milks can be classified based on different criteria, among them are its fat content, the concentration of milk, separation of the whey, the use of milk from different species, and the type of fermentation process. Based on the type of fermentation, there are the products with a lactic fermentation such as ymer, langfil, viili, yogurt, and acidified milk. Among the products in which lactic fermentation is combined with the production of alcohol are kefir and koumiss [8]. Today, the main function of fermented milk is to prolong shelf life, improve flavor and digestibility, and manufacture a wide range of dairy products. In fermented milk products, probiotic bacteria can act in the treatment of some infectious, atopic, and tumoral diseases, among others [23]. Fermented milks can be classified based on different criteria, among them are its fat content, the concentration of milk, separation of the whey, the use of milk from different species, and the type of fermentation process. Based on the type of fermentation, there are products with a lactic fermentation such as ymer, langfil, viili, yogurt, and acidified milk. Among the products in which lactic fermentation is

*2.2.1 Lactobacillus acidophilus*

during the manufacture of a product [8].

**2.3 Fermented beverages**

Bioghurt, Aktifit, Actimel, Bifilac, Kaiku, and Kefir [22].

combined with the production of alcohol are kefir and koumiss [8].

There are several genera of LAB, which are classified as homofermentative and heterofermentative based on the final product of their fermentation. The homofermentative produce lactic acid as a product of the fermentation of glucose. On the other hand, the heterofermentative produce lactic acid in addition to other products such as acetates, ethanol, and carbon dioxide as a product of its fermentation [18]. The LAB are characterized by Gram-positive cocci or bacilli, catalase and oxidase negative, facultative anaerobic, non-sporulated, and non-motile. In addition, they are tolerant acid, being able to grow some at pH values as low as 3.2 and others at

**20**
