-  A clear demonstration of acidification is found in yogurt, the product of milk fermentation by the Lactobacillus bulgaricus when they  acidify their environment through the conversion of pyruvate to lactate and adapt to the lower pH. This is also an essential process to regenerate NAD(+) used during glycolysis for them.

-During fermentation, lactic acid production causes the pH to fall to about 4.2, down from an initial value of 6.6 to 6.8 in milk.

-The low pH produced during  fermentation of lactose into lactic acid by Lactobacillus bulgaricus inhibits the growth of proteolytic bacteria.

bile salt tolerance.

Microencpasulation of various bacterial cultures including probiotics has been a common practice for extending their storage life and converting them into a powder form for ease of their use. There are several techniques such as spray drying, freeze drying, fluidized bed drying for encapsulating the cultures and converting them into a concentrated powdered form. 

Microencapsulation is a process in which the cells are retained within an encapsulating membrane to reduce cell injury or cell loss. The encapsulation techniques applied to probiotics for the use in fermented milk products or biomass production can be classified into 2 groups, depending on the method used to form the beads: extrusion (droplet method) and emulsion or two-phase system.

Extrusion is the oldest and most common approach to making capsules with hydrocolloids. It simply involves preparing a hydrocolloid solution, adding microorganisms to it, and extruding the cell suspension through a syringe needle in the form of droplets to free-fall into a hardening solution or setting bath. The supporting material used for extrusion is alginate, which is a linear heteropolysaccharide of D-mannuronic and L-guluronic acid extracted from various species of algae.

In emulsion technique, a small volume of the cell-polymer suspension (discontinuous phase) is added to a large volume of a vegetable oil (continuous phase) such as soybean oil, sunflower oil, canola oil or corn oil. The mixture is homogenized to form a water-in-oil emulsion. Once the water-in-oil emulsion is formed, the water-soluble polymer must be insolubilized (cross-linked) to form tiny gel particles within the oil phase. For food applications, vegetable oils are used as the continuous phase. There are many supporting materials used with the emulsion technique. These include a mixture of K-carageenan and locust bean gum,  cellulose acetate phthalate,  alginate,  chitosan  and gelatin. 

Because of the many benefits offered by encapsulation, entrapped microorganisms can be used to advantage for producing dairy products such as yoghurt, cheese and frozen milk products, as well as for biomass production. The continuous manufacture of yoghurt with entrapped microorganisms (Lb. delbrueckii ssp. bulgaricus and Str. thermophilus) is more complicated than the traditional batch method, but presents many advantages. It is possible to obtain a product with constant characteristics because the residence time, acidity and continuous inoculation of milk with a constant bacilli/cocci ratio can be controlled at a desired pH.

 

The study demonstrated “an efficient and rapid molecular genotyping method to identify strains with good fermentation traits”. The researchers conducted this study by identifying different “fermentation time, acidification rate, pH, titratable acidity, and flavor characteristics (acetaldehyde concentration)” from several L. bulgaricus strains.In terms of biotechnology application, it has “the potential to replace time-consuming conventional methods based on direct measurement of phenotypic traits.” 

 

 

The researchers conducted a kinetics study of lactic acid production from Carob pods syrup and Date syrup. So they used the cultures of L. bulgaricus and S. thermophilus as the “biologic material”, to study their growth in those 2 syrups. They found that “these medium are favourable to the lactic acid fermentations.” According to the researchers, “the different physicochemical and biochemical analyzes show the richness of date and carob pods syrups in nutritional elements that makes them favorable to the lactic acid fermentations.”

 

The researchers aimed to evaluate “the role of mono- and oligosaccharides present in fructo-oligosaccharides (FOS) mixtures as protective agents” for L. bulgaricus during its “freeze-drying and storage”. They wanted to identify the “protective effect” of FOS during the preservation of the bacteria. They found that the “protection is the result of a balance between monosaccharides, sucrose and larger FOS in the mixtures” where “the smallest sugars are more efficient in protecting lipid membranes, and the larger ones favor the formation of vitreous states.”

4) Ai, Z., Lv, X., Huang, S., Liu, G., Sun, X., Chen, H., . . . Feng, Z. (2017). The effect of controlled and uncontrolled pH cultures on the growth of Lactobacillus delbrueckii subsp. bulgaricus. LWT - Food Science and Technology, 77, 269-275. doi: http://dx.doi.org/10.1016/j.lwt.2016.11.057 

 

This study wanted to clarify “the effect of uncontrolled and controlled pH cultures on the growth of L. bulgaricus Q7” as previous studies proposed that “L. bulgaricus Q7 in uncontrolled pH cultures showed better acidic activity in milk”. “The growth kinetics, physiological state, amino acid consumption and necessary profiles of L. bulgaricus Q7 were investigated” and “the results showed that the average growth rate and final biomass of L. bulgaricus Q7 were higher in uncontrolled pH cultures than those in controlled pH cultures.” The results obtained from this study could help “industrial starter producers and fermented-product manufacturers by allowing them to formulate new strategies to enhance biomass" of the bacteria for dairy production.