**3.1 Biofilm formation**

 The incorporation, using different proportions of corn starch and buttermilk to obtain biopolymers, as well as the influence of temperature on the polymeric structure, is reported in the literature [13]. The study was justified by the application of the biopolymer in sustainable packaging, replacing polymers derived from petroleum, and reusing the by-product of the manufacture of butter. To obtain the biofilm, the author incorporated the phospholipids present in the milk derivative into polytetrafluoroethylene. The plates, containing the polymers, were dried during the minimum period of 24 hours in two different temperatures at 2% relative humidity. The thickness of the biofilms was monitored, which remained as a surface density of 55 g/m2 . The samples remained in desiccators under temperature control. The results indicated that in the polymers in which the buttermilk was incorporated, there was initially a separation of the phases, resulting from a certain incompatibility between buttermilk and starch, which significantly affected the modulus elasticity and tensile strength. The heating of the films, added with buttermilk, promoted a positive impact in relation to the resistance, which is justified by the gel formation that, during drying of the film, reduces the critical concentration for its formation. The permeability to water was not altered by the addition of up to 50% of buttermilk. Under heating, there was a decrease in the mass transport property due to the greater adhesion of the components of the polymer mesh. Finally, the rheological study classified the polymer as Newtonian, in addition to having antioxidant properties when subjected to heat treatment by the release of active peptides, and without antimicrobial activity under *Listeria innocua* [13]. In general, buttermilk, rich in proteins, has good film-forming ability by having plasticizers such as lactose.

#### **3.2 Beverage production**

A study investigated the use of buttermilk from fresh buffalo milk for the production of carbonated beverages flavored with fresh mango, orange, and pineapple fruit, varying the fruit juice concentration between 18, 20, 22, and 24% v/v of sugar between 8, 10, 12, and 14% m/v. The buttermilk used was 0.8% acidity, being first prefiltered to remove casein clots, and then filtered in millipore systems to obtain ultrafiltered buttermilk. Fresh fruit juices were also filtered to remove possible fibers. After the filtration processes, the buttermilk acquired low viscosity, since a large fraction of

the proteins and lipids were removed from it. Among the analyzed flavors, the drink with 24% v/v of fruit juice flavored pineapple and 12% of sugar was the most accepted during sensory analysis, possibly due to the smaller amount of total solids in relation to the others. However, the higher the total solids content, the lower the solubilization of CO2, which made the carbonation process difficult. The use of the fruit juice in the formulation helped to mask the astringent, sweet, and/or sour taste of buttermilk color, taste, aroma, and palate, as well as the overall appearance and acceptability of the product. The beverage produced had a higher concentration of proteins, vitamins, and minerals than market samples, as well as better physicochemical properties, and therefore had a better nutritional quality than the other samples analyzed [6].
