Biopolymers, particularly exopolysaccharides produced by microorganisms such as bacteria, yeasts, and algae, have gained popularity in recent years due to their physical, chemical, and functional properties that are widely useful in food, industrial, cosmetic, and pharmaceutical systems. Hyaluronic acid is one type of these polysaccharide. This study investigated the optimal conditions for producing hyaluronic acid from the Streptococcus thermophilus bacterial strain. The isolated Streptococcus thermophilus were cultured on MRS broth, Skim milk, and M17 broth with an addition of 1% lactose. The diagnosed bacterial strains were grown in 100 ml of culture media, placed in volumetric flasks of 250 ml capacity, and incubated at 42˚C for 24 hours, pH 6.8, inoculum volume 1%, and a vibrating incubator at 150 rpm. After the end of the fermentation period, the isolation and purification of HA have performed accordingly: proteins were removed using 1% trichloroacetic acid (TCA), and HA in the supernatant was collected by isopropanol precipitation. The collected HA was dialyzed against ultrapure water and lyophilized. The amount of acid produced was estimated. The results show that the best production of hyaluronic acid was from the S. thermophilus bacterial strain grown on the alternative medium containing whey at a ratio of 450 ml/L and 7.5 g/L yeast extract at 40 ˚C, with a 3% of inoculum volume and 102×108 colony-forming units/ml of bacterial cells, in pH 6.8 and agitation speed of 150 rpm for 18 h, which had the most significant effect on the fermentation process and gave the highest value of HA production of 0.598 g/L and biomass of 6.08 g/L. These results showed the best production method for HA to achieve maximal production yelled.
Keywords: Hyaluronic Acid; Optimal Conditions; S. thermophilus Bacteria Strain.