This study aimed to evaluate the health status of yogurt sold in public stores and assess the effect of chitosan addition on its quality. A total of 4 L of fresh raw cow's milk from the Faculty of Agriculture at Menoufia University was used. The milk was standardized to 3% fat, pasteurized at 85°C for 30 minutes, cooled to 45°C, and divided into two groups (2 L each). Active starter cultures of *Lactobacillus delbrueckii subsp. bulgaricus* and *Streptococcus thermophilus* were added as follows: G1 (control): 2% yogurt starter culture; G2: 2% starter culture + chitosan (2.5 mg/100 ml milk); G3: 2% starter culture + chitosan (5 mg/100 ml milk). Yogurt samples were incubated at 42°C until curd development and then refrigerated at 4°C. Sensory and microbiological evaluations were conducted periodically during storage.

Results revealed a progressive reduction in *L. delbrueckii subsp. bulgaricus*, *S. thermophilus*, yeast, and mold counts from day 0 (fresh curd) to the end of storage. Increased chitosan concentration enhanced yogurt freshness and improved sensory attributes, including texture and flavor. Higher chitosan levels also correlated with reduced microbial spoilage. This study demonstrates that chitosan fortification can enhance yogurt quality by improving its sensory characteristics and extending shelf life.