The effects of addition of tiger nut (Cyperus esculentus L. var. sativus Boeck) and probiotic bacteria on the formation of postbiotic metabolites in mozzarella cheeses maturedunder different conditions

In this research, the inclusion of tiger nut and probiotic bacteria in the production process of mozzarella cheese was examined to analyze the types and amounts of postbiotic metabolites formed during the cheese maturation process. Additionally, the functional and nutritional values, as well as the sensory and physicochemical properties of the enriched mozzarella cheeses, were evaluated. The study aimed to analyze the microbial activity of probiotic bacteria and their contribution to postbiotic metabolite production. The potential health and nutritional benefits of mozzarella cheeses enriched with tiger nut and probiotics were also investigated. This thesis aims to offer innovative approaches in the field of food science and technology, providing significant contributions to both industrial production and consumer health. Using a low-moisture (45-52% moisture) mozzarella cheese production method, cheese was produced from whole milk (3.25% fat) and skim milk (0.1% fat) with the addition of Lactobacillus acidophilus (ATCC 4356) and Lactobacillus casei (ATCC 393) cultures, and different proportions of tiger nut (0.25-0.5%). Following production, the cheeses were stored at 4°C with 85% relative humidity for 30 days. On the 0th, 15th, and 30th days of storage, the cheese samples were subjected to pH, titratable acidity, dry matter, water activity, meltability (Schreiber), tube test, burning, color, texture, microbiological, organic acid, and sensory analyses. In both whole milk and skim milk cheese samples, pH values increased during storage compared to the control group. Conversely, titratable acidity values showed a decrease compared to the control group, inversely proportional to the pH values. According to the research data, increases were observed in the values of dry matter, meltability (Schreiber), tube test, external stickiness, gumminess, chewiness, and microbiological analyses. Microbiological analysis results indicated that the lipolytic bacteria count was initially lower in skim milk samples, but higher than in whole milk samples by the end of the storage period. This phenomenon could be attributed to the barrier effect of fat on microorganisms, initially inhibiting bacterial growth. Secondly, the antimicrobial effect of secondary metabolites (such as short-chain fatty acids) produced by bacteria could have inhibited bacterial growth. Additionally, competition among microorganisms is considered a significant factor; the growth of lactic acid bacteria can severely suppress the growth of other bacteria in their environment. Consequently, it is hypothesized that in whole milk samples, lactic acid bacteria developed and suppressed the growth of other bacteria. Furthermore, the approximately 35-40% fat content of tiger nut may have contributed to this increase. Decreases were observed in water activity, hardness, elasticity, internal stickiness, and flexibility values. In whole milk and skim milk cheese samples, burning and color values generally decreased. However, in skim milk cheeses, the burning a* value increased in the control group, while in whole milk cheeses, the burning a* and color b* values increased in all samples. According to L. acidophilus counts, the T2B1 (Tiger nut: 0.5%, Bacteria: L. acidophilus) sample showed higher growth in both whole milk and skim milk cheese samples. According to L. casei counts, the T2B2 (Tiger nut: 0.5%, Bacteria: L. casei) sample exhibited higher growth in both whole milk and skim milk cheese samples. HPLC analysis results indicated that the detection of short-chain fatty acids (acetic, butyric, lactic, propionic) supported the contribution of added L. acidophilus and L. casei bacteria to the postbiotic cheese process. Keywords: Mozzarella, Postbiotic, Tiger nut, Probiotic