Effects of Adding Non-viable Lacticaseibacillus casei and Lactobacillus acidophilus on Physicochemical, Microbial, Chemical and Sensory Attributes of Probiotic Doogh

Background and Objective: Inactivated probiotics provide various health and technological benefits, making them appropriate for the production of functional dairy products. The aim of this study was to investigate effects of adding nonviable probiotics (Lactobacillus acidophilus LA -5 and Lacticaseibacillus casei 431) to doogh (a typical Iranian fermented milk drink). Material and Methods: Probiotics were inactivated by heat or sonication and added to the samples before or after fermentation. Various parameters such as pH, titratable acidity, redox potential, antioxidant capacity, color, viscosity, and phase separation, viability of traditional starter bacteria and probiotics and sensory characteristics were assessed during fermentation and refrigerated storage at 5 degree celsius. Results and Conclusion: Sonicated probiotic-containing treatments included the highest pH decrease rate (0.011 pH min(-1)) during fermentation, as well as the highest antioxidant capacity (16.45%) and viscosity (35.15 mPa.s), while heat -inactivated probiotic- containing treatments included the lowest viscosity (17.60 mPa.s). Treatments with viable probiotics reasonably included the highest post -acidification rate during storage (4.14 D-degrees d(-1)), compared to those containing nonviable cells, as well as the minimum phase separation rate. The b* and L* values of color did not differ significantly within treatments, but the highest a* value was observed in the treatments with sonication. The highest populations of Lactobacillus delbrueckii ssp. bulgaricus (log 11,891 CFU ml(-1)) and Streptococcus thermophilus (log 14,977 CFU ml(-1)) at the end of the storage were observed in treatments with heated probiotics (compared to viable probiotics) and treatments with sonicated probiotics, respectively. In addition, Lactobacillus acidophilus was more susceptible than Lacticaseibacillus case and included lower viability. Taste, mouth feeling and total acceptance of all samples did not differ significantly within treatments. The present study suggests that inactivated probiotics can successfully be used for the production of fermented milk beverages with appropriate sensory characteristics and higher antioxidant capacity, compared to the control group.