عنوان مقاله [English]
In today's world, there is a growing tendency towards producing healthy and nutritious food. Mint is a genus of plants that its healthy and nutritious effects have been proved. Adding probiotic bacteria to yogurt increases its nutritious benefits. This study aims at adding the extract and fiber of mint stalk to stirred yogurt containing Bifidobacterium Lactis bacteria (BB-12) as well as examining the viability of this bacterium. To do so, the response surface methodology and the central composite rotatable design were employed. The findings obtained from the analysis showed that there was a significant relationship between different concentrations of fiber and extract, and the viability of Bifidobacterium Lactis bacteria in the first day to the 21st day (P<0.01). Having applied the response surface method, the optimization depicted that the maximum viability of Bifidobacterium Lactis bacteria is only achieved when the concentration of extract and fiber are 0.1 and 1.3 percent, respectively. In these conditions, the utility of the model equals 0.94 and the number of Bifidobacterium Lactis bacteria is 7.11±0.005 log cfu/ml in the first day, 6.49± 0.035 log cfu/ml in the 7th day, 6.24 ± 0.055 log cfu/ml in the 14th day, and 5.41±0.17 log cfu/ml in the 21st. Since the produced yogurt under the condition of optimization contained at least 106 colony of bacteria per milliliter, the said product was called functional.