Investigation of the effect of using banana powder i̇n probiotic yogurt production on product properties

In this thesis, 4 different stirred probiotic yoghurts containing 0% (Control), 0.5%, 1%, 2% banana powder and Bifidobacterium animalis subsp. lactis BB-12 were investigated in terms of their physicochemical, microbiological, textural, rheological, color, and sensory properties during 28 days of storage period at 4 °C Dry matter, protein and ash contents of yoghurts were determined only on the 1st day of storage. On the other hand, pH, titratable acidity, microbiological, textural (hardness), rheological properties (apparent viscosity, flow behavior index, consistency coefficient), syneresis, water holding capacity, color (L*, a*, b*) and sensory properties (taste, color, appearance, consistency (in the mouth and with spoon), odour, general acceptance) were examined on the 1st, 14th and 28th days of storage. The use of different concentrations of banana powder in probiotic yoghurt production affected the incubation time. The incubation time decreased as the concentration increased. However, different banana powder concentrations did not show a significant effect on the pH and titratable acidity changes in samples during the storage period. It was determined that the effect of using different amounts of banana powder on the protein content of yoghurts was statistically significant (p<0.05), and as the banana powder concentration increased, the protein content decreased. In all samples, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus and Bifidobacterium animalis subsp. lactis BB-12 counts decreased during the storage period. Yet, this reduction was generally less than 1 log cfu/g and counts were not below the values 106-107 cfu/g, specified for probiotic foods. After 28 days of storage, higher Bifidobacterium animalis subsp. lactis BB-12 counts were observed in yoghurts containing 0.5% and 2.0% banana powder compared to the control sample (8.22±0.24 and 8.20±0.04 log cfu/g, respectively). vii Differences between the hardness values of yoghurts, containing different concentrations of banana powder, were not statistically significant (p>0.05). However, the effect of storage period on the hardness of yoghurts containing 0.5% and 2% banana powder was statistically significant (p<0.05). The hardness values of yoghurts generally increased throughout the storage period, and the hardness value of the sample containing 2% banana powder decreased on the 28th day of storage compared to the 14th day. The lowest hardness value during storage was measured in the yoghurt sample containing 2% banana powder. The effect of banana powder concentration and storage period on the rheological properties and color values of yoghurts was found statistically significant (p<0.05). In general, the effect of different concentrations of banana powder and storage period on the sensory properties of yoghurts was found significant (p<0.05). It was determined that the average general acceptance score of the sample containing 2% banana powder decreased during the storage period. When all the results of the study were evaluated, it was concluded that the samples containing 0.5% and 1% banana powder had properties close to the control sample and the use of banana powder did not cause any significant changes or negative effects on the properties of the probiotic yoghurts during storage period, and banana powder could be used in the production of probiotic yoghurts at less than 2%.