Determination of physicochemical and sensorial properties of yoghurt produced from whey powder obtained by different types of cheeses

This study aimed to use commercial whey powder, skim milk powder, and whey powders produced from ultrafiltrated white cheese whey, white pickled cheese whey, lor cheese whey in the production of stirred yoghurt and to compare physicochemical, microbiological and sensory properties of produced stirred yoghurts. In this study, wheys obtained during the production of white pickled cheese, lor cheese and ultrafiltrated white cheese were separately dryed by using a spray dryer under appropriate process conditions. The physicochemical properties of whey powders produced from wheys obtained different types of cheeses, commercial whey powder and skim milk powder were determined and these powders were used in the production of stirred yoghurt. Dry matter of milk used in stirred yoghurt production was adjusted as approximately 12.5% by using of whey powders produced from wheys obtained during the production of white pickled cheese, lor cheese and ultrafiltrated white cheese, and by commercial whey powder and skim milk powder. The stirred yoghurt samples were stored at 4°C for 30 days, and physicochemical, microbiological and sensorial properties of the stirred yoghurt samples were determined on days 1, 15 and 30 of the storage. The mean pH, titratable acidity, moisture, water activity, protein, lactose, ash and salt values of whey powders and skim milk powders ranged between 6.37 and 6.49%, 0.063% and 0.197%, 2.04% and 4.92%, 0.180 and 0.260, 2.93% and 34.71%, %40.25% and 71.58%, 4.59% and 7.06% and 0.82% and 1.88%, respectively. The effects of type of samples as the main variation source on the particle size, wettability, bulk density, tapped density, and colour values of the whey powders and skim milk powder were found be statistically significant (P<0.001). In the stirred yoghurt samples, the pH values decreased, and the titratable acidity values increased during the storage period. The apparent viscosity values of the stirred yoghurt samples produced using whey powders produced from wheys obtained during the production of white pickled cheese, lor cheese and ultrafiltrated white cheese, and commercial whey powder and skim milk powder were determined as 0.13, 0.15, 0.14, 0.15 and 0.48 Pa.s, respectively. Based on the results of rheological analysis, the power law model was more accurate for the stirred yoghurt samples. The highest number and perimeter of grains and visual roughness values were obtained by the stirred yoghurts produced using the skim milk powder. When the sensorial analysis results of the stirred yoghurt samples were examined, it was determined that the average color, visual consistency, particulate structure, serum separation and hardness scores of the samples were affected by the sample type at a statistically significant level (P<0.05), while there was no significant difference (P>0.05) in the serum separation scores. It was found that the sourness values of the stirred yoghurt samples increased and the salinity values decreased during the storage period. It has been evaluated that whey powders with different compositions and properties can be obtained by drying wheys obtained from different cheeses and that these powders may create differences in the properties of the products to be used.