The changes in some characteristics of the 'ayran' samples produced and stored by applying ultrasound in milk at different stages

This study aimed to determine the chemical, biochemical, physical, microbiological and sensory changes that occur during storage in ayran samples produced by applying ultrasound (US) at different stages (before pasteurization, after pasteurization and without pasteurization) with two different methods (adding water to yogurt and adding water to milk). The study was carried out in two stages. In the first stage, to determine the most ideal ultrasound parameters to be used in ayran production, ultrasound was applied to raw milk at 3 different power levels (75 W, 100 W and 125 W) and 4 different times (5, 10, 20 and 30 min.) and ayran production was carried out by the traditional method (adding water to yogurt). Acidity, pH, serum separation, viscosity and color analyses were performed on the produced ayran samples throughout storage period (1st, 7th, 14th and 21st days). According to the results obtained in the first stage, considering serum separation, viscosity and L* (brightness) value, the ideal ultrasound power used in ayran production was determined as 100 W and 20 min. In the second stage, ayran was produced with different methods [traditional method by diluting yogurt (G) and adding water to milk (S)] using 100 W power and 20 min. time; ultrasound was applied to the milk used in ayran production before pasteurization, after pasteurization and alone. The produced ayran samples were stored at +4 °C for 21 days and some quality properties were analyzed on the 1st, 7th, 14th and 21st days of storage. According to the results obtained in the second stage, it was concluded that ultrasound application after pasteurization using the traditional method was appropriate for serum separation, and ultrasound application after pasteurization by adding water to milk was appropriate for viscosity, and ultrasound application increased the L* (brightness) value of ayran samples. In addition, it was determined that ultrasound application alone negatively affected the % WSN, lipolysis, acetaldehyde, viscosity, yeast-mold and sensory taste and odor values of ayran samples. As a general result, it can be said that US application was found to be more appropriate in the ayran production method by diluting the yogurt and after pasteurization of the milk.