INVESTIGATION OF THE IMPACT OF THE THERMOSONICATION OPERATION ON DOOGH QUALITY AND ON THE SURVIVAL OF KLUYVEROMYCES MARXIANUS

Doogh is an Iranian drink produced from yoghurt. Swelling is an undesirable change of Doogh, usually caused by Kluyveromyces marxianus. The aim of this study was the investigation of the effect of the thermosonication process on Kluyveromyces marxianus survival as well as the determination of the impact of this process on other quality parameters (viscosity and serum separation). For this reason, Kluyveromyces marxianus (about 105 cells per milliliter) inoculated into Doogh samples, thereafter samples being exposed to various thermosonication process conditions. Results showed that the thermosonication operation resulted in the reduction of the yeast population of Doogh samples (p <0.05). The lowest yeast population was observed in the sample subjected to acoustic density=1w/ml, T= 60°C and t=30min (1.7±0.01CFU/ml). Other operation conditions also had impact on yeast survival (p <0.05). Thermosonication also had significant effects on the viscosity of the Doogh samples. Serum separation of samples was also measured and observation implied changing serum separation magnitude between different samples in comparison with the control sample (p <0.05).