Determination of eff ectiveness of ultras onication on some chemical and mi crobiological proper ties of apple juice by response surface methodolog

In this study, effect of ultrasonication on some chemical and microbiological properties of apple juice was determined by response surface methodology. Ultrasonication was treated to apple juice at varying amplitude levels (40-100 %), temperatures (30-60 °C) and treatment times of 2-15 minutes at a constant frequency of 20 kHz. A quadratic model for the changes of browning index (P<0.01), cloud value (P<0.05) and total phenolics (P<0.05) was found significant. The same model was also determined for the inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, yeast and mould. The quadratic model was determined for the variation of L*, a* and h values. On the other hand, 2FI model was found for the b* and C values. The results showed that amplitude, temperature and time had no significant effect on pH, °Bx and titratable acidity. The effect of amplitude on browning index did not found significant (P>0.05). It was observed browning index increased with increasing temperature, but decreased with increasing treatment time. The treatment time of ultrasonication had a significant effect on the level of cloud value, a decrease in the cloud value was obtained as the time increased (p<0.05). There is no effect of amplitude level and temperature on cloud value. A significant increase in total phenolics in apple juice was observed as the temperature increased. Amplitude level had no effect on all the visual colour values. Significant increase in L* value was observed as the temperature and time increased. A significant effect of amplitude level of ultrasonication was only found for the inactivation of Listeria monocytogenes.