Effect of Pasteurization, Centrifugation and Additives on Quality of Concentrated Yogurt (Labneh)

Pasteurization of yogurt by heat at 60-80°C or by addition of 0.2 to 2% hydrogen peroxide were investigated. Heat-treatment caused a very pronounced reduction in the bacterial count of yogurt samples. Addition of hydrogen peroxide was not effective at the low levels studied. Higher concentrations of hydrogen peroxide that were effective in reducing the bacterial population persisted in the food for more than 4 weeks. Heat-pasteurization in the presence of hydrogen peroxide, was very efficient in destroying bacterial cells and hastened the disappearance of hydrogen peroxide residues from the food. "Labneh", which is usually prepared from yogurt by filtering out the whey through a cloth, had an inferior texture when prepared from pasteurized yogurt. Milder heat treatment in the presence of hydrogen peroxide and addition of potassium sorbate and thickeners, greatly improved the quality and the shelf-life of labneh as confirmed by sensory evaluation experiments. Further improvements were possible by preparing labneh using centrifugation at various speeds for a short time.