Application of Hydrostatic Pressure to Yoghurt to Prevent its After-acidification

Abstract

Since high acidity in yoghurt which occurs during its storage and delivery is unpopular among consumers, the application of hydrostatic pressure to yoghurt to prevent its afteracidification (rise of acidity after packaging) was studied. Yoghurt was filled in flexible pouches and heatsealed. After applying hydrostatic pressure to the pouched yoghurt with a cold isostatic equipment MCT-150 S (Mitsubishi Heavy Industry Co.) under various pressures and temperatures, it was stored for two weeks at 10°C. The acidity, the number of vital Lactic acid bacteria and the texture of the yoghurt were evaluated periodically during the storage. The pressure treatment at below 200MPa for 10min at room temperature did not prevent the after-acidification, and the initial number of vital Lactic acid bacteria was maintained for two week storage. The pressure treatment at 200-300MPa for 10min at the same temperature prevented the after-acidification and maintained the initial number of vital Lactic acid bacteria. By the treatment at over 300MPa for 10min at the same temperature after-acidification was prevented and the number of vital Lactic acid bacteria was decreased as the applied pressure was increased. The texture of yoghurt was maintained regardless of the applied pressure when treatment temprature was below 20°C. Therefore, it was recognized that application of hydrostatic pressure at 200-300MPa to yoghurt was effective to maintain its quality during storage and delivery.