A Fundamental Study On The Ultra High Pressure Food Processing

In recent years, with the increasing requirements of food quality and safety, ultra high pressure food processing technology has attracted many attentions as a new non-thermal processing technology in food manufacture. Unlike the traditional heating processes, the ultra high pressure food processing does not damage original nutrients and natural flavor of the food products. Therefore, this technology is especially suitable for processing such products as juices and seafoods which have high requirements of maintaining original flavor. The aims of this work are to develop the method of process design, optimize process operation conditions, and provide a fundation for the development and industrialization of ultra high pressure food processing technology. Fruit juices (apple juice/orange juice) and seafoods (oyster/sea cucumber) are chosen as model materials to study the effects of ultra high pressure processing parameters on food microorganisms, enzymes and food quality. Proteins of soy, oyster and sea cucumber are used to study the effects of ultra high pressure processing on protein structure and solution properties. Wheat starch, corn starch, potato starch and sweet potato starch are employed to study the effects of ultra high pressure processing on starch structure and solution properties. The main results and conclusions are summarized as follows:The effects of pressure, pressure holding time and temperature on the total amount of microorganisms in the fruit juices and seafoods are investigated during the ultra high pressure food processing. The results show that microorganism inactivation rate increases and proliferation rate decreases with the increase of pressure, pressure holding time and temperature. A better sterilization can be achieved with the combined treatment of pressure and temperature.The effects of pressure, pressure holding time and temperature on the enzyme activity (polyphenol oxidase/peroxidase in juice and autoenzyme in sea cucumber) are studied. It is found that there is an enhancement of enzyme activity within a certain range of pressure and temperature, while the enzyme activity decreases in another range of pressure and temperature. The effect of the time on the enzyme activity is affected by pressure and temperature. When the enzyme activity increases with the pressure and temperature, it is also enhanced as time increasing. Otherwise, the enzyme activity decreases when the time increases.The effects of pressure on solubility, viscosity, and emulsifying properties of soy, sea cucumber and oyster protein solutions are studied. The degree of protein denaturation under high pressure is determined by DSC curve of the protein solution. The change of protein subunits obtained by SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) is used to analyze the effect of high pressure treatment on protein quaternary structure. The change of protein tertiary structure is studied by sulphydryl content measurement. The change of protein secondary structure is studied by IR spectra, while the change of protein primary structure by peptide bond content and pH value. The results indicate that viscosity, emulsifying properties, surface hydrophobicity and solubility of protein increase with the increase of the pressure. The secondary, tertiary and quaternary structures of protein are changed under a certain high pressure, while the primary structure of protein is not affected.The effects of high pressure on solubility, viscosity, transparency, gelatinization properties and other performance parameters of different materials (wheat, corn, potato and sweet potato starch solutions) are studied. The change of starch structure is observed by DSC curves and X-ray diffraction patterns. The solubility and transparency of the starch solution increase with the increase of the pressure, while viscosity, gelatinization temperature and gelatinization enthalpy decrease with the increase of the pressure.The effect of high pressure on food shelf life is studied by pH value, TVB-N content, and the changes of oysters and sea cucumbers appearances. The effect of high pressure on food nutrients is determined by the ash content and polysaccharide content. The results show that ultra high pressure treatment extends the shelf life of food, and protects food nutrients and physiologically active substances effectively.A model is established based on artificial neural network to study ultra high pressure food processing. After training the model with a large volume of experimental data, the effects of high pressure on sterilization and enzyme deactivation are simulated and predicted successfully.