21 High pressure processing Indrawati, A. Van Loey and M. Hendrickx Katholieke Universiteit, Leuven 21.1 Introduction Food quality, including colour, texture, flavour and nutritional value, is of key importance in the context of food preservation and processing. Colour, texture and flavour refer to consumption quality, purchase and product acceptability whereas the nutritive values (i.e. vitamin content, nutrients, minerals, health related food components)refer to hidden quality aspects. In conventional thermal processing, process optimisation consists of reducing the severity of the thermal process in terms of food quality destruction without compromising food safety. Due to the consumer demand for fresher, healthier and more natural food prod ucts, high pressure technology is considered as a new and alternative unit opera tion in food processing and preservation 21.2 High pressure processing in relation to food quality and safety The effect of high pressure on food microorganisms was reported for the first time by Hite in 1899, by subjecting milk to a pressure of 650MPa and obtaining a reduction in the viable number of microbes. Some years later, the effect of high pressure on the physical properties of food was reported, e.g. egg albumin co- angulation(Bridgman, 1914), solid-liquid phase diagram of water(Bridgman, 1912)and thermophysical properties of liquids under pressure(Bridgman, 1923). A more extensive exploration of high pressure as a new tool in food technology started in the late 1980s(Hayashi, 1989). Recently, extensive research has been conducted and is in progress on21 High pressure processing Indrawati, A. Van Loey and M. Hendrickx, Katholieke Universiteit, Leuven 21.1 Introduction Food quality, including colour, texture, flavour and nutritional value, is of key importance in the context of food preservation and processing. Colour, texture and flavour refer to consumption quality, purchase and product acceptability whereas the nutritive values (i.e. vitamin content, nutrients, minerals, health￾related food components) refer to hidden quality aspects. In conventional thermal processing, process optimisation consists of reducing the severity of the thermal process in terms of food quality destruction without compromising food safety. Due to the consumer demand for fresher, healthier and more natural food prod￾ucts, high pressure technology is considered as a new and alternative unit opera￾tion in food processing and preservation. 21.2 High pressure processing in relation to food quality and safety The effect of high pressure on food microorganisms was reported for the first time by Hite in 1899, by subjecting milk to a pressure of 650 MPa and obtaining a reduction in the viable number of microbes. Some years later, the effect of high pressure on the physical properties of food was reported, e.g. egg albumin co￾agulation (Bridgman, 1914), solid–liquid phase diagram of water (Bridgman, 1912) and thermophysical properties of liquids under pressure (Bridgman, 1923). A more extensive exploration of high pressure as a new tool in food technology started in the late 1980s (Hayashi, 1989). Recently, extensive research has been conducted and is in progress on