Food has to satisfy different requirements, which are partly inconsistent. On the one hand are microbiological safety and a long shelf life. On the other hand are maxima in freshness, nutritional value, taste and appearance. The challenge for the food industry is to satisfy consumer requests with appropriate conservation techniques. The use of different preservative agents or methods is usually linked with compromises. Popular in the food industry are conservation procedures based on physical operations, like pasteurization or sterilization through heat. A temperature treatment increases food safety with increasing temperature and retention time. However, at the same time, these parameters favor chemical reactions which destroy the original appearance of the food. Fewer compromises are necessary when non-thermal conservation procedures, like high-pressure treatment of food at moderate temperatures, are used. In contrast to thermal treatment, vitamins, essential amino acids, and color of the treated food remain nearly unaltered, while insuring the same level of food safety. However, high pressure can change the state of food or its components. Rather than the application of lower temperatures to solidify foods, solidification can also be achieved through the application of high pressure.
Superpressuring, a greater application of pressure necessary for solidification, should have similar effects on edible fats as supercooling, which involves cooling underneath the solidification point at atmospheric pressure. An investigation of this hypothesis is presented in this work.
As no techniques are established to investigate the crystallization of fat under pressures up to 450 MPa, this contribution focuses on the development of suitable measuring systems for this application. For in-situ observation, optical experiments based on turbidimetry, nephelometry and polar-light microscopy are used. These techniques, combined with specially developed evaluation algorithms, allow for the determination of the melting point, crystal growth, and crystal nucleation of fats under pressure. Thereby this self built polar-light microscope is especially suitable for measuring melting points and crystal growths. Crystal nucleation is best detected utilizing signals from light transmission and light scattering.
The resulting phase diagram of Triolein shows in contrast to other publications no linear correlation between pressure and temperature increase. High pressure application also seems to favor the generation of '-crystals compared to atmospheric pressure and not of -crystals as proposed in literature. Analogous to inducing more unstable polymorphic structures, the greater the supercooling temperature is, the experiments indicate that the greater the superpressuring is, the more unstable '- rather than the more stable -polymorphic structure is formed. As the '-form is the desired structure for edible fats in the food industry, this is a positive aspect.
The induction time is the delay between attaining crystallization conditions in regards to temperature and pressure and the first detection of a beginning crystallization. For fats, the induction time becomes disproportionately shorter with increasing pressure application. The pressure dependency of induction time by the same conditions in other aspects is qualitatively identical to the temperature dependency under atmospheric pressure. Pressure difference as the driving force for crystal nucleation appears to have the same result as temperature difference at atmospheric pressure. Superpressuring achieves the same results as supercooling. Thus, the generation of different polymorphic structures through superpressuring is proposed.
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Food has to satisfy different requirements, which are partly inconsistent. On the one hand are microbiological safety and a long shelf life. On the other hand are maxima in freshness, nutritional value, taste and appearance. The challenge for the food industry is to satisfy consumer requests with appropriate conservation techniques. The use of different preservative agents or methods is usually linked with compromises. Popular in the food industry are conservation procedures based on physical op...
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