Abstract

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Uniform cylindrical and long beetroots in at least two size classes are necessary in order to produce slices with a firm and brittle texture using a minimum amount of energy and control with cooking time, tempera-ture and peeling depth that is crucial. The steepest part of the firmness equation during cooking determines the velocity of temperature increase towards the root centre and the optimum brittleness occurs on the shallow part of the cooking curve. The purple and yellow colorants are degraded according to first order kinetic mechanism both during cooking and cooling. Peeling depth depends on heating and cooling rate that may be controlled efficiently. The colour change depends on oxygen availability and some of the degraded colorants may be rege-nerated using a nitrogen atmosphere by cooking, slicing and packing. Degradation rate of colorants may in-crease by interaction with mineral ions and may be counteracted using antioxidants and the colorants are de-graded by light and combinations of light and oxygen may decrease the level of colorants seriously especially by high temperature. Beetroots contain peroxidases and polyphenol oxidases that may promote oxidation of the colorants until the temperature cause inactivation of these enzymes. Cooking and pasteurization of beetroot cubes in one step increased colour stability because oxygen not is available inside the beetroot tissue. Degrada-tion of polymeric carbohydrates during cooking may increase drained weight. Leaching of soluted compounds such as potassium, nitrate and especially losses of sucrose may be reduced considerably by reusing of the cook-ing water up to at least twenty times without any off flavour in the final product. During storage of glass jars with beetroot slices may the colorants be degraded if the products are stored in light and especially if the jars contain air spaces.

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