Phänomenologie und Kinetik der L-Ascorbinsäure bei der Lagerung von Gemüse am Beispiel Kohlrabi (English shop)

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The L-ascorbic acid (AA) content of crop plants is influenced by a multitude of pre-harvest and post-harvest factors. The aim of this work is to investigate the influence of various storage factors, such as storage time, storage temperature, specific surface area and storage atmosphere, on the AA content of kohlrabi, since in particular only few studies exist to date on the influence of the specific surface area. Furthermore, moisture content and mass of the samples are determined. As a pre-harvest factor, the influence of different sulphur and nitrogen nutrition on the AA content of the fresh produce is additionally examined.

Kohlrabi samples of different specific surface area (cubes, sticks, small cubes, julienne, grated) are stored uncovered at different storage temperatures (0.5 °C, 6 °C, 12 °C) over a period of 6 days. AA content, moisture content and mass of the samples are determined every second day, the AA content by means of an enzymatic detection method (L-ascorbic acid colour test, R-Biopharm AG, Germany), the moisture content thermogravimetrically using an infrared moisture analyser (MA 45 Sartorius, Germany).

The relative AA content (c/c0) of the samples decreases exponentially with increasing specific surface area at all three storage temperatures investigated. A decrease with increasing storage temperature is only observed in samples with a large specific surface area (grated). The multivariate linear regression carried out additionally allows the AA content to be represented as a function of both storage factors and clearly shows that the influence of the specific surface area is considerably stronger than the influence of the storage temperature within the temperature range investigated. A decrease in the AA content with increasing storage time is only observed in samples with a large specific surface area (julienne, grated) over the course of the first 24 h. The AA content, which remains almost constant during further storage, can be attributed to a recycling of dehydro-L-ascorbic acid via the ascorbate-glutathione metabolism. The mass of the kohlrabi samples decreases linearly with increasing storage duration, storage temperature and specific surface area due to the release of CO2 by respiration. The moisture content is not influenced by these factors. The compensation of the evaporated water is attributed to the formation of H2O in the course of respiration and the ascorbate-glutathione metabolism.

A decrease in the AA content of the fresh produce as a result of increased nitrogen nutrition is only observed when considering the AA content per kohlrabi tuber.