ABSTRACT

Eija Bakken

The experiments of this thesis were conducted at the Department of Plant and Environmental Sciences, the Agricultural University of Norway, during the period 2000-2004. Part of the work was done in collaboration with Institute for Nutritional Research, University of Oslo, and Norwegian Food Research Institute (Matforsk). The collaboration with Institute for Nutritional Research was funded by the NFR (Norwegian Research Council) project “Bioactive compounds in fruits and vegetables and their capacity to regulate disease-associated genes” 2000-2002. The aim of this work was to examine the effect of maturity, fertilisation, and storage on the content of antioxidants and glucosinolates in selected species and varieties of vegetables. The thesis includes four papers. Two of these papers (I-II) focus on the antioxidant activity in cultivars of tomatoes as affected by maturity (I), fertilisation (II) and post-harvest ripening of mature green tomatoes (I). The third paper describes the effects of storage time and storage conditions on the antioxidant activity of cultivars of white-, red- and savoy cabbage (III). The fourth paper focuses on individual glucosinolates in cabbage as affected by maturity and fertilisation (IV). The experimental plant material was produced at the Agricultural University of Norway. The tomatoes were grown in greenhouses, whereas the cabbages were field grown in the seasons 2001 and 2002. An overview of the main variation in the data was obtained using Principal Component Analyses (PCA), whereas statistical differences between cultivars and treatments were obtained by Analyses of Variance (ANOVA).

Tomatoes ‘Durinta’, ‘Favorita’ and ‘Liberto’ were harvested mature green and vine ripe. The chemical analyses were performed on mature green, post-harvest ripened and vine ripe tomatoes. The tomatoes were analysed for colour (L*, a* and b*), dry matter, soluble solids, titratable acidity, vitamin C (L-ascorbic acid), and total antioxidant activity (FRAP value). Colour measurement was used as a non-destructive method to predict the total antioxidant activity in intact tomatoes (I). The main difference was observed between mature green and red fruits. Mature green fruits had high L*- and b*- values, whereas red fruits were high in a* value. A correlation between total antioxidant activity and chemical components measured was established. The L*- and b*-values were negatively correlated with FRAP (Ferric reducing ability of plasma) whereas titratable acidity, a*, hue, a*/b*, soluble solids, dry matter, vitamin C (L-ascorbic acid) were positively correlated with FRAP. The cherry tomato ‘Favorita’ was found to be significantly different from the other cultivars showing higher values of dry matter, soluble solids, titratable acidity and FRAP. The difference between FRAP values of post-harvest red and vine ripe tomatoes were non-significant for all cultivars. In another experiment the same tomato cultivars were grown at electrical conductivities of 2 and 5 mS cm-1 (II) and analysed as described in paper I. Tomatoes grown in soil and irrigated with a complete nutrition solution of electrical conductivity 2 mS cm^-1 were larger than tomatoes grown at 5 mS cm^-1. Again the main difference was observed between mature green and red fruits and ‘Favorita’ was higher in dry matter, soluble solids, titratable acids and FRAP. Dry matter, titratable acids and soluble solids were related to the fertiliser level whereas FRAP and vitamin C (L-ascorbic acid) was related to the cultivars. The highest levels of dry matter, titratable acidity and soluble solids were found in fruits grown at 5 mS cm^-1, whereas fruits grown at 2 mS cm^-1 showed higher a* - and b*-values.

Heads of white, red, and savoy cabbage were stored in cold storage (1 ºC) for 20 weeks in natural atmosphere or a controlled atmosphere of 3% O₂and 3% CO₂. There was no obvious effect of storage method on the antioxidant activity in cabbage (III). In cabbage the main difference was found between red cabbage, which was higher in FRAP, and white and savoy cabbage, which had the highest dry matter content. The total antioxidant activity of cabbage was not affected by storage time.

The individual glucosinolates in white cabbage, ‘Bartolo’, were identified as glucoiberin, progoitrin, sinigrin, gluconapin, and glucobrassicin (IV). Glucoinberin and sinigrin were the dominating glucosinolates. Cabbage heads were harvested at four different times after head formation. During the harvesting period there was an increase in head weight whereas the dry matter was significantly higher at the third harvest. The content of individual glucosinolates was found to be significantly lower at the latest harvest, except for progoitrin. There were no trends in the decrease of the different glucosinolates. Different levels of nitrogen and sulphur fertilisation had no effect on the content of glucosinolates in mature white cabbage. An increase in head weight and nitrogen content as a response to nitrogen fertilisation was observed whereas, the dry matter content decreased. The only significant effect of sulphur fertilisation was to increase the total content of sulphur in the cabbage heads.




Oppdatert: 22.11.04
Utskriftsvennlig versjon : Arkiv : Tips en venn