Characterization of postharvest changes in onion and their relation with storage time

Abstract: Onion (Allium cepa L.) is the most economically important Allium crop. The commercial cycle of onion starts with the harvest and expect for the bulbs a conservation in bulks or in storage area at controlled temperature and relative humidity. The storage period need a particular attention because coincides with the dormancy period, when plants stop their growth, so it is very important to prolong the storage potential as much as possible. The most important moment in onions cultivation is the moment when the dormancy start. Dormancy is a period where the biological activities of bulbs are reduced. This period starts when the climatic condition become unfavorable for the life of the bulbs, and is exactly when this period starts begin that the onions are harvested, because the consumption of energy and oxygen is low. Deterioration in store is largely due to resumption of growth. The long term aim of this project at Lund University in collaboration with Swedish Agricultural University is to find a compound that can be used as marker to determine the storage time of the onions. The objective of this MSc thesis was to develop methods and analysis to characterize onions during storage. An onion consists of different layers and they all differ from the outer shell to the center, so to monitor the ongoing biological activities in the onions during storage the three segments: outer layer, middle layer and the inner layer are studied. The results show that water activity show no correlation between samples according to harvest time. The results show some differences between growing fields, but there are similarities between the values of the bulbs from fields A and B, A and C and between C and D fields, the data show no significant differences in water activity trough the layers. The total soluble contents analysis indicates that there are not significant differences in onion according to the harvest time, while there any similarities in onion soluble content according to the analyzed layer, so it’s possible to say that each layer has different sugars content. As of the field effect is possible to say that there are similarities between field A,B and D, but those fields are significantly different from field C. The texture analysis shows that the hardness decrease from the outer to medium layers and from medium to inner layers, the growing field and the harvest time are not relevant in modifying the texture, there are also no significant difference between growing fields and harvest time. The dry matter results suggest a greatly dependence from the harvest time, and in lesser extent from the growing field. The fructan assay results shows that the most influent factors in this assay are the growing fields and the onion layer. An histochemical analysis was made to research difference in starch. This results of this study shows that the quality parameter are mostly dependent the growing field this suggest a correlation between the quality of the crop and the culture methods. Not very influent proved to be instead the harvest time, showing that the onion can keep for a long period of time the quality parameters in an acceptable range.