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Accueil du site → Doctorat → Brésil → Efeito do déficit hídrico em características químicas e bioquímicas da soja e na degradação da clorofila, com ênfase na formação de metabólitos incolores

Universidade de São Paulo (2009)

Efeito do déficit hídrico em características químicas e bioquímicas da soja e na degradação da clorofila, com ênfase na formação de metabólitos incolores

Borrmann Daniela

Titre : Efeito do déficit hídrico em características químicas e bioquímicas da soja e na degradação da clorofila, com ênfase na formação de metabólitos incolores

Influence of drought stress on chemical and biochemical characteristics of soybean and on chlorophyll degradation, with focus on the formation of non-coloured chlorophyll catabolites

Auteur : Daniela Borrmann

Université de soutenance : Universidade de São Paulo

Grade : Doutorado 2009

Résumé
Brazil is the second largest soybean (Glycine max L. Merrill) producer and exporter in the world. The production depends on climatic factors, like temperature and rain volume. Soybeans cultivated in the south of the country in 2005 suffered drought stress imposed by adverse high ambient temperature, accompanied by low humidity during the reproductive stage. Little information is available regarding drought stress on quality of grains. In this study, firstly, chemical and biochemical characteristics of five soybean samples belonging to three cultivars grown under drought stress and did not meet standards for marketing due to high amounts of green seeds, were evaluated. Grains were analyzed for several physicochemical ad biochemical parameters, including analysis of pigment contents, immediately after harvest and after 20 months of storage at room temperature. Acidity was measured additionally after 30 month of storage. Water activity and humidity were 0.6 - 0.7 and 8.7 % - 11.9 %, respectively, and did not change during storage time, but there was an increase in acidity, which alludes to lipase activity. The activity of lipoxygenase 1 was significantly prejudiced. Immediately after harvest, green pigments corresponded mainly to pheophytin a, followed by pheophytin b, small quantities of chlorophyll b and chlorophyll a and traces of other chlorophyll derivatives. After 20 months of storage almost all green pigments had disappeared. Drought stress probably enhanced membrane permeability, which led to a lower pH and promoted transformation of chlorophylls to pheophytins. In the second part of the study, the advanced stage of natural chlorophyll degradation was investigated, in which the green colour of the seeds disappears. This stage corresponds to the formation of non-coloured chlorophyll catabolites (NCC), but there are controversies if those are the final products. Thus, the formation and degradation of NCC during soybean (Glycine max L. Merrill) maturation and two post-harvest drying temperatures was investigated. Soybean was harvested at six maturation stages and the formation of NCC was analyzed by HPLC after drying at 40°C and 60°C. All samples contained fractions with an absorption maximum at 320 nm, which are considered typical for NCC. The amounts of NCC increased until 114 days after plantation, and were significantly lower in advanced maturation stages. In samples dried at 40°C and 60°C, NCC amounts were lower, due to inferior initial chlorophyll levels. These results indicate that the NCC in soybeans might not be the final products of chlorophyll degradation. Their reduction in advanced maturation stages may be due to further metabolization

Assunto(s) : Bioquímica de alimentos, Ciência dos alimentos, Climate conditions, Condições climáticas, Derivados incolores da clorofila, Non-coloured chlorophyll catabolites, Post-harvest drying, Qualidade dos grãos, Secagem pós-colheita, Seed quality, Soja (Glycine max L. Merrill), Soybean (Glycine max L. Merrill)

Présentation et version intégrale

Page publiée le 23 mars 2011, mise à jour le 4 juillet 2017