Comparison of nutritional composition and histological changes of the soybean seeds cultivated by conventional and organic farming systems after long-term storage - Preliminary study

Abstract

We investigated the effect of hermetic long-term (9-year) storage at room temperature on the chemical compositions and histological structure of soybean seeds that had been cultivated by two farming systems [conventional farming (CF) or organic (natural) farming (OF)]. Soybean seeds had been harvested from plants cultivated in the field under CF practices, or in a neighboring field where OF practices had been used for over 3 years. Protein content, calcium (Ca), potassium (K) and phosphorus (P) content of OF soybean seeds were higher than CF seeds just after harvesting. However, after long-term storage, protein content of OF soybean seeds was significantly higher than CF seeds. In addition, there were many minerals with a higher content (in particular, K) of OF soybean seeds. The breaking strength and pH of OF soybean seeds were higher than CF ones. Optical microscopic examination revealed collapsed tissue and gaps in the internal and external parts of CF soybean seeds. Transmission electron microscopic photographs of CF soybean seeds confirmed the presence of collapsed cell walls and protein bodies. These results indicate that the type of farming system (inorganic or organic fertilizers) used results in differences in chemical compositions and histological structure of product during storage. In addition, our results indicated that high-Ca content of OF soybean seeds strengthened cell wall structure, and prevented the loss of contents during storage.