Influence of Aging, Oxygen, and Moisture on Ethanol Production from Cabbage Seeds

Abstract

A seed quality test developed by Kataki and Taylor (1997) measures the anaerobic-to-aerobic (ANA) ratio of ethanol production and the relationship of the ANA ratio index-to-seed quality has been tested in several species. To expand the usefulness of the ANA ratio index and to optimize the test conditions, a series of studies was performed using cabbage (Brassica oleracea L. var. capitata L.) seeds as a model. It was hypothesized that ethanol production in cabbage seeds would be influenced by aging treatment, hydration level, seed integrity (grinding), and oxygen availability. Cabbage seeds were subjected to controlled aging treatments (40 °C at 70% relative humidity for 0, 7, 14, 21, and 28 d). Seed samples were incubated with a glucose (50 mm) potassium phosphate buffer (5 mm, pH 5.6) at 25 °C for 24 h (shorter than the time required for germination). The water concentration levels tested in the current study were 0.18, 0.22, 0.54, 0.80, 1.22, 1.86, 3.00, 5.67, and 10.0 g of H2O per gram of dry seeds. Ethanol production was measured in the supernatant of seed extracts using immobilized enzyme technology. The experiments were performed in ambient oxygen conditions and under nitrogen. Ethanol production was greater in aged than nonaged intact seeds at all water concentrations tested. Nonaged seeds under nitrogen had reduced ethanol production at ≤0.54 g of water per gram of seeds, indicating that low seed water concentration limited ethanol production. Nonaged seeds in ambient oxygen at ≥1.22 g of water per gram of seeds had elevated ethanol production, indicating that a hypoxic environment was created by excess seed water. Thus, a water concentration between these values is recommended for the ANA ratio index test for cabbage seeds. The opposite trend of lower ethanol production in aged than nonaged seeds was measured if seeds were ground before the hydration. Seed integrity experiments suggest that lower ethanol production observed in aged ground seeds may be attributed to hypoxia resulting from rapid hydration damage that results with loss of seed-coat integrity.