Optimisation of primed cabbage seed drying via quality models, state diagrams and two-stage drying

Seed industry relies on empirical guidelines for drying of high-quality vegetable seeds . More knowledge-based guidelines are needed to optimise drying regarding efficiency and drying time by keeping a certain quality constraint. This study has developed a new strategy for optimisation of Brassica oleracea (cabbage) seed drying. Two different quality models were evaluated to predict germination quality after drying. A statistical response surface model was most applicable and could describe 89 % of the variation of quality based on the drying conditions (air temperature, relative humidity (RH) and drying time). Energy efficiency was calculated for thin-layer cabbage drying resulting in efficiencies ranging from 5 to 55 %. Low relative humidity had the largest impact on increasing efficiency, followed by higher temperature and shorter drying time. Moreover, process and state diagrams, which is a novel approach in seed research, were constructed combining the relevant parameters such as drying conditions, seed quality and efficiency or seed temperature and moisture content (MC). Based on the process diagram, drying at 25 °C and 20 % RH for ca. 8hr is recommended for a quality above 95 %, a final MC of 5 % and the highest efficiency. Based on the seed state diagram, a critical seed temperature of about 40 °C for 5 % MC and 95 % germination quality is confirmed. For higher MC (25 %), a lower temperature of ca. 37 °C is recommended. In addition, two-stage drying was evaluated to optimise drying with two temperature steps. However, both low-to-high and high-to-low trials resulted in lower qualities than one-stage drying but more research is needed to further explore these strategies. Concluding, this study developed a novel strategy contributing to more knowledge-based guidance for optimal cabbage seed drying and for general process optimisation.