An innovative approach to pressing fully dehulled sunflower seeds in order to obtain a low fiber and high protein content in expellers

Abstract:
Sunflower kernels are rich in oil (550 g/kg DM) and protein (230 g/kg). However, when screw-pressing oilseeds, a certain amount of hulls is necessary to facilitate oil drainage and create friction, which increases pressure and temperature. This helps achieve the “oil release point,” but hulls also reduce the nutritional quality of the expellers by raising fiber content and lowering protein levels, limiting their use for monogastric animals.
A new technology has been developed to process fully dehulled sunflower seeds. The process includes adjusting moisture content and allowing time for the seeds to equilibrate in a dedicated bin, followed by screw pressing in a specially designed press that effectively lowers oil content while producing high-protein expellers. During testing, fully dehulled bakery-grade sunflower seeds were employed. They underwent both mechanical and optical sorting to ensure purity.
The primary purpose of moisture adjustment is to lower the “oil release point” so the screw press requires less pressure to extract the oil. At the same time, it is crucial to avoid over-moistening, which would cause the seed mass to collapse into a mushy structure and impede further oil outflow. After several test runs, the first pressing reduced the oil content to about 25%. A second pressing stage then lowered it to 117 g/kg DM, while protein content rose to 545 g/kg DM.
These expellers match the protein level of soybean extracted meal but retain a significantly higher oil content, providing superior energy value. As a result, they offer considerable potential in both feed and food industries, bringing higher added value and nutritional benefits.