The core spheres of our research-work activity
Thermal treatment processes
In crushing process engineering, thermal treatment processes are practiced upstream of pressing and downstream of solvent extraction (desolventizing), where they have substantial impacts on both process-plant energy costs and the quality of processed product.
Precooking oilseed upstream of pressing has several functions. The first, and most obvious, is that it reduces the viscosity of the oil. Pressing is analogous to percolation as an expression of Darcy’s law which states that the flow of a fluid is proportional to the pressure applied to it and to the porosity of the medium, and inversely proportional to viscosity. The upshot is that the hotter the oil, the more fluidity it has, and consequently, the more readily it will circulate around the pores of the cake.
The second effect of cooking oilseed is that it reduces moisture content. Water in the press cake acts as a plasticizer. A wet cake will behave more like a liquid than a solid, which means the effect of compression will tend to expel it at a faster flowrate by reducing its internal porosity, whereas a dry cake matrix will be less elastic, maintain a degree of porosity, and generate higher pressures as the volume gets reduced.
Cooking also has the effect of enabling oleosomes to coalesce. Oleosomes are tiny lipid droplets within plant cells that are stabilized by a semipermeable protein membrane. Under the combination of molecular agitation and protein coagulation, all of the oil contained in the cells tends to form a continuum that is easier to expel.
In parallel to these effects, cooking can also activate enzymes like the phospholipases that make phospholipids less hydratable, and lead to problems at refining. It can also lead to formation of Maillard reactions that reduce protein digestibility or, conversely, to inactivation of antinutritional factors such as soybean trypsin inhibitors.
Thermal treatment processes also affect the glucosinolates in rapeseed. The link below will take you to a poster reporting recent research on this topic.
Mechanical extraction of vegetable oils
Pressing is a technique that cannot extract more than 80%–90% of the oil from oil-rich seeds and 60–70% from less-oil-rich seeds like soybean.
In order to be made efficient, pressing requires a hydrothermal-process oilseed preparation step that carries high energy costs and—if too intensive—can erode product quality.
OLEAD is engaged in the drive to improve the efficiency of this process through several consortium-based research programmes—some over, others underway. A standout example is the Genergy project that was set up to better understand the relationships between oleosome properties and extraction resistance under the effect of mechanical pressing. Research led by CREOL back in the day had emerged evidence of a counterintuitive phenomenon as the effect of oilseed temperature on press performance loss at oil removal.
OLEAD is currently engaged in PhD research that aims to model continuous-extraction rapeseed pressing. This programme is financed by the FASO and has industry engagement.
Alternative solvents to hexane
The industry-standard hexane currently in use is derived from crude petroleum and contains an isomer (n-hexane) that has conformed human toxicity. It has neurotoxic effects and may impair fertility. Fortunately, the end-to-end process completely removes all n-hexane from commodity oils in the marketplace. Continuing to use hexane nevertheless runs counter to consumer demand for softer, greener processes.
CREOL has participated in several studies on alternative solvents to hexane.
We have investigated using ethanol and isopropanol. Ethanol makes a relatively poor solvent for oils. At ordinary cold-process temperatures, oil is relatively insoluble in ethanol, and the water in the seeds migrates into the alcohol, compounding what was already poor solubility. However, it looks like this solvent can be made workable for use, by increasing extraction temperature and properly drying out the material feedstock. A spin-off effect is that it improves oilcake quality by solubilizing low-nutritional-value polysaccharides to increase protein content. Note, too, a reduction in antinutritional factors of rapeseed.
Dehulling has been part of our centre’s DNA ever since CETIOM engineers devised and developed the rapeseed dehulling process in the 1970s.
Dehulling—the first stage of the crushing process—consists in stripping away the fibrous outer covering of the seeds so as to produce more protein-laden oilcakes and increase processing-plant throughput.
Dehulling for sunflower: The bulk of our research has revolved around sunflower. Of all the classic commodity oilcrops, sunflower seeds contain the more fibres. All of this fibre content is packed exclusively in the outer hull, which accounts for 25% of total mass of the sunflower ‘seeds’ (a misnomer, as technically speaking, they are achenes).
Modern sunflower varietals are more oil-rich and less easy to dehull than the old, more rustic varietals. Our contribution was to develop a lab test that can predict seed dehullability lot-by-lot, which then enables us to study the impact of any number of process parameters on dehullability.
Dehulling for linseed: OLEAD, in response to a project commission from Sofiprotéol, has developed an operational linseed dehulling process (the FUI [single inter-ministry fund] GRANOLIN biorefinery programme).