Abstract. The oil point in oilseeds refers to the minimum pressure, which is required to cause oil to emerge from the oil bearing material. Mechanical parameters relevant to expression of oil from three emerging oilseed crops were determined at their oil points and peak compression under the applied force. Oil contents of the batch of oilseeds used were determined using the soxhlet method. The efficiency of the compressive bulk expression scheme was determined as a function of oil yield determined during mechanical expression and the oil contents of the oilseeds. The oil point, oil yield and pressing performance varied significantly between the three crops. The oil points and volume deformation energy at oil points of camelina, pumpkin and sesame seeds were 8. 33, 7.43 and 3.36 MPa and 1.44, , respectively. Oil expression efficiency for these crops at 35.4 MPa, were 56.0, 53.6 and 28.3 %, respectively.

This study described the compression behaviour of bulk rapeseed using the universal compression testing machine and vessel diameter of 60 mm with a plunger. The pressing factors, namely the heat treatment temperature, speed, and force, were varied between 45 and 105°C, 5 and 25mm min −1 then 40 and 120 kN, respectively. The bulk rapeseed samples were measured at pressing heights between 20 and 100 mm. The parameters determined were maximum deformation (mm), deformation energy (J), oil yield (%), oil point strain (-), oil point force (kN), and oil point energy (J). Clearly, maximum deformation, deformation energy, and oil yield increased with the increase in force and heat treatment temperature, while that of speed showed a downward trend. A plot of the amounts of force and deformation displayed a smooth and serration curve characteristic. The area under the smooth curve behaviour described the compression process where the maximum rapeseed oil was obtained, while the serration pattern represented the ejection of the rapeseed cake through the holes of the pressing vessel as a result of the higher force and speed. The lower and upper oil points of rapeseed were detected at pressing heights 80 mm and 100 mm with corresponding strain values of 0.38 and 0.49 (-). This study provided vital information on rapeseed in axial pressing which can be applied in the industrial technology for optimizing the mechanical screw press oil production.

The study described the oil point and mechanical properties of roasted and unroasted bulk oil palm kernels under compression loading. The literature information available is very limited. A universal compression testing machine and vessel diameter of 60 mm with a plunger were used by applying maximum force of 100 kN and speed ranging from 5 to 25 mm min−1. The initial pressing height of the bulk kernels was measured at 40 mm. The oil point was determined by a litmus test for each deformation level of 5, 10, 15, 20, and 25 mm at a minimum speed of 5 mmmin−1. The measured parameters were the deformation, deformation energy, oil yield, oil point strain and oil point pressure. Clearly, the roasted bulk kernels required less deformation energy compared to the unroasted kernels for recovering the kernel oil. However, both kernels were not permanently deformed. The average oil point strain was determined at 0.57. The study is an essential contribution to pursuing innovative methods for processing palm kernel oil in rural areas of developing countries.

The behaviours of constrained bulk columns of seeds of 3 important leguminous feed crops under compressive force applied at a uniform rate of 10 mm min -1 up to 100 kN at ≈ 9% moisture content (in dry basis) were studied to establish parameters which are relevant to the design of equipment for achieving product densification. Deformation varied significantly (P < 0.02) with crop type and was the highest in lupine seeds. Feed pea had the highest strain resistance value. Both deformation energy and volume energy requirements varied significantly (P < 0.0001) with crop type. Moduli of deformation of compressed feed pea, lupine, and soybean at an applied force of 100 kN were 269.7, 306.3, and 455.2 MPa, indicating the proportionate resistance of the crop materials to compressive strain. Precisely 4.43, 3.76, and 3.15 MJ m -3 are required to achieve 56.7, 77.0, and 67.7% or 461.7, 539.3, and 500.4 kg m -3 gains in bulk density in feed pea, lupine, and soybean, respectively. Deformation and volume energy demands correlated negatively (r = -0.934 and r = -0.78) with lipid presence. Crops with more oil appeared to deform more easily under compressive force. Higher deformations and lower energy demands may be possible at optimal combinations of force, product moisture, and depth.

Compressive expression of oil from bulk seeds is a self‐limiting process and commonly adopted techniques for optimizing oil recovery result in alterations of the product and its quality. In this study, effects of select magnitudes of compressive stress and repetitive strain on mechanical response and performance during cold compressive expression of oil from sesame seeds were investigated and responses modeled using forward stepwise regression technique. Significant gains in oil yield and performance were achieved through repeated induction of strain and by increasing magnitudes of the applied stress. Cumulative improvement in the performance of the scheme over existing single cycle compression techniques ranged between 34.1 and 161.9% over the range of treatments investigated. Corresponding improvement in mechanical response was also achieved. Specific mechanical energy demand was less with every additional compression cycle. The pressure ratio at the oil point during each compression cycle was an important indicator of recoverable oil. Practical applications A technique for maximizing the yield of oil from oilseeds and efficiency during cold compressive expression is presented which may be incorporated in the design of compression devices or similar systems, which would permit repeated induction of stress with a view to optimizing process efficiency without denaturing the product or altering its quality. The pressure ratio at the oil point is also presented, which is a fitting indicator of requisite stress for optimizing yield and performance.