Nancy Kangas

CHARACTERIZATION OF PREPARATION PARAMETERS FOR IMPROVED SCREW PRESSING OF CRAMBE SEED

Screw pressing of niche oilseeds such as crambe may be a viable alternative to solvent extraction of oil. Cooking before pressing is known to improve oil recovery. Use of well–defined cooking conditions of time and temperature was expected to aid characterization of the relationship between cooking and press performance, and to reduce soluble seed protein according to a fundamental kinetic model. A pressure cooker modified to permit both steam injection and vacuum permitted the cooking of crambe seed at well–defined conditions of 90³C to 120³C for 5 to 20 min. Oil recovery increased with increasing cooking temperature and time to a maximum of 75.9% at 100³C and 12 min, versus 70.9% for uncooked seed, and a low of 70.6% at 120³C and 20 min. Oil recovery and press rate were nonlinear functions of cooking temperature and time. A cooking index based on soluble protein decreased according to a modified thermal processing model with D0 and z values of 3.3 min and 28³C, respectively. The index was also useful for identifying optimally cooked seed. Oil recovery increased with decreasing seed moisture content to a high of 82.5% recovery at 3.5% m.c. The approach described here may be extended to the tuning of other screw presses for crambe and other oilseeds.

SCREW PRESSING CHARACTERISTICS OF DEHULLED CRAMBE SEED

Screw press performance with a given oilseed depends on the method of preparation before pressing. Oil recovery and press rate of two screw configurations, R-8 and R-11, that differed in flight pitch, height, and width, were compared at dehulling levels from 0% to 100%. The oil recovery with the R-11 screw was better than that of the R-8 at dehulling levels >40%, and the press rate was similar. Thus, the R-11 was selected for a subsequent experiment involving four preparation parameters (dehulling level, cooking time, cooking temperature, and moisture content), each at five levels, using a central composite rotatable design. Multiple regression analysis of the experimental results revealed that linear, quadratic, and interaction terms of the parameters cooking time, cooking temperature, and dehulling level were non-significant even at P > 0.10; however, the linear term for moisture content was significant at P < 0.001. A comparison of oil recovery for cooked seed/kernel versus uncooked at different dehulling levels (30% to 70%) indicated a significant difference at P < 0.01, but the improvement in oil recovery due to cooking was small. A steady rise in oil recovery with decrease in moisture content from 9% to 3% was observed. Moisture content was the major factor influencing press rate, followed by dehulling level and cooking temperature, respectively. It was concluded that acceptable screw press performance was achieved with dehulled crambe seed, that proper moisture content adjustment before pressing dehulled seed was important, and that cooking dehulled seed was of negligible benefit.

Kinetic characterization of cooking-induced changes in crambe seed prepared for expelling

Abstract Expellers offer a viable means for extracting oil from crambe seed ( Crambe abyssinica ) and other niche oilseeds. Oilseeds are often cooked before expelling; however, little is known about the effects of cooking on the seed. Crambe seed (9% moisture) was cooked at exactly 80–112 °C for 5–20 min, using a bench-scale steam cooker developed for this purpose. Seed myrosinase activity decreased to below detection under the more intense conditions. Soluble protein content and light absorbance (280 and 420 nm) of aqueous seed extracts decreased with increased cooking time and temperature, in accordance with a first-order kinetic model. The D 0 and z -values for absorbance at 280 nm were 12.7 min and 36.6 °C, respectively. Measurement of absorbance at 280 nm is a simple, rapid analytical method that may be useful to tune the cooking conditions for improved expeller performance.