A new concept is described for mechanical extraction of oil from soybeans, using dry extrusion as a pretreatment. It was found that coarsely ground whole soybeans at 10 to 14% moisture could be extrusion cooked so that the extrudate emerges from the die in a semi‐fluid state. The dwell time within the extruder was less than 30 seconds, and the temperature was raised to about 135 C. The semi‐fluid extrudate was immediately pressed in a continuous screw press to obtain high quality oil and press cake. Extrusion prior to expelling greatly increased the throughput of the expeller over the rated capacity. An oil recovery of 70% was obtained in single pass expelling using pilot model expellers. Higher recovery rates can be expected with commercial scale expellers. The high temperature‐short time extrusion cooking process eliminates the prolonged heating and holding of raw material in conventional expelling. Under the experimental conditions, press cake with 50% protein, 6% residual oil and 90% inactivation of trypsin inhibitors was obtained. The low fat cake was easily ground in a hammer mill without the usual problems associated with milling of whole beans. The expelled oil was remarkably stable with an AOM stability of 15 hr, which is comparable to refined deodorized oil according to NSPA specifications. The new procedure offers potential for producing natural soybean oil and food grade low fat soy flour by a relatively low cost operation. It may be adopted as an improvement to existing conventional expelling operations in less developed countries or as a commercial or on‐farm operation for producing value added products from soybeans within the U.S.
The objective of this work was to study the effects of freezing conditions, processing and formulation variables on freeze-thaw (F-T) stability of Illinois soybean beverage. Objective and subjective evaluations were made on a sample before and after freezing. Total solids content of the supernatant from a centrifuged sample was used to calculate a F-T stability index. This index was below 35% for both plain base and plain beverage. The freeze-thaw stability was affected by freezing temperature, holding time before freezing, changing of temperature during frozen storage and desludglng. However, length of frozen storage and homogenization pressure had no apparent effect. Addition of sugars and salt resulted in a beneficial effect on the stability. In order to prevent visible freeze damage, approximately 7% sucrose or 5% dextrose hydrate were required in a beverage containing 0.2% salt.
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