Dry extrusion as an aid to mechanical expelling of oil from soybeans

Abstract

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.

Functional properties of low‐fat soy flour produced by an extrusion‐expelling system

“…LFSF is defined as having 5 to 6% residual fat (5). A significant number of small soybean processors, those that process between 6 and 120 tons of soybeans per day, utilize this technology because of the low capital investment costs, enhanced extraction capabilities, and the ability to produce oxidatively stable oils and meals low in FFA (4).…”

The protein dispersibility index in the quality control of heat-treated full-fat soybeans: an inter-laboratory study

“…This is in line with the results of Ruiz et al (2004) who established, in a trial with broilers fed extruded FFSBs, that body weight gain and FCR were best for treatment temperatures between 126 °C and 140 °C. Nelson et al (1987) stated that temperatures most commonly used commercially for extruding raw soybeans were between approximately 135 °C and 140 °C. Palic et al (2009) concluded from two separate trials with broilers that the optimum heat treatment of FFSBs was at 138 °C and 144 °C.…”

Advances in Soybean and Soybean By-Products in Monogastric Nutrition and Health

“…Methods of processing soybean and variations in processing also contribute to the overall quality of the soybean products. These include extrusion and expelling, solvent extraction (Woodworth et al, 2001;Nelson et al, 1987), roasting and Jet-sploding (Marty et al, 1994;Subuh et al, 2002), and micronization (Marty et al, 1994;Subuh et al, 2002). These methods lead to variations in nutrient composition of the final product (s).…”