L. S. Wei

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

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.

Aqueous enzymatic extraction of coconut oil

Aqueous extraction of coconut oil with various enzymes was investigated. Several enzyme preparations (cellulase, polygalacturonase, protease, and α-amylase) were used at different concentrations, pH, and temperature values to enhance oil extraction. After the oil had been released by the enzyme reaction, it was separated by centrifugation. The results showed that an enzyme mixture at 1% (w/w) each of cellulase, α-amylase, polygalacturonase, and protease at pH 7.0 and an extraction temperature of 60°C represented the most effective extraction conditions with an oil yield of 73.8%. Quality characteristics of the oil were as follows: moisture content, 0.11%; free fatty acid, 0.051%; peroxide value, 0.016 meq oxygen/kg; anisidine value, 0.026; iodine value, 8.3; saponification value, 260; and color, 0.6 (Y+5R). This technique for recovering oil from fresh coconut meat with enzymes is a significant improvement in both oil yield and quality over the traditional wet process.

Technical news feature

Soybeans from different maturation stages were tested for their chemical composition and storage stability. Maturation was arrested at specified times by spraying paraquat on the plant. The same level of trypsin inhibitor activity was found regardless of maturation. However, the lipoxygenase activity and phytate content were significantly lower in immature beans. Crude oil and protein contents were similar, regardless of maturation. The crude oils from immature samples were greener in color and higher in free fatty acid content than those from mature ones. Both yield of isolated soy protein and ratio of 7S to 11S protein in immature soybeans were lower than that from mature soybeans. During storage, lipoxygenase activity decreased independently of maturation but free fatty acid content in the crude oil increased at a faster rate in immature beans than that from mature ones.

Effect of enzyme inactivation on the extracted soybean meal and oil

The objective was prevention of lipoxygenase activity prior to oil extraction in order to obtain a meal of superior flavor quality and a crude oil of superior oxidative stability. Accordingly, experiments were performed in which soybeans were heated at various moisture contents and times to inactivate the enzyme system. Once the optimal conditions were determined, heat treated and raw beans were extracted in a laboratory system designed to simulate conditions in commercial solvent extraction and the component oil and meal were evaluated. Oxidative stability of the oil from heat-treated beans was increased as determined by the Swift stability test and an organoleptic evaluation. Similarly, organoleptic blandness ratings of the heat-treated meal were also superior to the meal produced from raw beans. It was concluded that steam heat treatment of soybeans prior to extraction was beneficial to quality of both oil and flake.

Effects of maturation and storage on solubility, emulsion stability and gelation properties of isolated soy proteins.

Solubility, emulsion stability and gelation of isolated soy proteins and their 7S and 11S fractions from three stages of seed maturity were studied. The pH-solubility profile was similar irrespective of maturation and six-month storage. The 11S protein was more soluble in the acidic pH range than the 7S protein. Oil-in-water emulsion stability of isolated soy protein from mature soybeans was higher than that from the immature ones. This is due to the fact that there was more 7S fraction in the mature soybeans, and 7S protein was found to form a more stable emulsion than that formed from 11S protein. The result suggests that isolated soy protein from mature soybeans would serve as a better emulsifying agent. Heat-induced soy protein gels became weaker as the soybeans became more mature. This can be attributed to the higher content in the immature soybeans of 11S fraction which gives a stronger gel than 7S fraction in the protein from immature soybeans.

Minimizing protein insolubilization during thermal inactivation of lipoxygenase in soybean cotyledons

ABSTRACTThe objective was to develop a procedure for inactivating lipoxy-genase in soybean cotyledons without losing protein solubility. The approach was to moisten cotyledons to one of 2 levels in soft water or carbonate buffers, steam for a short time, hold for a definite period at a known temperature, cool and analyze for enzyme activity and protein solubility. Temperature dependence of both inactivation and insolubilization kinetics was determined. Increasing temperature of steaming and holding favored our objective. At 16.3% moisture, the pH 9.8 buffer was beneficial but the pH 10.8 buffer was not. The holding period was not beneficial compared to steaming alone. Recommended conditions were adjustment of cotyledon moisture to 16.3% with pH 9.8 buffer and then heating in steam for about 10 sec; at temperatures of 91 C and above, 99% of the lipoxygenase could be inactivated with retention of over 70% protein solubility. The effect of buffers on kinetics of heat inactivation and insolubilization appeared to be related to the states of hydration water, i.e., the presence of solute water at the higher moisture content.

Identification of major triglycerides causing the clouding of palm olein

Clouding was obtained by storing palm olein at 12.5°C for up to 24h and was separated by centrifugation. the fat crystals were collected after washing with cold acetone. The crystals were identified according to their fatty acid and triglyceride composition, carbon number and degree of unsaturation. Palmitic-oleic-palmitic (POP) and palmitic-oleic-stearic (POS) levels were high in the cloud material, especially in that recovered between 15–18 h of storage. The increase in POP and POS concentrations was concomitant with a decrease in the content of palmiticoleic-oleic (POO). The least amount of POO was also obtained in clouds collected between 15–18 h of storage, compared to the original oil sample. The increase of palmitic acid explained that triglycerides conjugated with palmitic acid molecules in their acyl chains could have been crystallized, and crystallization could have taken place in the order of the number of palmitic molecule in the acyl chain. The concentrations of the other triglycerides did not change much throughout the storage period. Further storage caused the composition of the cloud to become similar to that of the original oil sample.

Effects of soaking soybeans in dilute acids on biologically active components

Soaking soybeans in dilute acids affected activities of lipoxygenase, trypsin inhibitor and urease. Effects of soaking time, acid concentration and soaking temperature were investigated. Lipoxygenase activity was completely eliminated by soaking in 0.3 M HC1 at either 23°C or 40°C for 8 hr. Less than 50% trypsin inhibitor remained and urease was inactivated to an acceptable level (0.04 ΔpH).

Effect of simulated freeze damage on soybean seed composition and functionality.

Two soybean varieties (Beeson and Williams) were harvested at various maturation levels by applying paraquat directly to the growing plant. The application of this herbicide to arrest growth was used to simulate freeze damage. The free fatty content and the photometric index declined from 0.61% to 0.19% and 301.56 to 201.90, respectively, as maturation progressed for the Beeson variety. Similar trends were found with the Williams variety. However, the amount of trypsin inhibitor differed between the two varieties depending upon maturation level.