Structure, Protein Interactions and In Vitro Protease Accessibility of Extruded and Pressurized Full‐Fat Soybean Flakes

Characterizing the Structural and Functional Properties of Soybean Protein Extracted from Full-Fat Soybean Flakes after Low-Temperature Dry Extrusion

The soy protein isolates (SPI) extracted from different extruded full-fat soybean flakes (FFSF), and their conformational and functional properties were characterized. Overall, the free thiol (SH) content of SPI increased when the extrusion temperature was below 80 °C and decreased at higher temperatures. Soy glycinin (11S) showed higher stability than β-conglycinin (7S) during extrusion. Results also indicated that the increase in some hydrophobic groups was due to the movement of hydrophobic groups from the interior to the surface of the SPI molecules at extrusion temperatures from 60 to 80 °C. However, the aggregation of SPI molecules occurred at extrusion temperatures of 90 and 100 °C, with decreasing levels of hydrophobic groups. The extrusion temperature negatively affected the emulsifying activity index (EAI); on the other side, it positively affected the emulsifying stability index (ESI), compared to unextruded SPI.

Conformational and Functional Properties of Soybean Proteins Produced by Extrusion-Hydrolysis Approach

The conformational and functional changes of soybean protein after a hybrid extrusion-hydrolysis method were evaluated. Three extrusion temperatures (60, 80, and 100°C) were used prior to enzymatic hydrolysis. The hydrolysis degrees, molecular weight profiles, solubilities, surface hydrophobicities, sulphydryl contents, disulfide bound, water holding capacity, emulsion, and foam properties of the protein isolated from the enzyme-hydrolyzed extruded soybeans were analyzed. It shows that extrusion caused significant changes in the hydrophobicity, molecular weight distribution, solubility, surface hydrophobicity, emulsification activity, and stability of the protein. The increase of molecular weights could be attributed to the formation of protein aggregates during extrusion. Extrusion and enzymatic hydrolysis led to a sharp increase in the number of disulfide bonds with a decrease of the sulphydryl group. The water holding capacity and the solubility of protein increased with the increase of extrusion temperature and hydrolysis time. Extrusion improved the emulsifying activity but reduced the emulsifying stability of the recovered proteins. Extrusion improved the foam capacity but reduced the foam stability of the proteins. The data demonstrated that the extrusion-hydrolysis treatment significantly altered the conformational and functional properties of soybean protein, which may be further optimized for the development of new soy protein ingredient with desired functional properties.

Effects of high-pressure processing and enzymatic dephosphorylation on phosvitin properties

BACKGROUND

Egg phosvitin could be a good source of functional peptides. Enzymatic dephosphorylation and high-pressure processing combined with thermal treatment applied before proteolysis could produce phosvitin hydrolysates with different properties compared to its native form.

RESULTS

Phosvitin structure was maintained overall during high-pressure treatment of 600 MPa applied at an initial temperature of 65 °C regardless of the pH and duration of treatment, confirming the high structural stability of this phosphoprotein. Treatment of phosvitin with phosphatase increased the degree of dephosphorylation from 24% to 63%, after 2 and 18 h, respectively. Moderate dephosphorylation of phosvitin prior to proteolytic digestion improved its hydrolysis, allowing formation of peptides with a molecular weight lower than 17,000 kDa as determined by size exclusion chromatography. Angiotensin-converting enzyme (ACE) inhibition and antioxidant activity of dephosphorylated and protease-treated phosvitin was increased by 52% and 39%, respectively, as compared to protease-digested native phosvitin.

CONCLUSION

Enzymatic dephosphorylation before proteolysis mimicking in vivo gut conditions improved ACE inhibition and antioxidant activity of phosvitin hydrolysates.

Efficiency of pretreatments for optimal enzymatic saccharification of soybean fiber

The effectiveness of several pretreatments [high-power ultrasound, sulfuric acid (H(2)SO(4)), sodium hydroxide (NaOH), and ammonium hydroxide (NH(3)OH)] to enhance glucose production from insoluble fractions recovered from enzyme-assisted aqueous extraction processing of extruded full-fat soybean flakes (FFSF) was investigated. Sonication of the insoluble fraction at 144 μm(pp (peak-to-peak)) for 30 and 60s did not improve the saccharification yield. The solid fractions recovered after pretreatment with H(2)SO(4) [1% (w/w), 90°C, 1.5h], NaOH [15% (w/w), 65°C, 17 h], and NH(3)OH [15% (w/w), 65°C, 17 h] showed significant lignin degradation, i.e., 81.9%, 71.2%, and 75.4%, respectively, when compared to the control (7.4%). NH(3)OH pretreatment resulted in the highest saccharification yield (63%) after 48 h of enzymatic saccharification. A treatment combining the extraction and saccharification steps and applied directly to the extruded FFSF, where oil extraction yield and saccharification yield reached 98% and 43%, respectively, was identified.

Comparison and optimization of enzymatic saccharification of soybean fibers recovered from aqueous extractions

Soybean insoluble fractions recovered from aqueous extraction processing (AEP) and enzyme-assisted AEP (EAEP) of full-fat soybean flakes (FFSF) and extruded FFSF were evaluated as a feedstock for the production of fermentable sugars using enzymes. Among the four insoluble fractions (AEP FFSF, EAEP FFSF, AEP extruded FFSF and EAEP extruded FFSF), the composition analysis revealed that the one recovered from EAEP of extruded FFSF had the highest glucan content, 16% [dry basis (db)], as compared to about 10% (db) for the other fractions. Thirty-three percent of the initial glucan of the insoluble recovered from AEP and EAEP of FFSF were converted into glucose using 33 FPU of Accellerase 1000/g-glucan. This saccharification yield was increased to 44% with extruded fibers. The higher saccharification yield of 49% was obtained at 45 °C, 1% glucan loading, and 101 FPU/g-glucan enzymes loading after 27 h of hydrolysis.

(31)P NMR phospholipid profiling of soybean emulsion recovered from aqueous extraction

The quantity and composition of phospholipids in full-fat soybean flour, flakes, and extruded flakes and in the cream fraction recovered after aqueous extraction (AEP) and enzyme-assisted aqueous extraction (EAEP) of these substrates were studied with (31)P NMR. Extruded flakes had significantly more phosphatidic acid (PA) than flakes and flour prior to aqueous extraction. The PA content of the cream recovered after AEP and EAEP of extruded flakes was similar to that of the starting material, whereas the PA content of the creams from flour and flakes significantly increased. Changes in the PA content could be explained by the action of phospholipase D during the processing step and aqueous extraction. Total phospholipids in the oil recovered from the creams varied from 0.09 to 0.75%, and free oil yield, which is an indicator of cream stability, varied from 6 to 78%. Total phospholipid did not correlate with emulsion stability when it was lower than 0.20%. Inactivation of phospholipase D prior to aqueous extraction of flour resulted in a cream emulsion less stable toward enzymatic demulsification and containing less PA and total phospholipids than untreated flour. The phospholipid distributions in the cream, skim, and insolubles obtained from AEP flour were 7, 51, and 42%, respectively.