Effect of ultrasound on compositional and emulsifying properties of soybean okara

MOSCOSO OSPINA, Y.A.; PORFIRI, M.C.; CABEZAS, D.M.

Congreso; 2021 AOCS Annual Meeting & Expo; 2021

American Oil Chemists' Society

High-intensity ultrasound is widely used in the food industry to modify structural and functionalproperties of macromolecules (proteins, polysaccharides, etc.), and to expand the range of potentialapplications. The objective of this research was to understand the effects of different ultrasoundtreatments on the compositional and emulsifying properties of different samples of soybean okara.Defatted solvent-free soy flour was extracted by adding 11 times the weight of distilled water, adjusting the dispersion to pH 9.0, and gently stirring during 30 min at 60 ± 2°C. The insoluble residue obtained after centrifugation (7000 g, 4°C, 15 min) was dried by a treatment with 2-propanol. This process allowed to obtain the UOK sample (un-sonicated okara). Furthermore, the soybean flour dispersion was subject to treatment in a probe-type ultrasonic homogenizer (Sonics Vibra Cells- 7070 J, 75% power, 10 min) before or after the alkaline extraction process, thus allowing to obtain the SOK and OKS samples, respectively. SOK have a higher yield and protein content than UOK and OKS, due to the insolubilization of protein structures after the ultrasound pretreatment. This compositional characteristic is caused by an increase in the content of the glycinin (11S) fraction of soybean storage proteins observed in its electrophoretic profile. In this sense, SOK dispersions presented the highest increase in the interfacial pressure at equilibrium (TD3 LMT-850, LAUDA) and in the complex viscosity at the oil/water interface as a function of time (AR-G2, TA Instruments). These characteristics allowed this sample to present the best emulsifying properties among the evaluated samples, analyzing the variation of De Brouckere (D4,3) mean diameters and the percentage of serum layer (SL%) as a function of time of coarse emulsions for 1 hour. In conclusion, the sonication process allows to generate compositional and structural modifications in the okara soybeans, thus varying their emulsifying properties significantly.