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. 2023 Jul 13;12(14):2698.
doi: 10.3390/foods12142698.

Valorization of Soybean Residue (Okara) by Supercritical Carbon Dioxide Extraction: Compositional, Physicochemical, and Functional Properties of Oil and Defatted Powder

Aunchalee Aussanasuwannakul  1 , Sumitra Boonbumrung  1 , Thidarat Pantoa  1
Affiliations

Valorization of Soybean Residue (Okara) by Supercritical Carbon Dioxide Extraction: Compositional, Physicochemical, and Functional Properties of Oil and Defatted Powder

Aunchalee Aussanasuwannakul et al. Foods. .

Abstract

In the context of food waste valorization, the purpose of this study is to demonstrate the complete valorization of soybean residue (okara) through supercritical carbon dioxide extraction (SCE). Okara oil (OKO) was separated from full-fat powder (FFP) using SCE with and without ethanol (EtOH) as a cosolvent. The kinetics of extraction, chemical composition, and physicochemical, functional, and health-promoting properties of OKO and defatted powder (DFP) were determined. The process yielded 18.5% oil after 450 min. The soluble dietary fiber and protein of the DFP increased significantly; its water and oil absorption capacities increased despite the decrease in swelling capacity corresponding to particle size reduction. The OKO was rich in linoleic and oleic acids, with a ratio of ω6-to-ω3 fatty acids = 9.53, and EtOH increased its phenolic content (0.45 mg GAE/g), aglycone content (239.6 μg/g), and antioxidant capacity (0.195 mg TE/g). The DFP paste showed gel-like consistency and shear-thinning flow behavior, whereas the OKO showed characteristic transition of the product and affected lubrication at contact zones. Both fractions showed potential as food ingredients based on their nutritional and functional properties, as well as the capability of modifying the microstructure of a model food system.

Keywords: antioxidants; ethanol; fatty acids; food ingredient; isoflavones; phenolics; rheology; supercritical fluid; tocopherols; tribology.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the decision to publish the results.

Figures

Figure 1
Figure 1
Detailed view of (a) the geometry used in rheometry and (b) the configuration used in tribometry.
Figure 2
Figure 2
Overall extraction curve for okara + CO2 obtained at 300 bar, 50 °C. Blue line represents the extraction during the constant extraction rate (CER) period, orange line is during the falling extraction rate (FER) period, and green line is during the diffusion-controlled (DC) rate period.
Figure 3
Figure 3
R output of a simple linear regression of extraction yield on extraction time during the constant extraction rate (CER) period.
Figure 4
Figure 4
Raw material powder for SCE (FFP), okara powder after SCE at 300 bar, 50 °C (DFP), and commercial okara powder.
Figure 5
Figure 5
Functional properties of fresh okara, FFP, DFP, and commercial benchmarks: (a) water absorption capacity (WAC, g/g); (b) oil absorption capacity (OAC, g/g); (c) swelling capacity (SC, mL/g). a–d Means with different letters within the same response are different (p < 0.05; n = 3).
Figure 6
Figure 6
OKO after SCE at 300 bar 50 °C with and without EtOH, commercial refined soybean oil, and commercial unrefined cold-pressed soybean oil.
Figure 7
Figure 7
Viscosity curve of (a) okara paste and (b) okara oil compared with commercial benchmarks and (c) yogurt fortified with okara extracts.
Figure 8
Figure 8
Friction profile of DFP and FFP paste, OKO, and commercially refined soybean oil.
Figure 9
Figure 9
Friction profile of yogurt fortified with okara extracts.
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