Protein enrichment of defatted soybean flour by fine milling and electrostatic separation

February 05, 2019

The production of soy protein isolates (SPI) and soy protein concentrates (SPC) with wet fractionation consumes a lot of water and energy. Meanwhile, the ingredients lose their native state and part of their functionality due to the harsh processing conditions.

This study proposed a dry fractionation method combining fine milling and electrostatic separation for the preparation of soybean protein-enriched fractions retaining the native state of the protein. The dry fractionation route contributes to the development of a more sustainable food production chain. During this research, the enrichment of soybean flour in protein by defatting soybean flakes followed by dry fractionation of the defatted flour has been investigated. Impact milling and tribo-electrostatic separation have the advantage to enrich protein without compromising its native functional properties. Defatting was carried out with two methods, i.e. petroleum ether extraction and oil pressing.

The defatting process is a critical pre-treatment to detach protein bodies from lipids and make it possible to achieve protein enrichment. Scanning Electron Microscope pictures showed the protein bodies kept intact after solvent extraction, but more entangled with other components during oil pressing. Moderate impact milling (classifier wheel speed of 3000 rpm) effectively liberated protein bodies whilst eliminating agglomeration of small particles. In the next step, electrostatic separation was conducted with both a charging slit and a spiral charging tube. The spiral charging tube gave higher yields than the slit on the protein rich fraction because prolonged residence time in the spiral tube significantly increased the charge of particles and facilitated their separation afterwards.

During this work a protein enriched fraction with a protein content of 52 g/100 g dry basis have been collected. A soy protein enrichment of 15% was achieved and 66% of the protein was recovered from the soy flour. Concluding, we could achieve protein enriched soy flour by defatting, followed by moderate milling and electrostatic separation with spiral charging tube. This study showed the feasibility to dry-enrich soy protein with this approach consisting of combined impact milling and electrostatic separation.

If you would like more information or would like to discuss this research further please contact Qinhui Xing

Each year EFFoST and Cargill present the student of the year award to six students and also give them the opportunity to showcase their research. In this article, Qinhui Xing who won the popular vote prize for the student of the year discusses her research. Currently, Quinhui is a PhD student at Wageningen University and Research, The Netherlands.


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