Phosphorus recovery from waste streams of soy protein concentrate and isolate production from defatted soybean flour

Abstract: Effects of excess phosphorus (P) in waste streams obtained from soy-based protein production on the environment and potential utilization of waste streams as P-source are two significant understudied areas. Soybean-based protein ingredients for food products retain comparatively enhanced functional properties and are cheaper than other plant-based proteins. Soybean protein can be extracted and utilized as a food ingredient primarily by preparing soy protein concentrates (SPC) and soy protein isolates (SPI) from defatted soy flour (DSF). In a typical soybean processing facility, along with the soy products and soy-protein preparations, the recovery of phosphorus as a coproduct will enhance the economic feasibility of the overall process as the recovered P can be used as fertilizer. In this study, the SPC and SPI were prepared from the DSF following conventional protocols and P flow in these processes was tracked. In SPC production, ~59% of the total P was retained with SPC and ~34% was in the aqueous waste streams. For SPI process ~24% of total P was retained with SPI and ~59% was distributed between the waste solid residue (~40%) and aqueous streams (~19%) obtained in the process. Phosphorus from all the waste aqueous streams, prior to their disposal, can be significantly reduced by a calcium-phytate precipitation method to avoid subsequent eutrophication. About 80 to 89% P removal from the waste aqueous streams was achieved by Ca-phytate precipitation. However, the SPI process solid residue with ~40% P can be used potentially as a P-fertilizer as other applications of this residue are unspecified.

Keywords: Phosphorus recovery, Soy protein concentrate, Soy protein isolate, wastewater treatment