The recovery of sinapic acid from the waste permeate from yellow mustard protein isolation

A process for recovering sinapic acid from waste permeate generated from processing yellow mustard protein isolate has been developed. Due to the low concentration of solids in the waste permeate, a nanofilter with molecular weight cut-off of 1000Da was used for removing most of the water. The volume of starting material was concentrated 5-fold, whilst approximately 74% of sinapine was retained. Sinapic acid was then released from sinapine, an esterified form, by an alkaline hydrolysis with 4M NaOH for 4 hr. The hydrolyzed solution was acidified to pH 2 to prevent oxidation of the sinapic acid and to precipitate the remaining proteins. As a result, more than 84% of the permeate protein was precipitated, and was subsequently removed using centrifugation. Sinapic acid and other phenolics were extracted by an organic solvent system (diethyl ether and ethyl acetate (1:1)). Under the optimum extraction conditions approximately 95% of the sinapic acid was extracted to the solvent phase. Sinapic acid was further purified by strong basic ion-exchange chromatography. Approximately 19 bed volumes of the solution containing sinapic acid obtained from the previous extraction step were fed to the chromatographic column at 30 mL/min before sinapic acid absorbed by the resins was eluted with a mixture of methanol and 1 M acetic acid (4:6). The effluent obtained from the elution process was freeze-dried to obtain a purified product. More than 38% of the sinapic acid from the starting waste permeate was finally recovered and the resulting product contained about 85% of total phenolics (81% sinapic acid and 1.7% of p-hydroxybenzoic acid). The recovered product was tested for its antioxidant activity with the DPPH radical scavenging method. Data derived from the tests showed that the potencies in terms of EC50 between the recovered product and a pure commercial sinapic acid were comparable.