Detoxification of Rapeseed Protein Products by an Activated Carbon Treatment

Abstract

Rapeseed protein, extracted at pH 10 from rapeseed meal (Brassica campestris var. Span) and isoelectrically precipitated, contained 0.75mg 3-butenyl isothiocyanate, 0.57mg 4-pentenyl isothiocyanate and 0.51mg 5-vinyl-2-oxazolidinethione (goitrin) per g solids after myrosinase treatment.A two-stage process was developed to decrease the levels of these toxins. A suspension of isoelectrically precipitated protein was incubated at pH 7.2 with crude myrosinase and passed through a granular activated carbon column at pH 10. 4-Pentenyl isothiocyanate decreased to 0.006mg/g and only traces of other toxins were detected, 99.96% elimination of aglycones of glucosinolates present in the original meal. Carbon treatment alone in the pH range from 3 to 10 removed over 93% (maximum 98% of pH 3) of isothiocyanates. The detoxification efficiency decreased at pH above 10. The carbon treatment was also partially effective in nitrile removal. It was found that ground white mustard could replace crude myrosinase for hydrolysis of glucosinolates.A 24-hour storage of aglycone-containing protein solutions caused increased losses of isothiocyanates by increasing pH from 5 to 10, probably due to pH-dependent isothiocyanate-protein interaction.Although the carbon treatment almost completely removed purifieid glucosinolates from their aqueous solutions when unhydrolyzed, the results were not reproducible with solutions containing rapeseed protein.