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Detoxification of rapeseed protein isolates by an activated carbon treatment Woyewoda, Andrew Dennis

Abstract

Rapeseed protein isolate from pH 10 NaOH extraction was analyzed by gas chromatography (isothiocyanates) and UV absorption (goitrin) (Youngs and Wetter, 1967) and found to contain glucosinolates at levels equivalent to 0.75 mg 3-butenyl isothiocyanate, 0.57 mg 4-pentenyl isothiocyanate, and 0.51 mg oxazolidinethione (goitrin) per g isolate. A two-stage process was developed to decrease the levels of these toxins. Isolate slurry was incubated at pH 7.2 with crude myrosinase extracted from white mustard seed (to convert glucosinolates to isothiocyanates and goitrin), adjusted to pH 10, and passed through a granular activated carbon column. Subsequent analysis revealed only 0.006 mg 4- pentenyl isothiocyanate per g isolate. Goitrin was not detectable. Infrared analysis confirmed that the column was also partially effective in nitrile removal. To eliminate the need for myrosinase purification, the process was modified to include ground white mustard seed addition directly to rapeseed meal slurry. After incubation, the protein was extracted, purified by isoelectric precipitation, re-dissolved, and treated by the activated carbon column. This modification was included in the "recommended detoxification procedure". Subsequent experiments on protein extracts prepared and carbon treated at pH's from 3 to 12, inclusive, revealed that all treatments in the range of pH 3 to 10 were at least 93% effective in isothiocyanate removal. A lower efficiency was observed above pH 10. Storage tests (24 hours) on aglycone containing protein solutions showed increased loss of isothiocyanates with increasing pH from 5 to 10. This could be due to their interaction with protein (Bjorkman, 1973). The column completely removed chromatographically purified glucosinolates from aqueous solution. However, the results could not be duplicated for solutions containing rapeseed protein. Glucosinolate content was determined by trimethylsilation and gas chromatography (modified method of Underhill and Kirkland, 1971).

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