DETERMINATION OF SH‐ AND SS‐GROUPS IN SOME FOOD PROTEINS USING ELLMAN'S REAGENT

SULFHYDRYL (SH) and disulfide (SS) groups have been widely implicated as im­ portant functional groups in many food proteins. The formation of {3-lactoglobu­ lin-K-casein complexes when milk is heated may occur through the SS inter­ change reaction (Sawyer, 1969 ). The thick gel of egg white is considered to consist of large glycoprotein molecules crosslinked by SS bonds and a reductive mechanism has been proposed to explain the thinning reaction which occurs on ag­ ing of eggs (Shenstone, 1968). Further, it is well documented that addition of SH compounds to flour drastically weakens the rheological properties of the flour (Kuninori and Sullivan, 1968 ). Interac­ tions between SS and SH groups of flour have been suggested to explain, in part, this change. A simple method for the measurement of SH and SS groups in foods would clearly be desirable. Assay procedures utilizing Ellman's reagent (Ellman, 19 59) have the advantage of being simple, rapid and direct (Kalab, 1970) and have yielded values comparable with other analytical methods for SH groups (Fernandez-Diez et al., 1964) and for SS groups (Atassi et al., 1970) in purified proteins. In this report a method for the deter­ mination of both SH and SS groups utiliz­ ing Ellman's reagent is applied to flour, egg white, milk and their products.