White grapes darken during drying and subsequent storage of the resulting raisins; the freshly expressed, unheated juice becomes brown on standing; and white wines slowly darken during aging. Since it appears that oxidizing enzymes are involved, at least to a considerable extent, in these changes, the investigation reported in this paper was undertaken upon some of the properties of the oxidizing enzymes occurring in certain Vinifera grapes, particularly of the Sultanina (Thompson seedless) variety.
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