The hydrogen sulfide reacts with iron salts to produce a black precipitate. Urea TDA Tryptophane deaminase forms indolepyruvic acid from tryptophane. Indolepyruvic acid produces a brownish-red color in the presence of ferric chloride. Tryptophane VP Acetoin, an intermediary glucose metabolite, is produced from sodium pyruvate and indicated by the formation of a colored complex. Conventional VP test may take up to 4 days, but by using sodium pyruvate, the time required has been shortened.
Creatine intensifies the color when tests are positive.
Sodium Pyruvate Creatine GEL Liquefaction of gelatin by proteolytic enzymes releases a black pigment which diffuses throughout the tube. GLU MAN INO SOR RHA SAC MEL AMY ARA Utilization of the carbohydrate results in acid formation and a consequent pH drop. The indicator changes from blue to yellow. If there is no color change after the addition of zinc, this is indicative of the complete reduction of nitrates to nitrogen gas or to an anaerogenic amine.