BIOCHEMICAL AND MODEL CHEMICAL-REACTIONS FOR THE BASIS OF RED PIGMENT IN FLUE-CURED TOBACCO

Polyphenol oxidase (PPO) preparations from green tobacco leaves oxidized chlorogenic and caffeic acids to o-quinones, which reacted in vitro with nornicotine to produce red color at 570 nm. Activity was not obtained when ferulic acid was used as a substrate. Variable temperature data showed PPO was stable for 1 h at 75-degrees-C. Nicotine, myosmine, pyrrolidine, asparagine, alanine, and glutamic acid failed to react with chlorogenic acid and enzyme; nor did these compounds interfere with color development between nornicotine and o-quinones. Aqueous ethanolic extracts (80%) gave similar red color from tobacco grade FR and cherry red tobacco (CR) but a brown color from orange tobacco grade F. Alkaloid analysis showed CR and FR grade tobaccos contained higher levels of nornicotine than F grade tobacco. Model chemical reactions with nornicotine showed coupling of nornicotine with o- and p-quinones by Schiff base and Michael addition reaction.