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Foods -- Vegetables

What causes some vegetables to become discolored?

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Garlic, blue color - Raw garlic contains an enzyme system that if not inactivated by heating, reacts with sulfur (in the garlic) and copper (from water or utensil) to form blue copper sulfate. This is not harmful. Garlic, green color - If the garlic was not fully mature or dry, pigments in the garlic may turn green when in the presence of acid. Garlic will also turn green (develop chlorophyll) if it experiences a radical temperature change or is exposed to sunlight. Garlic is best harvested at night and then kept in the dark. It is conditioned or stored for 32 days at or above 70-80 degrees F to prevent greening. This is not harmful. Brine, red color - If the water lines were flushed out shortly before the water was used in pickling iron oxide (rust) may have been present. The discoloration should disappear after several months of storage. Dill, pink or red color - This is a change in pigments and is harmless. Cauliflower, pink or gray - The pigments in cauliflower are usually colorless or you may see a little purple pigment. In the presence of iron, these pigments may turn pink or gray. It is a harmless reaction. You may minimize the color change by blanching the cauliflower 2-3 minutes in boiling water containing 2-3 tablespoons lemon juice per gallon of water. Light colored fruit or vegetables, darkening. Cider vinegar may darken light colored fruits and vegetables. Use white distilled vinegar in the pickling solution. Exposure to air at the top of the canning jar will cause browning over time. This occurs because the food is not covered with liquid or processing was inadequate. Sauerkraut, pink or dark. Pink color in kraut is caused by the growth of yeast organisms on the surface of the kraut. This is caused by too much salt, an uneven distribution of salt, or inadequate liquid to cover the kraut during the fermentation period. The only way to get the proper ratio of cabbage to salt is to weigh the cabbage. Dark kraut may be caused by unwashed and improperly trimmed cabbage, insufficient juice to cover cabbage during fermentation, exposure to air, high temperatures during fermentation, processing and storage, and a long storage period. Off colors, off odors and soft texture are signs of spoiled kraut. Red cabbage in the presence of iron will turn a dirty pinkish gray during fermentation. It is almost impossible to avoid some iron contamination.

PREPARED BY: Angela M. Fraser, Ph.D., Associate Professor/Food Safety Specialist, and Carolyn J. Lackey, Ph.D., R.D., L.D.N., Professor/Food and Nutrition Specialist, North Carolina State University (August 2004)

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