The green oat story: possible mechanisms of green color formation in oat products during cooking.
Consumers occasionally report greenish colors generated in their oat products when cooking in tap water. Here we have investigated pH and ferrous (Fe(2+)) ion as possible mechanisms for this color change. Steel-cut oat groats can turn brown-green color when cooked in alkaline conditions (pHs 9 to 12). Extraction of this color with methanol, and high-pressure liquid chromatography indicated a direct association of this color with the phenolic acid or avenanthramide content of the oat. The presence of 50 mM NaHCO(3) in water will cause oat/water mixtures to turn alkaline when cooked as CO(2) is driven off, generating OH(-) ion. Although tap water rarely, if ever, contains so much bicarbonate, bicarbonate is used as a leavening agent in baking applications. Industrial interests using baking soda or alkaline conditions during oat processing should be aware of possible off color generation. We have also found that as little as 10 ppm Fe(2+) will turn oat products gray-green when cooked. The aleurone stained darker than the starchy endosperm. Other divalent cations, such as Ca(2+) or Mg(2+) had no effect on cooked oat color. As much as 50 ppm Fe(2+) may be found in freshly pumped well water, but Fe(2+) reacts quickly with oxygen and precipitates as Fe(OH)(3). Thus, some freshly pumped well water may turn oats green when cooked, but if the water is left under atmospheric conditions for several hours, no discoloration will appear in the cooked oats.
Doehlert
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USDA-ARS Wheat Quality Laboratory, Harris Hall, North Dakota State Univ., Fargo, ND 58108-6050, USA. douglas.doehlert@ndsu.edu
Simsek
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Wise
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D000704:Analysis of Variance; D018554:Avena / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003116:Color; D003124:Colorimetry; D003258:Consumer Behavior; D003296:Cooking / Q000379:methods*; D002523:Edible Grain / Q000737:chemistry; D005433:Flour / Q000032:analysis; D005511:Food Handling / Q000379:methods*; D005524:Food Technology / Q000379:methods; D006863:Hydrogen-Ion Concentration; D062385:Hydroxybenzoates / Q000032:analysis; D007501:Iron / Q000737:chemistry; D010858:Pigmentation; D010936:Plant Extracts / Q000032:analysis; D012639:Seeds / Q000737:chemistry*; D017693:Sodium Bicarbonate / Q000737:chemistry; D013053:Spectrophotometry; D014867:Water / Q000737:chemistry; D062367:ortho-Aminobenzoates / Q000032:analysis / Q000138:chemical synthesis / Q000737:chemistry / Q000302:isolation & purification; D002934:Cinnamates; D000094162:Phytoalexins
D062385:Hydroxybenzoates; D007501:Iron; D010936:Plant Extracts; D017693:Sodium Bicarbonate; D014867:Water; D062367:ortho-Aminobenzoates; C514463:avenanthramide-2C; C546196:avenanthramide B; D002934:Cinnamates; D000094162:Phytoalexins; C546195:avenanthramide A; C017616:phenolic acid