Abstract
The effects of pH on the nonenzymatic reactions of dopachrome leading to brown to black melanin formation were examined. At pH 5.0, the changes in dopachrome absorbance at 480 nm and formation of melanin were slow. After 7–8 hours the absorbance decreased to approximately one half of the original dopachrome solution.
At pH 7.0 the changes were much more rapid. After 17 min the absorbance decreased by 0.15. An equivalent decrease in absorbance at pH 5.0 required almost 4 hours. At pH 7.0 the absorbance at 480 nm decreased to a minimum after 43 min and then increased for 4 hours when the absorbance of the pinkish grey solution was the same as the original orange dopachrome solution.
Thus, the pH of any treatment used to inhibit enzymatic blackening is very important in determining the amount of discoloration finally obtained. A pH of 5.0 or lower which would inhibit both the nonenzymatic and enzymatic reactions in the blackening reaction would be most desirable unless flavor or texture problems arise.
Resumen
Se examinaron los efectos de pH en las reacciones no enzimáticas de dopacromo para la formación de melanina marron a negra. A pH 5.0, los cambios en la absorbancia de dopacromo a 480 nm y la formación de melanina fueron lentas. Después de 7–8 horas la absorbancia disminuyó a aproximadamente la mitad de la original solución de dopacromo.
A pH 7.0, los cambios fueron mucho más rápidas. Después de 17 min. la absorbancia disminuyó 0.15. Una disminución equivalente en absorbancia a pH 5.0 tomó 4 horas. A pH 7.0, la absorbancia a 480 nm disminuyó a un mínimo después de 43 min y entonces aumentó por 4 horas cuando la absorbancia de la solución rosada-gris fue la misma como la original solución anaranjada de dopacromo.
Así, el pH de cualquier tratamiento usado para inhibir el ennegrecimiento enzimático es muy importante en la determinación de la cantidad de descoloramiento obtenida finalmente. Un pH de 5.0 o menor, el cual inhibirá las reacciones enzimáticas y no enzimáticas en la reacción de ennegrecimiento sería lo más conveniente a menos que se presenten problemas de sabor a textura.
Similar content being viewed by others
Literature Cited
Amla, B. L. and F. J. Francis. 1961. Effect of pH of dipping solution on the quality of prepeeled potatoes. Am Potato J 38 (4):121–130.
Dawson, C. R. and R. J. Magee. 1955. Plant tryosinase (Polyphenol oxidase).In Methods in Enzymology (S. P. Colowick and N. O. Kaplan, eds.), Vol. II, p. 817, Academic Press, New York.
Duckworth, H. W. and J. E. Coleman. 1970. Physicochemical and kinetic properties of mushroom tyrosinase. J Biol Chem 245 (7): 1613–1625.
Fling, M., N. H. Horowitz and S. F. Heinemann. 1963. The isolation and properties of crystalline tyrosinase from Neurospora. J Biol Chem 238:2045–2053.
Graubard, M. and J. M. Nelson. 1935. Tyrosinase action on mono- and dihydric substrates. J Biol Chem 111:757–770.
Iritani, W. H. and L. Weller. 1974. Some factors influencing the pH of apical and basal portions of Russet Burbank and Norgold potatoes. Am Potato J 51:119–125.
Lerner, A. B. and T. B. Fitzpatrick. 1950. Biochemistry of melanin formation. Physiol Rev 30:91–126.
Muneta, Paul. 1967. Possible interaction of chlorogenic acid, tyrosine and bisulfite in enzymatic blackening of potatoes. Am Potato J 44:236–240.
Muneta, P. and Hsi Wang. 1977. Influence of pH and bisulfite on the enzymatic blackening reaction in potatoes. Am Potato J 54(2):73–81.
Robertson, J. and A. Smith. 1931. A study of the hydrogen ion concentration of the potato tuber. Biochem J 25:763–769.
Author information
Authors and Affiliations
Additional information
Published with the approval of the Director of the Idaho Agricultural Experiment Station as Research Paper No. 76511.
An erratum to this article is available at http://dx.doi.org/10.1007/BF02875351.
Rights and permissions
About this article
Cite this article
Muneta, P. Enzymatic blackening in potatoes: Influence of pH on dopachrome oxidation. American Potato Journal 54, 387–393 (1977). https://doi.org/10.1007/BF02852759
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF02852759