Dear Brian,
Black spots (melanosis) form on crustacean shell within a few hours after
harvest without refrigeration. The reaction is an enzymatic process. The
reaction involves the oxidation of phenols to quinones by polyphenol
oxidase (PPO), a copper-containing oxidase. Subsequently a non-
enzymatic polymerization of the quinones occurs, leading to the formation
of dark, high molecular weight pigments. This same series of reactions is
responsible for enzymatic browning in fruits and vegetables. PPO is
unique in that it catalyses two different types of reactions involving
phenolic compounds. The first reaction involves hydroxylation of
monophenols (such as tyrosine) to produce o-diphenols, and in the
second reaction PPO oxidizes o-diphenols to o-quinones.
Regards,
Mauricio Gonzalez
> Dear list
> Recently I received a complaint from a customer re white spot in
> frozen raw shell on shrimp. Can anybody from this list provide me with
> info as to what this is, and what is the cause?
>
> Brian Cuff
> bcuff@fpil.com
>
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MAURICIO GONZALEZ
Ph.D. Engineering Sciences
Docteur en Sciences de l'Ingénierie
Doctor en Ciencias de la Ingeniería
Marine Products Research and Development Center Inc
Centre de Recherche et de Développement des Produits Marins Inc
Centro de Investigación y Desarrollo de Productos Marinos Inc
218 J.D.Gauthier Boulevard, 5th floor
218, boulevard J.-D.-Gauthier, 5e étage
218, bulevar J.-D.-Gauthier, 5to piso
E8S 1P6, Shippagan
New Brunswick, Canada
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