Pigment degradation in frozen foods

Technical information Food refrigeration and freezing Chemical Changes Produced By Freezing And Frozen Storage

Chemical Changes Produced By Freezing And Storing The Frozen

During freezing of food, water is transferred into ice crystals and dissolved substances a concentrate in a frost-free matrix. Slow freezing leads to maximum ice crystal purity and maximum concentration of dissolved substances in the unfrozen phases leading to equilibrium conditions.

In contrast, rapid freezing leads to a significant seizure of solutes by the cultivation of crystals and a lower concentration of dissolved substances in a frost-free phase. The elevated concentrations of dissolved substances in a frost-free matrix increases the ionic strength and can produce changes affecting the structure of biopolymers. The structure of water and water solutions of interaction can be changed and interactions of macromolecules, such as proteins may increase. The formation of ice crystals can produce release of the contents of food tissues; reactions that are not commonly found in intact cells may arise as a result of freezing the process. The possibility that the enzymes come in contact with different substrates increases, which leads to deterioration during storage in the frozen state.

Most enzymes show the considerable activity after freezing and thawing, and many enzymes, show significant activity in the partially frozen systems.

Freezing can give unusual effects in chemical reactions, temperature and concentration of the reagents in a frost-free phase (freezing effect concentration) are the main factors of change in the reaction rates in frozen products. In many frozen systems, reaction rates, as a function of temperature pass through a maximum temperature below the starting point of freezing. This is a consequence of opposing factors: the low temperature, which bring reaction rates down, and the increase in the concentration of the solute in a frost-free phase, which could increase these reaction rates. For example, the oxidation of myoglobin (meat pigment) was accelerated at temperatures close to 5C (Lanari et al., 1990; Lanari and Zaritzky, 1991).

The most important chemical changes that may continue during the freezing and storage of frozen are: enzymatic reactions, protein denaturation, lipid oxidation and degradation of pigments and vitamins, taste and deterioration (Zaritzky, 2006)...

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