FREEZING AND COLD STORAGE 295 



glaze. Colloids and thickeners such as Irish moss extractives, cellulose 

 gum, and pectinates have been used to improve the effectiveness of the 

 glaze. An alginate referred to as 'Trotan" is being used commercially in 

 the glazing of packaged mackerel fillets^^. Dassow, et al.,^ reported a glaze 

 of corn syrup solids to be effective in increasing the shelf life of frozen 

 salmon steaks. The writer has found that water glazes containing sodium 

 alginate or carboxymethylcellulose were not any more effective than a 

 plain ice glaze in extending the shelf life of frozen packaged whiting and 

 round haddock. 



Antioxidants have been incorporated into dips or glazes in an attempt 

 to reduce oxidation and rancidity of fatty fish^*'^^ Banks ^ found that 

 ascorbic acid and ascorbates, different gallates, and other antioxidants 

 retarded development of rancidity in different species of fish, but the 

 effect varied greatly and was generally unreliable. Piskarev, et al.,^^ re- 

 ported that sprats glazed with water containing ascorbic acid devel- 

 oped foreign taste and odor and kept no better than water-glazed fish. 

 Bramsnaes^, however, found that development of rancidity of fat in 

 frozen rainbow trout could be delayed by dipping in a weak solution of 

 ascorbic acid or other antioxidants. 



The present trend is to use packaging materials wherever possible to 

 protect the product from loss of moisture and oxidation. Glazes are still 

 used for some whole halibut, salmon, or fresh water fish and fish steaks 

 or portions readily susceptible to rancidity. Ice glaze is the only one used 

 commercially. Antioxidants are seldom used in glazing materials because 

 their influence is not significant. 



Relative Humidity. The relative humidity is a comparison of the 

 amount of moisture in the air, at a particular temperature, to that which 

 the air can theoretically hold. Air at a certain temperature will hold only 

 so much water; then precipitation of moisture in the form of rain or frost 

 will occur. As the temperature of the air decreases, its ability to hold 

 moisture also decreases. The air also exercises a certain vapor pressure, 

 which increases because of moisture content and temperature. 



Frozen fishery products contain about 80 per cent water and therefore 

 have a relatively high moisture-vapor pressure. As the relative humidity 

 of the storage environment is decreased, the moisture-vapor pressure of 

 the air decreases proportionally, causing a greater difference between the 

 moisture-vapor pressure of the product and the surrounding air. Moisture 

 then migrates from the product to the surrounding air until equilibrium 

 is established. The rate at which the moisture is removed from the product 

 is a direct function of the difference in the vapor pressure between product 

 and air. 



Fishery products are subjected to storage, transportation, and handling 



