FISHERY BULLETIN; VOL. 69. NO. 2 



study is specifically concerned with the effects 

 that holding in modified refrigerated brine con- 

 taining dissolved carbon dioxide" has on the 

 storage life and quality of rockfish and chum 

 salmon. 



PRINCIPLES OF THE MODIFIED 

 REFRIGERATED BRINE SYSTEM 



EFFECTS OF DISSOLVING CO. IN 

 REFRIGERATED BRINE 



Carbon dioxide is a relatively inert chemical 

 compound. It is almost odorless and, in the gas- 

 eous form, is colorless. Combined with water, 

 it forms carbonic acid, a weak acid. Depending 

 on the conditions, only part of the CO2 added 

 to the water is dissolved. The undissolved CO2 

 either rises to the surface of the solution and is 

 wasted away or else becomes suspended as gas 

 bubbles, thereby forming carbonated water. 

 The amount of CO2 that can be dissolved by 

 water depends on the pressure and temperature. 

 The higher the pressure of the COl' and the low- 

 er the temperature of the water (at least, down 

 to 35° F), the greater the amount of CO2 dis- 

 solved. (We found that lowering the temper- 

 ature below 35° F did not increase solubility.) 



When chilled brine is saturated with CO2, its 

 pH is reduced from about 7.5 or higher to about 

 4.0. This change in pH from the alkaline to 

 the acid condition helps to inhibit the growth 

 of bacteria that contribute to sjjoilage ( Wheaton, 

 1960). But pH control is not the only oper- 

 ative factor. Dissolved CO2 seems to inhibit 

 the metabolic processes of spoilage organisms 

 and, of course, temperature control is important 

 in slowing growth rate. 



Although the modified refrigerated brine tech- 

 nique produces positive effects with regard to 

 the control of bacteria, the addition of CO2 can, 

 under certain conditions, produce undesirable 

 side effects. These effects are manifested in the 

 form of accelerated corrosion rates of metals 

 exposed to seawater containing high concen- 

 trations of the dissolved CO2. 



REFRIGERATED BRINE EQUIPMENT 



The equipment we used consisted of two fi- 

 ber glass-insulated 55-gal epoxy-coated drums 

 and a brine chiller. 



We cooled the drums by circulating refriger- 

 ated brine from the lirine chiller through 200 

 ft of 3/i-inch polyvinyl chloride tubing wound 

 around the outside of the drums in series and 

 returned to the chiller (Figure 1). 



Polyethylene liners with a capacity of about 

 30 gal were suspended in the drums by clamps. 

 (The purpose of the liners was to keep the fish 

 away from the cold sides of the drum, where 

 they tend to freeze.) 



Each drum was equipped with a Moyno° pump 

 (Figure 2) for recirculating chilled brine (a so- 

 lution containing 3.3' r sodium chloride) .' The 

 brine was circulated by the pumps through a 

 fitting in the bottom of the polyethylene liner. 

 It was then forced through fish that had been 

 placed in the liners, whereupon it overflowed 

 back into the drums. The brine in the drums 

 was picked up by a suction hose and recycled 

 through the pumps at the rate of 10 gal/min. 

 For maximum diffusion into the brine, the CO2 

 gas was fed into the suction side of the circu- 

 lating pump at the rate of 0.2 ft\ hr. The brine 

 in the other drum was left untreated for use 

 as a control. 



STORAGE LIFE AND QUALITY OF 



ROCKFISH HELD IN MODIFIED 



REFRIGERATED BRINE 



OBJECTIVE MEASUREMENTS 



Both bacteriological and chemical measure- 

 ments were made. All measurements reported 

 here were made in dujilicate. 



* In this report, the term "modified refrigerated 

 brine" will henceforth mean brine containing dissolved 

 carbon dioxide (CO2). 



' The use of trade names is merely to simplify de- 

 scriptions; no endorsement is implied. 



' Sodium chloride brine was u.sed in lieu of natural 

 seawater because clean seawater was not convenient to 

 the laboratory. However, this technique has previously 

 been used by Collins (1950), Davis and Clark (1944), 

 and others and found to give good results. In compar- 

 ative experiments conducted by Roach and Harrison 

 (1954) and more recently by this laboratory (unpub- 

 lished), the test results showed that fi.sh held in re- 

 frigerated brine were of equal quality to fish held in 

 refrigerated seawater. 



434 



