BARNF.TT ET AL : USE OF CARBON DIOXIDE IN BRINE 



Table 1. — Chemical and microbiological changes occurring in COj-treated refrigerated brine and in untreated re- 

 frigerated brine, and in the flesh of rockfish held in these brines. 



Samples judged by appearance and ador to be inedible ond unfit for tasting. 



The storage of rockfish in the refrigerated 

 brine containing the CO2 was terminated after 

 17 days. At this time, the results of the total 

 plate counts made on the flesh of the fish showed 

 that the microbial poiiulation had not changed 

 significantly from the initial total plate count 

 of 10'' organisms per gram of flesh. 



Chemical Measurements 



pH. — The pH of the flesh of the rockfish and 

 of the brines was measured by means of a Beck- 

 man combination electrode. The pH of the flesh 

 was measured by inserting the tip of the elec- 

 trode into the flesh (Patashnik, 1966). 



Table 1 gives the results of the pH measure- 

 ments of the fish and the brine. After 8 days 

 of continuous recirculation, the pH of the con- 

 trol brine changed from a slightly acid condition 

 (pH 6.8) to a slightly alkaline condition (pH 

 7.3). This change coincided with an increase 

 in the microbial population in the control brine 

 and was probably due to the formation of ammo- 

 nia and amines from the bacterial degradation 

 of proteins dissolved in the brine. 



The initial jiH of the brine treated with CO2 

 shows the eflfect of the dissolved CO2. The 

 measurement was made before the fish were 

 loaded into the brine. The subsequent increase 

 in the pH of the brine in the presence of addi- 

 tional CO2 may be attributed to the buff'ering 

 by the soluble proteins in the blood and slime. 

 After the 8th day of the experiment, the pH 

 of the brine treated with CO2 did not increase 

 significantly. 



Between the initial examination and that on 



the 3rd day, the pH of the flesh of the fish held 

 in the brine treated with CO2 dropped appre- 

 ciably. This change was coupled with an in- 

 crease in the concentration of the CO2 in the 

 flesh. As storage continued, the pH returned to 

 the same level (6.4 to 6.5) as that of the flesh 

 held in the untreated brine. 



COa concentration. — The concentration of CO2 

 in the flesh and brine was measured by the 

 method of Umbreit, Burris, and Stauff'er (1957). 

 The procedure was essentially as follows: A 

 slice of fish was removed from the thickest part 

 (dorsal side) of the fish. The sample was then 

 carefully sectioned into horizontal cuts about 

 i4.-inch thick and the individual cuts analyzed. 

 A sample of the flesh or of brine was blended 

 in Tris bufl^er (hydro.xymethyl) aminoethane at 

 a pH of about 9. Five grams of the mixture 

 was added to a Warburg flask, and 0.7 ml of 0.5 

 M citrate buff'er at pH 4.0 was added to the 

 side arm of the flask. After the flask and its 

 contents came to equilibrium at 38° F in a water 

 iiath, the contents of the side arm were tipped 

 into the flask. The increase in manometric 

 pressure was recorded at irregular intervals of 

 time ranging up to 10 min. The amount of CO2 

 evolved was calculated from a standard curve 

 prepared by determining the changes in pres- 

 sure after measured amounts of acid were tipped 

 into known concentrations of bicarbonate. 



Penetration studies carried out on whole rock- 

 fish showed that CO2 difl'used into the flesh very 

 slowly. The maximum dejjth of penetration in- 

 to the flesh was 0.75 inch. This depth was 

 reached in about 8 days of storage. The highest 



437 



