BARNETT ET AL, ; USE OF CARBON DIOXIDE IN BRINE 



of the two storage environments, the fish held in 

 the modified brine water were organoleptically 

 acceptable and of good quality after 17 days of 

 storage. The subsequent refrigerated shelf life 

 of this product was not determined. 



STORAGE LIFE AND QUALITY OF 



CHUM SALMON HELD IN MODIFIED 



REFRIGERATED BRINE 



OBJECTIVE MEASUREMENTS 



Both bacteriological and chemical measure- 

 ments were made. All the reported measure- 

 ments were made in duplicate. 



Bacteriological Measurements 



Materials and methods. — Described here are 

 the samples of salmon and of brine and the meth- 

 ods of making total plate counts. 



About 300 lb. of fresh seine-caught chum 

 salmon, Oncorhynchits keta, were obtained in 

 the round from Bellingham, Wash. The salmon, 

 which weighed about 10 to 13 lb. each, were di- 

 vided into two lots of equal size. Each lot was 

 loaded at a one-to-one brine-to-product ratio by 

 weight into a drum of circulating brine con- 

 taining 3.3^; NaCl (see footnote 4). The 

 salmon had been held in ice and, at this time, 

 were less than 24 hr out of the water. 



The brine was precooled and treated as was 

 described in the section on rockfish. 



Three salmon and a sample of brine were re- 

 moved periodically for examination. The fish 

 samples were used to make both the objective 

 and subjective measurements at each sampling. 



Total bacterial plate counts were made of the 



bacteria on the skin of the fish. Samples of the 

 bacteria were obtained by the swab technique 

 of Tretsven (1968). Briefly, the procedure con- 

 sisted in swabbing the skin of the fish with a 

 sterile swab through a 2 cm' hole cut into the 

 center of a sterilized metal template. The tip 

 of the swab was broken off in such a way that 

 it fell into 10 ml of a O.K^ peptone solution, 

 which was then mixed. Appropriate serial di- 

 lutions were made from this mixture and were 

 plated out on the TPY medium (see the bac- 

 teriological section described under rockfish) for 

 the determination of total bacterial counts. 



In previous experiments at this laboratory, 

 the swab technique gave results similar to those 

 obtained from samples of flesh. Because of this 

 finding and because of the relative simplicity of 

 the swab technique, we used it in this experi- 

 ment. Total plate counts of the bacteria in the 

 brine were made by the method used in the rock- 

 fish experiment. 



Results and discussion.- — Table 3 shows the 

 total plate counts made on the untreated and 

 treated brines. In the control brine, the bac- 

 terial population steadily increased during the 

 18-day experiment. About the 7th day of stor- 

 age, the brine evidenced a slight odor of spoilage. 

 By the 11th day, the untreated brine smelled 

 intensely putrid. At that time, the total plate 

 count exceeded 10" organisms per milliliter. 



The effect of CO2 is demonstrated by the es- 

 sentially unchanged bacterial population in the 

 treated brine during the experiment. The bac- 

 terial population increased between the 3rd and 

 9th days but appeai'ed then to stabilize. During 

 the experiment, the brine remained odorless and. 



Table 3. — Chemical and microbiological changes occurring in C02-treated refrigerated brine and in untreated re- 

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



439 



