MFR PAPER 1326

Use of Carbon Dioxide Dissolved inRefrigerated Brine for the Preservationof Pink Shrimp (Panda/us spp.)

HAROLD J. BARNETT, RICHARD W. NELSON,PATRICK J HUNTER, and HERMAN GRONINGER

ABSTRACT-The need to travel farther to productive fishing grounds has madeit increasingly difficult for Pacific Northwest and Alaska fishermen to land iced,whole pink shrimp of high quality. Comparative studies were conducted to deter­mine the effectiveness of holding pink shrimp in ice, untreated refrigerated brine,and refrigerated brine treated with carbon dioxide as a means of increasing thekeeping quality of the landed shrimp. Holding the shrimp in the brine-C02 mixtureinhibited bacterial and enzymatic changes causing spoilage and extended thekeeping quality of the shrimp from 3 to 4 days in ice to 6 days or more in the treatedbrine. Recommendations are made for additional studies prior to commercialapplications.

tabl ished for many areas to prevent de­pletion of stocks. and vessels fre­quently travel farther to fish, making itincreasingly more difficult to bring infull loads of acceptable quality shrimp.The time limit of 4 days in iced storagetherefore becomes a controlling factorin expanding the fishing areas. Thus.there is a need for methods of preserva­tion that permit the retention of qualityduring longer periods of storage on thevessel.

Existing information describing teststo preserve pink shrimp in refrigeratedseawater (RSW) indicates that thetechnique gives good results (Roachand Harrison. 1954; Stern, 1958; CoI­Iins, I960a; Seagran et al .. 1960; andIdyll et al. I); nevertheless. it has neverbeen consistently satisfactory on acommercial scale. Some failures ean beattributed to poorly engineered andmisused systems, but allowing for vari­ation in commercial applications,RSW-heJd shrimp are usually no betterin quality than iced shrimp held for thesame period.

In studies to improve the RSWmethod (Barnett et al., 197 I), we found

Figure I. -A typical north Pacific shrimp boat.

INTRODUCTION

The pink shrimp (Pandaills spp.)fishery makes an important contribu­tion to the volume and value of thefisheries of the Paci fic coast andAlaska. Annual catches in recent yearshave exceeded 130 million pounds(Paci fic Packers Report. 1977) and val­ues in excess of $15 mill ion ex-vessel.

The north Pacific pink shrimp aresmall, from 80 to 120 whole shrimp perpound commonly, and are usuallystored whole in ice aboard the fishingvessel (Fig. I). Because they spoil eas­ily, the shrimp must be delivered to theprocessing plant within 3-4 days afterharvesting. However, because of therapid growth in the shrimp industry

The authors are with the Northwestand Alaska Fisheries Center, Utiliza­tion Research Division, NationalMarine Fisheries Service, NOAA,2725 Montlake Boulevard East,Seattle, WA 98112.

since the late 1950' s. fishing groundslocated near processing ports are nolonger as productive as they once were.As a result catch quotas have been es-

'ldyll.C. P.. J. B. Higman.andJ. B. Siebenaler.1952. Experiments on the holding of frcsh shrimpin refrigerated seawater. Processed Report. ML2738. 23 p. Fla. State Board Conserv.

24 Marine Fisheries Review

Figure 2.-Brine chiller unit for shrimp-holding experiment. Refrigeration unit is at left.Epoxy-lined holding tanks with plastic cooling coils used to chill the tanks are being coveredwith insulation.

that CO:! gas dissolved in chilled brineeffectively retarded the growth ofspoilage bacteria on wholt: fish. Carbondioxide has been experimentally usedbefore to preserve finfish and pinkshrimp (Coyne. 1932, 1933; Hjorth­Hansen. 1933; Stansby and Griffiths.1935; Makashev. 1954); however. ex­cept for a study (Anonymous. 196R)conducted by the FiskerministerietsFors0gabortorium, the research hasheen confined mainly to the effective­ness of storage in controlled gaseousatmosphere. Because the results of ourtests in preserving fish in the CO:!­refrigerated brine were so promising.experiments were initiated to determinethe effectiveness of the techniqueapplied to pink shrimp. The study de­scribed here is concerned with the stor­age life. quality, and composition ofpink shrimp held in refrigerated brinecontaining dissolved CO2 ,

REFRIGERATEDBRINE EQUIPMENT

Although the use of CO2 in brine hasfavorable results with respect to in­creased storage life of both fish and thebrine, the addition of CO2 has undesir-

able sidc effects such as the accelera­tion of con'osion rates of metals cominginto contact with the acidified brine.For example. NaCl brine saturated withCO 2 is moderately acid and highl y cor­rosive (Barnell et al .. 1971). To lessenthe occurrence of corrosion in ourshrimp experiments in the laboratory,we used the equipment described in theinitial publication. This consisted oftwo fiberglass, insulated, 55-gallon.epoxy-coated drums and a brine chiller(Fig. 2). Polyethylene liners were sus­pended in the drums to prevent theshrimp from freezing to the sides of thedrums. Rotary-type circulating pumpswere used for recirculating chilled brine(a solution containing 3.0 percent NaCIand comparable to RSW)2. Carbondioxide gas was fed through a J~-inch

"Sudium chluritJe brine was used in lieu uf naturalseawater because clean seawater was not conve­nienlly available 10 the laboratory. This tcchniquehad been uscd by othcrs (Cullins. I960b: Seagranet al .. 1960: Davis and Clark. 1944) and found togivc goutJ rcsults. tn comparativc experimcnts.Roach and Harrison ( 1954) dcmonstrated that fishheld in refrigerated brine werc uf equal yuality 10

fish hdcl in RSW. The tcrm RSW is II'erel"orcfrequenlly used to refer to either th" ,ea"ater Of

:1.0 percent "lit brine media.

Tygon:l hose into the suction side of oneof the pumps for maximum diffusion.

EXPERIMENTS ANDOBSERVATIONS ON STORAGE

LIFE AND Ql'ALITY

The shrimp (Panda/us jordani) usedfor the experiment were caught in atrawl off the coast of Oregon. In prepar­ing the samples, 375 pounds of shrimpcaught about 24 hours before were di­vided into three equal lots. One lot wasiced in a plastic bin and held in a refrig­erated room at 34 oF. The other two lotswere placed in the polyethylene-lineddrums at a shrimp-to-brine ratio asclose to I: I (weight/ weight) as possi­ble.

One tank of brine had been treatedwith CO2 gas before the shrimp wereloaded into it. The gas was fed into thebrine continuously throughout the ex­periment at a rate 01'0.2 foot:l/hour. Thesecond tank of brine was not treatedwith CO 2 , The temperature of the brinein both tanks was maintained at30 ±0.5°F.

Periodically. shrimp from threestored lots and a sample of brine fromeach of the brine storage experimentswere removed for examination.

Criteria used for evaluation includedsensory attributes. chemical and physi­cal changes. and bacteria counts ofshrimp held in RSW modified withCO2, RSW, and in ice.

Bacteriological MeasurementsTotal bacterial plate counts were

made on the shrimp by the methodsdescribed by Pelroy and Eklund (1966).Briefly, the method is as follows: 45g of headed shrimp (shells on) werehomogenized aseptically with 180 mlof sterile O. I percent peptone solutionat 3.8°F. Serial dilutions in 0.1 percentpeptone-water were prepared for pourplates from the homogenate.

Total plate counts were made by useofTPY solution (1.5 percent trypticase,0.5 percent peptone , 0.5 percent yeastextract, 0.2 percent glucose, 0.5 percent

"Rcference 10 tralk names docs not imply en­dorsement hy the National Marinc Fishcres Ser­vice. NOAA.

Sepremba /978 25

2.4

2.2

2.0

0.5

Saltconc.flesh(%)

2.0 x 10'

1.1 xl0'1.1 x105

2. L< 10'1.2xl0'

2.8xl0'657.1

5.6504.6002.11.8x 10'4.0xl0'

2.3x 10'3.8xl0'7.8

83

8.21.190790

482

o

0.41.6x 10'

1.6x f(J6

8.0

821.012

1.364

co,conc.flesh

(ppm)

Table 1.-Microblologlcal and chemical changes occurring in ice, untreated refrigerated brine, CO 2-treated refrigerated brine, and in the flesh of shrimp held In these brines.

Data on icing Data on refrigerated brine without CO2 Data on refrigerated brine with CO2

Total Talai Totalbacterial Salt bacterial Salt bacterialcounts conc. C02 conc. counts cone. CO? conc. counts

pH flesh Ilesh flesh brine pH flesh brine flesh flesh brine pH flesh brineflesh (No./g) (%) (ppm) (ppm) flesh brine (No.lg) (No./ml) (%) (ppm) (ppm) flesh brine (No./g) (brine)

7.4 3.4xlO' 0.5 1.364 462 7.4 7.0 3.4xl0' 0.5 1.364 2.552 7.4 4.3 3.4xl()57.5 1.9xtO' 1.3xlO' 6.3 9.6xlO' 6.5xlO'7.7 5.5xlO' 2.1 2.900 5.300 7.2 6.4 8.0xl0'

Sioragetime

(Days)

o1234567

Table 2.-Sensoryevafuatlons of shrimp held In Ice, untreated refrigerated brine, and CO,'treated refrigerated brine.

General comments on raw and cooked shrimp samples

I Siorage lime given IS the number of days held allhe laboralory. The shrimp was held iced approximalely 24 hours aboard lhefishing vessel before delivery.'A score of 10 denotes a product of highest quality: one 01 5 denotes a product of borderline quality.3Too spOIled to taste.

Good color and odor

Good color and odor

Good color, odor. andlIavor. slightly

sally. firm lexlure

water and raw shrimp flesh. The pHvalues of the brines are given in TableI. Almost without exception, the pH ofthe flesh of the shrimp held in ice and inuntreated brine increased during stor­age. These changes occurred simul­taneously with increases in microbialpopulations in both flesh and brinesamples. The pH increase in both theshrimp and the brine was probably dueto ammonia from the growth of bac­teria.

In the case of CO2-treated brine,there was an initial and rapid increase inpH from 4.3 to 6.3, This is attributed tobuffering by proteins and other solublecomponents from the shrimp. The ini­tial pH measurement was made beforethe shrimp came into contact with thebrine. The pH of the brine was reason­ably constant at about 6.4 after that time.The pH of the flesh of the shrimp held in

Excellent quality Excellent quality Excellent qualityGood color. odor buf Good color. odor bUf Good color. odor. andsome loss 01 lIavor some loss 01 flavor: flavor: slightly salty

slightly saltySlight loss of color,

bland lIavor, softtexture, slightly

saltyPale color, slight

spoilage odor

Slight-moderate. lossof color. moderate off­

odor. bland flavorsoN texture

Unacceptable, moderateloss of color, strongspoilage odor. poorflavor, soft texture

Unacceptable. Strongspoilage odor, poorflavor. soft texture

6.7 Good color. odor. andflavor. Slightlytough, salty.

Chemical MeasurementspH

A Beckman combination electrodewas used to measure the pH of theshrimp flesh and brines. The shrimp wasprepared for analysis by homogenizinga 2: I mixture by weight of distilled

count was observed on the fifth day ofthe test corroborating the organolepticfindings that the shrimp were spoiled(Table 2).

Bacterial counts of the shrimp held inthe modified brine (Table I) were alsoreduced initially by the dilution effectof the brine. There was an increase inbacteria in the shrimp after 2 days ofstorage but counts in both the shrimpand brine remained below the levelconsidered to be indicative of spoilagefor the remainder of the experiment.

NaCI, and 1.5 percent agar). Countswere made on the brines by taking J-mlsamples, making appropriate serial di­lutions in 0.1 percent peptone-watermixture, and plating out into the TPYmedium. The plates were incubated at22°C for 5 days. Table I shows theresults for total bacterial plate countanalysis on the shrimp and brine sam­ples.

Bacterial counts of the shrimp held inice increased from 10 5 to 10 6

organisms/gram during the first 2 daysof the experiment. A count of 106

organisms/gram usually indicatesspoilage. At this time, the shrimp hadbeen out of the water about 3 days andshowed some loss of color and a slightoff-odor. Although no bacterial countswere made between the second and fifthdays of the test, the iced shrimp werejudged subjectively to be spoiled on thefourth day of the experiment (Table 2).By the fifth day of storage, the iced'shrimp were putrid. Total plate countshad risen to 1.6 x 108 organisms/gram.

Bacterial counts decreased in theshrimp held in the untreated brine (Ta­ble I) during the initial stages of stor­age, probably due to a washing anddiluting effect of the brine. The shrimphad an off-odor suggestive of incipientspoilage by the fourth day, althoughplate counts were below 106 organ­isms/gram at the time. The fewer num­bers of bacteria found in both thesl1rimp and the brine compared withshrimp in ice was due in part to thelower storage temperature and probablyalso selective bacterial growth patternsthat may occur in the nearly anaerobicenvironment of the brine (Shewan,1964). A sharp increase in bacteria

26 Marine Fisheries Review

the modified brine dropped slightly dur­ing the experiment but remained withinthe normal pH range of good qualityshrimp. Although tests for ammoniawere not made, the good quality and thelower pH of the shrimp throughout the 7days of storage indicated that little or noammonia was formed.

CO 2 Concentration

Analyses for CO 2 content in the fleshand brines were carried out as previ­ously described by Barnett et al.(1971). Test results showed (Table I)that relatively high levels of CO2 asbicarbonate existed in the meat of thefresh raw shrimp, The concentration ofCO2 in the flesh appeared to remain rela­tively constanl in the flesh during icedstorage. The shrimp held in the un­treated brine showed a reduction in theconcentration of CO2 in the flesh duringstorage. A significant increase in CO2

content of the brine accompanied thegeneral decrease of CO2 in the flesh.The change suggests that the increase inCO2 was contributed by protein andmetabolic products dissolved from theshrimp,

The flesh of the shrimp held in mod­ified brine contained considerably moreCO2 than did the flesh of the iced andbrine-held shrimp, The modified brine,of course, contained a high concentra­tion of CO 2 throughout the holdingperiod.

It is apparent that the high concentra­tions of CO2 in the flesh and brine inhib­ited microbial growth sufficiently to ex­tend the storage Iife of the shrimp.Similar observations were made byMakashev (1954) and King and Nagel(1967).

Salt Concentration

The concentration of sodiumchloride was measured by the methodsdescribed in Horwitz (1960). Resultsare shown in Table I. The salt contentof the iced shrimp was 0.5 percent ini­tially and decreased to zero during 5days of storage. The maximum con­centration of salt in the flesh of theshrimp held in untreated brine was 2. Ipercent. This concentration wasreached by the second day of storage,after which there was no change. The

September 1978

absorption of salt in the flesh of theshrimp held in the modified brine wasclosely comparable. The ultimate con­centration of salt in the flesh of theCO2 -brine-held shrimp was 2.4 per­cenl. This was reached after 7 days ofstorage. Similar findings were made byCollins (l960a, 1961) in detailedstudies to determine the changes thatoccur in pink shrimp held in ice and inrefrigerated brine storage. He also ob­served in the study that water, ash, andsolids contents in the system changed asa function of time causing both the rawand cooked meats to lose considerablesolids.

Sensory Evaluation

Samples of shrimp from each vari­able in the experiment were examinedat intervals to evaluate sensorychanges. Samples of each wereevaluated both raw and cooked.

Raw Shrimp

During the first 3 days of storage, theraw shrimp from each of the storageexperiments were considered to be ofacceptable quality. During this time,however, signi ficant changes were ob­served in the quality of both iced- anduntreated-brine-held shrimp. Thesewere in the form of loss of natural odorsand pink color. No significant loss ofcolor or development of off-odors wasdetected in the shrimp held in the CO2 ­

treated brine. By the fourth day of theexperiment, iced shrimp displayedstrong ammoniacal odors indicative ofmicrobial spoilage, They were judgedto be spoiled at this time. After 5 daysof storage, a pronounced sour odorexisted in the untreated brine andshrimp. By this time, the shrimp ,hadlost all their natural color and were to­tally unacceptable. The brine wasbrown-black in color, the result of whatappeared to be an enzymatic reaction.

After 6 days, the shrimp held in theCO2-modified brine retained much oftheir natural pink color and were essen­tially odorless. There were no off-odorsin the brine which was light pink incolor. The high concentration of CO2

clearly inhibited the enzymatic changescausing the discoloration of the shrimpand brine when no CO2 was added,

Cooked Shrimp

The shrimp from each experimentalstorage condition were prepared fortaste panel evaluation by cooking inboiling brine containing 3.0 percentNaCI by weight for 3 minutes. Theywere then cooled in running tap water.For the purpose of tasting, the brine­held shrimp were cooled slightly longerthan the iced shrimp to remove excesssalt. The cooked samples wereevaluated for appearance, odor, flavor,texture, and overall quality using a 10­point numerical scale. Results are givenin Table 2,

The data show that the iced shrimpdeclined quite rapidly in quality andwere unacceptable on the fourth day ofstorage. Similarly, the shrimp held inthe untreated brine declined in qualityand were judged by the taste panel to beunacceptable by the fifth day. Althoughthe overall quality of the shrimp held inthe modified brine decreased during the~xperiment, the product was con­sidered to be organoleptically accept­able after 6 days of storage. Except for aslightly tougher texture and somewhatsalty flavor, the product was compar­able to the quality of shrimp held in icefor 2 or 3 days.

SUMMARY ANDRECOMMENDAnONS

Storing north Pacific pink shrimp at30 OF in refrigerated brine treated withCO2 doubled the storage life of theshrimp to 6 days or more comparedwith 3-4 days for the shrimp held in ice,The effect of the dissolved CO2 was toslow the rate of growth of spoilage bac­teria and was caused apparently both bythe lower pH of the brine and a specificinhibition by the CO2 . A black discol­oration was evident in the head and gutof shrimp after 2 or 3 days of iced stor­age and in both the brine and shrimpafter 5 days when no CO2 was added.This discoloration is allributed to anenzymatic reaction. The shrimp andCO2-treated brine showed no discolora­tion after 6 days indicating effectiveinhibition of the enzymatic reaction bydissolved CO2 .

The modified seawater techniqueshould be considered for commercial

27

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use; however, it is recommended thatadditional experimental investigationsbe conducted to determine what effectholding pink shrimp in modified brinehas on machine peeling characteristics,yield, and the acceptahiJity and qualityof both the frozen and canned products.

LITERATURE CITED

Anonymous. 1968. Main experimental results:fresh fish. In Fiskerministeriets f'or­s0gslaboratoriu m. Copenhagen, Denmark.Arsberetning fro Fors0gsiaboralOrium for'1967. p. 44-45.

Barnell. H. J .. R. W. Nelson. P. J. Hunter. S.Bauer. and H. Groninger. 1971. Studies on theuse of carbon dioxide dissolved in refrigeratedbrine for the preservation of whole fish. Fish.Bull .. U.S. 69:4~~-442.

Collins. J. I960a. Processing and quality studiesof shrimp held in refrigeratcd sea water and ice.Pari I - Preliminary obsen'ations on machin,,­peeling charaeterislics and product quality.Commer. Fish. Rev. 22(~): 1-5.

1960b. Processing and qual it)'studies of shrimp held in refrigerated sea water

and ice. Part 4 - Interchange of the componcntsin the shrimp-refrigerated-sea water system.Commer. Fish. Rev. 22(7):9-14.

19111. Processing and qualilystudies of shrimp held in refrigerated sea waterand Ice. Part 5 -Interchange of components in ashrimp-ice system. Com mer. Fish. Rev.23(7): I-~.

Coyne. F. P. 19~2. The effect of carbon dioxideon bacterial growth with special reference 10

the preservation of fish. Pari I. Chem. Ind.(Land.) 51: 119-121

19~~. The eI'fecl of carbon dioxideon bacterial growth with special reference tothe preservati"n of fish. Part II Gas storage offresh fish J. Soc. Chem. Ind Lond. 52: 19-24

Davis. H. c.. and G. H. Clark. 1944. Holdingsardines in chilled brine. Pac. Fisherman42(9):4~.

Hjorlh-Hansen, S. 1933. Investigations rdatingto the cooking and handling of fresh shrimp.Annu. Rep. Norw. Fish. 3: 1-21.

Horwitz. W. (editor). 1960. Official methods ofanalysis. 9th ed. Assoc. Ofr Agric. Chern ..Wash .. D.C., 832 p.

King. A. D .. Jr .. and C. W. Nagel. 1967. Growthand inhibition of a Pseudomonas by carbondioxide. J. Food Sci. ~2:575-579.

Makashev, A. P. 1954. The use of carbon dioxide

in the storage of slightly salted fish. RybnoeRhozyaistra 12:4'l-5~.

Pacific Packers Report. 1977. Supplement to Na­tional Fisherman 57( 12): 1-88.

Pelroy, G. A .. and \iI. W. Eklund. 1966.Chanl'.es in the microftora of vacuum­packaged. irradiated petrale sole (Eopselfajordani) fillets stored at 0.5 0c. Appl. Micro­bioI. 14:921-927.

Roach. S. W .. J. S. \iI. Harrison. 1954. Cse ofchilled seawater and dilute brines in place ofice for holding shrimp aboard a fishing vessel.Fish. Res. Board Can .. Prog. Rep. Pac. CoastStn.98:23-24.

Seagran. H., J Collins, and J. Iversnn. 1960.Processing and quality studies of shrimp heldin refrigerated sea water and ice. Part 3 - Hold­ing variables and keeping quality of the rawwhole shrimp. Commer. Fish. Rev. 22(5): 1-5.

Shewan, J. \iI. 1964 Bacteriology of fish storedin chilled seawater. In Fish handling and pres­ervation, p. 95-109. Proc. Meet. Fish.Technol., Scheveningen, Netherlands.

Stansby, M. E .. and F. P. Griffiths. 19~5. Carbondioxide in handling fresh fish - haddock. Ind.Eng. Chern. 27: 1452-1458.

Stern, J A. 1958. The new shrimp industry ofWashington. Proe. Gulf Caribb. Fish. Insl ..10th Annu. Sess., p. 37-42.

28

MFR Paper 1326. From Marine Fisheries Review, Vol. 40, No.9, September1978. Copies of this paper, in limited numbers, are available from 0822, UserServices Branch, Environmental Science Information Center, NOAA, Rockville,MO 20852. Copies of Marine Fisheries Review are available from the Superin­tendent 01 Documents, U.S. Government Printing Office, Washington, DC20402 for $1.10 each.

Marine Fisheries Review