AN EXPERIMENTAL INVESTIGATION OF DRY FISH MANUFACTURE b C. E. ST. C. Gunasekera and Nihd IN. Silvea Department of Fisheries.. Colombo. Ceylon.

The importance of the dried fish indastr+ in Ceyfon and the disadvantages in the local methods of fish curing are discussed. Results of some chemical and bacteriological studies into the preservation of fwh by salt are described. After investigating several methods of curing, the most satisfactory results were obtained by a process involving the removal of gats and gills and the extraction of surface blood by a dip in 10% brine prior to salting in brine maintained at saturation. But salt alone was found to be insuficient to prevent bacterial decomposition especially due to strains of red halophiles, to which however a 0.5% aaueons solution of citric atid proved inhibitory and a 2% dution bactericidal. The viability of common fod poiswing pathogens in saturated salt was also decreased and the growth of fungi prevented by this concentration of citric acid. Citric acid besides its bacteridical and fungistatic properties, increased the initial rate of salt penehation, thus shortening the period of time during which the fish is most liable to decompose. The salt-citric acid protection permits slow air drying without deterioration; apart from its superiority to direct szm&yhg, the process is thus made independent of adverse weather conditions.

The manufacture of dried fish in Ceylon the wed product the only form of fish available was at one time one of the major industries of in many meas. Curing fish is also a useful the Island. Deraniyagala ( 1953) bas mced the cottage industry as it often supplements the main causes that led to its decline, which were meagre income of fishermen enabling them to the imposition of meson tbe product as well as make the best use of occasional surpluses and of repressive levies on the salt upon which the less popular varieties. Further, severd fishing industry mainiy depended. areas such as the islands off the northern coast are out of contact with the fresh fish markets increase Furthermore, the in facilities for and curing is the only way of utilizing the catch. the storage, transport and distribution of fish favoured the use in its fresh form of a greater In recent yeaxs the quantitative increase propmtion of the raw material formerly available in the catch of rough (anpopular 1 fish in the for curing. Various artempts to revive the trawler landings ( SivaIingam, 1954) also makes industry such as the abolition of the fish tax, an the economic utilization of these varieties one import duty on dried fish and a scheme fur of the important problems of local commercial subsidised salt production had limited success. trawling. Curing will partly solve this problem ' by the conversion of this unmarketabk fish into Nevertheless, even today the dried bh marketable cured fish. industry is of considerable local importance. Fish, fresh or cured, is a rich source of protein In Ceylon, fish are cured commercially by the lack of which has been reported as one of the three main methods. On the hot sands on the major nutritional deficiencies in the local diet, beaches of the dry zone, small species are dried especially among the poorer classes ( Nicholls whole witbout any treatment or addition of salt. and de Silva, 1954 ). Fresh fish requires special By its nature this method has a very limitc: facilities, such as refrigeration, forits transport application. The second method uses salt only and storage, which limit its distribution making in a dry cure but relies on a hot sun for drying Proc. Indo-Pacijc Fish. Coun., 7 ( 11-111): 101-106, 1957. and is thus altogether dependent on the weather. done on cleaned cubes of flesh of catfish Tachy- The third method uses " Coraka" ( the dried sums INe.tumal thaassinrrs (RuppeI1) one of the carpels of the fruit of GarciniQ canzbogb, whose varieties commody chosen for curing. active preseming agent seems to be an acid 1, in a wet cure which gives a type of pickled hh. Rubbing dry saIt into incised flesh followed Methods of preparation and variations in flavour by sundrying proved unsatisfactory as the from district to district suggest that this last . salting appeared umven md the exposed 0esh method is a complicated cure involving ferment- attract@ flies during the early stage8 of the cure. ation. Other types of cure, such aa smoking are Rubbing with dry salt allowing a brine to form done on so smd1 a scale that their output is with the addition of saturated salt solution to negIigible. cover the flesh, proved more satisfa~foryas the brine protected the flmh and ensured even A1 these methods have remained anti- contact with the sdt. Peterson and Weerakoon quated and unhygienic, and they result in a ( 1951.) reported similar obsemations. Tb'e exact product of poor quality, the expsure for sale of strength of the salt solution required was which has often acted to the detriment of the investigated by the immersion of pieces of flesh entire cured fish industry. Rehabilitation of the in brines of varying salinity. The stable solution industry therefore necessitates not only an was found to be a saturated solution containing improvement in methods of manufacturebut also solid salt. Flesh in 10 % and 15 % brine decom- the education of tbe producer to the recognition posed in two days, in 70% brine in 13 days, in of the need for sanitary curing yds, clean 100% brine in 20 days while flesb in saturated utensib and the use of dean salt and undecum- brine with solid salt remained stable for over two raw present work was posed materid. The months. In all solutions fat separated out slowly directed towards the solution of one aspect of on the surface and after a few da~supported a this problem to the development of a satisfactory fungal growth which was skimmed off. The commercial curing process for dry-salted fish. entire solution was changed occasiomlly when the fungus could not be removed oornpleteb fmm solution. The preparation of dry fish may be divided into three stages: preliminary treatment of raw When flesh is immersed in brine, the material, salting and drying: moisture in the flesh diffuses into the brine and salt from the brine penetrates into the flesh. To of Rehharp treaimmt raw moteriak follow this process, analyses of moisture and not Fish are bled at sea and it seems impractical salt were done on flesh immersed in saturated to do so on board local craft. Large size bh are brine containing solid salt. Before immersion, gutted on board trawlers but even this practice moisture was 77% and salt negligible. After two is unfamiliar to most of our fishermen. After the days the moisture content fell to 55% and salt catch is landed, the &st operation found neces- increased to 21% After a week the moisture sary of . is the removal gut and gills as retention of was still 55%and salt 21%. This ratio represents these organs soon leads to serious decomposition. a 27% wlw salt solution in the flesh, a solution The head and backhesections tend to discolour which is saturated. fa other experiments the due to exudation of oil which is also liable to salt content meabove 27% probably due to tbe turn rancid. It is tberefore suggested for good absorption efFects of the material, Hence within quality fdlets that these bony portions be pro- two days salt penetration is complete and the cessed separately from the flesh. Our experi- salt is in equilibrium as a saturated solution in ments have shown that the presence of scales does the flesh and in the outside Iiquor. A saturated not interfere with ming if the fish are 6lleted solution in the %eshis possible only with a brine nor incisions necessary are for a successful cure. containing solid sdt. As the flesb was not bled, surface and diffused blood was effectively removed as suggested by The oil content of tb flesh showed a 3atvis I 1950) by brining for about half an hour demeaae during processing. Raw flesh contained in approximately 10% solution of salt. 22%oilcalculated on dry weight, which decreased S~~IKKIn order to simplify the investiga- to 11% after salt saturation md to 4% after pro- tion of the salting process, preliminary work was longed air drying. Ibinq : Several workers have urged the The general bacterial flora of fresh fish adoption of air-drying in preference to sun- caught in om waters indude Micrococcrar, Achro- drping in the manufacture of dried fish. Jarvis mobmter, Flavobacterium, Pseudomonas and vari- forms. (19501 points out that oxidation, rusting and ous bacillary Most of these are proteolytic and able to cause rapid spoilage changes in the . sun-burn set in warm climates if sun-drying muscle, is (1951 fish but are generally inhibited by a practised. Linton and Wood 1 have concentration of approximately l5% salt. How- an shown that under conditions of rapid dry& mer, certain strains of marine bacteria are able impervious sdt-protein crust is formed which to tolerate high concentrations of salt while a inhibits further drying. This crust is more likely few find salt essential for their growth. These to form under local conditions of sun-drying. A Iatter are died 'Halopbiles' and certain pigment further disadvantage of sun-dqing is its depen- producing groups, the 'Red HaIopbiles', togethex dence on the weather. with certain fungal molds, are the chief agents responsible for deterioration in salted fish. The rate of air-drying is ewtrolIed by a number of factors, chiefly humidity, air velocity The control of bacterial reddening and and temperature. Air-drying under cover is fungal molds has been recognised as one of the dower than sundrying and consequently twds major problems of the salt fish industry. (Lobe11 to form an encrustation of salt crystals which and Puncochar,1947 1. Improvements in proces- considerably detracts from the the appearance of sing methods, use of pure steifised salt and the ha1product. Similar surface deposits have chemical additives to tbe final product have been been observed by Cooper and Wood ( quoted by suggested as a means of control in this connec- Linton and Wood, 1945) during slow &-drying. tion. Sterile methods of operation are impxac- The formation of these deposits was reduced by tical under Iocal conditions of manufacture and an increase in air velocity. The wind velocities even if it were possible to obtain a sterile final at the main curing stations ate well within the prodnct, exposure during storage and transport optimum range recommended by the Tomy will make it liable to snbsequent contamination Research Station (Katugampola, 1950 unpublis- leading to spoilage. Chemical methds of oontml hed 1. But the figures for humidity I Observatory therefore seem to as the only alternative. Annual Reports) are outside the range of 40-50 suggested as optimum by Linton and Wood Various chemical additives are in com- ( 1945 1. Fortunately, the high air velocities and mercial use in different countries. These include high temperatnres at our curing stations com- boric acid, benzoic acid, sodium or magnesium pensate for the higb local humidity. benzoate and sodium propionate. Their use in the industry is restricted either by their cost or Drying on the beaches in covered sheds the terms of Fd& Drags Acts. Recently, the which permit free drtlation of air thus provides use of sorbic acid has been recommended for dry su6cientIy favourable conditions for a satisfac- salted fish but it has proved inefiective against tory cure if the tendency of the fie& to red halophiles. ( Boyd and Tam, 1955 1. In local decompose can be controlled during this compa- commercial practice lime juice (citric acid 1 ratively slow process. . vinegar ( acetic acid ) and ' GoraEca ' (tartaric acid) are used as presematives. Goraka and Conl~olof Batwid Decomposition: Prese- vinegar are used to obtain a distinctly &vowed' rvation is basically an interruption of the natural specialty product while citric acid is used mainly action. the changes which occur in dead tissue. These for its preservative Therefore use preservative changes are oxidative, autolytic and bacterial in of citric acid as a chemical for dw fish was investigated. nature. The preservative action of salt is chiefly due to the withhwal of moisture from the Mixed strains of red halopbiles were tissues thus inhibiting the growth and activity isolated from salt fish and cultured using the of spoilage bacteria. Among other factors improved Lockhead's Medium I Dussault and involved are the direct action of the sdt itself La Chanee, 1952 ). A concentration of 0.5% on the tissues, the enzyrqes and the -bacteria citric acid incorporatd into the medium was ( Shewan, 1949; TressIer and Lemon, 1451 1. suEcient to inhibit the growth of these bacteria Concentrations beyond 2% killed them and yielded 45 1b. of cured product. In commercial inhibited almost all types of contaminating practice it should prove possible to re-use the fungi. salt - citric acid solution thus making the process Survival of bacteria of epidemiological more economical. The quantities of salt and importance was also studied from inoculations citric acid can be reduced if the product requires made into sterile juice from fish muscle, equal no protection during the curing process, as may volumes of sterile juice and saturated 'salt, and happen under conditions giving a rapid hygienic cure. The minimum amounts would be, salt similar juice and saturated salt to which had been added 2% citric acid. Within the first two hours sufficient to saturate and citric acid equivalent all the bacteria were killed by a saturated salt to 2% of the final moisture content in the cured solution containing 2% citric .acid, while B. coli, fish. Staph. aureus, Strep. faecalis, Shigella and A rough marketing test on this product Salmonella survived this period of time in fish in a polythene wrap showed that it appealed juice with or without an equal volume of more to the educated group ( clerks etc. 1 than to saturated salt. Experiments on the survival of the working class group. The appeal lay prim- these organisms in salted fish cured in brine arily in the hygienic appearance of the product containing 2% citric acid gave closely similar while the complaint against it was that it lacked results. the flavour of dried fish sold in the market. The flavour of market dried fish is largely due to Besides its bactericidal and fungistatic decomposition during curing. As far as the properties, citric acid increased the initial rate of salt penetration thus shortening the period of local consumer was concerned, our dried fish was time during which fish is most liable to different from the market varieties with which decompose. In experiments using 5 - gram he is familiar and therefore had to be accepted samples, a time lag of 10 minutes was observed on its own merit as a new product. between the time taken for the salt concentration to reach the same value (in the 5-15 Zrange in DISCUSSION two pieces of flesh, one in salt and the other in Based on the experiments described, an salt - citric acid. This time lag increased to one ~mprovedmethod for the manufacture of dried hour when samples weighing 50 g. were used. fish may be suggested. This method involves Such an increase becomes significant under brining, air - drying and the use of citric acid as conditions conducive to rapid spoilage such as a preservative. The main advantage of the the high temperature prevailing in the tropics. process is the stability of the product during The application of these results in a commercial manufacture and storage. , Further, as was process was achieved by using as brining earlier noted, slow air~dryingcan be practised solution, a 2% citric acid to which excess salt only if the product can be protected from was added. Although the water from the flesh spoilage during this period. The incorpora- diffusing into the solution diluted it (by about tion of citric acid provides a process which is 50%). sufficient citric acid ~enetratedinto the independent of weather conditions. This sta- flesh to attain the inhibitive range of over 2% in bility and protection are achieved by the the final product. When maximum protection increased rate of salt penetration, the bactericidal was required, a 2% solution was made available action of the citric acid in the presence of salt from the start of the cure by adding citric acid and the preservative action of the salt itself. equal to 2% of the total water (free and in fish) present in the curing vat. For salting 100 lb. The entry of the salt into the flesh is of catfish fillets (obtained from 200 lb. of gutted essentially osmotic in nature. When salt raw material) it was found necessary to use 4 penetrates, it causes the precipitation of the gallons of water to which were added 35 lb. of proteins and the saturation of the residual water salt and 2 Ib. ( 2% of total water) of citric acid. in the cell. Penetration of the salt ceases when After three days brining (to ensure complete a saturation value of 27 % wlw is reached inside salting) the loss in weight of the fillets was10 lb. the cell. Values observed above this ratio in our After complete air drying the fillets weighed 55 experiments suggest that salt is also absorbed lb. ( 35%moisture). Heads and bones ( approx. by various cell constituents, probably the protein 50% of raw material ) ~rocessed separately reticulum. Citric acid in common with other organic acids influences the entry of salts by increasing the permeabilitp of ihe dI membrane. BOYD,J.W. and H.L.A. TARE( 1%). Inhibition The to time taken for the salt inside the cell of mold and yeast devefopments in fish reach a sufficient concentration is thus lessened. Products. Food Td.,9 18). The antibacterial effect of the salt-citric DESKVA, C.C. ( 1955 1. Protein maI-nutrition. acid is thought to be due to the enhancd activity Presidentid Address, Sehn A, Proc. 10th of the salt in the presence of acids. It has been Annual Sess. CeyhAss. Adv. Sc. by Nunheimer aad Fabian ( 1940) that iin shown DERANNAGALA,P.E.P. ( 1933 ). Cured marine Smphylocci, the the case of food poisoning prducts of Ceylon. Ceyhn J. Sc., 5 (c). addition of acid reduces by 50% the amount of sodium chloride necessary for germicidal action. DUSSAULT,H.P. and RA. LA CHANCEI 1952 ). An It has also been reported that certain groups of improved medium for red halophilie bacteria bacteria including aerobic and anaerobic from salt fish. J. Fish. Res. Bd Canada. 9 (3). spore- bearers are inhibited by concentrations ERICSON,F.J. and F.W. Fabian ( 1942 ). Preser- of salt that permit the growth of lactic acid ving and germicidal action of various sugars bacteria which produce snfficient lactic acid to and organic acids on yeast and bacteria. supplement the inbibitmy action of salt (Jacobs, Food Res., 1: 68. 19-44 1. The susceptibility to salt in acid is even greater in the case of proteolytic and peptolytic HESS. E. and N.E. GIBBONSI 1942 ) . Studies on bacteria ( Ericson and Fabian, 1942 ). salt fish-X, Effects of disinfectants and presematives on red hdophilic bacteria. J. In addition to the effect of the hydrogen Fish Res. Bd. Canada, 6 (1). ion, Nun beimer and Fabian (1940)have reported that the germicidal and antiseptic groperties of JACOBS. M.B. ( 1944 ). The Chemistry and Techno- acids are also due to the un-ionised molecule logy of Food Procducss. VoC. II, Inter-Science itself or the anion or both, Hess and Gibbons Publishers Inc., New York, U.S.A. { f 942 ) in similar observations have noted that JARWS. N.D. (1933). Curing of Fishery Products. citric acid and lactic acid were more effective ,Re$. Rep. 18, Fish and Wildlife. Service, US. than acetic acid, although this is a skonger acid. Department of Interior. Our experiments also suggest that while acids affect the activi* of salt as a preservative, the KATUGA~OLA.D. C. ( 195 0 ) . ( Unpublished 1 citrate radicle is also of significance in this Bacterial standards for Ceylon dry fish. Rep. connection. lkpt, Health, Ceylon. LINTON.C.P. and A.N. WOOD(1947). Drying of heavily salted fish. 1. Fish. Res. Bd. Canada, We wish to thdthe. Medical Research 6 (5). lnstit ute for the facilities granted to conduct oux LOBELL.M. J. and J.F. ~COCHAR( 1947 ) . The brlcteriologica3 experiments and especially to Mr. Venezuelan salt fish industry. U.S. Fish rand D.C. Katugampola of the Food Research Section Wildlife Service, Fishery Leaflet 240. for Ms interest and valuable suggestions. NICHOLM.L. ( 1947). Eat and be healthy. We also acknowledge with thanks the Associated Newspapers of Ceyh, Ltd., (Lake work done by our laboratory assistants, Messrs. House, Colombo, and Landham House, A.H.W. Mendis and K.J.M.S. Gfero, in these Regent St London, W. 1). investigations. N~HEWEI.T.D. and F. W. FAFUN ( 1940 1. This paper records a part of the Technct h0uence oi organic acids, sugars md sodium logical Research work in the Department of &hide upon strains of fd poisoning Fisheries sponsored by the Canadian Fisheries staphylococci. American I. Pub. Hdth, 30 : Project in Ceylon. 1ON. P-m. E. and AH. W-OOM (1951). Expeti- tion of bh. J, Rqy. Sun. Ins., 69 (4) ments on salting and drying of Ceylon fwh: Recommendations of aperts on 6sf;wies SIVMGU. S. ( 1954 1. (In print ) Wadge Bank development research, 40- econmnnics and fisheries. (Paper read at 10th Annd industrial problem. Appdiz 7, Sesswnal Seasion of Cq.lon Ass. Ado. Sc. ) Paper PI, Govt. of Ceylon. Tm.D.K. and J. M. Lmo~( 1951 ). Marint SEEWAN.J. M. ( 1949 ). Some bacterioIogieal prod& of Commerce I2nd edition ). Reinbold aspects of handing, messing and distribu- PubIishing Corporation, New York, US.&