Development and shelf life evaluation of Tilapia ( Oreochro1nis spp.) marinades

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1 Development nd shelf life evlution of Tilpi ( Oreochro1nis spp.) mrindes M.M. Rthnyke, V.P.N. Prsdi* nd C.V.L. Jysinghe Deprtment of Food Science nd Technology, Fculty of Livestock Fisheries nd Nutrition, Wymb University of Sri Lnk, Mkndur, Gonwil, Sri Lnk. Abstrct Tilpi (Oreochromis spp.) consumption is limited due to its strong muddy odour nd the difficulty of processing. In ddition, consumption of tilpi is miniml in urbn res bect1se of the low vilbility. There re no processed mrket products of tilpi vilble in Sri Lnk. Therefore, this study ws designed to develop new mrinde for tilpi nd to evlute the shelf life of the product. Twelve different tretments of vrying mounts of vinegr, slt, chili powder, white pepper nd grlic powder were pplied to filleted tilpi, nd three best tretment combintions were selected using sensory evlution test. Processed tilpi ws stored in the freezer t -4 C. Treted smples were subjected to evlution of sensory profile: tste, odour, colour, texture nd overll cceptbility. Anlysis of the shelf life ws crried out by using the totl plte count, fecl coliform test, cidity nd ph t weekly intervls. Results reveled tht the third tretment (vinegr 75 ml, slt 5 g, chili powder 5 g, white pepper 5 g nd grlic powder 5 g) ws best in terms of colour, texture, odour, tste nd the overll cceptbility ccording to the estimted medins (6, 6, 6 nd 6.33 respectively). There ws no significnt difference between the first nd the third tretment in terms of odour nd overll cceptbility. There ws no significnt difference between the three vcuum pcked tretments for cidity nd ph. Acidity nd ph of the three tretments were t n cceptble level, which ws below ph 5.3 nd bove 1.95% cidity. Averge bcteril count ws 10 colonies nd 1.33xl0 6 colonies respectively in vcuum pcked tretments nd bottled smples fter one week. The cecptblc level of bcteril colonies is l.00xl0 5 Vcuum pcked tretments showed one month shelf life. In conclusion, mrindes cn be developed from tilpi with plesnt tste nd cceptble textur~. Keywords: Tilpi mrinde, vcuum pckging, sensory evlution, shelf life *Corresponding uthor- Emil: nirmlprsdi@yhoo.com, nirmlvp@gmil.com 11

2 Journl of the Ntionl Aqutic Resources Reserch nd Development Agency Introduction Tilpi is member of the lrge fmily known s Cichlids. Of the mny vrieties oftilpi, the commonly cultivted species re Oreochromis niloticus nd Oreochromis mossmbicus (Pilly, 1990). Tilpi is freshwter fish species, but cn lso live in brckish.wter nd is found in tropicl ses (Sugunn, 1997). The lrge mjority (over 96%) of Sri Lnkns consume fresh or proce~sed fish, which provide n estimted 65% of the men nnul niml protein intke (Sugunn, 1997) of the popultion. The demnd for inlnd nd mrine fish, however, is highly demrcted. In poorer, rurl inlnd res, predominnt demnd is for the cheper, fresh inlnd fish vrieties. The estimted production of inlnd fishery in Sri Lnk is 20% of the totl fish production. Of this, 80% is contributed by tilpi species (Sugunn, 1997). Tilpi is highly nutritious food item providing 93 kcl of energy, g of protein, 3 7 mg of sodium, 0.5 mg of iron, 1 '.0 g of totl ft, 50 mg of cholesterol nd 90 mg of omeg-3 ftty cids per 100 g of fish (Anon, 2006). It is therefore, n importnt source of niml protein for protein-limited inlnd communities in Sri Lnk. Mrindes re semi preserves; cid, usully cetic cid, nd slt re dded to the fish to retrd the ction of bcteri nd enzymes, resulting in product with chrcteristic flvour nd n extended but limited shelf life. The cetic cid in the form of vinegr produces the tenderness chrcteristic of mrindes (Clucs, 1981 ). This is lrgely due to the ction of some of the proteolytic enzymes tht cuse the prtil brekdown of the protein nd the relese of some free mino cids which give the products its chrcteristic tste. The ft content of the flesh lso contributes to the flvour. Some of the cetic cid combines chemiclly with the proteins, controls the ph nd selectively llows the utolytic rections to tke plce. Mrinting lso mkes the flesh of the fish firmer in texture; the more slt tht is dded, the firmer the flesh becomes due to the removl of wter nd the cogultion of protein. The mounts of cid nd.slt required cn be reduced ifthe prod\1ct is kept frozen until consumed (Mcly, 2001 ). Freezing is the esiest, most convenient, nd lest time-consuming method of preserving food. The extreme cold temperture slows the growth of microorgnisms nd the chemicl chnges tht ffect qulity or cuse spoilge. Freezing does not, however, sterilize food or. destroy the orgnisms tht cuse spoilge. During freezing; enzyme ction is slowed but does not stop. If not inctivted, these enzymes cn cuse colour nd flvour chnges nd loss of nutrients even during storge in the freezer (Anon, 2006b ). Some bcteri nd enzymes remin ctive in mrindes throughoutthe storge, even in the presence of cid nd slt, nd eventully the flesh will dissolve completely. This residul ction is desirble in some semi-preserves, for exmple, those in which slt lone or mixture of slt nd sugr re used to preserve the fish; the products of bcteril nd enzymic ction produce the typicl flvour of the product (Borgstrom, 1989). 12

3 M.M. Rthnyke, V.P.N. Prsdi nd C.V.L. Jysinghe Mrindes my he conveniently divided into three groups; cold mrindes, cooked mrindes nd fried mrindes. Cold mrindes re preserved in mixture of cetic cid nd slt, without giving ny het tretment. In cooked mrindes, fish re plced in hot solution (85 C solution of cetic cid nd slt). Fried mrindes re preserved by frying or bking before being pcked in n cetic cid nd slt solution. Mrindes my be prepred from whole or dressed fishes (Merinodol, 1969). Normlly, fish which hve high ft content is used for the preprtion of mrinted products (e.g. pelgic fish such s herrings nd srdines). There re severl mrinted fish products, such s mrinted herrings, mussels nd milk fish, vilble in other counties (Mcly, 2001 ). Even though there is comprtively high yield of tilpi in inlnd res of Sri Lnk, tilpi consumption is limited due to its strong fishy odour nd the difficulty of processing. Moreover, though it is very nutritious food, consumption of tilpi is miniml in urbn res becuse of the low vilbility. It would be pproprite, therefore, to develop suitble novel product from tilpi s redy to cook product, to increse its utiliztion (e.g. mrinting). At present, there is no processed mrket product of tilpi vilble in Sri Lnk. This study ws undertken, therefore, to develop new mrinde of tilpi with plesnt tste nd medium texture, which is lso sfe to consume, over resonble period of storge. It is expected tht such product would populrize reltively underutilized source of nutrition mong the Sri Lnkn popultion. Mterils nd l\1ethods Tilpi (Oreochromis spp.) smples were obtined from the Mgl Tnk, Nikwertiy nd trnsported on ice to the lbortory. Ingredients (vinegr, tble slt, white pepper, chili powder, grlic powder) used for product development v-.rere purchsed loclly. Jn the lbortory, Tilpi fish were filleted nd used for preprtion of mrindes. Initilly, twelve tretments using vrying combintions of vinegr, tble slt, white pepper nd chili powder were used to prepre the mrindes. After storing for one week nd being pcked in glss bottles nd kept in the freezer, they were subjected to sensory evlution tests. T.o determine the most preferred tretments, five point hedonic scle (5- Like very much, 1- Dislike very much) ws used. The three most cceptble of the 12 tretments were selected for further studies (Tble 1 ). Tilpi smples were subjected to these three tretments nd the mrinted products were bottled nd vcuum pcked nd kept in freezers. Bottled products nd vcuum pcked products were subjected to sensory evlution nd shelf life nlysis. Three tretments were evluted for sensory ttributes with respect to colour, tste, texture, flvour nd the overll cceptbility ccording to Meilgrd et l., ( 1999). A pnel of 25 semi-trined individuls nd modified 7-point hedonic scle were used to 13

4 Journl of the Ntionl Aqutic Resources Reserch nd Development Agency evlute the tretments (7-Like very much, I-Dislike very much). Friedmn test ws used to nlyze the results of the sensory evlution using computer sttisticl pckge (Minitb). The shelf life of the vcuum pcked nd bottled mrindes were evluted by testing for cidity, ph, Totl Plte Count of the product t weekly intervls; fecl coliform test were lso crded out t the sme time. Totl Plte Count ws done using i:iutritive gr medi nd the spred plte method (Grbutt, 1997). Smples from ech tretment were nlyzed in triplicte. Totl fecl coliform test ws done w:>ing the MPN technique (Grbutt, I 997). Tble 1. Different tretments pplied for fish fillets (four fillets) Tretments Quntity of ingredients Vinegr Slt Chili White Grlic (ml) (g) powder pepper powder (g) (g) (g) First Second Third Results nd Discussion The different tretments used in the three mrindes for tilpi fish fi11ets re shown in Tble I. Results showed tht the third tretment (vinegr 75 ml, slt 5 g, chili powder 5 g, white pepper 5 g nd grlic powder 5 g) ws best in terms of colour, texture, odour, tste nd the overll cceptbility ccording to the estimted medin (6, 6, 6 nd 6.33 respectively). There ws no significnt difference, however, between the first nd the third tretments (Tble 1) in terms of odour nd the overll cceptbility. Sensory ttributes There ws significnt difference between the second nd the first tretment in terms of odour nd the overll cceptbility. When the cid nd slt were combined, it gve chrcteristic odour to the mrindes. If there re reltively high cid levels compred to slt, the product hs n uncceptble odour. The second tretment (without chili) ws significntly different for odour nd the overll cceptbility from the other two tretments. 14

5 M.M. Rthnyke, V.P.N. Prsdi nd C.V.L. Jysinghe 7 6 i::::.:: "O CJ E "O ~ '1 5 4 e 3.;z r;;: "' 2 0 colour texture odor o''erll cceptbility Sensory ttributes Tretment 3 [:!Tretment 1 D Tretment 2 Fig. l. Estimted medin in three vcuum pcked smples ccording to sensory ttributes. Note: Similr chrcters indicte no significnt difference mong smples with ech ttribute t P<0.05 Sensory ttributes of the three different tretments re presented in Fig. 1. There ws significnt difference between ech of the three tretments in tem1s of colour nd texture. Colour difference is due to dditives such s chili powder, white pepper nd grlic powder. The combined effect of slt nd vinegr is quite different. Even slightly cidic slt solution cn mke fish flesh noticebly firmer nd cn reduce swelling. There ws significnt difference between the second nd the third tretment in the texture; the likely reson being the high slt concentrtion though the sme mount of cid ws used. Conversely, ddition of higher cidity levels with the sme proportion of slt produces firmer flesh (Merinodol, 1969). Thus, the first nd the third tretment were significntly different with respect to texture. Sensory evlujion ws not crried out on the bottled smples due to their bd odour, cloudiness nd high microbil count s result of the spoilge of the mrindes. The three min fctors for spoilge of mrindes re chemicl fctors, microbil fctors nd enzymtic ction. Chemicl ction involves oxidtion of ft contined within the ftty tissues of the fish. The colour nd the viscocity of the ft chnges nd the mrindes develop strong tste. Microbil ction involves bcteril decomposition of the fish flesh. This cn be due to the 16,v hygienic prctices used during the processing of the product. Enzymtic ction is due to the ction of vrious enzymes found in the fish fillets. They spoil the tissue by the process of utolysis nd mke the fish susceptible to bcteril ttck. It re~mlts in the formtion of mino cids, mmoni, crbon dioxide nd voltile bsic compounds (Shmmi nd Bhtngr, 2002) nd gives bd odour to the 15

6 Journl of the Ntionl Aqutic Resources Reserch nd Development Agency product. In ddition, high slt concentrtion cuses protein solubiliztion nd imprts cloudiness to the product. Microbiologicl studies Tble 2. Microbiologicl chnges of vcuumed pcked mrindes nd bottled mrindes Prmeter Amount Bottled Vcuum pcked TPC l.33x 10 6 (three smples) (one week) <30 colonies (three smples) (After 4th week) Fecl coliform (-) ve (-) ve Note: Men vlue of triplictes is mentioned. Tble 2 presents the microbiologicl chnges of vcuumed pcked mrindes nd bottled mrindes. The cceptble level of bcteril colonies is l.00xl0 5 (Grbutt, 1997). Vcuum pcked mrindes re sfer for consumption thn bottled mrindes becuse they were negtive for fecl coliforms nd hd n cceptble vlue for the totl plte count. According to the totl plte count results, the vcuum pcked products hd shelf life of one month. Physico-chemicl studies ::: c Ill"''' ~ st 2nd 3rd 4th time (weeks) -Treutment l.. "~ Tretment 2 Trentment 3 Fig. 2. ph chnges of three vcuum pcked smples with time. Note: Similr letters indicte no significnt difference mong ech smple with time t P<

7 M.M. Rthnyke, V.P.N. Prsdi nd C.V.L. Jysinghe Chnges in ph nd totl cidity in the three vcuum pcked smples with time re presented in Fig. 2 nd Fig. 3. It cn be seen tht there ws no sif:,rnificnt difference between the three vcuum pcked tretments in these prmeters. Acidity nd ph of ll three tretments were below 5.3 (ph) nd bove 1.95% cidity which re cceptble levels. Anerobic conditions cn led to the growth of Clostridium hotulinum, which cn produce the toxin cusing botulism. Since this orgnism cn multiply within 24 hours, the cid concentrtion must be high enough to ensure tht the ph will be below the mximum of 5.3 within 24 hours. This cn be chieved t cid levels bove 1.95 % (Borgstrom, 1989). 3.4 ~.2.~ ~ 2.6 < st 2nd Jrd 4th Time (weeks) - Tretment I --Tretment 2 Trcntment 3 Fig. 3. Note: Acidity vlue chnges of vcuum pcked smples with time. Similr letters indicte no significnt difference mong ech smple with time t P<0.05 When prepring the mrindes, there re two min considertions in choosing the concentrtion of slt nd cid; firstly, Lhe solut1on should hve n equl distribution of slt in the tissue fluid of the fish nd in the solution. Secondly, prt of the cetic cid should be bound'by the fish fillets (Mcrinodol, 1969). The shelf lite of the mrindes my be severl months in the freezer but only few weeks t tropicl mbient tempertures. Moreover, if the utolytic enzymes nd the bcteri remin ctive, the shelf life of mrindes is limited even under frozen conditions. The shelf life cn be extended by dding sugrs to the mrinde. This reduces the wter ctivity of the product nd inhibits the growth of bcteri. Moreover, the pckging is lso importnt to increse the shelf life. The pckging used must be 17

8 Journl of the Ntionl Aqutic Resources Reserch nd Development Agency impermeble to wter vpour, oxygen nd flvour voltiles. Double lminted high density polyethylene ws used s pckging mteril in vcuum pckging to fulfill the bove requirements nd it is suitble for mrinted products. It should be noted however, tht strict hygiene nd storge control prctices re required with this type of product, where the cidity is not necessrily high enough to stop the growth of pthogens (Hobbs nd Roberts, 1993 ). Conclusion Results of this study show tht mrindes with plesnt tste nd good texture cn be developed from tilpi. Vcuum pcked mrindes were sfer to cons~1me thn bottled mrindes. These novel mrindes developed possessed good qulity nd high consumer cceptnce. Since only 50% of the tilpi met cn be used for the tilpi mrinde production the production cost is high. Therefore, further reserch should be crried out to reduce the cost of production nd to extend the shelf life of the product. Acknowledgements The stff members of The Ntionl Aqutic Resources Reserch & Development Agency re grtefully cknowledged for their vluble support given to complete the study successfully. References Anon (2006). l.html. Anon (2006b ). _feture. php?ffid=5 8. Borgstrom, G. (1989). Fish s Food (Vol 3, prt 1 ), pp Acdemic Press, New York. Clucs, I.J. (1981). Fish Hndling Preservtion & Processing in the Tropics, p 140. Tropicl Product Institute, London. Grbutt, J. (1997). Essentil of Food Microbiology, pp Bh Press, Gret Britin. Hobbs, B.C. nd Roberts, D. ( 1993) Food Poisonings nd Food Hygiene, 6th edition, pp Edwrd Arno Id, London. Mcly, R. (2001 ). Mrindes. Ministry of Agriculture, Fisheries nd Food, Torry Reserch Sttion. Meilgrd, M., Civille, G.V. nd Thoms, B. (1999). Sensory Evlution Techniques, 3'd edition. CRC Press LLC, Florid. 18

9 M.M. Rthnyke, V.P.N. Prsdi nd C.V.L. Jysinghe Merinodol, A. ( 1969) Fish curing nd Processing, pp MIR Publishers, Moscow. Pilly, T.V.R. ( 1990). Aquculture Principles nd Prctices, pp University Press, Cmbridge. Shmmi, Q.J. nd Bhtngr, S. (2002)AppliedFisheries, pp Agrobios, Indi. Skirk, R. nd Swyer, R. ( 1991) Person's Composition nd Anlysis offoods, 9 'edition, p 461. Addison Wesley Longmn Ltd., Englnd. Sugunn, V.V. ( 1997) Food nd Agriculture Orgniztion of the United Ntions. Fisheries Mngement of Smll Wter Bodies in Seven Countries in Afric, Asi nd Ltin Americ. 19