Ahmad, F. B. H.

Bakar, Jamilah

I. A., Nurul

Yusof, Salmah

Universiti Putra Malaysia Institutional Repository

UPM Research Report1998: Volume2EFFECT OF ACID WASHINGS ON THE QUALITY OFBLACK TILAPIA FILLETSI.A. Nurul, B. Jamilah, F.B.H. Ahmad and Y. SalmahFaculty of Food Science and BiotechnologyUniversiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaKeywords: acid washings, black tilapia, sensory,GeMS profile, SEM.IntroductionMuddy characteristics in freshwater fish can render the fishand its products unmarketable or decrease in its acceptability.This has been reported for catfish cultured in Mississippi,USA, trout in Canadian waters and similar findings on Ma-laysian freshwater fish such as tilapia, catfish and carp.Freshwater fish is mainly produced through aquaculture andglobally it is an important source of protein. The local prac-tice to decrease this muddy odour and flavour which is fre-quently associated with freshwater fish is by washing the fishwith acidic substances such as tamarind juice, lime or aceticacid. Therefore, this study was focused on the determinationof the ability of several organic acid solutions in removing orreducing these unwanted characteristics. Other effects of thetreatment, may it be positive or negative on the quality of thefish was also documented.Materials and MethodsLive tilapia were brought to the faculty laboratory and killedby a sudden blow on the head. This was to ensure extremefreshness of the starting material. They were then split intoexperimental lots for various treatments. Washings withvarious concentrations of tartaric, citric and acetic acids so-lutions for 10 min were carried out. After which they wererinsed in distilled water to remove any residue of the washingsolutions. The effectiveness of the washing treatments weredetermined by identifying the residual muddy characteristicsin the fish muscle through sensory evaluation by trained pan-elist as well as through gas chromatography and mass spec-trum (GCMS) output. The physical changes in the muscle214were investigated through scanning electron microscopy(SEM) whereby the depth and degree of muscle degradationwere observed.Results and DiscussionThe results indicate that the effectiveness of the washingtreatments in the removal of the muddy component varieswith the acid used. The acids also had the ability to camou-flaged the muddy characteristics as commented by the panel-lists. Unlike the alkali washing treatment, the reduction ofthe muddy odour and flavour works through a differentmechanism. The apparent absence of geosmin (since throughGCMS analysis) can be due to the conversion of the geosmininto an odourless compound i.e. argosmin beside the possi-bility that it is leached into the washed water. Increasing theconcentration of all acids above O.125M seems to result innegative effects to the fish muscle characteristics. Texture ofthe fish muscle becomes fibrous and increases in opacity un-like in alkali washings where the muscle turned into gel-liketranslucent substance. Increases in the yellowness of thesamples were also observed. All quality indicators moni-tored tend to indicate that acid washings may be superior toalkali washings, however, the main drawback is the depth ofpenetration of the acid into the muscle. The outer musclelayers were found to denature and thus formed a distinctouter zone preventing further penetration of the acids fromthe washed solution into the interior layer. Hence decreasingthe effectiveness of the treatment since the denatured layerwill also prevent the leaching of the geosmin and 2-methylisoborneol (Mill). Electron microscopy also showedthat the muscle had different pattern of denaturing upon ex-posure to different acids.ConclusionsThe acid washings of the fish muscle is effective in reducingthe muddy flavour and odour of the fish muscle. It also hasthe ability to camouflage the muddy character. The effec-tiveness of the acid washings varies. Washings should not becarried out with acid concentration above 0.125 M when thec.ont~ct~me is for 10 min. The noticeable textural degrada-non IS different from that observed in alkali washings.Supported by IRPA Grant 03-02-04-1XJ32

Effect of acid washings on the quality of black tilapia fillets

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Effect of acid washings on the quality of black tilapia fillets

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