Abdul Rahman, Russly

Bakar, Jamilah

Che Man, Yaakob

Lam, S. F.

Mohsin, A. K. M.

Selamat, Jinap

Yusoff, Anida

Universiti Putra Malaysia Institutional Repository

FOR Category F10800: Biological SciencesEFFECT OF ALKALI WASHINGS ON THE QUALITYOF BLACK TILAPIA FILLETSB. Jamilah, A.K.M. Mohsin, S.F. Lam, Y. Anida,S. Jinap, A.R. Russly and Y.B.Che ManFaculty of Food Science and BiotechnologyUniversiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaKeywords: alkali washings, black tilapia, sensory,quality.IntroductionIn the last few years, aquaculture is the main contributor tothe increase in the landings of fish world-wide. Some fresh-water fish and black tilapia in particular have strong muddyodour and flavour which is mainly due to their eating habits.These muddy characteristics are mainly attributed to thepresence of geosmin and 2-methylisoborneol in the fish mus-cle. At present, no reports have been made available as tothe method of reducing or removing of this component dur-ing the on-line processing of freshwater fish. The currentpractice is to hold live fish for several days or weeks in cleanwater prior to processing. The project has the objective ofidentifying pre-processing procedures such as washing to re-duce this earthy component and thus rendering the end prod-uct to be more marketable. Additional benefits of the proce-dure identified such as increase in the whiteness of the mus-cle (an important index in fish quality) is also taken into ac-count. Other quality attributes of the fish are also noted todetermine the total effect of the treatment on the overallquality and the acceptability of the fish under different han-dling conditions such as.during frozen storage.Materials and MethodsLive tilapia are brought to the faculty laboratory and killedby a sudden blow on the head. This is to ensure extremefreshness of the starting material. They were then split intoexperimental lots for various treatments. Washings withvarious concentrations of NaOH and KOH solutions for 5 to20 min were carried out. After which they were rinsed in~istilled water to remove any residue of the washing solu-nons. The efficacy of the washing treatments was exaarninedat two different levels. One, on more general aspects such assensory characteristics, texture and color instrumentally: theother, on the molecular level whereby the denaturation of themyofibrillar protein and volatile and the non-volatile compo-nents of the muscle was determined. The effect of the treat-ment on the lipid stability of the fish was also investigated.Results and DiscussionThe overall results indicate that the alkali washings could re-duce the muddy component in the fish muscle within 5 to 10min washings depending on the strength of the solutionsused. Colour of the exposed surface of the fillets also in-crease in whiteness according to the Hunter colour scheme.However, increasing the concentration of the NaOH solutiongreater than 0.5N will result in denaturation of the muscleand ~ change in the colour of the surface area. A strong cor-relation was also obtained between the instrumental texturereading and the texture response from the sensory evaluation.This apparent observation is supported by changes in thethermogram (Differential Scanning Colorimetry) of the actinand the myosin component and the solubility characteristicsof the myofibrilla protein. Confirmation of the pattern of de-naturation of the myofibrils by SDS-PAGE is currently pur-sued. Difficulty is encountered in getting the bands due tothe low ~oncentration of the myofibril extract. Lipid beingthe next Important component in the fish muscle and mainlyexisting in the relatively unsaturated form is also crucial indeciding the usefulness of the whole experimental exercise.The peroxide and TBARS values, the fatty acids profile andFI1R characteristics are currently compiled.ConclusionsThe alkali washings of the fish muscle is effective in reduc-ing the muddy flavour and odour of the fish muscle. How-ever, washings should not be carried out with very strong al-kali solutions since it is detrimental to the texture and the~olour of the sample thus indirectly affecting its marketabil-ity,Supported by IRPA Grant 03-02-04-0032213

Effect of alkali washings on the quality of black tilapia fillets

http://psasir.upm.edu.my/42557/1/Effect%20of%20alkali%20washings%20on%20the%20quality%20of%20black%20tilapia%20fillets.pdf

Effect of alkali washings on the quality of black tilapia fillets

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