STARTER CULTURE DEVELOPMENT AND FERMENTATION OF OROCHROMISNILOTICIS (NILETILAPIA) PREPARED WITH DIFFERENT MARINATING AGENTS

Abstract

ABSTRACT Fermentation of fish is meant to extend the shelf life of fish, improve sensory characteristicsand enableconsumerstoaccess benefitingmicroorganisms.Dried fermentedfishare stapleinmany cuisines, particular in coastal areas. However, discrepancies in fermentation methods and sensory qualityhaveasubstantialimpactonconsumer'sacceptabilityandfoodsafety.Thisresearch aimedtoscreenforpossibleisolatesthatcouldbeusedasstarterculturesduringspontaneous fermentation of Oreochromis niloticus,identify the best isolates using morphological, biochemicalandmoleculartechniques,fermentwiththeselectedisolatesandtodetermine sensory acceptabilityof dried fermented fish. Marinated fish were spontaneouslyfermented at 10‘Cfor12daystoisolatestarterculturesanddeterminebestfermentationperiod.Coloniesof bacteria isolated with MRS (de Man Rogosa and Sharpe agar) plates during spontaneous fermentationof Oreochromisniloticus were characterized, identified and used as starter cultures. Fermentedfishwereovendriedat60’Cfor 12hours. Proximateanalysis ofdried fermentedfish was done using standard methods. The appearance, aroma, taste, tactile texture, overall acceptabilityoffermentedfishwereevaluated.Datawereanalyzedusingone-wayanalysisof variance, followedby Duncan's multiple range test, Pñ0.05 was consideredsignificant. Results of fermentationperiodonphysicochemicalparametersrevealed10daysfermentationperiodat10 ‘*wasthe best as protein content increased from initial 23.05 to 29.03 in com base fermented fish and23.86to30.83incassavabasefermentedfish.Suspectedcontaminatingorganismswere completelyinhibited bytheactivitiesofthestartercultures;thesystembecameslightlyacidic withTotalbacteriacount(TBC)7.8^109/cfuandLacticacidbacteria (LAB) 3.1•10'/cfu for com base while for cassava base, TBC-1.2•109/cfu and LAB-2.2•105/cfu for cassava base. Comparativeproximateanalysisoffreshfish,fermentedfishanddriedfermentedfish showed protein content of(24.12, 31.92, 30.04 %), Fat content of(2.69, 2.16, 1.88 %), and Ash content of (5.82,7.23,9.12%),respectively.Themainandinteractiveeffectsofbaseandisolateson sensoryacceptabilityshowedthatcarbohydrate baseshadnosignificant(P>0.05)effecton fermented fish acceptability.Starter cultures had significant effect on taste (P= 0.004) and aroma (P=0.009).Combinedeffectofcarbohydratebaseandstartercultureshadsignificanteffecton appearance(P=0.002)and aroma(P= 0.004).Sensoryattributes revealedthat the effects of the three starter cultures on the fermented fish were not significantly different (P>0.05). The selected bacteriaisolateswereidentifiedasLactobacilluspentosusstrain,Streptococcusthermophilusstrain1,and Streptococcus thermophilus strain2,respectively. Dried fermented fishhad improvedvaluescomparedwithfreshfish inNa(62.80+3.4vs.52.50z2.3),andFe (41.90+6.7) mg/100g. Thisstudydemonstratesthepotentialofthesedeveloped stainsasstarter cultures to improve the quality and nutritionalvalue of fermented Oreochromis niloticus.