EFFECTS OF SOME PROCESSING PARAMETERS ON THE CHEMICAL PROPERTIES OF SMOKED CATFISH (Clarias gariepinus)

Abstract

Clarias gariepinus or African sharp tooth catfish is a species of catfish of the family Clariidae. It has both health and economic benefits but with a short storage life. To curb spoilage, increase shelf life and add value to products, this study investigated the effect of different processing parameters such as osmotic dehydration (OD), fish size (FS) and smoking temperature (ST) on the chemical qualities and predicted the best drying kinetics model for smoking of Clarias fish. Osmotic dehydration (OD), was employed using sodium chloride (20 obrix and 25 obrix at 40 oC for 6 hours ) on two sizes of Clarias; the small (200-450 g) and big (800-1000 g). A sawdust –fuelled smoking kiln fitted with analog temperature sensor was subsequently used to smoke dry the samples at 70 oC and 150 oC. The samples were weighed at regular interval of 1hour until three consecutive constant weights were achieved; indicating equilibrium conditions. The data obtained were thereafter used to calculate the moisture ratio in order to determine the drying kinetics. The control samples (fresh), Osmotic dehydration (OD) samples and the osmotic dehydrated smoked dried samples (ODSD) were subjected to proximate analysis (moisture, ash, protein, fat, carbohydrate); oxidative tests (free fatty acid, peroxide value, thiobarbituric acid (TBA), pH); and mineral analysis using standard methods The result indicated significant difference (p< 0.05) in the moisture, protein and fat contents of ODSD samples when compared with the control samples. The dual processing effect had a positive effect with an increasing value in protein, fat and significant reduction in moisture content. The small sample has 25.11, 46.59, 0.45 and 14.69, 4.56, 14.69 for protein, fat and moisture content at 150 oC with 20% OD and control, respectively; while at the same temperature with 25% the big sample and control has 25.28, 36.50, 36.50 and 16.94, 4.56, 71.58% for protein, fat and moisture respectively. OD resulted to a decrease in pH from 7.20 in control sample to a range of 6.70-6.90; while ST further had the pH decreased to 6.30-6.5 and 6.5-6.70 for small and big sizes respectively. The ODSD samples were within the acceptable limit of 6.8 to 7.0. The OD samples gave a lower FFA value (0.24- 0.45) while on the ODSD samples, FFA (20%, 150 oC) gives 2.36% and ( 20%,70 oC) gives10.00% increased with increase in drying time. The peroxide value also increased with increase in drying time with value ranging from 6.74 to 16.28 mEq/kg and 7.60 to 20.78 mEq/kg for the 150 oC small and 70 oC big respectively. The treatment yielded samples with high concentrations of potassium, calcium and heavy metals (Cd and Cr) were within tolerable limit, the minor elements (Ni, Mn and Cu) were also in traced amount in all the samples studied. Twelve drying model equations were selected from literature to identify suitable ones for fitting moisture ratio data obtained from the drying of the sample with optimum properties. The results were compared for their goodness of fit in terms of correlation coefficient (R2), reduced chi square (χ2) and root mean square error (RMSE). The study reveals that the processing parameters (size, osmotic concentration and smoking temperature) had a significant role on the chemical properties of Clarias gariepinus. However it can thus be concluded that small catfish osmotic dehydrated at 20 % and smoked dried at 150 oC gave the optimum quality for a long and lasting catfish. The size and temperature has greater influence on the water loss while concentration and size influence the solid gain. Also, Midilli Kucuk was found to be the best and most suitable to describe the drying behavior of Clarias gariepinus with the optimum processing parameter for small sample treated with 20% osmotic solution and smoked dried at 150 oC.