EFFECT OF DRYING AND STORAGE ON THE PHYSICO-CHEMICAL CHARACTERISTICS AND PROTEIN QUALITY OF SMOKED HORSE MACKEREL (TRACHURUS TRACHURUS) FILLETS
This study assessed the effect of drying on smoked horse mackerel fillets during storage at room temperature. Smoked horse mackerel (Trachurus trachurus) fillets were prepared by smoking brined horse mackerel fillets in a traditional improved kiln for 4 hours at 60 – 70oC. The fillets were later oven-dried at 65-70oC for 0, 2, 4, 6, and 8 hours, spread on perforated trays and stored at room temperature of 24.5 – 34oC and relative humidity range of 59 – 87%for a period of 30 days. The samples were tested after every 10 days for physico-chemical, microbial and sensory qualities as well as for amino acid composition. The results obtained showed that smoking reduced the moisture content from 73.61 to 20.93% which led to concentration of other proximate components. There was a significant difference (p<0.05) in the proximate composition of the dried samples with drying treatment and on storage. Drying treatment decreased the moisture content of the smoked fillets from 20.93 to 14.57% on the 0 day while the other components increased significantly presumably due to increase in dry matter with protein forming the largest in quantity (65.30 – 70.93% on 0 day). With the exception of control, caloric values for all the samples were within the range of United States Recommended Dietary Allowance (US/RDA) of 450 – 600 kcal/100g. Thiobarbituric acid value (TBA), peroxide value (PV), and free fatty acid (FFA) increased with drying treatment while pH, soluble protein and in-vitro protein digestibility (IVPD) decreased. Sample dried for 8hrs recorded the highest range of values in TBA (0.574 to 1.040), PV (5.40 to 16. 88 M.eq/Kg), and FFA (0.671 to 1.109% oleic acid). Control sample had the highest range of values in pH (6.49 to 6.22), soluble protein (54.78 to 48.29%), IVPD (99.44 to 94.07%). There was a general decline in all the analyzed parameters at the end of the storage period. Drying treatment and storage severely affected the amino acid composition with control sample showing highest concentration of 47.10 to 27.42 g/100g protein. Microbial growth was not detected in freshly smoked and dried samples; however storage significantly increased the total viable and mould growth to a range of 2.98×103 – 5.00×105 cfu/g and 2.76×103 – 4.73×103 cfu/g respectively for all the treated samples on the 30th day with 8hrs dried sample recording the least growth. Sensory results revealed decline in sensory qualities but was still acceptable after 30 days of storage. The study showed that drying treatment enhanced the shelf stability of the smoked horse mackerel fillets. However, it also indicated that long time drying treatment and storage time could negatively influence the protein quality of horse mackerel fillets stored at room temperature.