Qualitative Characteristics of Hot Smoked, Cold Smoked and Ovenried Heterotis Niloticus under Cold Storage Temperature Condition

Abstract

The quality characteristics of processed fresh Heterotis niloticus collected from Badagry Lagoon area of Lagos was investigated under different processing methods.

Hot smoked (at 80⁰c at 12 hours per day for two days), Cold smoked (at 30⁰c for 18 hours) and oven dried (at 60⁰c for two days) with regular turning of the fish manually. Each of the processed samples (consisting of 20 samples in each treatment.) were separately kept in transparent nylon and put in a freezer for 12 week at -25⁰c. Samples were taken fortnightly for various analysis. A total of 80 fresh Heterotis niloticus (descaled, degutted and washed with clean water) averaging 350 ± 0.88gm, total length 26.50 ± 0.64 cm) were collected for this study. Initial and final proximate analysis for the different processed fish samples were taken as well as chemical analysis (P.V, F.F.A and T.V.B-N), organoleptic assessment (appearance, taste, texture and odour) and microbial analysis (isolation, identification and count) were also examined at two weeks interval. The initial and final proximate analysis of cold smoked processed Heterotis niloticus had highest moisture content of 32.73% (initial ), and 27.21%  (final), protein (41.20% and 42.32%). Oven dried; moisture content (27.80%, 25.70%), protein (37.40%, 38.83%) while Hot smoked, also had a moisture content of (28.71%, 26.68%) crude protein (38.75% and 39.26%) respectively. Chemical parameters were significantly different p?0.05 for the three processing methods (cold smoked, hot smoked and oven dried as follows,. TVB-N (3.11, 2.54 and 2.60) mg N/100gm., FFA (5.21%, 4.68% and 4.85% ) and PV mean values(4.31,3.75 and4.85) meq/kg respectively. The organoleptic assessment score was just satisfactory at eight week of storage, especially for odour, but Hot smoked samples was still good at 10^th week and oven dried samples was satisfactory. Microbial count (bacteria and fungi), the cold smoked product was significantly different at p?0.05 from the other two processing methods. Mean bacteria count was highest (70.14cfu/gm), followed by oven dried (2.14 cfu/gm) and least (2.00 cfu/gm) in hot smoked. Mean total microbial count was highest (575 cfu/gm) for cold smoked, 28 cfu/gm (oven dried) and the heat is 24 cfu/gm in hot smoked. The best processing method is hot smoking with the least microbial count 24 cfu/gm, T.V.B-N 2.54 mg N/100gm, F.F.A 4.68% and 3.75 meq/kg. spoilage increase with storage length with positive correlation (r) recorded for all the parameters in the 3 processing methods. Microbial count /isolation was not recorded for (0-8weeks) in hot smoked fish fish with Staphylococous aureus and Pseudomonas aeruginosa not represented throughout the 12weeks of study. In oven dried, bacteria and fungi were represented as from the 12^th weeks while only two fungi specie (Aspeigillus niger and Sacchromyces sp occurred only in the 10^th week. All the microbial species were represented through the 12weeks in the oven dried fish. Organoleptic assessment showed hot smoked with the best appearance, taste, texture and odour (with mean scores of (4.74, 5.02, 4.72, and4.79) followed by oven dried (4.62,4.71,4.70, and 4.64); while the worst processing method is cold smoked (4.10, 3.95, 4.07 and 3.26) with just satisfactory (3.95 and 3.26) taste and odour at 12 week of cold storage at -25⁰c

Keywords: Quality characteristics, Cold smoked, Oven dried.