Effect of salting and smoking-method on the keeping quality of chub mackerel (Scomber japonicus): biochemical and sensory attributes
Introduction
Smoke curing is a traditional fish preservation method of considerable economic importance worldwide. Smoke, is produced by the process of incomplete combustion of wood. It consists of numerous individual components namely: aldehydes, ketones, alcoholes, acids, hydrocarbons, esters, phenols, ethers, etc. (Doe, 1998; Guillen & Errecalde, 2002). These components are transfered to the smoked goods by deposition on their surface and subsequent penetration into their flesh (Doe, 1998).
Smoking imparts a characteristic flavour and colour to the fish. In addition, smoking increases the shelf-life of fish as a result of the combined effects of dehydration, antimicrobial and antioxidant activity of several of the smoke constituents mainly: formaldehyde, carboxylic acids, phenols (Doe, 1998, Horner, 1997, Leroi and Joffraud, 2000a, Rorvik, 2000). An additional preservative effect is owed to salting which comprises the first step of the fish smoking process.
The preservative effect of salting is mainly due to the decrease in water activity (aw) and thus prevention of growth of many spoilage microorganisms along with the formation of a more membranous surface which further inhibits the growth of microorganisms (Horner, 1997, Leroi and Joffraud, 2000a, Rorvik, 2000). Moreover, chloride ions are toxic for some microorganisms (Leroi, Joffraud, & Chevalier, 2000b).
There are three methods used to smoke fish: the traditional method by combustion, at either low temperature (cold smoking ⩽ 30 °C) or high temperature (hot smoking ⩾ 60 °C); use of a high voltage electrostatic field which accelerates smoke deposition; and use of liquid smoke which lowers the content of polynuclear aromatic hydrocarbons (potently carcinogenic compounds) in liquid smoked fish (Doe, 1998, Duffes, 1999, Espe et al., 2002, Hattula et al., 2001, Sigurgisladottir et al., 2000).
Production of smoked fish in Greece has rapidly increased over the past few years; from 1010 tons/year in 1996 to 2350 tons/year in 1999 (Anonymous, 2000). Among smoked species the hot-smoked products are the most widely consumed in Greece.
Hot-smoking is a pasteurizing process, the preservative effect of which depends on the composition and preparation of raw material, temperature, relative humidity, density and composition of the smoke as well as the smoking time (Doe, 1998, Kolodziejska et al., 2002).
Chub mackerel (Scomber japonicus) is a common fish in the Mediterranean sea. Statistical data show that 3041 tons were caught in Greece in 1999 corresponding to 6% of the harvesting of all fish species (Anonymous, 2000). Chub mackerel is usually sold as a raw product. The application of hot smoking for the extension of the shelf-life is a process of interest, given that chub mackerel is generally a fatty fish which spoils easily.
The objectives of the present work were to study the effects of salting and different hot smoking procedures on chub mackerel fillet quality as assessed by sensory analysis and determination of biochemical indices.
Section snippets
Fish samples
Fresh chub mackerel was purchased from local distributors approximately 12 h after harvesting and transferred within one hour to the fish processing plant (TSIALIOS S.A., Ioannina, Greece) in sealed foamed polystyrene boxes containing ice. The average weight of the whole fish was 500 g. Average length was 25 cm. Fishing ground was the Ionian Sea, Greece. Catching method used was surrounding nets fishing. The fish were subsequently headed and filleted. The fillets were separated into four
Determination of moisture content
Moisture content of chub mackerel fillets are given in Table 1. Mean moisture values of 59.0% and 58.1% were recorded for samples smoked by method 1 and 2, respectively. The corresponding mean values for unsalted non-smoked (USNS) and salted non-smoked (SNS) samples were 75.2% and 74.9%, respectively.
There were no statistically significant differences (p < 0.05) in moisture content between fillets smoked by the two different methods or between USNS and SNS samples.
The smoking process resulted in
Conclusions
Present results indicate that application of smoking method 2 resulted in a product with more distinct smoked odour, taste and colour which were retained throughout the 30 day storage period of the study. The prolongation of smoking time (method 2) resulted in the deposition of more smoke constituents with antioxidant and antimicrobial activity (phenols, formaldehyde, etc.) which contributed to the extension of shelf-life of the product. Both smoking methods produced good quality chub mackerel
Acknowledgements
The authors acknowledge the fish processing plant (TSIALIOS S.A., Ioannina, Greece) for the smoking of fish.
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