And therefore a multisensor concept

And therefore a multisensor concept has been introduced based on simultaneous instrumental analysis of various sensory related attributes (Olafsdottir et al., 2004).
The detection of specific spoilage organisms (SSO) like She- wanella putrefaciens, Pseudomonas ssp. and Photobacterium phosphoreum is considered more reliable than total viable counts (TVC) to accurately evaluate the freshness or spoilage level of fish products (Dalgaard, 2000; Gram etal., 2002).The potential of H2S- producing organisms, like S. putrefaciens,todevelopsulfur compounds contributing to off-flavor described as onion, cabbage and putrid spoilage odors at advanced stages of storage in fish is well known (Miller et al., 1973a; Herbert et al., 1975). S. putrefaciens has been identified as the main SSO in whole cod (Herbert and Shewan, 1976; Jørgensen et al., 1988)aswellasin aerobically stored haddock fillets (Levin, 1968; Chai et al., 1971). Development of ammonia-like and fishy off-flavors has been related to fish spoilage bacteria like S. putrefaciens and P. phosphoreum that can reduce TMAO to TMA (Jørgensen and Huss, 1989; Dalgaard, 1995). P. phosphoreum was identified as an important TMA producer in iced cod and in cod fillets (Van Spreekens, 1974; Van Spreekens and Toepoel, 1981) and has been suggested as the main spoilage organism in packed cod fillets, although this bacterium does not produce intensive off odors (Dalgaard et al., 1993; Dalgaard, 1995).Other well knownspoilage bacteria likePseudomonas spp.do not produce TMA from TMAO (Castelletal.,1959). Earlier studies on the formation of odorous degradation compounds in fish (cod, haddock and rockfish) from the North Atlantic area showed that pseudomonads, in particular P. fragi, were responsible for quality changes and development of sweet,fruity off odors inchilledfish (Castell andGreenough, 1957; Castell et al., 1959; Miller et al., 1973b). More recently the importance of pseudomonads in spoilage in fish species from the Mediterranean Sea (Koutsoumanis and Nychas, 1999) and American plaice (Lauzon, 2000) has been reported. Growth of pseudomonads species was modeled as a function of storage time and correlated well with organoleptical shelf-life in Mediterranean species (Koutsoumanis and Nychas, 2000).
Predictive microbiology as a tool to study the microbial ecology in food has gained considerable interest (Ross and Mc- Meekin, 1994). Kinetic models based on the Arrhenius equation have been developed to describe the relationship between tem- perature and relative spoilage rate for muscle foods. Recently models based on enumeration of specific spoilage organisms (SSO)to determine the remaining shelf-life offish products have been developed (Dalgaard et al., 1997a; Koutsoumanis and Nychas, 2000; Koutsoumanis, 2001; Dalgaard, 2002). Com- parison of the chemical profiles of spoiled seafoods and of the metabolites produced by potential spoilage organisms has only been used to a limited extent for characterization of SSOs (Gram and Dalgaard, 2002). More knowledge on the chemical charac- terization of spoilage processes of muscle food and their corre- lations with sensory and microbiological changes is needed (Dainty, 1996). Multi-compound indices based on gas chroma- tography analysis of the main compounds produced by bacteria during spoilage have been suggested to evaluate the complex changes occurring in fish products stored under different con- ditions (Lindsay et al., 1986; Olafsdottir and Fleurence, 1998; Jørgensen et al., 2000, 2001; Olafsdottir et al., 2005).