The dominating growth ofP. phosphor

The dominating growth ofP. phosphoreum may possibly be explained by the pH and conditions that probably favored its growth. It is likely that microaerophilic conditions developed in plastic wrapped fillets in the styrofoam boxes (containing 11 fillets, approximately 5 kg) with the production of bacterial car- bon dioxide influencing the pH. However, this can not be con- firmed since the CO2 level in the headspace of the boxes was not measured.
3.4. Electronic nose measurements evaluation of microbial metabolites
Responseofthe electronicnose sensorsasa function ofstorage time was characterized by an initial lag phase and a steep slope at the end as seen for the CO sensor response (Fig. 4b). This can partly be explained by the low sensitivity of the sensors (Ola- fsdottir etal.,2002) and the fact that highmicrobialcellcounts are needed to produce metabolites in high enough concentrations to be detected by the sensors. The large standard deviation observed for the electronic nose responses (Fig. 4b, c, d) is related to their volatile nature and hence their sensitivity to slight changes in temperature during sampling. (Olafsdottir, 2003). The electro- chemical gas sensors in the FreshSense electronic nose have different selectivity and sensitivity towards selected standards representative forthe main classes ofcompounds producedin fish during spoilage (Olafsdottir et al., 1998, 2002). The CO sensor detects volatile alcohols, aldehydes and esters, the NH3 sensor is selective for ammonia and amines and the H2SandSO2 sensors detect sulfur compounds. However, some cross sensitivity has been observed for the CO and the H2S sensors (Olafsdottir et al.,
2002).
3.4.1. CO sensor
The CO sensor was the most sensitive of the sensors and increasing response was noticed earlier than for the other sensors, suggesting the presence of alcohols or aldehydes early in the spoilage process. The response of the CO sensor (Fig. 4b) showed the same trend for the spoilage rate of the sample groups of haddock fillets stored at different temperatures as shown by the sensory analysis. An increase (p

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The dominating growth ofP. phosphoreum may possibly be explained by the pH and conditions that probably favored its growth. It is likely that microaerophilic conditions developed in plastic wrapped fillets in the styrofoam boxes (containing 11 fillets, approximately 5 kg) with the production of bacterial car- bon dioxide influencing the pH. However, this can not be con- firmed since the CO2 level in the headspace of the boxes was not measured.3.4. Electronic nose measurements evaluation of microbial metabolitesResponseofthe electronicnose sensorsasa function ofstorage time was characterized by an initial lag phase and a steep slope at the end as seen for the CO sensor response (Fig. 4b). This can partly be explained by the low sensitivity of the sensors (Ola- fsdottir etal.,2002) and the fact that highmicrobialcellcounts are needed to produce metabolites in high enough concentrations to be detected by the sensors. The large standard deviation observed for the electronic nose responses (Fig. 4b, c, d) is related to their volatile nature and hence their sensitivity to slight changes in temperature during sampling. (Olafsdottir, 2003). The electro- chemical gas sensors in the FreshSense electronic nose have different selectivity and sensitivity towards selected standards representative forthe main classes ofcompounds producedin fish during spoilage (Olafsdottir et al., 1998, 2002). The CO sensor detects volatile alcohols, aldehydes and esters, the NH3 sensor is selective for ammonia and amines and the H2SandSO2 sensors detect sulfur compounds. However, some cross sensitivity has been observed for the CO and the H2S sensors (Olafsdottir et al.,2002).3.4.1. CO sensorThe CO sensor was the most sensitive of the sensors and increasing response was noticed earlier than for the other sensors, suggesting the presence of alcohols or aldehydes early in the spoilage process. The response of the CO sensor (Fig. 4b) showed the same trend for the spoilage rate of the sample groups of haddock fillets stored at different temperatures as shown by the sensory analysis. An increase (p<0.05) was first detected between days 2 and 3 for samples stored at 15 °C, between days 2 and 7 for samples stored at 7 °C, between days 4 and 9 for the 0 °C a and between days 5 and 7 for the 0 °C + abuse. The difference in spoilage rate of the sample groups stored at 0 °C in 2001 and 2003 observed by sensory analysis was supported by the more rapid increase in the CO sensor response in 2003, indicating more production of metabolites like alcohols, aldehy- des and esters resulting in the shorter sensory shelf-life.Earlier gas chromatography studies on volatile compounds in haddock fillets showed that volatile esters and alcohols in had- dock stored in ice coincided with the response of the CO sensor and development of fruity, sweet odors detected in the spoiled fillets (Olafsdottir, 2003). Pseudomonas spp., including P. fragi, has been associated with the sweet, fruity off odors and onion- like odors often encountered on commercially prepared fillets