Importance of autolysis and microbiological activity on quality of cold-smoked salmon

The relative importance of autolysis and microbiological activity on spoilage of cold-smoked salmon and the origin of the chemical compounds hypoxanthine, acetic acid, trimethylamine and total volatile bases were studied in a storage experiment of dry salted and injection-brined, vacuum-packed salmon with normal and reduced loads of microorganisms. Comparative studies of cold-smoked salmon with a reduced and normal load of microorganisms showed that microbiological activity caused production of the characteristic spoilage odours and flavours, while the autolytic enzymes from the fish tissue had major impact on the textural deterioration. Total volatile bases and hypoxanthine were produced in significantly higher levels in salmon with a normal bacterial load. Sixty-eight per cent of the hypoxanthine found in stored samples originated from microbiological conversion of inosine to hypoxanthine. The concentration of acetic acid only increased in samples with a normal load. At the onset of spoilage, the microflora in dry salted salmon was dominated by marine vibrio in contrast to the injection brined product where a mixture of Enterobacteriaceae and lactic acid bacteria were prevalent. The different ratios of hypoxanthine produced to trimethylamine also suggested that spoilage of salmon salted by the two methods was caused by different microorganisms.