A novel packaging method with a dissolving CO(2) headspace combined with organic acids prolongs the shelf life of fresh salmon

The aim of this study was to evaluate a novel packaging method for fresh fish and to determine its effect on the bacterial growth in fresh salmon. Fresh salmon was packed with a small amount of 100% CO(2) (gas/product ratio 0.2/1.0 v/v) and a brine solution containing various combinations of citric acid (3% w/w, pH 5), acetic acid (1% w/w, pH 5) and cinnamaldehyde (200 microg/ml). Total bacterial counts, counts of sulphur reducing bacteria, lactic acid bacteria and Enterobacteriaceae as well as the bacterial composition in the product after storage were determined. The combination of CO(2) and organic acids completely inhibited bacterial growth during 14 days of storage at 4 degrees C both in inoculation experiments and in experiments on salmon with natural background flora. CO(2), acetic acid and citric acid alone each inhibited the growth of total bacterial counts, lactic acid bacteria, sulphur reducing bacteria and Enterobacteriaceae, but effects were enhanced in combinations. The addition of cinnamaldehyde did not influence bacterial growth. Analysis of the bacterial flora of salmon inoculated with different spoilage bacteria showed that Photobacterium phosphoreum and Carnobacterium maltaromaticum remained the dominating species after inoculation while Yersinia aldovae, Aeromonas salmonicida and Shewanella putrefaciens were outcompeted by other species. In addition, lactic acid bacteria from the natural background flora grew to high numbers. Combinations of CO(2) and acetic acid reduced the relative abundance of P. phosphoreum. All CO(2) dissolved in the product, thereby creating a product with the outer appearance of a vacuum package. Further work is needed to determine consumer acceptability of acid concentrations and to implement the packaging method for industrial purposes. However, implication of this packaging method in the industry may lead to a new packaging technology, combining the advantages of vacuum packaging (low space requirement) and modified atmosphere packaging (antimicrobial effect of CO(2)).

Evolution of Volatile Fraction and ATP Related Compounds During Storage of Desalted Cod (Gadus morhua)

The objective of this work was to study the evolution of the volatile fraction, and ATP and its breakdown products, in desalted cod thermally treated (water blanching, steam blanching and microwave heating), stored at 4 °C. All analyses were carried out at 0, 7, 14, 21, and 28 days of storage, as in the treated samples as in the control samples (desalted cod without thermal pre-treatment). The study of the volatile fraction revealed a similar behavior of the water blanched and steam blanched samples, by one hand, and of the control samples and those treated with microwave, on the other hand. This fact would imply a lower effectiveness of the microwave treatment on the preservation of the initial odor of desalted cod. The initial K1-values were lower in control and microwave samples than in water and steam blanched samples. However, the higher increase of K1-values throughout the storage in control and microwave samples would indicate a higher spoilage for these samples during the studied period. According to these results, the two blanching treatments were more effective than microwave heating in the preservation of desalted cod.

Microbial and sensory changes during refrigerated storage of desalted cod (Gadus morhua) preserved by combined methods

Water blanching and the use of additives (potassium sorbate and citric acid) combined with different types of packaging (air, vacuum "VP" and modified atmosphere packaging "MAP": 60% CO(2), 30% N(2) and 10% O(2)), were studied as new methods of preservation of chilled desalted cod. Microbial counts and total volatile basic nitrogen (TVB-N) analyses were carried out during a period of 42 days on all samples stored at 4 degrees C. No Aeromonas or sulphite-reducing Clostridium were isolated from any of the analysed samples. The lowest microbial counts of mesophilic, psychrotrophic, Pseudomonas, moulds and yeasts, were found in samples with additives in all kinds of packaging. These samples in VP or MAP maintained an excellent microbial quality throughout the 42 days of storage, with mesophilic and psychrotrophic counts always below 4 log CFU/g. Counts of the four microorganisms above-mentioned in blanched samples packaged with air, exceeded 5 log CFU/g on days 21-28, so it became necessary to use VP or MAP to maintain these microorganisms at an acceptable level for the entire storage period. TVB-N contents were low in samples with additives, regardless of the kind of packaging, as well as in blanched samples packaged in VP and MAP, never reaching 25 mg/100 g. Since there were no significant differences either in microbial growth or in TVB-N between samples in VP and MAP, a sensory analysis was performed only in desalted cod submitted to the two treatments (blanching and additives) combined with VP, both in raw and cooked samples. The results of this analysis showed that the addition of potassium sorbate and citric acid did not alter the typical organoleptic features of desalted cod. The sensory characteristics of both blanched samples and those with additives in VP showed no change during the period of the study.