Spoilage of King Salmon (Oncorhynchus tshawytscha) Fillets Stored Under Different Atmospheres

Effect of Vacuum and Modified Atmosphere Packaging on the Shelf Life and Quality of Gutted Rainbow Trout (Oncorhynchus mykiss) during Refrigerated Storage

The quality changes of gutted rainbow trout in vacuum packaging (VP) and modified atmosphere packaging (MAP) with 40% CO2 + 60% N2 (MAP1), 60% CO2 + 40% N2 (MAP2), and 90% CO2 + 10% N2 (MAP3) were evaluated. The samples were stored at 3 ± 0.5 °C, and on days 1, 4, 7, 10, 13, and 16 of storage, microbiological, chemical, and sensory testing was performed. The aerobic plate count (APC) and psychrotrophic bacteria count (PBC) in VP fish exceeded the conventional limit of 7 log cfu/g on day 10, and in MAP1 and MAP2 fish on day 16, whereas in MAP3 fish, their number remained below that limit during the experiment. MAP significantly slowed down the growth of Enterobacteriaceae in trout, and the degree of inhibition increased with increasing CO2 concentration in the gas mixture. The lowest lactic acid bacteria numbers were detected in VP fish, whereas the highest numbers were determined in trout packaged in MAP2 and MAP3. Significantly lower numbers of hydrogen sulfide-producing (H2S) bacteria were detected in fish packed in MAP. Distinct patterns were observed for pH among treatments. The lowest increase in TBARS values was detected in VP and MAP3 fish, whereas in MAP1 and MAP2 fish, the TBARS values were higher than 1 mg MDA/kg on day 16 of storage when a rancid odor was detected. MAP inhibited the increase in total volatile basic nitrogen (TVB-N) content of trout compared to trout packaged in a vacuum. The sensory attributes of trout perceived by the sensory panel changed significantly in all experimental groups during storage. Based primarily on sensory, but also microbial, and chemical parameters, MAP has great potential for preserving fish quality and extending the shelf life of gutted rainbow trout from 7 days in VP to 13 days in MAP1 and MAP2, and to 16 days in MAP3.

Combined Treatments of High Hydrostatic Pressure and CO2 in Coho Salmon (Oncorhynchus kisutch): Effects on Enzyme Inactivation, Physicochemical Properties, and Microbial Shelf Life

This study focused on applying different high hydrostatic pressure + carbon dioxide (HHP + CO2) processing conditions on refrigerated (4 °C, 25 days) farmed coho salmon (Oncorhynchus kisutch) to inactivate endogenous enzymes (protease, lipase, collagenase), physicochemical properties (texture, color, lipid oxidation), and microbial shelf life. Salmon fillets were subjected to combined HHP (150 MPa/5 min) and CO2 (50%, 70%, 100%). Protease and lipase inactivation was achieved with combined HHP + CO2 treatments in which lipase activity remained low as opposed to protease activity during storage. Collagenase activity decreased approximately 90% during storage when applying HHP + CO2. Combined treatments limited the increase in spoilage indicators, such as total volatile amines and trimethylamine. The 150 MPa + 100% CO2 treatment was the most effective at maintaining hardness after 10 days of storage. Combined treatments limited HHP-induced color change and reduced the extent of changes caused by storage compared with the untreated sample. Microbial shelf life was extended by the CO2 content and not by the HHP treatments; this result was related to an increased lag phase and decreased growth rate. It can be concluded that combining HHP and CO2 could be an effective method of inactivating endogenous enzymes and extend salmon shelf life.

Development of Models To Relate Microbiological and Headspace Volatile Parameters in Stored Atlantic Salmon to Acceptance and Willingness To Prepare the Product by Senior Consumers

Microbial spoilage of salmon occurs during extended refrigerated storage and is often accompanied by unpleasant aromas. When spoilage is detected, it is assumed that consumers will reject the product for consumption. Because sensory panels of trained individuals or consumers are expensive and labor intensive, identification of microbiological or chemical indicators to characterize the extent to which fish has spoiled is needed when experimental process and storage treatments are being evaluated. A consumer panel of 53 senior citizens (60 to 85 years of age) evaluated in duplicate raw salmon subjected to 10 storage conditions, and the fish quality was targeted to range from fresh to very spoiled. This population group was chosen because they would be expected to have a greater prevalence of olfactory impairments and higher odor thresholds than the general population; in turn, a shorter safety margin or time period between product rejection due to spoilage and the generation of Clostridium botulinum toxins would be likely. Low hedonic scores for aroma and overall acceptance (2 or 3 of 9), corresponding to "dislike very much" to "dislike moderately," did not equate with unwillingness to prepare the sample for consumption by up to seven panelists (13%) when the product was presumed to have already been purchased. Despite these outliers, significant models (P = 0.0000) were developed for the willingness of consumers to prepare the sample for consumption and the sample's aerobic and anaerobic microbiological populations and two volatile peaks with Kovats indices of 640 and 753. However, these models revealed that the levels of microbiological and chemical markers must be very high before some consumers would reject the sample; hence, spoilage detection by smell would likely not be an adequate safeguard against consuming salmon in which C. botulinum toxin had been generated.

Enhancement of Modified Atmosphere Packaged Farmed Atlantic Halibut (Hippoglossus Hippoglossus) Fillet Quality by Soluble Gas Stabilization

The suitability of soluble gas stabilization (SGS) to dissolve CO2 into Atlantic halibut ( Hippoglossus hippoglossus) fillets prior to modified atmosphere packaging (MAP) were investigated. Two levels of CO2 partial pressures (200 and 400 kPa) and two levels of time (1 and 2h) with SGS treatment was used in a factorial design, and compared to conventional MAP. Headspace gas volume (mL), headspace gas composition (%), drip loss (%), pH, microbiological characteristics, off-odor and color were assessed on the packaged fillets. Increased partial pressure and increased SGS treatment time before MAP significantly ( p<0.001) increased the CO2 content in the packaged fillets and counteracted package collapse. No interaction between the time and partial pressure was found. SGS treatment significantly ( p = 0.038) reduced aerobic plate count (APC) and psychrotrophic count (PC). APC and PC increased significantly the tree first sampling days during storage (7, 15, and 21) and stabilized from day 21 to day 28. H2S producing bacteria and Brochothrix thermosphacta was not affected by the SGS treatment. H2S producing bacteria decreased significantly from day 7 to day 15. SGS treatment decreased the drip loss significantly ( p = 0.006). Color and pH were not affected by the SGS treatment. No difference in the off odor was found between the treatments. Based on off odor analysis, the shelf life of the halibut fillet in this trial exceeded 28 days.

Could modifications of processing parameters enhance the growth and selection of lactic acid bacteria in cold-smoked salmon to improve preservation by natural means?

Several smoking conditions were examined with the objective of enhancing the numbers of lactic acid bacteria (LAB) by natural means in vacuum-packaged cold-smoked salmon during 21 days of storage at 5 degrees C. Three combinations of salting, drying, and smoking were used: (i) dry salting x time of salting (2 or 6 h); (ii) wet salting (6 h) x dry salting (6 h) x with or without sugar; and (iii) wet salting (6 h) x dry salting (6 h) x different times of smoking (2 or 6 h of drying and 2 or 6 h of smoking). Two batches were processed for each set of conditions. Determinations of pH and salt content in the water phase were carried out for products in each treatment. Microbiological analyses (total viable count, total LAB, Lactobacillus spp., and Enterobacteriaceae) also were conducted at the beginning of storage (t0) and after 21 days of refrigerated storage (tl). There were differential increases in total LAB and lactobacilli during the storage period according to the treatment performed. The most effective treatment to enhance LAB growth was 6 h of dry salting with sugar, 6 h of drying, and 2 h of smoking. These salting-drying-smoking conditions also selected the LAB as the dominant flora at the end of the storage period. The LAB promoted by these processing parameters seem to be potentially useful protective cultures because of their anti-Listeria activity. From the results of this research, we conclude that it is possible to enhance the growth of LAB in general and that of inhibitory strains in particular by suitable choices of processing parameters.

Analysis of volatile compounds as spoilage indicators in fresh king salmon (Oncorhynchus tshawytscha) during storage using SPME-GC-MS

A method was developed for the analysis of salmon volatiles using solid-phase microextraction and gas chromatography-mass spectrometry. This method was used to monitor the volatiles of fresh king salmon (Oncorhynchus tshawytscha) stored in ambient air or in a 40:60 (v/v) mixture of CO2:N2 over time. The levels of several of the volatile compounds were found to change during storage, with some showing a clear difference between storage in air and storage in CO2:N2. Of these, several alcohols (cyclopentanol, Z-2-penten-1-ol, 1-penten-3-ol, and 1-octen-3-ol) and aldehydes (hexanal, octanal, E-2-pentenal, and E-2-hexenal) were identified as potential markers for salmon freshness. Several other volatiles (acetoin, ethyl benzene, propyl benzene, styrene, 3-methyl butanoic acid, and acetic acid) were identified as potential markers for salmon spoilage. A comparison of salmon harvested with and without the "rested harvesting" technique showed that E- and Z-isoeugenol levels were increased by the use of the isoeugenol based anesthetic. The use of the anesthetic did not affect the levels of any of the other compounds identified.