The soluble gas stabilization (SGS) method involves the dissolution of CO2 into the food muscle at low temperatures with elevated pressure. As temperature abuse or fluctuations negatively influence CO2 dissolution, which affects the quality of fish muscle, thus the present work aims to investigate the impact of SGS-based hurdle technologies on the overall quality of Atlantic salmon loins in the cold chain.
The effect of SGS on the quality of vacuum-packed (VP) Atlantic salmon loins during cold storage (4 and 8℃) was studied in the first part of the thesis (experiment 1). The microbial activity on the salmon loins was examined by quantifying (i) natural microbiota and (ii) Listeria innocua as an inoculated model organism. The second part (experiment 2) of the thesis focused on the combined effect of superchilling and SGS on the quality of vacuum-packed pre-rigor salmon loins during cold chain temperature fluctuations. The salmon fillets were initially kept at a superchilled temperature (-2℃) until SGS treatment to aim for maximum absorption and dissolution of CO2 into the fish muscle. Then, the samples were subjected to vacuum packaging and stored at 0 and 4℃ for 5 days (initial storage) to mimic the temperature fluctuations during transport and then shifted to three different temperatures (0, 4, and 8℃) for long-term storage to mimic the temperature fluctuations in supermarket cabinets/consumer fridges. The growth of natural microbiota and physiochemical parameters of the above samples were systematically evaluated.
Experiment 1 revealed that despite the storage temperatures (4 and 8℃), the SGS-VP method significantly prolonged the lag phase and reduced the growth of inoculated L. innocua and natural microbiota (aerobic and H2S producers, (p < 0.05)). Similarly, L. innocua growth was substantially inhibited until 30 days in SGS-VP samples stored at 4℃. In experiment 2, even at temperature fluctuations (0 to 8℃), the superchilled SGS-VP method significantly prolonged the lag phase of the natural microbiota (aerobic, psychrotrophic, and lactic acid bacteria) of salmon loins when compared to the superchilled VP method. Overall, the SGS-vacuum packaging combined with the constant storage temperature of 0℃ accounts for reduced bacterial growth among all groups. However, the differences in the mean psychrotrophic plate counts were lower or insignificant between the superchilled SGS-VP and superchilled VP samples at different storage temperatures (0, 4, and 8℃). In both experiments (experiments 1 and 2), the SGS method significantly controlled the psychrotrophic bacterial growth at a constant storage temperature of 4℃ (p = 0.000), but not at 8℃.
Considering the physiochemical parameters, both experiments pointed out that the SGS technology could maintain the freshness of salmon muscles stored at 4℃ (p < 0.05); however, the prolonged exposure of SGS-pretreated samples at different temperature fluctuations (0℃ ↔ 4℃, 4℃ → 8℃, 0℃ → 8℃) could not maintain the freshness of salmon samples in experiment 2. The application of the SGS method did not influence biogenic amines (except cadaverine) formation, and the color parameters (measured only in experiment 2) were also unaffected, except at the constant storage temperature of 4℃.
Keywords: Soluble gas stabilization, CO2 solubility, superchilling, cold chain, high-quality salmon, temperature fluctuations, cold storage.