Predictive model for the growth of spoilage bacteria on modified atmosphere packaged Atlantic salmon produced in Australia

Strain-specific Growth Parameters are Important to Accurately Model Bacterial Growth on Baby Spinach in Simulation Models

Digital tools to predict produce shelf life have the potential to reduce food waste and improve consumer satisfaction. To address this need, we (i) performed an observational study on the microbial quality of baby spinach, (ii) completed growth experiments of bacteria that are representative of the baby spinach microbiota, and (iii) developed an initial simulation model of bacterial growth on baby spinach. Our observational data showed that the predominant genera found on baby spinach were Pseudomonas, Pantoea and Exiguobacterium. Rifampicin-resistant mutants (rifR mutants) of representative bacterial subtypes were subsequently generated to obtain strain-specific growth parameters on baby spinach. These experiments showed that: (i) it is difficult to select rifR mutants that do not have fitness costs affecting growth (9 of 15 rifR mutants showed substantial differences in growth, compared to their corresponding wild-type strain) and (ii) based on estimates from primary growth models, the mean (geometric) maximum population of rifR mutants on baby spinach (7.6 log10 CFU/g, at 6°C) appears lower than that of the spinach microbiota (9.6 log10 CFU/g, at 6°C), even if rifR mutants did not have substantial growth-related fitness costs. Thus, a simulation model, parameterized with the data obtained here as well as literature data on home refrigeration temperatures, underestimated bacterial growth on baby spinach. The root mean square error of the simulation's output, compared against data from the observational study, was 1.11 log10 CFU/g. Sensitivity analysis was used to identify key parameters (e.g., strain maximum population) that impact the simulation model's output, allowing for prioritization of future data collection to improve the simulation model. Overall, this study provides a roadmap for the development of models to predict bacterial growth on leafy vegetables with strain-specific parameters and suggests that additional data are required to improve these models.

Effect of modified atmosphere packaging with different gas mixtures on the texture and muscle proteins of Pacific white shrimp (Litopenaeus vannamei) during cold storage

In this study, the effect of modified atmosphere packaging with different gas mixtures on texture and muscle properties of Pacific white shrimp (Litopenaeus vannamei) during refrigerated storage was studied via texture profile, water holding capacity (WHC), protein properties (Ca2+-ATPase, TCA-soluble peptides, myofibrillar/sarcoplasmic protein content), and microbial counts. The results showed that the antibacterial effect of Modified atmosphere packaging (MAP) was correlated with the increase of CO2 with the presence of low level of O2. Though MAP without O2 had a higher whiteness value but also had higher bacterial counts and total volatile basic nitrogen (TVB-N) values compared with other MAP-groups. In general, a gas composition of 80% CO2 + 5%O2 + 15% N2 treatment had lowest microbial counts and reduced TVB-N values by 22.85% in comparison with the control on day 10. However, MAP was found to have a complicated impact on muscle protein and texture of shrimp. 60% CO2 + 5% O2 + 35% N2 and 40% CO2 + 5% O2 + 55% N2 had an advantage in maintaining springiness and the content of myofibrillar/sarcoplasmic proteins. The correlation analysis showed that WHC had stronger relationship with springiness, resilience, myofibrillar protein content. Therefore, regarding the texture and protein properties, the concentration of CO2 in MAP for Pacific white shrimp should not be higher than 60%.

Effects of Modified Atmosphere Packaging with Varied CO2 and O2 Concentrations on the Texture, Protein, and Odor Characteristics of Salmon during Cold Storage

The effect of gas ratio on the growth of bacteria has been well demonstrated, but some adverse effects of modified atmosphere packaging (MAP) on seafoods have also been found. To provide a better understanding of the effects of CO₂ and O₂ concentrations (CO₂ from 40% to 100% and O₂ from 0% to 30%) in MAP on the texture and protein contents and odor characteristics of salmon during cold storage, the physiochemical, microbial, and odor indicators were compared with those without treatment (CK). Generally, MAP treatments hindered the increase of microbial counts, total volatile basic nitrogen, and TCA-soluble peptides, and decreased the water-holding capacity, hardness, springiness, and sarcoplasmic and myofibrillar protein contents. The results also indicated that 60%CO₂/10%O₂/30%N₂ was optimal and decreased the total mesophilic bacterial counts by 2.8 log cfu/g in comparison with CK on day 12. In agreement, the concentration of CO₂ of 60% showed the lowest myofibrillar protein degradation, and less subsequent loss of hardness. The electronic nose characteristics analysis indicated that 60%CO₂/20%O₂/20%N₂ and 60%CO₂/10%O₂/30%N₂ had the best effect to maintain the original odor profiles of salmon. The correlation analysis demonstrated that microbial growth had a strong relationship with myofibrillar and sarcoplasmic protein content. It can be concluded that 60%CO₂/10%O₂/30%N₂ displayed the best effect to achieve the goal of preventing protein degradation and odor changes in salmon fillets.

Spoilage evaluation of raw Atlantic salmon (Salmo salar) stored under modified atmospheres by multivariate statistics and augmented ordinal regression

The development of quality monitoring systems for perishable food products like seafood requires extensive data collection under specified packaging and storage conditions, followed by advanced data analysis and interpretation. Even though the benefits of using volatile organic compounds as food quality indices have been recognized, few studies have focused on real-time quantification of the seafood volatilome and subsequent systematic identification of the most important spoilage indicators. In this study, spoilage of Atlantic salmon (Salmo salar) stored under modified atmospheres (% CO₂/O₂/N₂) and air was characterized by performing multivariate statistical analysis and augmented ordinal regression modelling for data collected by microbiological, chemical and sensory analyses. Out of 25 compounds quantified by selected-ion flow-tube mass spectrometry, ethanol, dimethyl sulfide and hydrogen sulfide were found characteristic under anaerobic conditions (0/0/100 and 60/0/40), whereas spoilage under air was primarily associated with the production of alcohols and ketones. Under high-O₂ MAP (60/40/0), only 3-methylbutanal fulfilled the identification criteria. Overall, this manuscript presents a systematic and widely applicable methodology for the identification of most potential seafood spoilage indicators within the context of intelligent packaging technology development. In particular, parallel application of statistics and modelling was found highly beneficial for the performance of the quality characterization process and for the practical applicability of the obtained results in food quality monitoring.

From Culture-Medium-Based Models to Applications to Food: Predicting the Growth of B. cereus in Reconstituted Infant Formulae

Predictive models of the growth of foodborne organisms are commonly based on data generated in laboratory medium. It is a crucial question how to apply the predictions to realistic food scenarios. A simple approach is to assume that the bias factor, i.e., the ratio between the maximum specific growth rate in culture medium and the food in question is constant in the region of interest of the studied environmental variables. In this study, we investigate the validity of this assumption using two well-known link functions, the square-root and the natural logarithm, both having advantageous properties when modeling the variation of the maximum specific growth rate with temperature. The main difference between the two approaches appears in terms of the respective residuals as the temperature decreases to its minimum. The model organism was Bacillus cereus. Three strains (B594, B596, and F4810/72) were grown in Reconstituted Infant Formulae, while one of them (F4810/72) was grown also in culture medium to calculate the bias factor. Their growth parameters were estimated using viable count measurements at temperatures ranging from 12 to 25°C. We utilized the fact that, if the bias factor is independent of the temperature, then the minimum growth temperature parameter of the square-root model of Ratkowsky et al. (1982) is the same for culture medium and food. We concluded, supported also by mathematical analysis, that the Ratkowsky model works well but its rearrangement for the natural logarithm of the specific growth rate is more appropriate for practical regression. On the other hand, when analyzing mixed culture data, available in the ComBase database, we observed a trend different from the one generated by pure cultures. This suggests that the identity of the strains dominating the growth of mixed cultures depends on the temperature. Such analysis can increase the accuracy of predictive models, based on culture medium, to food scenarios, bringing significant saving for the food industry.

Modified Atmosphere Systems and Shelf Life Extension of Fish and Fishery Products

This review aims at summarizing the findings of studies published over the past 15 years on the application of modified atmosphere (MA) systems for shelf life extension of fish and fishery products. This review highlights the importance of CO₂ in the preservation of seafood products, and underscores the benefits of combining MA technology with product storage in the superchilled temperature range. It is generally accepted that MA technology cannot improve product quality and should not be utilized as a substitute for good sanitation and strict temperature control. Benefits derived from application of MA, however, can significantly impact preservation of product quality and it subsequent shelf-life. For this reason, this review is the first of its kind to propose detailed handling and quality guidelines for fresh fish to realize the maximum benefit of MA technology.