Oxidative Stability of Side-Streams from Cod Filleting-Effect of Antioxidant Dipping and Low-Temperature Storage.

Currently, side-streams (e.g., head, backbone, tail, and intestines) generated in the fish processing industry often end up as low-value products for feed applications or even as waste. In order to upcycle such side-streams, they need to be preserved to avoid oxidative degradation of the lipids between the generation point and the valorization plant. In the cod filleting industry, three main solid side-streams: viscera, heads, and backbones, are obtained. Hence, this study aimed to identify the most efficient antioxidant for preserving the cod side-streams using a dipping-based strategy prior to pre-valorization storage at low temperatures (ice and frozen storage). The dipping solutions evaluated contained: (i) a lipophilic rosemary extract (0.05% and 0.2% in 0.9% NaCl), (ii) Duralox MANC (a mixture of rosemary extract, ascorbic acid, tocopherols, and citric acid; 2% in 0.9% NaCl), and (iii) NaCl (0.9%) w/w solution. One group was not dipped. No dipping and dipping in NaCl were included as controls. The results showed a positive effect of dipping with solutions containing antioxidants as measured by peroxide value (PV), TBA-reactive substances (TBARS), and sensory profiling, e.g., rancid odor. Moreover, the oxidative stability increased with decreased storage temperature. The cod side-streams were in general most efficiently preserved by Duralox MANC, followed by the lipophilic rosemary extract (0.2%), compared to no dipping and dipping in NaCl solution and the lower concentration of the lipophilic rosemary extract (0.05%). The efficiency of the antioxidant treatments was independent of the side-stream fraction and storage temperature. Thus, using antioxidant dipping combined with low temperature storage is an efficient preservation method for maintaining the quality of the lipids in cod solid side-streams during their pre-valorization storage.

Cardinal parameter growth and growth boundary model for non-proteolytic Clostridium botulinum - Effect of eight environmental factors.

A new cardinal parameter growth and growth boundary model for non-proteolytic C. botulinum was developed and validated for fresh and lightly preserved seafood and poultry products. 523 growth rates in broth were used to determine cardinal parameter values and terms for temperature, pH, NaCl/water activity, acetic, benzoic, citric, lactic and sorbic acids. The new growth and growth boundary model included the inhibiting interactive effect between these factors and it was calibrated using growth curves from 10 challenge tests with unprocessed seafood. For model evaluation, 40 challenge tests with well characterized fresh and lightly preserved seafood were performed. Comparison of these observed growth curves and growth rates (µmax-values) predicted by the new model resulted in a bias factor (Bf) of 1.12 and an accuracy factor (Af) of 1.40. Furthermore, the new model was evaluated with 94 growth rates and 432 time to toxin formation data extracted from the scientific literature for seafood, poultry, meat, pasta and prepared meals. These data included responses for 36 different toxigenic strains of non-proteolytic C. botulinum. The obtained Bf-/Af-values were 0.97/2.04 for µmax-values and 0.96/1.80 for time to toxin formation. The model correctly predicted 93.8% of the growth responses with 5.6% being fail-safe and <1% fail-dangerous. A cocktail of four non-toxin producing Clostridium spp. isolates was used to develop the new model and these isolates had more than 99.8% 16S rRNA gene similarity to non-proteolytic C. botulinum (Group II). The high number of environmental factors included in the new model makes it a flexible tool to facilitate development or reformulation of seafood and poultry products that do not support the growth of non-proteolytic C. botulinum. Further, evaluation of the new model with well characterized products is desirable particularly for meat, vegetables, pasta and prepared meals as well as for dairy products that was not included in the present study.

Superchilling in combination with modified atmosphere packaging resulted in long shelf-life and limited microbial growth in Atlantic cod (Gadus morhua L.) from capture-based-aquaculture in Greenland.

Sensory, chemical and microbial changes for Atlantic cod (Gadus morhua L.) filets from capture-based-aquaculture in Greenland were studied. The objective was to determine shelf-life and indices of spoilage for iced or superchilled fillets when stored in air, or modified atmosphere packed (MAP; 40% CO2 and 60% N2). MAP iced storage extended the sensory shelf-life from 15 days to 21 days compared to storage in air. With superchilling at -1.7 °C sensory shelf-life was above 32 days, and no formation of total volatile nitrogen (TVN) was observed irrespective of storage in air or MAP. pH of ≥7.0, TVN (≥35 mg-N/100 g) and trimethylamine (≥20 mg-N TMA/100 g) were promising indices of spoilage. Aerobic viable counts were less valuable indices of spoilage as the dominating microbiota of cod in air (Pseudomonas spp., Photobacterium spp., Shewanella spp., Acinetobacter spp.) changed to Photobacterium spp. in MAP cod. Spoilage activity determined as the yield factor for TVN formation was 6-200 folds higher for Photobacterium spp. compared to Shewanella spp. and Pseudomonas spp. Photobacterium carnosum was responsible for TVN formation in iced cod irrespective of storage in air or MAP, and it was identified at the specific spoilage organism that limited iced product shelf-life.

Modeling Growth of Listeria and Lactic Acid Bacteria in Food Environments.

Predictive food microbiology models can facilitate the assessment and management of microbial food safety. Importantly, the combined effect of storage conditions and product characteristics can be predicted by successfully validated models. This makes it easier and faster to develop or reformulation safe food recipes and predictions can be used to documents safety of available foods. The effect of various product characteristics and storage conditions must be taken into account and extensive mathematical models including the effect of these environmental factors are needed. Here the development, evaluation and application of an extensive growth and growth boundary model for Listeria monocytogenes including the effect of 12 environmental factors as well as the growth dampening effect of lactic acid bacteria is described. The Food Spoilage and Safety Predictor software is used to illustrate how predictions can be applied.

Development and validation of a stochastic model for potential growth of Listeria monocytogenes in naturally contaminated lightly preserved seafood.

A new stochastic model for the simultaneous growth of Listeria monocytogenes and lactic acid bacteria (LAB) was developed and validated on data from naturally contaminated samples of cold-smoked Greenland halibut (CSGH) and cold-smoked salmon (CSS). During industrial processing these samples were added acetic and/or lactic acids. The stochastic model was developed from an existing deterministic model including the effect of 12 environmental parameters and microbial interaction (O. Mejlholm and P. Dalgaard, Food Microbiology, submitted for publication). Observed maximum population density (MPD) values of L. monocytogenes in naturally contaminated samples of CSGH and CSS were accurately predicted by the stochastic model based on measured variability in product characteristics and storage conditions. Results comparable to those from the stochastic model were obtained, when product characteristics of the least and most preserved sample of CSGH and CSS were used as input for the existing deterministic model. For both modelling approaches, it was shown that lag time and the effect of microbial interaction needs to be included to accurately predict MPD values of L. monocytogenes. Addition of organic acids to CSGH and CSS was confirmed as a suitable mitigation strategy against the risk of growth by L. monocytogenes as both types of products were in compliance with the EU regulation on ready-to-eat foods.

Modelling and predicting the simultaneous growth of Listeria monocytogenes and psychrotolerant lactic acid bacteria in processed seafood and mayonnaise-based seafood salads.

A new combined model for Listeria monocytogenes and psychrotolerant Lactobacillus spp. was constructed and evaluated for processed seafood and mayonnaise-based seafood salads. The new model was constructed by combining existing cardinal parameter models for L. monocytogenes and Lactobacillus spp. using the classical Jameson effect to model microbial interaction. Maximum population density (MPD) values of L. monocytogenes were accurately predicted in processed seafood with a known initial cell concentration of Lactobacillus spp. For these experiments, average MPD values of 4.5 and 4.3 log (cfu/g) were observed and predicted, respectively for L. monocytogenes. In seafood salads, growth of L. monocytogenes continued at a reduced growth rate after Lactobacillus sakei had reached their MPD. This growth pattern was successfully described by an expanded version of the classical Jameson effect model, but only for products with pH of 6.0 or higher. For seafood salads with pH below 6.0 the performance of the new model was unacceptable, primarily due to prediction of no-growth by L. monocytogenes when growth was actually observed. Within its range of applicability the new model can be valuable for risk assessment and risk management of processed seafood as well as for evaluating the compliance of products with the EU regulation for ready-to-eat foods.

Development and validation of an extensive growth and growth boundary model for psychrotolerant Lactobacillus spp. in seafood and meat products.

A new and extensive growth and growth boundary model for psychrotolerant Lactobacillus spp. was developed and validated for processed and unprocessed products of seafood and meat. The new model was developed by refitting and expanding an existing cardinal parameter model for growth and the growth boundary of lactic acid bacteria (LAB) in processed seafood (O. Mejlholm and P. Dalgaard, J. Food Prot. 70. 2485-2497, 2007). Initially, to estimate values for the maximum specific growth rate at the reference temperature of 25 °C (µref) and the theoretical minimum temperature that prevents growth of psychrotolerant LAB (T(min)), the existing LAB model was refitted to data from experiments with seafood and meat products reported not to include nitrite or any of the four organic acids evaluated in the present study. Next, dimensionless terms modelling the antimicrobial effect of nitrite, and acetic, benzoic, citric and sorbic acids on growth of Lactobacillus sakei were added to the refitted model, together with minimum inhibitory concentrations determined for the five environmental parameters. The new model including the effect of 12 environmental parameters, as well as their interactive effects, was successfully validated using 229 growth rates (µ(max) values) for psychrotolerant Lactobacillus spp. in seafood and meat products. Average bias and accuracy factor values of 1.08 and 1.27, respectively, were obtained when observed and predicted µ(max) values of psychrotolerant Lactobacillus spp. were compared. Thus, on average µ(max) values were only overestimated by 8%. The performance of the new model was equally good for seafood and meat products, and the importance of including the effect of acetic, benzoic, citric and sorbic acids and to a lesser extent nitrite in order to accurately predict growth of psychrotolerant Lactobacillus spp. was clearly demonstrated. The new model can be used to predict growth of psychrotolerant Lactobacillus spp. in seafood and meat products e.g. prediction of the time to a critical cell concentration of bacteria is considered useful for establishing the shelf life. In addition, the high number of environmental parameters included in the new model makes it flexible and suitable for product development as the effect of substituting one combination of preservatives with another can be predicted. In general, the performance of the new model was unacceptable for other types of LAB including Carnobacterium spp., Leuconostoc spp. and Weissella spp.

Effect of brine marination on survival and growth of spoilage and pathogenic bacteria during processing and subsequent storage of ready-to-eat shrimp (Pandalus borealis).

The effect of brine marination at chill temperatures on survival and growth of spoilage and pathogenic bacteria during processing and subsequent storage of ready-to-eat cold water shrimp was studied. Survival and growth of Lactobacillus sakei, Listeria monocytogenes, Salmonella, Staphylococcus aureus and Vibrio parahaemolyticus were examined. The effect of brine composition and pH was determined in 12 screening experiments without addition of shrimp. Sixteen challenge tests with shrimp were then carried out to examine the effect of brine composition and storage temperature on survival and growth during processing and subsequent storage of brined and drained shrimp in modified atmosphere packaging (MAP). Different brines with (i) acetic and lactic acids (AL) or (ii) benzoic, citric and sorbic acids (BCS) were studied. V. parahaemolyticus was inactivated in brine AL without shrimp whereas concentrations of all the examined microorganisms were reduced in brine BCS. A significant effect of brine pH on inactivation was observed and inactivation during chill marination of shrimp in brine was reduced compared to the effect of brine alone. This was explained by a relatively fast increase of pH in the brine during marination of shrimp. For shrimp in brine BCS, reductions were observed for V. parahaemolyticus and Salmonella, whereas inactivation in shrimp was only noticed for Salmonella in brine AL. The observed reductions were too small to be used in practise for decontamination of shellfish. None of the examined pathogens was able to grow at 7°C in brined and drained MAP shrimp that resembled commercial products. However, reducing the concentration of acetic and lactic acids by 50% resulted in relatively fast growth of L. monocytogenes in brined and drained MAP shrimp at 7°C. Growth of S. aureus and Salmonella was observed in similar products stored at 15°C. V. parahaemolyticus was reduced in brined and drained MAP shrimp stored at both 7 and 15°C. Based on the results of the present study, L. monocytogenes was identified as the greatest potential risk with respect to the safety of brined and drained MAP shrimp. The potential of L. sakei as spoilage bacterium in brined and drained MAP shrimp was confirmed. Importantly, growth rates of L. sakei and L. monocytogenes in brined and drained MAP shrimp were predicted accurately by available mathematical models. Thus, these models can be used for product development and establishment of shell-life for ready-to-eat shrimp taking into account both quality and safety aspects.

Predicting growth rates and growth boundary of Listeria monocytogenes - An international validation study with focus on processed and ready-to-eat meat and seafood.

The performance of six predictive models for Listeria monocytogenes was evaluated using 1014 growth responses of the pathogen in meat, seafood, poultry and dairy products. The performance of the growth models was closely related to their complexity i.e. the number of environmental parameters they take into account. The most complex model included the effect of nine environmental parameters and it performed better than the other less complex models both for prediction of maximum specific growth rates (micro(max) values) and for the growth boundary of L. monocytogenes. For this model bias and accuracy factors for growth rate predictions were 1.0 and 1.5, respectively, and 89% of the growth/no-growth responses were correctly predicted. The performance of three other models, including the effect of five to seven environmental parameters, was considered acceptable with bias factors of 1.2 to 1.3. These models all included the effect of acetic acid/diacetate and lactic acid, one of the models also included the effect of CO(2) and nitrite but none of these models included the effect of smoke components. Less complex models that did not include the effect of acetic acid/diacetate and lactic acid were unable to accurately predict growth responses of L. monocytogenes in the wide range of food evaluated in the present study. When complexity of L. monocytogenes growth models matches the complexity of foods of interest, i.e. the number of hurdles to microbial growth, then predicted growth responses of the pathogen can be accurate. The successfully validated models are useful for assessment and management of L. monocytogenes in processed and ready-to-eat (RTE) foods.

Development and validation of an extensive growth and growth boundary model for Listeria monocytogenes in lightly preserved and ready-to-eat shrimp.

An existing cardinal parameter growth and growth boundary model for Listeria monocytogenes (O. Mejlholm and P. Dalgaard, J. Food Prot. 70:70-84 and 2485-2497, 2007) was expanded with terms for the effects of acetic, benzoic, citric, and sorbic acids to include a total of 12 environmental parameters and their interactive effects. The new model predicted growth rates (micro(max) values) of L. monocytogenes accurately with bias and accuracy factors of 1.0 and 1.5, respectively, for 16 batches of brined shrimp with benzoic, citric, and sorbic acids. Corresponding values of 0.9 and 1.2, respectively, were obtained for five batches of brined shrimp with acetic and lactic acids. Growth and no-growth responses of L. monocytogenes were also appropriately predicted with 88% correct prediction for 26 experiments with brined shrimp. The new model performed better than existing L. monocytogenes models with a comparable degree of complexity. The high number of environmental parameters, including six organic acids (acetic acid, benzoic acid, citric acid, diacetate, lactic acid, and sorbic acid), allows the new model to predict the effect of substituting one set of preserving parameters for another. The new model also allowed the distance between the growth boundary and specific product characteristics to be quantified by a psi value. This can be of practical importance in the development or reformulation of seafood with preserving parameters that prevent growth of L. monocytogenes and take variability in product characteristics into account.

Microbial changes and growth of Listeria monocytogenes during chilled storage of brined shrimp (Pandalus borealis).

Thirteen storage trials and ten challenge tests were carried out to examine microbial changes, spoilage and the potential growth of Listeria monocytogenes in brined shrimp (Pandalus borealis). Shrimp in brine as well as brined and drained shrimp in modified atmosphere packaging (MAP) were produced and studied. Different recipes were used to study the effect of preserving parameters (organic acids, pH and NaCl) on growth of microorganisms and shelf life at 7-8 degrees C or 12 degrees C. Particularly, brines with different concentrations of (i) benzoic, citric and sorbic acids or (ii) acetic, citric and lactic acids were studied. Furthermore, the effect of adding diacetate to brined shrimp was evaluated. A single batch of cooked and peeled shrimp was used to study both industrially and manually processed brined shrimp with respect to the effect of process hygiene on microbial changes and the shelf life of products. Concentrations of microorganisms on newly produced brined shrimp from an industrial scale processing line were 1.0-2.3 log (CFU g(-1)) higher than comparable concentrations in manually processed samples. This resulted in a substantially shorter shelf life and a more diverse spoilage microflora of the industrially processed brined shrimp. In addition, shelf life of brined shrimp was affected by the types and concentrations of organic acids and by the storage temperature as expected. The effect of MAP was less pronounced. Eighty-two isolates from the spoilage microflora of brined shrimp were identified and they included 53 lactic acid bacteria, 6 coagulase negative Staphylococcus spp., 18 Pseudomonas fluorescens and 5 yeast isolates. After storage at 7 degrees C, P. fluorescens, Enterococcus-like isolates, E. malodoratus, Carnobacterium maltaromaticum, coagulase negative Staphylococcus spp. and Lactobacillus sakei constituted the dominating microflora of shrimp in brines that contained benzoic, citric and sorbic acids as preservatives. L. sakei dominated the spoilage microflora of brined and drained MAP shrimp, and of brined shrimp preserved using acetic, citric and lactic acids, irrespective of packaging conditions. Shrimp in brine with benzoic, citric and sorbic acids prevented growth of L. monocytogenes during more than 40 days at 7 degrees C when the preserving parameters resembled those of commercial products. However, small changes in the preserving parameters and, particularly, reduced concentrations of benzoic acid led to growth of L. monocytogenes in brined shrimp. The present study provides significant new information on microbial changes, shelf life and growth of L. monocytogenes in brined shrimp. This information can facilitate development of new and safe brined shrimp products.

Modeling and predicting the growth of lactic acid bacteria in lightly preserved seafood and their inhibiting effect on Listeria monocytogenes.

A cardinal parameter model was developed to predict the effect of diacetate, lactate, CO2, smoke components (phenol), pH, NaCl, temperature, and the interactions between all parameters on the growth of lactic acid bacteria (LAB) in lightly preserved seafood. A product-oriented approach based on careful chemical characterization and growth of bacteria in ready-to-eat seafoods was used to develop this new LAB growth model. Initially, cardinal parameter values for the inhibiting effect of diacetate, lactate, CO2, pH, and NaCl-water activity were determined experimentally for a mixture of LAB isolates or were obtained from the literature. Next, these values and a cardinal parameter model were used to model the effect of temperature (T(min)) and smoke components (P(max)). The cardinal parameter model was fitted to data for growth of LAB (mu(max) values) in lightly preserved seafood including cold-smoked and marinated products with different concentrations of naturally occurring and added organic acids. Separate product validation studies of the LAB model resulted in average bias and accuracy factor values of 1.2 and 1.5, respectively, for growth of LAB (mu(max) values) in lightly preserved seafood. Interaction between LAB and Listeria monocytogenes was predicted by combining the developed LAB model and an existing growth and growth boundary model for the pathogen (O. Mejlholm and P. Dalgaard, J. Food Prot. 70:70-84). The performance of the existing L. monocytogenes model was improved by taking into account the effect of microbial interaction with LAB. The observed and predicted maximum population densities of L. monocytogenes in inoculated lightly preserved seafoods were 4.7 and 4.1 log CFU g(-1), respectively, whereas for naturally contaminated vacuum-packed cold-smoked salmon the corresponding values were 0.7 and 0.6 log CFU g(-1) when a relative lag time of 4.5 was used for the pathogen.

Modeling and predicting the growth boundary of Listeria monocytogenes in lightly preserved seafood.

The antimicrobial effect of diacetate and lactate against Listeria monocytogenes was evaluated in challenge tests with vacuum-packaged or modified atmosphere packaged (MAP) cold-smoked salmon, marinated salmon, cold-smoked Greenland halibut, marinated Greenland halibut, and gravad salmon. MAP cold-smoked salmon with the addition of 0.15% (wt/wt) diacetate prevented the growth of L. monocytogenes for more than 40 days at 8 degrees C, whereas the addition of 0.15% (wt/wt) diacetate reduced the growth rate of the pathogen in MAP cold-smoked Greenland halibut. This difference between the two types of products was explained by a higher content of naturally occurring lactate in cold-smoked salmon (0.77 to 0.98%, wt/wt) than in cold-smoked Greenland halibut (0.10 to 0.15%, wt/wt). In fact, the addition of 0.15% (wt/wt) diacetate and 0.75% (wt/wt) lactate to MAP cold-smoked Greenland halibut prevented the growth of L. monocytogenes for more than 45 days at 8 degrees C. A mathematical model that included the effect of diacetate, lactate, CO2, smoke components, nitrite, pH, NaCl, temperature, and interactions between all these parameters was developed to predict the growth boundary of L. monocytogenes in lightly preserved seafood. The developed growth boundary model accurately predicted growth and no-growth responses in 68 of 71 examined experiments from the present study as well as from literature data. Growth was predicted for three batches of naturally contaminated cold-smoked salmon when a no-growth response was actually observed, indicating that the model is fail-safe. The developed model predicts both the growth boundary and growth rate of L. monocytogenes and seems useful for the risk management of lightly preserved seafood. Particularly, the model facilitates the identification of product characteristics required to prevent the growth of L. monocytogenes, thereby making it possible to identify critical control points, and is useful for compliance with the new European Union regulation on ready-to-eat foods (EC 2073/2005).