The effect of high hydrostatic pressure,sodium nitrite and salt concentration on the growth of Listeria monocytogenes on RTE ham and turkey

Growth of Listeria monocytogenes was evaluated for up to 182 days after inoculation on ready-to-eat (RTE) sliced ham and turkey breast formulated with sodium nitrite (0 or 200 ppm), sodium chloride (1.8% or 2.4%), and treated (no treatment or 600 MPa) with high hydrostatic pressure (HHP). HHP at 600 MPa for 3 min resulted in a 3.85–4.35 log CFU/g reduction in L. monocytogenes. With formulations at similar proximate analyses, one of the evaluation days (day 21) without HHP showed significantly greater growth of L. monocytogenes in ham than in turkey breast, but there were no significant differences on other evaluation days or with HHP. There were no differences in growth of L. monocytogenes due to sodium chloride level. Sodium nitrite provided a small, but significant inhibition of L. monocytogenes without HHP, but addition of sodium nitrite did not significantly affect growth of L. monocytogenes with use of HHP.     

The effect of pH and nitrite concentration on the antimicrobial impact of celery juice concentrate compared with conventional sodium nitrite on Listeria monocytogenes

The objectives of this study were to evaluate the impact of pH and nitrite from celery juice concentrate (CJ) on the growth of Listeria monocytogenes in broth and on ham slices, and to evaluate the impact of pH and nitrite from CJ on quality attributes of the ham. The pH of both broth and ham were increased by the addition of CJ. The CJ was less effective than conventional nitrite at 100 mg/kg nitrite in broth, but in ham, the CJ treatments at both 100 and 200 mg/kg resulted in growth of L. monocytogenes (p > 0.05) similar to that of the conventional nitrite at the same concentrations. Reducing the pH of CJ before addition to the ham had greater impact on L. monocytogenes growth at 200 mg/kg nitrite than at 100 mg/kg. Celery juice concentrate may increase meat product pH which could have implications for the antimicrobial impact of nitrite in some products.     

High hydrostatic pressure processing of sliced fermented sausages: A quantitative exposure assessment for Listeria monocytogenes

Fermented sausages have traditionally been considered to be safe products from a microbiological point of view, mainly due to nitrite addition, their low a_w and reduced pH. However, post-process contamination during slicing and packaging operations may increase microbial concentration and prevalence on final products. A stochastic simulation modelling approach was conducted to determine the extent of Listeria monocytogenes survival on sliced chorizo submitted or not to high hydrostatic pressure (HHP) treatments after post-process contamination (i.e., cross-contamination during slicing). A probabilistic model comprising nine steps from mixing of raw materials to consumption was constructed. The effects of various initial levels of L. monocytogenes in the meat batter (−1.43–3 log cfu/g), HHP treatments (400–600 MPa/18 °C for 0–12 min) and nitrite concentrations (0–150 ppm) on L. monocytogenes distribution were assessed by means of the application of predictive models, literature information and data obtained experimentally. Once implemented, the probabilistic model was simulated by using Monte Carlo analysis. The probability distribution of L. monocytogenes contamination levels was determined for various scenarios. Model outputs showed that cross-contamination during slicing was an important source contributing to increase pathogen prevalence and concentration on final products, with transferred levels equal to 0.59 ± 0.48 log cfu/g. Under all simulated scenarios, formulation and storage conditions, the level of L. monocytogenes on sliced vacuum-packed chorizo at the consumption phase was estimated to be lower than 100 cfu/g and pressure treatments at 600 MPa for 10–12 min would result in non-contaminated packs. Overall, the probabilistic model developed in this study from raw material reception up to the end of the shelf-life (i.e., 90 days) of sliced fermented sausages is proposed as a suitable tool to determine combinations of HHP treatments and nitrite concentrations ensuring the compliance with microbiological criteria.     

The effect of NaCl-free processing and high pressure on the fate of Listeria monocytogenes and Salmonella on sliced smoked dry-cured ham

NaCl is an important multifunctional ingredient applied in dry-cured ham elaboration. However, its excessive intake has been linked to serious cardiovascular diseases causing a recent increase in the development of reduced salt products. In the present study Listeria monocytogenes and Salmonella, food-borne pathogens which can cross-contaminate post processed products, were spiked with < 100 CFU/g on slices of both standard (S) and NaCl-free processed (F) (elaborated with KCl + potassium lactate instead of NaCl) smoked dry-cured ham. Although L. monocytogenes and Salmonella counts decreased faster in S ham, pathogens were present in both types of non-pressure treated ham during the entire refrigerated storage period (112 days). Pressurisation at 600 MPa for 5 min caused the elimination of both pathogens in S ham after 14 days. In contrast, Salmonella and L. monocytogenes were present in F ham until days 28 and 56, respectively, indicating that the NaCl-free processed dry-cured ham had lower stability than standard smoked dry-cured ham.     

Application of an active alginate coating to control the growth of Listeria monocytogenes on poached and deli turkey products

The relatively high prevalence of Listeria monocytogenes in ready-to-eat (RTE) turkey products is of great concern. The overall objective of this study was to develop antimicrobial edible coating formulations to effectively control the growth of this pathogen. The antimicrobials studied were nisin (500 IU/g), Novagard CB 1 (0.25%), Guardian NR100 (500 ppm), sodium lactate (SL, 2.4%), sodium diacetate (SD, 0.25%), and potassium sorbate (PS, 0.3%). These were incorporated alone or in binary combinations into five edible coatings: alginate, κ-carrageenan, pectin, xanthan gum, and starch. The coatings were applied onto the surface of home-style poached and processed deli turkey discs inoculated with ~ 3 log CFU/g of L. monocytogenes. The turkey samples were then stored at 22 °C for 7 days. For poached and processed deli turkey, the coatings were found to be equally effective, with pectin being slightly less effective than the others. The most effective poached turkey treatments seemed to be SL (2.4%)/SD (0.25%) and Nisin (500 IU/g)/SL (2.4%), which yielded final populations of 3.0 and 4.9 log CFU/g respectively compared to the control which was 7.9 log CFU/g. For processed deli turkey, the most effective antimicrobial treatments seemed to be Nisin (500 IU/g)/SD (0.25%) and Nisin (500 IU/g)/SL (2.4%) with final populations of 1.5 and 1.7 log CFU/g respectively compared to the control which was 6.5 log CFU/g. In the second phase of the study, home-style poached and store-purchased roasted (deli) turkey inoculated with the pathogen at a level of ~ 3 log CFU/g were coated with alginate incorporating selected antimicrobial combinations and stored for 8 weeks at 4 °C. Alginate coatings supplemented with SL (2.4%)/PS (0.3%) delayed the growth of L. monocytogenes with final counts reaching 4.3 log CFU/g (home-style poached turkey) and 6.5 log CFU/g (roasted deli turkey) respectively while the counts in their untreated counterparts were significantly higher (P < 0.05) reaching 9.9 and 7.9 log CFU/g, respectively. This study therefore demonstrates the effectiveness of using alginate-based antimicrobial coatings to enhance the microbiological safety and quality of RTE poultry products during chilled storage.     

Effect of meat ingredients (sodium nitrite and erythorbate) and processing (vacuum storage and packaging atmosphere) on germination and outgrowth of Clostridium perfringens spores in ham during abusive cooling

The effect of nitrite and erythorbate on Clostridium perfringens spore germination and outgrowth in ham during abusive cooling (15 h) was evaluated. Ham was formulated with ground pork, NaNO₂ (0, 50, 100, 150 or 200 ppm) and sodium erythorbate (0 or 547 ppm). Ten grams of meat (stored at 5 °C for 3 or 24 h after preparation) were transferred to a vacuum bag and inoculated with a three-strain C. perfringens spore cocktail to obtain an inoculum of ca. 2.5 log spores/g. The bags were vacuum-sealed, and the meat was heat treated (75 °C, 20 min) and cooled within 15 h from 54.4 to 7.2 °C. Residual nitrite was determined before and after heat treatment using ion chromatography with colorimetric detection. Cooling of ham (control) stored for 3 and 24 h, resulted in C. perfringens population increases of 1.46 and 4.20 log CFU/g, respectively. For samples that contained low NaNO₂ concentrations and were stored for 3 h, C. perfringens populations of 5.22 and 2.83 log CFU/g were observed with or without sodium erythorbate, respectively. Residual nitrite was stable (p > 0.05) for both storage times. Meat processing ingredients (sodium nitrite and sodium erythorbate) and their concentrations, and storage time subsequent to preparation of meat (oxygen content) affect C. perfringens spore germination and outgrowth during abusive cooling of ham.     

Modeling the growth of lactic acid bacteria in sliced ham processed by high hydrostatic pressure

The main responsible for the spoilage of cooked cured meat products stored under refrigerated and anaerobic conditions are lactic acid bacteria. The application of high hydrostatic pressure (HHP) reduces the lactic acid bacterial growth extending the product shelf-life and preserving natural taste, texture, color and vitamin content. This work studied the influence of pressure level and holding time on the lactic acid bacterial growth in vacuum-packaged sliced ham. Modified Gompertz and Logistic models were used to fit experimental data obtained from post-treatment microbial counts carried out along the product storage. Samples of sliced vacuum-packaged ham treated by HHP and control samples (non-treated) were stored at 8 °C until the microorganism population reached 10⁷ CFU/g. An experimental planning 2² with triplicate at the central point was designed to determine the influence of pressure level (200, 300, and 400 MPa) and holding time (5, 10, and 15 min) on the product shelf-life. The results have shown that the pressure intensity and the holding time significantly influenced microbial population over the product storage. Shelf-life of ham treated at 400 MPa for 15 min was extended from 19 (control samples) to 85 days.     

Effects of natural antimicrobials on inhibition of Listeria monocytogenes and on chemical, physical and sensory attributes of naturally-cured frankfurters

Due to regulations for natural and organic processed meats, sodium nitrite and many antimicrobials cannot be used. Therefore, natural and organic processed meats are more susceptible to pathogenic bacterial growth, and natural alternatives to chemical preservatives are needed. Inhibition of Listeria monocytogenes, and quality characteristics of frankfurters manufactured with 3% cranberry powder, or with 1% or 2% cranberry powder each with either cherry powder (0.6%), lime powder (60 mg/kg), or a blend of cherry, lime and vinegar (1.4%) were investigated. Cranberry powder at 3% significantly reduced L. monocytogenes growth by 5.3 log CFU/g compared to the uncured co006Etrol (P < 0.05). However, cranberry addition over 1% also resulted in significant product pH decline and negatively impacted the color, texture and sensory attributes of the frankfurters.     

Effect of lactoferrin and its derivatives against gram-positive bacteria in vitro and, combined with high pressure, in chicken breast fillets

The bactericidal activity of lactoferrin (LF), amidated lactoferrin (AMILF), pepsin digested lactoferrin (PDLF), and its activated (ALF) commercial form, against six strains of three gram-positive bacterial species was investigated. Listeria monocytogenes was most sensitive in vitro, Staphylococcus aureus showed a moderate resistance, and Enterococus faecalis was highly resistant to antimicrobials. When chicken breast fillets were inoculated with L. monocytogenes CECT5725 and treated with antimicrobials, reductions were below 0.5 log CFU/ml in all cases. In combination with high pressure (HHP) treatment at 400 MPa for 10 min, antimicrobials showed a slight additional bactericidal effect, always below 1 log CFU/g. Incorporation of antimicrobials 18 h before or 1 h after HHP treatment generally yielded better results than incorporation 1 h before HHP treatment, although reductions remained below 1.5 log CFU/g in all cases. LF and its derivatives showed a limited potential for pathogen control in meat.     

Bactericidal activity of lauric arginate in milk and Queso Fresco cheese against Listeria monocytogenes cold growth

Lauric arginate (LAE) at concentrations of 200 ppm and 800 ppm was evaluated for its effectiveness in reducing cold growth of Listeria monocytogenes in whole milk, skim milk, and Queso Fresco cheese (QFC) at 4°C for 15 to 28 d. Use of 200 ppm of LAE reduced 4 log cfu/mL of L. monocytogenes to a nondetectable level within 30 min at 4°C in tryptic soy broth. In contrast, when 4 log cfu/mL of L. monocytogenes was inoculated in whole milk or skim milk, the reduction of L. monocytogenes was approximately 1 log cfu/mL after 24 h with 200 ppm of LAE. When 800 ppm of LAE was added to whole or skim milk, the initial 4 log cfu/mL of L. monocytogenes was nondetectable following 24 h, and no growth of L. monocytogenes was observed for 15 d at 4°C. With surface treatment of 200 or 800 ppm of LAE on vacuum-packaged QFC, the reductions of L. monocytogenes within 24 h at 4°C were 1.2 and 3.0 log cfu/g, respectively. In addition, the overall growth of L. monocytogenes in QFC was decreased by 0.3 to 2.6 and by 2.3 to 5.0 log cfu/g with 200 and 800 ppm of LAE, respectively, compared with untreated controls over 28 d at 4°C. Sensory tests revealed that consumers could not determine a difference between QFC samples that were treated with 0 and 200 ppm of LAE, the FDA-approved level of LAE use in foods. In addition, no differences existed between treatments with respect to flavor, texture, and overall acceptability of the QFC. Lauric arginate shows promise for potential use in QFC because it exerts initial bactericidal activity against L. monocytogenes at 4°C without affecting sensory quality.     

Effect of high-pressure processing on reduction of Listeria monocytogenes in packaged Queso Fresco

The effect of high-hydrostatic-pressure processing (HPP) on the survival of a 5-strain rifampicin-resistant cocktail of Listeria monocytogenes in Queso Fresco (QF) was evaluated as a postpackaging intervention. Queso Fresco was made using pasteurized, homogenized milk, and was starter-free and not pressed. In phase 1, QF slices (12.7 × 7.6 × 1 cm), weighing from 52 to 66 g, were surface inoculated with L. monocytogenes (ca. 5.0 log₁₀ cfu/g) and individually double vacuum packaged. The slices were then warmed to either 20 or 40°C and HPP treated at 200, 400, and 600 MPa for hold times of 5, 10, 15, or 20 min. Treatment at 600 MPa was most effective in reducing L. monocytogenes to below the detection level of 0.91 log₁₀ cfu/g at all hold times and temperatures. High-hydrostatic-pressure processing at 40°C, 400 MPa, and hold time ≥15 min was effective but resulted in wheying-off and textural changes. In phase 2, L. monocytogenes was inoculated either on the slices (ca. 5.0 log₁₀ cfu/g; ON) or in the curds (ca. 7.0 log₁₀ cfu/g; IN) before the cheese block was formed and sliced. The slices were treated at 20°C and 600 MPa at hold times of 3, 10, and 20 min, and then stored at 4 and 10°C for 60 d. For both treatments, L. monocytogenes became less resistant to pressure as hold time increased, with greater percentages of injured cells at 3 and 10 min than at 20 min, at which the lethality of the process increased. For the IN treatment, with hold times of 3 and 10 min, growth of L. monocytogenes increased the first week of storage, but was delayed for 1 wk, with a hold time of 20 min. Longer lag times in growth of L. monocytogenes during storage at 4°C were observed for the ON treatment at hold times of 10 and 20 min, indicating that the IN treatment may have provided a more protective environment with less injury to the cells than the ON treatment. Similarly, HPP treatment for 10 min followed by storage at 4°C was the best method for suppressing the growth of the endogenous microflora with bacterial counts remaining below the level of detection for 2 out of the 3 QF samples for up to 84 d. Lag times in growth were not observed during storage of QF at 10°C. Although HPP reduced L. monocytogenes immediately after processing, a second preservation technique is necessary to control growth of L. monocytogenes during cold storage. However, the results also showed that HPP would be effective for slowing the growth of microorganisms that can shorten the shelf life of QF.     

Model for Listeria monocytogenes inactivation on dry-cured ham by high hydrostatic pressure processing

The aim of the work was to develop and validate a model of the inactivation of Listeria monocytogenes on dry-cured ham by high hydrostatic pressure (HHP) processing, as a function of the technological parameters: intensity, length and fluid temperature. Dry-cured ham inoculated with L. monocytogenes was treated at different HHP conditions (at 347-852 MPa; for 2.3 to 15.75 min; at 7.6 to 24.4 °C) following a central composite design. Bacterial inactivation was assessed in terms of logarithmic reductions of L. monocytogenes counts on selective media. According to the best fitting and most significant polynomial equation, pressure and time were the most important factors determining the inactivation extent. The significance of the quadratic term of pressure and time indicated that little effect was observed below 450 MPa, whereas holding time longer than 10 min did not result in a meaningful reduction of L. monocytogenes counts. Temperature did not show significant influence at the range assayed. The model was validated with results obtained from further experiments and bibliographical data within the range of the experimental domain. The accuracy factor and bias factor were within the proposed acceptable values indicating the suitability of the model for predictive purposes, such as prediction of the process criteria to meet the Food Safety Objectives. The results of this work may help food processors to select optimum processing conditions of HHP.     

Application of high pressure processing to reduce verotoxigenic E. coli in two types of dry-fermented sausage

The effect of high pressure processing (HPP) on the survival of verotoxigenic Escherichia coli (VTEC) in two types of Norwegian type dry-fermented sausages was studied. Two different types of recipes for each sausage type were produced. The sausage batter was inoculated with 6.8 log₁₀ CFU/g of VTEC O103:H25. After fermentation, drying and maturation, slices of finished sausages were vacuum packed and subjected to two treatment regimes of HPP. One group was treated at 600 MPa for 10 min and another at three cycles of 600 MPa for 200 s per cycle. A generalized linear model split by recipe type showed that these two HPP treatments on standard recipe sausages reduced E. coli by 2.9 log₁₀ CFU/g and 3.3 log₁₀ CFU/g, respectively. In the recipe with higher levels of dextrose, sodium chloride and sodium nitrite E. coli reduction was 2.7 log₁₀ CFU/g in both treatments. The data show that HPP has a potential to make the sausages safer and also that the effect depends somewhat on recipe.     

Efficiency of high hydrostatic pressure at 600 MPa against food-borne microorganisms by challenge tests on convenience meat products

The food-borne pathogens Listeria monocytogenes, Salmonella enterica, Staphylococcus aureus, Yersinia enterocolitica and Campylobacter jejuni, and the spoilage lactic acid bacteria (LAB), Escherichia coli and the yeast Debaryomyces hansenii were inoculated on slices of cooked ham, dry cured ham and marinated beef loin. During storage at 4 °C, L. monocytogenes and LAB increased up to 3.5 log units while the other species, unable to grow under refrigeration, continued at the spiking level. The application of a 600 MPa treatment effectively inactivated most of the microorganisms, the counts of which, except for LAB that increased in cooked ham and in beef loin, progressively decreased or maintained below the detection limit during the whole storage (120 days at 4 °C).     

Evaluation of atmospheric pressure plasma to improve the safety of sliced cheese and ham inoculated by 3-strain cocktail Listeria monocytogenes

The objective of this study was to evaluate the efficacy of atmospheric pressure plasma (APP), which is capable of operating at atmospheric pressure in air, in sliced cheese and ham inoculated by 3-strain cocktail of Listeria monocytogenes (ATCC 19114, 19115, and 19111, LMC). The process parameters considered were input power (75, 100, 125, and 150 W) and plasma exposure time (60, 90, and 120 s). Microbial log reduction increased with increases of input power and plasma exposure time. After 120 s APP treatments at 75, 100, and 125 W, the viable cells of LMC were reduced by 1.70, 2.78, and 5.82 log in sliced cheese, respectively. More than 8 log reductions can be achieved in 120 s at 150 W. In contrast, reductions after 120 s ranged from 0.25 to 1.73 log CFU/g in sliced ham. Calculated D values, the exposure time required to inactivate 90% of a population, from the survival curves of 75, 100, 125, and 150 W of APP treatments were 71.43, 62.50, 19.65, and 17.27 s for LMC in sliced cheese, respectively, and those in sliced ham were 476.19, 87.72, 70.92, and 63.69 s. No viable cells were detected at 125 and 150 W of APP treatment in sliced cheese, irrespective of plasma exposure time, after 1 week at a detection limit of 10¹ CFU/g. These results indicate that the inactivation effects of APP on L. monocytogenes are strongly dependent on the type of food.     

High hydrostatic pressure treatment for manufacturing of garlic powder with improved microbial safety and antioxidant activity

The traditional method of manufacturing garlic powder (GP) that includes simple grinding of air-dried garlic slices has problems of microbial safety and a pungent flavour for this product. Microbiologically safe GP with a less pungent flavour and better antioxidant activities was manufactured using high hydrostatic pressure (HHP), wet grinding and freeze-drying process. The numbers of total aerobic bacteria and yeasts and molds in untreated (without HHP) GP were 3.64 and 2.47 log CFU/g respectively. Garlic powder treated with 600 MPa HHP for 5 min exhibited a total aerobes count of 1.62 CFU/g and a yeasts and molds count of 1.43 log CFU/g. The diallyl disulfide content, which is responsible for the pungent odour of garlic, was also significantly reduced by HHP due to a decrease in the alliinase activity. Hence, a novel process using HHP can help to produce GP with improved microbial safety, flavour and nutrition.     

High hydrostatic pressure processing reduces Salmonella enterica serovars in diced and whole tomatoes

Fresh and fresh-cut tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. One effective post harvest treatment to reduce Salmonella enterica in tomatoes may be high pressure processing (HPP). The objectives of the study were to determine the potential for HPP to reduce S. enterica serovars Newport, Javiana, Braenderup and Anatum in tryptic soy broth (TSB) and to determine the effect of HPP to reduce the most pressure resistant of the four serovars from fresh diced and whole tomatoes. To evaluate pressure resistance, TSB containing 8 log CFU/ml of one of the four serovars was packaged in sterile stomacher bags and subjected to one of three different pressures (350, 450 or 550 MPa) for 120 s. The most pressure resistant S. enterica serovar evaluated was Braenderup. Subjecting the broth culture to 350, 450 and 550 MPa resulted in a 4.53, 5.74 and 7.09 log reduction in S. Braenderup, respectively. Diced tomatoes (150 g) and whole red round tomatoes (approximately 150 g) were inoculated with 0.1 ml of 9.1 log CFU/ml S. Braenderup, and subjected to the same pressure treatments (350, 450 or 550 MPa). Significant reductions of S. Braenderup concentrations in diced tomatoes (P < 0.05) were seen after processing at 350 (0.46 CFU/g), 450 (1.44 log CFU/g), and 550 MPa (3.67 log CFU/g). In whole tomatoes, significant reductions (P < 0.05) were also seen at 350 (1.41 log CFU/g), 450 (2.25 log CFU/g) and 550 MPa (3.35 log CFU/g). HPP may be an effective post harvest strategy to reduce low levels of S. enterica contamination in whole and diced tomatoes.     

Growth potential of Listeria monocytogenes strains in mixed ready-to-eat salads

In this study, a microbiological challenge test in three artificially contaminated retail mixed mayonnaise-based ready-to-eat salads stored at refrigerator temperatures (3 °C and 7 °C) for 48 h was carried out. Shrimp-tomato salad, smoked ham salad and garlic cheese salad were separately contaminated by a suspension of particular Listeria monocytogenes strains. The number of L. monocytogenes, Enterobacteriaceae, staphylococci and total plate count (CFU/g) was determined. Listeria monocytogenes growth potential in the salads was calculated and evaluated.A significant increase in total plate count and L. monocytogenes count throughout storage of all three investigated salads was found. Enterobacteriaceae levels were high at the beginning in all salads but significantly (p < 0.05) decreased throughout the experiment depending on the temperature.All investigated L. monocytogenes strains demonstrated growth at both temperatures but expressed different growth potential. Especially garlic cheese salad and smoked ham salad were able to support the growth of Listeria. Shrimp-tomato salad supported growth the least. The growth potential increased with the increasing temperature and exceeded 0.5 log₁₀ CFU/g in many cases. If the potential for growth is > 0.5 log₁₀ CFU/g, food products can potentially endanger human health. Reference strain (ATCC 7644) showed the least growth potential almost in all cases in comparison with strains isolated from frozen pollock loins and from thermally treated specialty sausage containing preservatives. To eliminate the occurrence of microbiological risks, the shelf-life of the studied salads was estimated.     

Inactivation of Listeria monocytogenes in raw and hot smoked trout fillets by high hydrostatic pressure processing combined with liquid smoke and freezing

High hydrostatic pressure (HHP; 200 MPa for 15 min), liquid smoke (0.50%, v/v) and freezing (−80 °C, overnight) was used to eliminate Listeria monocytogenes in BHI broth, raw and smoked trout. The bactericidal effect of liquid smoke solutions (L9 and G6), HHP and their combinations was evaluated against L. monocytogenes LO28, EGD-e and 10403S and further continued with the most resistant strain (10403S) to the combined treatment. For first time, a synergistic effect of liquid smoke and HHP was observed and was further enhanced by freezing prior to HHP. The effect of HHP and liquid smoke, prior to freezing was highest in BHI compared to raw and smoked trout. A major synergistic effect of HHP, liquid smoke and freezing was observed, reaching a 5.48 or 1.93 log CFU/g reduction when smoked or raw trout was used respectively. Furthermore, high injury levels occurred, among treatments reaching up to 55.98%.Industrial relevanceThis paper illustrates for first time, the possibility of using a very low pressure in combination with liquid smoke and freezing to eliminate L. monocytogenes. It was demonstrated that treatment of trout samples with liquid smoke followed by freezing prior to pressurization at 200 MPa for 15 min reduced the number of L. monocytogenes by more than 5-log CFU/g. Such a remarkable bacterial inactivation at a very low pressure (compared to common industrial practices) is a significant achievement that could allow production of safer and novel products by HHP at an affordable price, as the cost of equipment manufacture as well as the maintenance and running costs could be reduced substantially at lower operation pressures.     

High hydrostatic pressure modification of whey protein concentrate for improved functional properties

Whey protein concentrate (WPC) has many applications in the food industry. Previous research demonstrated that treatment of whey proteins with high hydrostatic pressure (HHP) can enhance solubility and foaming properties of whey proteins. The objective of this study was to use HHP to improve functional properties of fresh WPC, compared with functional properties of reconstituted commercial whey protein concentrate 35 (WPC 35) powder. Fluid whey was ultrafiltered to concentrate proteins and reconstituted to equivalent total solids (8.23%) as reconstituted commercial WPC 35 powder. Solutions of WPC were treated with 300 and 400 MPa (0- and 15-min holding time) and 600 MPa (0-min holding time) pressure. After HHP, the solubility of the WPC was determined at both pH 4.6 and 7.0 using UDY and BioRad protein assay methods. Overrun and foam stability were determined after protein dispersions were whipped for 15 min. The protein solubility was greater at pH 7.0 than at pH 4.6, but there were no significant differences at different HHP treatment conditions. The maintenance of protein solubility after HHP indicates that HHP-treated WPC might be appropriate for applications to food systems. Untreated WPC exhibited the smallest overrun percentage, whereas the largest percentage for overrun and foam stability was obtained for WPC treated at 300 MPa for 15 min. Additionally, HHP-WPC treated at 300 MPa for 15 min acquired larger overrun than commercial WPC 35. The HHP treatment of 300 MPa for 0 min did not improve foam stability of WPC. However, WPC treated at 300 or 400 MPa for 15 min and 600 MPa for 0 min exhibited significantly greater foam stability than commercial WPC 35. The HHP treatment was beneficial to enhance overrun and foam stability of WPC, showing promise for ice cream and whipping cream applications.