Effect of combining nisin and/or lysozyme with in-package pasteurization on thermal inactivation of Listeria monocytogenes in ready-to-eat turkey bologna

Achieving a targeted lethality with minimum exposure to heat and preservation of product quality during pasteurization is a challenge. The objective of this study was to evaluate the effect of nisin and/or lysozyme in combination with in-package pasteurization of a ready-to-eat low-fat turkey bologna on the inactivation of Listeria monocytogenes. Sterile bologna samples were initially treated with solutions of nisin (2 mg/ml = 5,000 AU/ml = 31.25 AU/cm2), lysozyme (10 mg/ml = 80 AU/ml = 0.5 AU/cm2), and a mixture of nisin and lysozyme (2 mg/ml nisin + 10 mg/ml lysozyme = 31.75 AU/cm2). Bologna surfaces were uniformly inoculated with a Listeria suspension resulting in a population of approximately 0.5 log CFU/cm2. Samples were vacuum packaged and subjected to heat treatment (60, 62.5, or 65 degrees C). Two nonlinear models (Weibull and log logistic) were used to analyze the data. From the model parameters, the time needed to achieve a 4-log reduction was calculated. The nisin-lysozyme combination and nisin treatments were effective in reducing the time required for 4-log reductions at 62.5 and 65 degrees C but not at 60 degrees C. At 62.5 degrees C, nisin-lysozyme-treated samples required 23% less time than did the control sample to achieve a 4-log reduction and 31% less time at 65 degrees C. Lysozyme alone did not enhance antilisterial activity with heat. Results from this study can be useful to the industry for developing an efficient intervention strategy against contamination of ready-to-eat meat products by L. monocytogenes.     

Determination of thermal lethality of Listeria monocytogenes in fully cooked chicken breast fillets and strips during postcook in-package pasteurization

Fully cooked chicken breast fillets and strips were surface inoculated with a cocktail of Listeria monocytogenes culture. The inoculation level was 10(7) to 10(8) CFU/g meat. The inoculated products were vacuum packaged and pasteurized at 90 degrees C with a pilot-scale steam or hot water cooker. After heat treatment, the survivors of L. monocytogenes were enumerated. No significant difference was found on survivors of L. monocytogenes between steam- and hot water-treated products. To achieve a 7-log10 (CFU/g) reduction, approximately 5, 25, and 35 min were needed for single-packaged fillets, 227-g package strips, and 454-g strips, respectively. The results from this study were subsequently verified by a computer model that could predict the thermal lethality of pathogens in fully cooked meat and poultry products during postcook in-package pasteurization.     

Effect of combining nisin and/or lysozyme with in-package pasteurization for control of Listeria monocytogenes in ready-to-eat turkey bologna during refrigerated storage

This study investigated the efficacy of in-package pasteurization combined with pre-surface application of nisin and/or lysozyme to reduce and prevent the subsequent recovery and growth of Listeria monocytogenes during refrigerated storage on the surface of low-fat turkey bologna. Sterile bologna samples were treated with solutions of nisin (2 mg/ml=5000 AU/ml), lysozyme (10 mg/ml=80 AU/ml) and a mixture of nisin and lysozyme (2 mg nisin+10mg lysozyme/ml) before in-package pasteurization at 65 degrees C for 32s. In-package pasteurization resulted in an immediate 3.5-4.2 log CFU/cm(2) reduction in L. monocytogenes population for all treatments. All pasteurized treatments also resulted in a significant reduction of L. monocytogenes by 12 weeks compared to un-pasteurized bologna. In-package pasteurization in combination with nisin or nisin-lysozyme treatments was effective in reducing the population below detectable levels by 2-3 weeks of storage. Results from this study could have a significant impact for the industry since a reduction in bacterial population was achieved by a relatively short pasteurization time and antimicrobials reduced populations further during refrigerated storage.     

Numerical analysis of survival of Listeria monocytogenes during in-package pasteurization of frankfurters by hot water immersion

ABSTRACT:  The objective of this research was to develop and validate a more accurate method to analyze and calculate the inactivation of Listeria monocytogenes in frankfurter packages during postlethality hot water immersion heating and the subsequent cooling processes. Finite difference analysis with implicit scheme was used to simulate the heat transfer process during in-package pasteurization of frankfurters. A volumetrically distributed simulation method was developed to calculate the lethality of the thermal treatment. The simulation method was validated using frankfurter packages inoculated with a 4-strain cocktail of L. monocytogenes. Experimental results showed that the numerical analysis model could accurately simulate the heat transfer process during heating and cooling of frankfurter packages. The simulated temperatures on the surface or in the middle of the package matched very closely with the experimental observations. Using the simulated temperature distribution in the packages, the integrated lethality simulation method, based on the volumetric distribution of bacteria, could accurately predict the reduction in the bacterial counts. The calculation results were on average within 0.3 log(CFU/g) difference from the experimental observations, while the General Method systematically underestimated the bacterial reductions by approximately 0.9 log(CFU/g). The study shows that the integrated lethality method is more accurate than the General Method in calculating the lethality of thermal processes for conduction-heated foods.     

Lethality of Salmonella and Listeria innocua in fully cooked chicken breast meat products during postcook in-package pasteurization

The process lethality model was used to predict the thermal kill of Salmonella and Listeria innocua in fully cooked and vacuum-packaged chicken breast meat during hot-water postprocess pasteurization. Time-temperature profiles of the meat samples during treatment and D-values (decimal reduction times) and z-values (change in temperature required to change the D-value) for Salmonella and L. innocua in the same meat product were used in the prediction of lethality. The results of the model prediction were compared with those of the inoculation study for the same meat product at a 95% confidence level of up to 10(7) CFU/g for Salmonella and L. innocua. The thermal lethality predictions obtained with the process lethality model for Salmonella and L. innocua were within the 95% confidence level for the experimental data from the inoculation study, suggesting that the process lethality model was a useful tool for the determination of the kill of Salmonella or L. innocua at up to 10(7) CFU/g in fully cooked chicken breast meat products during postprocess pasteurization with hot water.     

Barrier properties of carrageenan/pectin biodegradable composite films

In this work the barrier properties of biodegradable films for food packaging using commercial pectin and k- carrageenan and nanoclays organically modified were studied. Films (67% k-carrageenan) and different amounts of nanoclays (1, 5 and 10%) were prepared by casting. A pronounced decrease in the water vapour permeability with the higher driving force used (RH 92% - 65%) is observed. It reduces about 35% of its initial value at 10% nanoclay content. The films permeability to carbon dioxide also reduces 50% for 1% nanoclay content. Films barrier properties may be further improved by enhancing the particles dispersion and exfoliation degree.     

Thermal inactivation of Listeria monocytogenes on ready-to-eat turkey breast meat products during postcook in-package pasteurization with hot water

The inactivation of Listeria monocytogenes during postcook in-package pasteurization was evaluated for fully cooked turkey breast meat products (4-kg packages). The products were surface-inoculated to contain 10(7) CFU of L. monocytogenes per cm2 of product surface. The inoculated products were vacuum-packaged in different thicknesses (0.08 to 0.33 mm) of packaging films and treated with hot water at 96 degrees C. After heat treatment, the products were immediately cooled in an ice water bath at 0 degrees C. The relationship between heating time and product surface temperature was determined for different thicknesses of packaging films. The effectiveness of heat treatment for inactivating the pathogen was affected by product surface roughness. About 50 min of heating time was needed to achieve a thermal kill of 7 log10 CFU/cm2 on products with surface roughness up to 15 mm in depth. The cooling time needed after a heat treatment increased with an increasing endpoint temperature of the heated product and the heat penetration depth reached in the product. The cooling time needed to cool the product from 71 degrees C to 4 degrees C was about 2.5-fold the heating time.     

Validation of a time-temperature-integrator for thermal processing of foods under pasteurization conditions

In this work, a general theory for the development of a Time Temperature Integrator, TTI-system, is outlined. A z-value (or activation energy) of the TTI-system equal to that of target index is crucial for the usefulness of a system to monitor the impact of thermal processes on foods. The proposed TTI, namely the heat-stable fraction of peroxidase covalently immobilized on porous glass beads in dodecane, can be used to indicate the intensity of a delivered pasteurization process when a z-value of 10°C is used for calculating the lethality. Lethalities read from the bio-indicator showed excellent agreement with those integrated from the measured time-temperature data.     

Chitosan-based biodegradable functional films for food packaging applications

Chitin is the structural material of crustaceans, insects, and fungi, and is the second most abundant biopolymer after cellulose on earth. Chitosan, a deacetylated derivative of chitin, can be obtained by deacetylation of chitin. It is a functionally versatile biopolymer due to the presence of amino groups responsible for the various properties of the polymer. Although it has been used for various industrial applications, the recent one is its use as a biodegradable antimicrobial food packaging material. Much research has been focused on chitosan-based flexible food packaging and edible food coatings to compete with conventional non-biodegradable plastic-based food packaging materials. Various strategies have been used to improve the properties of chitosan - using plasticizers and cross-linkers, embedding the polymer with fillers such as nanoparticles, fibers, and whiskers, and blending the polymer with natural extracts and essential oils and also with other natural and synthetic polymers. However, much research is still needed to bring this biopolymer to industrial levels for the food packaging applications.Industrial relevanceAs a major by-product of the seafood industry, a massive amount of crustacean shell waste is generated each year, which can be used to produce value-added chitin, which can be converted to chitosan using a relatively simple deacetylation process. Being extracted from a bio-waste product using many energy-efficient methods, chitosan is much cheaper as compared to other biopolymers. Nevertheless, the exceptional properties of chitosan make it a relatively stronger candidate for food packaging applications. Chitosan has already been used in various industries, such as biomedical, agriculture, water treatment, cosmetics, textile, photography, chromatography, electronics, paper industry, and food industry. This review article compiles all the essential literature up to the latest developments of chitosan as a potential food packaging material and the outcomes of its practical utilization for this purpose.     

Use of biodegradable films for fresh cut beef steaks packaging

A comparative study on the use of biodegradable films for fresh cut meat packaging is presented. Beef steaks were packaged using three different films: polyvinyl chloride (PVC), which is actually used to package this food product, a biodegradable polymeric film composed of starch and polyester and a biodegradable film composed of a mixture of three biodegradable polyesters. The packaged beef steaks were stored at 4 and 15 °C to simulate actual storage conditions and thermal abuse, respectively. Colour, total viable counts as well as spoilage microorganism counts were monitored over a period of 6 days. No substantial differences were observed among the beef steaks packaged using the three investigated films, suggesting that biodegradable films, such as those used in this investigation, could be advantageously used to replace PVC films in packaging of fresh processed meat, reducing in this way the environmental impact of polymeric films.     

Physical performance of biodegradable films intended for antimicrobial food packaging

Antimicrobial films were prepared by including enterocins to alginate, polyvinyl alcohol (PVOH), and zein films. The physical performance of the films was assessed by measuring color, microstructure (SEM), water vapor permeability (WVP), and tensile properties. All studied biopolymers showed poor WVP and limited tensile properties. PVOH showed the best performance exhibiting the lowest WVP values, higher tensile properties, and flexibility among studied biopolymers. SEM of antimicrobial films showed increased presence of voids and pores as a consequence of enterocin addition. However, changes in microstructure did not disturb WVP of films. Moreover, enterocin-containing films showed slight improvement compared to control films. Addition of enterocins to PVOH films had a plasticizing effect, by reducing its tensile strength and increasing the strain at break. The presence of enterocins had an important effect on tensile properties of zein films by significantly reducing its brittleness. Addition of enterocins, thus, proved not to disturb the physical performance of studied biopolymers. Development of new antimicrobial biodegradable packaging materials may contribute to improving food safety while reducing environmental impact derived from packaging waste. Practical Application: Development of new antimicrobial biodegradable packaging materials may contribute to improving food safety while reducing environmental impact derived from packaging waste.     

Computational fluid dynamics analysis for process impact assessment during thermal pasteurization of intact eggs

Transient temperature and albumen velocity profiles during thermal pasteurization of intact eggs were studied using a commercial computational fluid dynamics (CFD) package. Simulated temperature profiles were in close agreement with experimental data for eggs of different sizes. Convective heat transfer only occurred in the egg white fraction, and conductive heat transfer only occurred in the yolk. For process assessment, a generally accepted kinetic inactivation model for Salmonella Enteritidis was incorporated into the CFD analysis. Minimum process times and temperatures needed to provide equivalent pasteurization at 5-log reductions of the target microorganism were obtained on a theoretical basis. The combination of CFD analysis and inactivation kinetics can be very useful for assessing pasteurization of intact eggs and can enable processors to gain a better understanding of these processes and to establish process conditions for consumer-safe eggs.     

Design and evaluation of a continuous flow microwave pasteurization system for apple cider

The purpose of this project was to design a continuous flow microwave pasteurization system and to evaluate the following process parameters: volume load size (0.5 and 1.38 l), input power (900–2000 W), and inlet temperature (3°C, 21°C, and 40°C). Water and two apple ciders, one from a cold press and the other from a hot press extraction, were the fluids used to study the heating characteristics. Volumetric flow rate and absorbed power were criteria in the evaluation. The microwave pasteurization system consisted of helical coils throughout a large cavity oven, which was shown to produce uniform and reproducible heating throughout the cavity. Fluid viscosity of water and cider was measured at temperatures between 20°C and 70°C to characterize the flow in helical coils based on the Dean number. Process lethality was verified based on inoculation of Escherichia coli 25922 in apple cider, in which the pasteurization process resulted in a 5-log₁₀ reduction.     

热杀菌结合冷藏改善绿芦笋汁的贮藏稳定性研究

为研究热杀菌处理对绿芦笋汁贮藏稳定性的影响,通过121℃、3min(F03min)处理绿芦笋汁,并置于(4±1)℃条件下冷藏,定期测定其各指标(菌落总数、色泽、可溶性蛋白、总糖、总酚、总黄酮、VC含量与DPPH自由基清除能力)的变化。结果表明:F03min热杀菌处理可将芦笋汁中的固有微生物完全杀死,且在芦笋汁冷藏的120d均无微生物生长;F03min杀菌处理结合冷藏可有效抑制绿芦笋汁贮藏期间L*和a*值的上升,延缓可溶性蛋白、VC、总酚和DPPH自由基清除能力的下降,维持总糖和总黄酮含量的稳定,保持绿芦笋汁的贮藏稳定性,有效延长绿芦笋汁的贮藏货架期,使其冷藏期延长至120d。      

热杀菌结合冷藏改善绿芦笋汁的贮藏稳定性研究

为研究热杀菌处理对绿芦笋汁贮藏稳定性的影响,通过121℃、3min(F03min)处理绿芦笋汁,并置于(4±1)℃条件下冷藏,定期测定其各指标(菌落总数、色泽、可溶性蛋白、总糖、总酚、总黄酮、VC含量与DPPH自由基清除能力)的变化。结果表明:F03min热杀菌处理可将芦笋汁中的固有微生物完全杀死,且在芦笋汁冷藏的120d均无微生物生长;F03min杀菌处理结合冷藏可有效抑制绿芦笋汁贮藏期间L*和a*值的上升,延缓可溶性蛋白、VC、总酚和DPPH自由基清除能力的下降,维持总糖和总黄酮含量的稳定,保持绿芦笋汁的贮藏稳定性,有效延长绿芦笋汁的贮藏货架期,使其冷藏期延长至120d。     

Recent advances in biobased and biodegradable polymer nanocomposites,nanoparticles, and natural antioxidants for antibacterial and antioxidant food packaging applications

Inorganic nanoparticles (NPs) and natural antioxidant compounds are an emerging trend in the food industry. Incorporating these substances in biobased and biodegradable matrices as polysaccharides (e.g., starch, cellulose, and chitosan) and proteins has highlighted the potential in active food packaging applications due to more significant antimicrobial, antioxidant, UV blocking, oxygen scavenging, water vapor permeability effects, and low environmental impact. In recent years, the migration of metal NPs and metal oxides in food contact packaging and their toxicological potential have raised concerns about the safety of the nanomaterials. In this review, we provide a comprehensive overview of the main biobased and biodegradable polymer nanocomposites, inorganic NPs, natural antioxidants, and their potential use in active food packaging. The intrinsic properties of NPs and natural antioxidant actives in packaging materials are evaluated to extend shelf-life, safety, and food quality. Toxicological and safety aspects of inorganic NPs are highlighted to understand the current controversy on applying some nanomaterials in food packaging. The synergism of inorganic NPs and plant-derived natural antioxidant actives (e.g., vitamins, polyphenols, and carotenoids) and essential oils (EOs) potentiated the antibacterial and antioxidant properties of biodegradable nanocomposite films. Biodegradable packaging films based on green NPs—this is biosynthesized from plant extracts–showed suitable mechanical and barrier properties and had a lower environmental impact and offered efficient food protection. Furthermore, AgNPs and TiO₂ NPs released metal ions from packaging into contents insufficiently to cause harm to human cells, which could be helpful to understanding critical gaps and provide progress in the packaging field.     

Assessing the suitability of polylactic acid flexible films for high pressure pasteurization and sterilization of packaged foodstuff

Effects of high pressure (HP) pasteurization and sterilization processes on the properties of commercial biodegradable polylactic acid (PLA), used as packaging material, have been investigated. HP treatments have been performed at pressures of 200, 500 and 700 MPa on PLA pouches, containing different types of food, i.e. tap water, solid carrots, carrot juice and carrot puree. Process temperature was in the ranges 25–40 and 90–110 °C, respectively for HP pasteurization and HP sterilization.