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Mechano-bactericidal (MB) nanopatterns have the ability to inactivate bacterial cells by rupturing cellular envelopes. Such biocide-free, physicomechanical mechanisms may confer lasting biofilm mitigation capability to various materials encountered in food processing, packaging, and food preparation environments. In this review, we first discuss recent progress on elucidating MB mechanisms, unraveling property–activity relationships, and developing cost-effective and scalable nanofabrication technologies. Next, we evaluate the potential challenges that MB surfaces may face in food-related applications and provide our perspective on the critical research needs and opportunities to facilitate their adoption in the food industry.

Concentration of milk in the dairy industry is typically achieved by thermal evaporation or reverse osmosis (RO). Heat concentration is energy intensive and leads to cooked flavor and color changes in the final product, and RO is affected by fouling, which limits the final achievable concentration of the product. The main objective of this work was to evaluate forward osmosis (FO) as an alternative method for concentrating milk. The effects of fat content and temperature on the process were evaluated, and the physicochemical properties and sensory qualities of the final product were assessed. Commercially pasteurized skim and whole milk samples were concentrated at 4, 15, and 25°C using a benchtop FO unit. The FO process was assessed by monitoring water flux and product concentration. The color of the milk concentrates was also evaluated. A sensory panel compared the FO concentrated and thermally concentrated milks, diluted to single strength, with high temperature, short time pasteurized milk. The FO experimental runs were conducted in triplicate, and data were analyzed by single-factor ANOVA. Water flux during FO decreased with time under all processing conditions. Higher temperatures led to faster concentration and higher concentration factors for both skim and whole milk. After 5.75 h of FO processing, the concentration factors achieved for skim milk were 2.68 ± 0.08 at 25°C, 2.68 ± 0.09 at 15°C, and 2.36 ± 0.08 at 4°C. For whole milk, after 5.75 h of FO processing, concentration factors of 2.32 ± 0.12 at 25°C, 2.12 ± 0.36 at 15°C, and 1.91 ± 0.15 at 4°C were obtained. Overall, maximum concentration levels of 40.15% total solids for skim milk and 40.94% total solids for whole milk were achieved. Additionally, a triangle sensory test showed no significant differences between regular milk and FO concentrated milk diluted to single strength. This work shows that FO is a viable nonthermal processing method for concentrating milk, but some technical challenges need to be overcome to facilitate commercial utilization.

Irradiation with deep-ultraviolet light-emitting diodes (DUV LEDs) is emerging as a low energy, chemical-free approach to mitigate microbial contamination, but the effect of surface conditions on treatment effectiveness is not well understood. Here, inactivation of L. innocua and E. coli ATCC25922, as examples of Gram-positive and Gram-negative bacteria, respectively, by DUV LED of 280 nm wavelength was studied. Surface scenarios commonly encountered in environmental, clinical or food processing environments were used: nutrient rich surfaces, thin liquid films (TLF), and stainless steel surfaces (SS). DUV LED exposure achieved 5-log reduction for both strains within 10 min in most scenarios, except for TLF thicker than 0.6 mm. Inactivation kinetics in TLF and on dry SS followed the Weibull model (0.96 ≤ R2 ≤ 0.99), but the model overestimated inactivation by small-dose DUV on wet SS. Confocal microscopy revealed in situ that bacteria formed a dense outer layer at the liquid-air interface of the liquid droplet, protecting the cells inside the droplet from the bactericidal DUV. This resulted in lower than anticipated inactivation on wet SS at small DUV doses, and deviation from the Weibull model. These findings can be used to design effective DUV LED disinfection strategies for various surface conditions and applications.

Staphylococcus epidermidis and Staphylococcus aureus, two bacterial strains commonly associated with biofilm-related medical infections and food poisoning, can rapidly colonize biotic and abiotic surfaces. The present study investigates the ability of anodic alumina surfaces with nanoporous surface topography to minimize the attachment and biofilm formation mediated by these pathogenic bacterial strains. Early attachment and subsequent biofilm development were retarded on surfaces with nanopores of 15-25 nm in diameter compared to surfaces with 50-100 nm pore diameter and nanosmooth surfaces. After 30 min of incubation in nutritive media, the biomass accumulation per unit surface area was 2·93 ± 1·72 µm3 µm-2 for the 15 nm, 3·49 ± 1·97 µm3 µm-2 for the 25 nm, as compared to 14·04 ± 6·39 µm3 µm-2 for the nanosmooth, 11·88 ± 9·72 µm3 µm-2 for the 50 nm and 12·09 ± 11·84 µm3 µm-2 for the 100 nm surfaces respectively. These findings suggest that anodic alumina with small size nanoscale pores could reduce the incidence of staphylococcal biofilms and infections, and shows promise as a material for a variety of medical applications and food contact surfaces. SIGNIFICANCE AND IMPACT OF THE STUDY: This paper reports on a simple, robust and scientifically sound method to reduce attachment and biofilm formation by Staphylococcus aureus and Staphylococcus epidermidis to abiotic surfaces using a carefully designed nanoscale topography. This approach can help to reduce the incidence of staphylococcal biofilms and infections without imposing selective stresses on bacteria, thus preventing the creation of resistant strains.

Acid whey from Greek-style yogurt (GAW) has become abundantly available in recent years. Due to its low solids content, low pH, high lactose and mineral content, GAW is challenging to transport and process. In this study, a combination of reverse osmosis (RO) and forward osmosis (FO) was developed for the nonthermal concentration of GAW. Permeate flux, retentate concentration, and specific energy were evaluated for the individual and combination processes. GAW (6.6°Brix) was concentrated to 19.6°Brix by RO (3 × ), then to 40.2°Brix (6 × ) by FO. During the concentration, permeate fluxes dropped from 33.2 L/m2h to 2.6 L/m2h for RO and from 3.6 L/m2h to 1.6 L/m2h for FO. The specific energy consumption was 0.29 kWh/kg water for RO and 0.65 kWh/kg water for FO, from which half pertains to the osmotic agent regeneration. This combination process can become an efficient nonthermal method for concentrating challenging or sensitive liquid foods and beverages.

In this work, pressure-assisted enzymatic gelation was applied to milk proteins, with the goal of enhancing the structure and stability of pressure-created milk protein gels. High-pressure processing (HPP) at 600 MPa, 3 min, and 5°C was applied to milk protein concentrate (MPC) samples of 12.5% protein concentration, both in the absence and in the presence of calf chymosin [up to 60 IMCU (international milk-clotting units)/kg of milk] or camel chymosin (up to 45 IMCU/kg of milk). Gel hardness, water-holding capacity, and degree of proteolysis were used to assess network strength and shelf stability. The processing trials and all measurements were conducted in triplicate. Statistical analyses of the data were performed by ANOVA, at a 95% confidence level. After HPP treatment, we observed significant structural changes for all samples. Pressurization of MPC, with or without chymosin addition, led to extensive protein aggregation and network formation. The strength of HPP-created milk protein gels without chymosin addition, as measured by the elastic modulus (G′), had a value of 2,242 Pa. The value of G′ increased with increasing chymosin concentration, reaching as high as 4,800 Pa for samples with 45 IMCU/kg of camel chymosin. During 4 wk of refrigerated storage, the HPP and chymosin MPC gels maintained higher gel hardness and better structural stability compared with HPP only (no chymosin) MPC gels. The water-holding capacity of the gels without chymosin remained at 100% during 28 d of refrigerated storage. The HPP and chymosin MPC gels had a lower water-holding capacity (91–94%) than the HPP-only counterparts, but their water-holding capacity did not decrease during storage. Overall, these findings demonstrate that controlled, fast structural modification of high-concentration protein systems can be obtained by HPP-assisted enzymatic treatment, and the created gels have a strong, stable network. This study provides insights into the possibility of using HPP for the development of milk-protein-based products with novel structures and textures and long refrigerated shelf life, along with the built-in safety imparted by the HPP treatment.

In this study, we investigated the effect of pH and calcium on the structural properties of gels created by high-pressure processing (HPP, 600 MPa, 5°C, 3 min) of milk protein concentrate (MPC, 12.5% protein). The pH level of the MPC was varied between 6.6 and 5.1 by adding glucono-δ-lactone (GDL), and the calcium content was varied from 24 to 36 mg of Ca/g of protein by adding calcium chloride. The rheological properties and microstructure of the pressure-treated MPC were assessed. The pressurization treatments and analytical testing were conducted in triplicate. Data were analyzed statistically using one-way ANOVA with Tukey's honestly significant difference post hoc tests. A pressurization time of 3 min was sufficient to induce gel formation in MPC at pH 6.6, so it was used throughout the study. Adjusting either pH or calcium affected the structure of the HPP-created milk protein gels, likely by influencing electrostatic interactions and shifting the calcium–phosphate balance. Gels were formed after pressurization of MPC at pH above 5.3, and increasing the pH from 5.3 to 6.6 resulted in stronger gels with higher values of elastic moduli (G′). At neutral pH (6.6), adding calcium to MPC further increased G′. Scanning electron microscopy showed that reducing pH or adding calcium resulted in more porous, aggregated microstructures. These findings demonstrate the potential of HPP to create a variety of structures using MPC, facilitating a new pathway from dairy protein ingredients to novel, gel-based, high-protein foods, such as puddings or on-the-go protein bars.

This work explores the structural effects of high‐pressure processing (HPP) on starch in mixed pea protein–starch systems of varying concentrations. Reconstituted pea protein concentrate containing 9, 12, and 15% (w/w) protein, without added starch or in combination with 4 or 8% (w/w) pea starch, respectively, were subjected to HPP at 600 MPa for 4 min, at 5°C. Structural changes were investigated using dynamic rheology, scanning electron microscopy, and differential scanning calorimetry (DSC). The addition of starch enabled the formation of weak gels, at protein concentrations below the minimum required for gelation. Above the minimum protein concentration for gelation, starch addition resulted in stronger gels. Starch acted mainly as a filler in the pressure‐induced protein gel matrix, and starch granules remained intact after HPP. DSC analyses confirmed that starch remained ungelatinized after HPP, likely due to the limited availability of water in the mixed systems during HPP. PRACTICAL APPLICATIONS: The structure of pressure‐induced protein gels can be enhanced by adding starch. Besides being a low‐cost ingredient, starch remains ungelatinized after high‐pressure treatment, and thus can act like a fiber. Therefore, pressure‐treated protein–starch mixtures may lead to the development of low‐glycemic index, high‐protein products.

Bacterial spores present in milk can cause quality and shelf-life issues for dairy products. The objectives of this study were to evaluate the effectiveness of microfiltration (MF) in removing Bacillus licheniformis and Geobacillus sp. spores from skim milk using membranes with pore sizes of 1.4 and 1.2 µm, and to investigate the role of spore surface properties in MF removal. Cell sizes were determined by scanning electron microscopy, surface charge by zeta potential analysis, and surface hydrophobicity by contact angle measurements. Commercially pasteurized skim milk was inoculated with a spore suspension at about 106 cfu/mL, and then processed by MF using ceramic membranes at 6°C, a cross-flow velocity of 4.1 m/s, and transmembrane pressure of 69 to 74 kPa. Total aerobic plate and spore counts in the milk were determined before and after MF. All processing runs and surface and product analyses were conducted in triplicate, and data were analyzed statistically. For the same strain, spores were shorter and wider than vegetative cells, averaging 1.37 to 1.59 µm in length and 0.64 to 0.81 µm in width. Reduction of B. licheniformis spores significantly increased with a reduction in MF pore size, from 2.17 log for 1.4-µm pore size, to 4.57 log for 1.2-µm pore size. Both pore sizes resulted in almost complete removal of Geobacillus sp. spores. All spores and the ceramic membrane had a negative surface charge at milk pH, indicating an electrostatic repulsion between them. Bacillus licheniformis spores were hydrophilic, whereas Geobacillus sp. spores were hydrophobic. Consequently, Geobacillus sp. spores had a tendency to cluster in skim milk, preventing their passage even through the 1.4-µm MF membrane, whereas some B. licheniformis spores could still pass through a 1.2-µm membrane. This study demonstrates that efficient removal of spores from skim milk by cold MF may require a smaller membrane pore size than required for removal of vegetative cells of the same species, and that cell surface properties may interfere with the outcome of filtration as would be anticipated based on size alone.

Hydrophilic surfaces of both abiotic and biological origin have been shown to bear particle-exclusion zones as large as hundreds of micrometers at liquid-solid interfaces. Here we present the first systematic investigation and evidence for bacteria-free exclusion zones for several bacterial strains, including pathogens associated with hospital infections and/or foodborne outbreaks: Staphylococcus aureus, Escherichia coli O157:H7, and Listeria monocytogenes. Tests were carried out both in a phosphate buffer, as well as triptic soy broth (TSB) of high ionic strength. Bacterial cell density distribution at the Nafion-liquid interface was visualized using confocal laser scanning microscopy. A robust image analysis method was developed to generate a profile of cell concentration near the interface and quantify EZ size. Results revealed an exclusion zone (EZ) of 40-60μm and a transition zone (TZ) of 40-80μm for bacterial cells suspended in tryptic soy broth. There were no statistical differences in the size of EZ and TZ for the bacterial strains tested with the same substrate, but differences existed for different substrates tested, implying a physicochemical underpinning for EZ. In a test conducted with E. coli, cells progressively penetrated EZ over 2days. Furthermore, EZ-bearing Nafion had 80% less biomass accumulation of E. coli over 2days compared to an EZ-less, hydrophilic, smooth aluminum oxide surface. This suggests that EZ may represent the first line of defense, spatially and temporally, against bacteria approaching certain hydrophilic surfaces. These findings could have important implications in developing biofouling-resistant material surfaces for applications sensitive to bacterial attachment and biofilm formation.

This study investigated the effects of HPP and heat treatment on digestibility and trypsin inhibitor activity in lentil protein concentrate (LPC) and faba bean protein concentrate (FPC). LPC and FPC with 15 g protein/100 g were treated with HPP (600 MPa/5 °C/4 min) or heat (95 °C/15 min), then subjected to in vitro digestion. Digesta were analyzed by SDS-PAGE for hydrolyzed protein fraction patterns and their concentrations. The concentration of peptides and free amino acids was also determined. The effect of HPP and heat treatment on trypsin inhibitor activity was determined for 5 g protein/100 g LPC and FPC. HPP and heat treatments led to different hydrolyzed peptide patterns after gastric digestion. HPP resulted in comparable or greater gastric digestibility than untreated controls, but higher gastric proteolysis than heat treatment. Neither treatment impacted overall in vitro protein digestibility, for either LPC or FPC. HPP slightly reduced trypsin inhibitor activity (~8% for LPC, ~6% for FPC), while heat treatment led to much greater reductions (86% for LPC, ~78% for FPC) than untreated controls. Overall, HPP and heat treatment did not negatively impact lentil and faba bean protein quality, which is useful information for developing new food product applications.

Utilization of pulse proteins in food products is increasingly explored, but the effect of processing on their quality and functionality is not well known. The effects of high pressure processing (HPP; 600 MPa, 5 °C, 4 min) and heat treatment (95 °C, 15 min) on the structure and functionality of pulse (lentil, pea, faba bean) proteins were evaluated, at protein concentrations characteristic for fortification of beverages (5 g/100 g) and gel formation (15 g/100 g). Structural changes were investigated by differential scanning calorimetry, rheological analyses, and surface hydrophobicity measurements. Sample solubility, water holding capacity, emulsifying and foaming properties were determined and compared to untreated controls. HPP and heat denatured pulse proteins and increased their surface hydrophobicity (p

Reconstituted micellar casein concentrates and milk protein concentrates of 2.5 and 10% (wt/vol) protein concentration were subjected to high-pressure processing at pressures from 150 to 450 MPa, for 15 min, at ambient temperature. The structural changes induced in milk proteins by high-pressure processing were investigated using a range of physical, physicochemical, and chemical methods, including dynamic light scattering, rheology, mid-infrared spectroscopy, scanning electron microscopy, proteomics, and soluble mineral analyses. The experimental data clearly indicate pressure-induced changes of casein micelles, as well as denaturation of serum proteins. Calcium-binding αS1- and αS2-casein levels increased in the soluble phase after all pressure treatments. Pressurization up to 350 MPa also increased levels of soluble calcium and phosphorus, in all samples and concentrations, whereas treatment at 450 MPa reduced the levels of soluble Ca and P. Experimental data suggest dissociation of calcium phosphate and subsequent casein micelle destabilization as a result of pressure treatment. Treatment of 10% micellar casein concentrate and 10% milk protein concentrate samples at 450 MPa resulted in weak, physical gels, which featured aggregates of uniformly distributed, casein substructures of 15 to 20 nm in diameter. Serum proteins were significantly denatured by pressures above 250 MPa. These results provide information on pressure-induced changes in high-concentration protein systems, and may inform the development on new milk protein-based foods with novel textures and potentially high nutritional quality, of particular interest being the soft gel structures formed at high pressure levels.

The role of pectin in membrane fouling during cold MF of apple cider was investigated. Clarified apple juice with four different concentrations of pectin was subjected to cold MF, at pore sizes above 0.45 μm. The experimental data shows that pectin plays a significant role in membrane fouling, and its fouling effect increased with increasing concentration. The association of pectin with polyphenols and proteins, which results in colloidal haze particles with low surface electrical charge, seems to be the major factor in fouling during cold MF of apple cider. Depectinization was beneficial to MF with pore sizes below 0.45 μm, for which fouling is dominated by cake layer formation. Depectinization had a negative effect on MF flux for pore sizes above 0.8 μm, since the size reduction of haze particles accentuated pore constriction and blockage, which dominate fouling in large pore MF. These findings have practical implications for the development of efficient, commercially viable, cold MF processes for minimally processed apple cider.

Postprocessing cross-contamination of cheese can lead to both food safety issues and significant losses due to spoilage. Pulsed light (PL) treatment, consisting of short, high-energy, broad-spectrum light pulses, has been proven effective in reducing the microbial load on cheese surface. As PL treatment effectiveness is limited by light-cheese interactions, the possibility to improve its effectiveness by combining it with the antimicrobial nisin was explored. The effect of natamycin, which is added to cheeses as an antifungal agent, on PL effectiveness was also investigated. Pseudomonas fluorescens, Escherichia coli ATCC 25922, and Listeria innocua were used as challenge microorganisms. Bacterial cultures in stationary growth phase were diluted to initial inoculum levels of 5 or 7 log cfu per cheese slice. Slices of sharp white Cheddar cheese and white American singles were cut in rectangles of 2.5 × 5 cm. For cheese slices receiving antimicrobial treatment before PL, slices were dipped in natamycin or nisin, spot inoculated with 100 μL of bacterial suspension, and then treated with PL. Cheese slices receiving PL treatment before antimicrobials were spot inoculated, treated with PL, and then treated with antimicrobials. The PL fluence levels from 1.02 to 12.29 J/cm2 were used. Survivors were enumerated by standard plate counting or the most probable number technique, as appropriate. All treatments were performed in triplicate, and the data were analyzed using a general linear model. Treatment with nisin or natamycin before PL decreased the effectiveness of PL for all bacteria tested. For instance, PL reduced P. fluorescens on Cheddar cheese by 2.19 ± 0.27 log after 6.14 J/cm2, whereas combination treatments at the same PL fluence yielded barely 1 log reduction. Inactivation of L. innocua on Cheddar was only 0.78 ± 0.01 log when using PL after nisin, compared with a 1.30 ± 0.76 log reduction by nisin alone. This was attributed to the absorption of UV light by the 2 antimicrobials, which diminished the UV fluence received by the bacteria. Increased inactivation was obtained when antimicrobials were applied after PL. On process cheese, a maximum reduction of 3.73 ± 0.96 log of L. innocua was obtained at 9.22 J/cm2 for PL followed by nisin, compared with 3.01 ± 0.48 by PL alone. This study demonstrates that antimicrobials may increase the antimicrobial effectiveness of PL on cheese surface, but the order of treatments is critical.

This study investigated the effect of sublethal temperatures on the efficacy of pulsed light (PL) treatment for the inactivation of Listeria innocua, Escherichia coli ATCC 25922, and Pseudomonas fluorescens. A thin layer of clear, liquid phosphate buffer inoculated with one of the challenge organisms, at a concentration of about 108 CFU/mL, was equilibrated to a temperature ranging from 5 °C to 50 °C and then treated with PL, at doses between 1.02 and 12.29 J/cm2. All treatments were performed in triplicate. In the temperature range of 5 °C to 40 °C, the average maximum reductions for L. innocua, E. coli, P. fluorescens were 6.27 ± 0.23 log CFU, 6.66 ± 0.36 log CFU, and 6.15 ± 0.19 log CFU, respectively. Temperature did not affect PL inactivation of E. coli or P. fluorescens, but a modest synergistic effect between PL and temperature was observed for L. innocua treated above 40 °C. Industrial relevance This study suggests that PL inactivation of bacteria is independent of temperature in the sublethal range 5 °C to 40 °C. The practical benefit of this finding is that PL treatments can be conducted in a wide range of environmental temperatures, without any change in the outcome of the treatment.

This work demonstrates the use of high pressure processing (HPP) to induce structural modifications in pea protein concentrates (PPC). Reconstituted PPC with 8–24 g protein /100 g water were subjected to HPP at 250–550 MPa for 15 min, at 20–33°C, or heat treatments at 95°C for 15 min. Structural changes were investigated using dynamic rheology, scanning electron microscopy, differential scanning calorimetry, and mid‐infrared spectroscopy. Gel formation occurred at 16 g protein /100 g water concentration and 250 MPa for the HPP‐treated samples, and at 12 g protein /100 g water concentration for the heat‐treated samples. Gel strength increased with both pressure level and protein concentration. Heat‐treated samples exhibited greater gel strength than pressure‐treated samples at the same protein concentration. A greater extent of protein denaturation, aggregation, and network formation occurred with increasing pressure level, due to protein tertiary and quaternary conformation changes. Starch granules present in PPC retained their structure and were not gelatinized even at 550 MPa. These findings can be used to create novel pea protein products with interesting structures and superior sensory and nutritional properties. PRACTICAL APPLICATIONS: This work shows that a range of unique pea‐based products, such as puddings or tofu analogs, can be created by low temperature HPP treatment of pea protein concentrates at different pressure levels and protein concentrations. This process has the potential to better preserve the organoleptic and nutritional properties of the final products compared to traditional, heat based processing methods. These findings can be also extended to create other pulse protein products using high pressure processing.

Pulsed Light (PL) is effective for inactivation of bacteria in food and non-food systems, yet the mechanisms of inactivation are not fully understood. In this work, the response of Listeria monocytogenes to PL and continuous ultraviolet light (UV) was investigated using whole genome DNA microarray analysis. Suspensions of L. monocytogenes were treated with 3.20 J/cm 2 of PL and 33 mJ/cm 2 of UV, respectively, which yielded comparable levels of inactivation. In a separate experiment, cells were exposed to 3.20 J/cm 2 of full spectrum PL and UV-blocked PL. Whole genome microarray analysis of L. monocytogenes was performed to identify differential gene expression after the treatments, using a 1.5 fold change cutoff and adjusted P

The main goal of this study was to evaluate the effectiveness of a combination of antimicrobial films and Pulsed Light (PL) on inactivation of Listeria innocua on Cheddar cheese surface, and maintaining of product quality during refrigerated storage. The properties of antimicrobial starch films (ASF) containing sodium benzoate (ASF-SB), citric acid (ASF-CA), and both (ASF-CASB), prepared by casting and irradiated with PL, were evaluated. These films were used as packaging for Cheddar cheese slices that were surface inoculated with L. innocua at an initial inoculum level of 7 log CFU per cheese slice. PL had no effects on the structure of ASF. PL applied in combination with ASF-CA achieved an average of 4.5 log CFU reduction of L. innocua after 3 days of storage at 4 °C. However, significant changes in physicochemical properties of cheese, including pH, moisture level and mechanical properties, were observed after 7 days of refrigerated storage. These results suggest that, while PL-ASF can be effective in reducing L. innocua on Cheddar cheese surface, this combination treatment may induce some quality changes in the product.

The objective of this investigation was to develop the mathematical models that included the effects of time, temperature, pH and substrate concentration on the non-enzymatic browning reaction. Glycine-glucose solutions were used as food models. Experimental data of 420-nm browning absorbance, which were converted into s-curved Xt values, were used for the modeling and validation processes. The impacts of multiple factors on browning were well expressed by a combined use of modified Gompertz, Arrhenius and interaction polynomial models and a data conversion technique (R2 ≥ 0.9441). The browning rates varied greatly (λ = 7.46–888 min and umax = 0.06 to 26.90 min−1), depending on temperature, pH and concentration. The activation energy (Ea) values of λ (62–120 kJ/mol) and umax (87–129 kJ/mol) varied, depending more on concentration than pH. Although non-enzymatic browning reactions are complex with a variety of pathways and reactive products in response to multiple factors, they are likely modellable so that the benefits (food quality based on color and aroma) and harmful properties (e.g., carcinogens) of browning can be better managed.

The objective of this study was to evaluate the effectiveness of cold microfiltration (MF), alone or in combination with heat treatment, in extending the shelf life of skim milk. Raw skim milk underwent MF at 6 ± 1°C with a ceramic membrane of 1.4-μm pore size, at a transmembrane pressure of 75.8 kPa and a crossflow velocity of 7 m/s. Samples of raw skim milk; MF skim milk; high-temperature, short-time (HTST)-pasteurized milk; and MF+HTST-pasteurized skim milk were stored at 6°C for 92 d. During the shelf-life study, the total bacterial count and degree of proteolysis were evaluated weekly. The study was replicated 3 times. Cold MF was very effective in reducing the microbial load in skim milk, and an average of 3.4 log reduction in vegetative bacteria was obtained. Although HTST pasteurization reduced the bacterial load by ∼2 log, the MF+HTST process resulted in near complete elimination of vegetative microflora, with a total of ∼4 log reduction. A 9-member sensory panel found no significant differences between skim milk samples processed with or without MF. The MF+HTST skim milk had only minor microbial growth after 92 d at 6°C, but its proteolytic shelf life was limited by plasmin activity. A reduction of plasmin activity and a slower rate of proteolysis were obtained by increasing the heat treatment temperature to 85°C. The results of this study can be used to make decisions regarding processing strategies that lead to increased skim milk shelf life.

This article provides composition information for 3 abundantly available but little characterized dairy coproduct streams: acid whey from Greek yogurt (GAW), acid whey from cottage cheese (CAW), and milk permeate (MP). Three replicate samples obtained on different dates from several dairy processors were analyzed. The main component in all streams was lactose, with up to 3.5, 2.1, and 11.9% in GAW, CAW, and MP, respectively. Crude protein content ranged from 1.71 to 3.71 mg/g in GAW, 1.65 to 5.05 mg/g in CAW, and 3.2 to 4.35 mg/g in MP, and pH ranged from 4.21 to 4.48, 4.35 to 4.51, and 5.4 to 6.37, respectively. Chemical oxygen demand varied from 52,400 to 62,400 mg/L for GAW, 31,900 to 40,000 mg/L for CAW, and 127000 to 142,000 mg/L for MP; biochemical oxygen demand ranged from 45,800 to 50,500 mg/L (GAW), 32,700 to 40,000 mg/L (CAW), and 110,000 to 182,000 mg/L (MP). The GAW had the lowest pH (4.21-4.48) and highest mineral content of all streams. These data will assist processors and researchers in developing value-added uses of these dairy coproducts.

Pulsed light (PL) technology involves applying a few very short pulses (1 µs to 0.1 s) of high-intensity, broad-spectrum light to kill viruses, bacteria, yeasts, and molds. The key component of a “pulsed light unit” is a flashlamp filled with an inert gas, typically xenon, which emits radiation in the range 200–1100 nm, spanning the ultraviolet (UV) to near-infrared region. The main mechanism by which PL causes cell death is the effect of UV light on microbial DNA. However, other mechanisms, including photochemical and photothermal effects, have also been reported. Survival curves for PL treatment are non-linear. The effectiveness of PL is affected by the interaction of the substrate with the incident light. Therefore, the treatment is most effective on smooth, non-reflecting surfaces or in clear liquids. The most suitable food industry applications include disinfection of food contact surfaces, including food packaging, and surface decontamination of unpackaged foods, food packaged in UV-transparent materials, fruit juices, and water. The chapter provides an overview of the principles of PL technology, the main factors influencing its performance, and the current and potential applications for food safety and preservation.

Mango puree was produced out of Banaganappalli mango variety, a local species of mango grown in India. This puree was blended with starch, glycerol along with gelatin and defatted soy protein for casting the composite edible films. Utilization of excess mango available in high season, defatted soy protein from the waste of soy industry could help to reduce waste and additionally commercial grade starch, glycerol and gelatin was used to produce a value added product. Mango puree in 100 ml aqueous solution. Optical, mechanical, barrier, water resistance, thermal and morphology properties of all mango puree edible films were investigated. The composite yellowish films exhibited tensile strength, elongation at break, water vapour permeability, water solubility, melting temperature, crystallinity and were in the range of 4.26 Mpa to 5.89 MPa, 18.08% to 25.09%, 5.69 g.mm.kPa-1h-1m-2 to 8.56 g.mm.kPa-1h-1m-2, 35.30% to 51.57%, 154.35oC to 175.69 oC, 21.98% to 25.22% respectively. With these properties along with lower moisture content made the films useful for wide range of food packaging applications such as edible films having mango flavor.

In this study, the effect of Pulsed Light (PL) treatment as a cross-linking method on the properties of casein films was evaluated. Casein films were prepared from micellar casein concentrate, with 5 g/100 g glycerol added as a plasticizer. The UV-curable resins PEG (200) diacrylate and PEG (400) diacrylate were added as photo-initiators. Films were prepared by casting and equilibrated under a range of relative humidity (%RH), then treated with Pulsed Light (PL), with up to 15 pulses of light on each side, at a fluence of 1.57 J/cm2 per pulse. The microstructure, mechanical and water barrier properties, water sorption and hydrophobicity of the films were evaluated. PL treatment of casein films with up to 12 pulses increased the films' smoothness and homogeneity, while higher levels of treatment caused structural defects. Mechanical strength and elongation of some of the films, particularly those with added PEG (400) diacrylate, were significantly increased by PL, but no improvement of their water vapor permeability was observed. The incorporation of PEG (200) diacrylate resulted in highly porous film microstructures, and interesting photo-patterning effects observed at high PL doses. These results indicate the potential of PL for creating protein films with unique characteristics and functionality.

Microfiltration (MF) of apple cider using four membrane pore sizes was investigated. MF with 0.2 and 0.45 μm pore sizes, and with 0.8 and 1.4 μm pore sizes, respectively, resulted in similar flux behavior and MF juice characteristics. Clear juice was obtained using all four pore sizes. MF did not cause any significant changes in pH and °Brix, regardless of pore size. Viscosity of the MF juice was lower than of the unfiltered apple cider for all membranes, but the viscosity decrease was the largest for the 0.2 and 0.45 μm membranes, due to the low transmission of pectin into the MF juice. Pectin transmission was 3–9% of the initial pectin content for the 0.2 μm membrane, 6–51% for the 0.45 μm. 45–100% for the 0.8 μm, and 60–100% for the 1.4 μm membrane. Apple cider haze particles that were smaller or of size comparable with the membrane pore size were deemed responsible for fouling, while particles much larger than the pores did not have a significant contribution to fouling. The fouling of 0.2 μm and 0.45 μm membranes was dominated by cake layer formation (external fouling), while fouling of the 0.8 μm and 1.4 μm membranes was dominated by pore constriction and pore blocking (internal fouling).

Cheese products are susceptible to postprocessing cross-contamination by bacterial surface contamination during slicing, handling, or packaging, which can lead to food safety issues and significant losses due to spoilage. This study examined the effectiveness of pulsed-light (PL) treatment on the inactivation of the spoilage microorganism Pseudomonas fluorescens, the nonenterohemorrhagic Escherichia coli ATCC 25922 (nonpathogenic surrogate of Escherichia coli O157:H7), and Listeria innocua (nonpathogenic surrogate of Listeria monocytogenes) on cheese surface. The effects of inoculum level and cheese surface topography and the presence of clear polyethylene packaging were evaluated in a full factorial experimental design. The challenge microorganisms were grown to early stationary phase and subsequently diluted to reach initial inoculum levels of either 5 or 7 log cfu/slice. White Cheddar and process cheeses were cut into 2.5×5 cm slices, which were spot-inoculated with 100 µL of bacterial suspension. Inoculated cheese samples were exposed to PL doses of 1.02 to 12.29 J/cm(2). Recovered survivors were enumerated by standard plate counting or the most probable number technique, as appropriate. The PL treatments were performed in triplicate and data were analyzed using a general linear model. Listeria innocua was the least sensitive to PL treatment, with a maximum inactivation level of 3.37±0.2 log, followed by P. fluorescens, with a maximum inactivation of 3.74±0.8 log. Escherichia coli was the most sensitive to PL, with a maximum reduction of 5.41±0.1 log. All PL inactivation curves were nonlinear, and inactivation reached a plateau after 3 pulses (3.07 J/cm(2)). The PL treatments through UV-transparent packaging and without packaging consistently resulted in similar inactivation levels. This study demonstrates that PL has strong potential for decontamination of the cheese surface.

The effects of suspended insoluble solids (SIS) concentration and particle size, and the time after apple pressing on the efficiency of UV treatment of cloudy apple juice were evaluated. Clear model solutions (formulated to resemble physicochemical characteristics of apple juice) and commercial apple juice, containing different solids concentrations, were treated using a CiderSure reactor at 14 mJ cm−2 UV dose. Particle size effect was assessed on model solutions treated at 7 mJ cm−2 UV dose. The juice flow rate through the UV machine was determined. All samples were inoculated with Escherichia coli ATCC 25922 (106–107 CFU ml−1) and UV treated at 214.5 ml s−1 fixed flow rate. Log reductions were calculated. Increasing SIS concentrations did not significantly affect the juice flow rate (P > 0.05) but adversely affected the inactivation of E. coli (P < 0.05). For solutions treated at 7 mJ cm−2, a negative linear relationship between SIS and flow rate was observed and particle size significantly affected the flow rate (P < 0.05). A negative effect of time after apple pressing on the juice flow rate was observed and this effect was apple cultivar-dependent, thus UV efficiency would be improved if time after pressing is minimized. United States Department of Agriculture/[2010-51110-21511]/USDA/Estados Unidos National Institute of Food and Agriculture/[2010-51110-21511]/NIFA/Estados Unidos Fulbright International Exchange Program/[]//Estados Unidos Cornell University/[]//Estados Unidos UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Agroalimentarias::Centro Nacional de Ciencia y Tecnología de Alimentos (CITA)

This work reports on a simple, robust and scientifically sound method to develop surfaces able to reduce microbial attachment and biofilm development, with possible applications in medicine, dentistry, food processing, or water treatment. Anodic surfaces with cylindrical nanopores 15 to 100 nm in diameter were manufactured and incubated with Escherichia coli ATCC 25922 and Listeria innocua. Surfaces with 15 and 25 nm pore diameters significantly repressed attachment and biofilm formation. Surface-bacteria interaction forces calculated using the extended Derjaguin Landau Verwey-Overbeek (XDLVO) theory indicate that reduction in attachment and biofilm formation is due to a synergy between electrostatic repulsion and surface effective free energy. An attachment study using E. coli K12 strains unable to express appendages also suggests that the small-pore surfaces may inhibit flagella-dependent attachment. These results can have immediate, far-reaching implications and commercial applications, with substantial benefits for human health and life.

This study presents a rheological and chemical evaluation of the changes induced by heating of micellar casein (MCN) – soy proteins (SP) mixtures. Individual and mixed (1:1) protein preparations of 10 g/100 g and 15 g/100 g concentration were prepared and heat treated for 15 min at 40 °C, 60 °C and 95 °C, respectively. After cooling to 20 °C, their steady-shear and dynamic rheological properties were determined. Apparent viscosity of MCN, SP and their mixtures increased with concentration. Most heat treated MCN–SP mixtures had liquid-like behavior, except the 15 g/100 g mixture, which formed a gel after treatment at 95 °C. A differential solubility method was used to investigate the degree of protein denaturation, and non-reducing SDS-PAGE analysis to identify specific protein fractions in the heat treated protein systems. Heat treatments did not induce any chemical interactions between soy proteins and casein micelles in the mixed MCN–SP systems, but the 95 °C treatments induced denaturation and subsequent interactions among soy proteins when the critical concentration for gelation was exceeded. Nonetheless, mixtures with interesting rheological properties were obtained, which could be used in the development of high protein foods with unique textural and mouthfeel characteristics.

Inactivation of Listeria innocua on food packaging materials by Pulsed Light (PL) treatment was investigated. Coupons of low density polyethylene (LDPE), high density polyethylene (HDPE), polyethylene-laminated ultra-metalized polyethylene terephthalate (MET), polyethylene-coated paperboard (TR), and polyethylene-coated aluminum foil paperboard laminate (EP) were inoculated with L. innocua cells in stationary growth phase. Inoculated coupons (∼8 CFU/coupon) were treated with Pulsed Light fluence of up to 8.0 J/cm 2 , and survivors were determined. Reductions up to 7.2 ± 0.29, 7.1 ± 0.06, 4.4 ± 0.85, 4.5 ± 1.32, and 3.5 ± 0.82 log CFU/coupon were obtained on LDPE, HDPE, MET, TR, and EP, respectively. Inactivation data were used to determine Weibull kinetic parameters and predict inactivation in a wide range of fluence. Increasing surface reflectivity and surface roughness appeared to induce lower inactivation. Minimal surface heating was observed for all materials except MET, on which significant heating occurred. These results demonstrate the potential of Pulsed Light as an effective method for decontaminating food packaging materials.

Efforts for developing protein films as biodegradable packaging materials have increased in recent years. One of the drawbacks of such films is that their functional properties are generally inferior to those of synthetic films. Although protein films typically have excellent gas barrier properties, they tend to have higher water vapor permeability, are mechanically weaker, and have lower elongation as compared to most synthetic polymers. This paper will review the various methods that have been reported to enhance the physical and barrier properties of protein films. The effects of film formulation and preparation conditions, including plasticization, pH alteration, and lipid addition, on the functional properties of protein films are discussed. The paper also offers a comprehensive review of the various methods used to modify protein film functional properties, including cross-linking techniques induced by heat, chemical, enzymes, and irradiation, and use of nanocomposites to enhance their barrier properties. A critical comparison of the different technical solutions is offered, and the challenges and potential applications of these films are discussed.

The objective of this study was to examine the effect of pulsed light (PL) treatment on the color, oxidative stability, and onset of molding of Cheddar cheese. Slices of sharp white Cheddar cheese of 2.5 × 5 cm were treated on one side with PL doses from 1.02 to 12.29 J/cm2, sealed in polyethylene bags, and stored at 6°C for up to 1 mo. Peroxide value, color parameters, and the onset of molding were evaluated. No significant changes in color or peroxide value were observed for PL-treated samples compared with the untreated controls. Pulsed light was able to significantly delay surface molding during refrigerated storage, with a PL dose of 9.22 J/cm2 delaying the onset of molding by 7 d. The effect of PL on the taste, appearance, and acceptability of Cheddar cheese slices treated with a PL dose of 9.22 J/cm2 on each side was assessed. In triangle tests, 60 untrained panelists were unable to detect significant differences between the control and PL-treated samples, although PL had a significant effect on overall liking, flavor, and appearance. These findings suggest that although PL can be effective for surface decontamination of cheese, it may have some detrimental effects on sensory properties.

Pulsed light (PL) treatment has been viewed as an alternative to thermal treatments for the inactivation of pathogenic and spoilage microorganisms in recent years. The objectives of this study were to quantify the effectiveness of PL on inactivating Escherichia coli in cow milk and to evaluate the effect of total solids and fat content on inactivation. Samples of reconstituted milk with variable total solids levels (9.8, 25, and 45%) and commercial cow milk with different fat contents (skim milk, 2% fat, and whole milk) were inoculated with nonpathogenic E. coli ATCC 25922 at a concentration of 10(7)cfu/mL. One milliliter of the inoculated sample was placed in a thin layer in a glass chamber and exposed to PL doses of up to 14.9 J/cm(2), both in static mode and turbulent mode. Survivors were quantified using standard plate counting. All experiments were performed in triplicate. Pulsed light treatment of the concentrated milks of 25 and 45% solids content resulted in reductions of less than 1 log, even in turbulent mode, whereas for the milk with 9.8% solids content, reduction levels of 2.5 log cfu were obtained after treatment with 8.4 J/cm(2) in turbulent mode. In the skim milk, a 3.4 log cfu reduction at 14.9 J/cm(2) was obtained and a plateau of the inactivation curve typical of PL treatment was not achieved. Under the same conditions, both 2% and whole milk attained inactivation levels greater than 2.5 log cfu. These data indicate that PL is effective for the inactivation of E. coli in milk, but has limited effectiveness for microbial inactivation in concentrated milk, due to the absorption of light by the milk solids and shielding of the bacteria in the concentrated substrates. Milk fat also diminishes the effectiveness of PL to some extent, due to light-scattering effects.

This work focused on evaluating the effects of UHT sterilization and in-container retorting on the stability and physical properties of micellar casein concentrates (MCC). The study was performed on MCC obtained by membrane separation, with casein concentrations between 5 and 10%. The UHT and retorting regimens were designed to achieve the same microbial inactivation effect. Ultra-high temperature treatment was performed in a pilot-scale MicroThermics heating system (MicroThermics Inc., Raleigh, NC), and retorting in an FMC multipurpose laboratory retort (Steritort; FMC Corp., San Jose, CA). The heat-treated and the non-heat-treated MCC controls were evaluated for pH, mineral profile, ζ-potential, particle size, and rheological properties for up to 24h after heat treatment. The treatments were performed in triplicate, and differences among samples were evaluated using statistical analyses. Retorting resulted in slight aggregation in the MCC, whereas UHT caused the formation of visible aggregates and coagulation. The UHT-treated MCC had higher viscosity than retorted MCC, and displayed predominantly solid-like rheological behavior, indicative of structure formation. These effects were, at least in part, attributed to a change in mineral equilibrium, which affected the stability of the casein micelles, but additional mechanisms such as κ-casein dissociation may also play a significant role in these heat-induced changes. Drying of MCC accentuated the observed instabilities, as dried and reconstituted micellar casein concentrates (R-MCC) were more unstable to UHT sterilization than the MCC that had not undergone drying. The results of this study provide valuable information about the sterilization behavior and physical properties of MCC, which can be useful to processors in the development and manufacture of shelf-stable casein-based products and beverages.

In the Luangwa Valley, Zambia, persistent poverty and hunger present linked challenges to rural development and biodiversity conservation. Both household coping strategies and larger-scale economic development efforts have caused severe natural resource degradation that limits future economic opportunities and endangers ecosystem services. A model based on a business infrastructure has been developed to promote and maintain sustainable agricultural and natural resource management practices, leading to direct and indirect conservation outcomes. The Community Markets for Conservation (COMACO) model operates primarily with communities surrounding national parks, strengthening conservation benefits produced by these protected areas. COMACO first identifies the least food-secure households and trains them in sustainable agricultural practices that minimize threats to natural resources while meeting household needs. In addition, COMACO identifies people responsible for severe natural resource depletion and trains them to generate alternative income sources. In an effort to maintain compliance with these practices, COMACO provides extension support and access to high-value markets that would otherwise be inaccessible to participants. Because the model is continually evolving via adaptive management, success or failure of the model as a whole is difficult to quantify at this early stage. We therefore test specific hypotheses and present data documenting the stabilization of previously declining wildlife populations; the meeting of thresholds of productivity that give COMACO access to stable, high-value markets and progress toward economic self-sufficiency; and the adoption of sustainable agricultural practices by participants and other community members. Together, these findings describe a unique, business-oriented model for poverty alleviation, food production, and biodiversity conservation.

Pulsed light (PL) technology is able to effectively destroy a wide variety of food spoilage and pathogenic microorganisms. However, the effectiveness of PL treatment depends on direct exposure of the target microorganisms to the short, high energy pulses of light. The complex physical and chemical properties of foods affect the way light propagates through a given food substrate, and thus there is a real potential for insufficiently or non-uniformly treated products. The objective of this work was to develop a method for predicting levels and spatial distribution of microbial inactivation in PL treatment of liquid substrates, and to validate the predictions with experimental data. Three liquids with different composition and optical properties (BPB, TSB, apple juice) were inoculated with either Escherichia coli ATCC 25922 or Listeria innocua FSL C2-008 and treated with PL, in two different geometries. The Weibull model was used to describe the microbial inactivation kinetics for each organism. The kinetic equations were coupled with previously determined equations describing either the total fluence ( F total ) or UV fluence ( F UV ) distribution in each of the liquids, for either cylindrical or rectangular prismatic geometries. COMSOL simulation software was used to generate maps of spatial distribution of microbial inactivation and to predict the average volumetric inactivation for each substrate. The model that used F total provided gross over-estimations for microbial inactivation, while using F UV as the treatment dose yielded reasonably good predictions of microbial inactivation, especially for the more opaque and turbid substrates. This approach can help processors determine which substrates would be suitable for PL treatment, and to design highly effective and uniform PL treatments.

The objective of this study was to investigate the effect of concentration and temperature on the rheological properties of soy proteins (SP) and micellar casein (MCN) systems. Individual and mixed (1:1) protein systems of 2–15% concentration were prepared and heat treated for 5 min at 40–90 °C. After cooling to 20 °C, their rheological properties were determined using steady-shear rheology. Zeta potential and particle size measurements were also conducted. Both proteins were negatively charged under all experimental conditions, but the absolute values of zeta potential and thus the stability of the protein solutions decreased with temperature and concentration. For SP solutions, viscosity and apparent yield stress increased with concentration. Shear thinning behavior was prevalent, becoming more pronounced with increasing concentration. Heat treatments at T ≥ 80 °C induced glycinin denaturation, followed by aggregation and network formation when C ≥ 7.5%. Heat treatment did not significantly affect viscosity of MCN systems, while increasing concentration resulted in a significant increase in apparent viscosity and apparent yield stress. Most MCN systems exhibited Newtonian flow behavior, with the exception of systems with C ≥ 12.5% treated at T ≥ 80 °C, which became slightly shear thickening. Mixed SP–MCN systems mimicked the behavior of SP, with most values of rheological parameters intermediate between SP and MCN-only systems. Mixtures of 7.5–12.5% concentration treated at 90 °C displayed local phase separation, low viscosity and apparent yield stress, while 15% mixtures treated at 90 °C showed protein aggregation and incipient network formation. The data generated in this study can be used to develop a range of protein based products with unique flow characteristics and storage stability.

Pulsed light (PL) is a technology that uses short, high-energy pulses of UV-rich broad spectrum light to inactivate a range of pathogenic and spoilage microorganisms in foods and on food contact surfaces. Microbial inactivation is directly related to the energy dose (fluence) received by the target microbes. Since fluence decays away from the lamp source due to light absorption and scattering phenomena, it is necessary to accurately quantify the fluence received locally within a substrate in order to design uniform antimicrobial PL treatments. The main objective of this work was to quantify and map the spatial distribution of both total and UV fluence both in air and in liquid substrates with different optical properties. Butterfield’s phosphate buffer (BPB), trypticase soy broth (TSB), and apple juice (clarified apple cider) were used as substrates and Listeria innocua was used as the challenge microorganism. A pyroelectric head, and a UV–VIS–NIR spectrophotometer connected to a 1000 μm optical fiber, were used to measure the fluence in air and the three liquid substrates. Fluence was measured at incremental distances from the lamp, along the x-, y- and z-axes. As expected, fluence decreased with increasing distance from the lamp, in all three directions. A 3-parameter Gaussian model described well the spatial distribution of fluence, both in air and in the liquid substrates. Overall, this study emphasizes the fact that substrate–light interactions affect the spatial distribution of fluence within a substrate, and these non-uniformities need to be taken into account when developing commercial applications of PL.

The main objective of this work was to evaluate the effectiveness of pulsed light (PL) treatment for the inactivation of Escherichia coli in liquids with different levels of clarity. Nonpathogenic E. coli ATCC 25922 and pathogenic E. coli O157: H7 were used as challenge organisms. Butterfield's phosphate buffer (BPB), tryptic soy broth (TSB), apple juice, and apple cider were used as substrates. The inoculated liquids were placed in a thin layer (1.3 mm) into glass chambers (23 by 53 by 11 mm) and exposed to PL doses of up to 13.1 J/cm2. PL treatments were performed in a Xenon RS-3000C PL unit, both in static mode and under turbulence. Survivors were determined by standard plate counting or the most-probable-number technique. For static treatments, reduction levels exceeding 8.5 log were obtained in BPB for all strains and reduction levels of about 3.5 log were obtained in TSB. For apple juice, inactivation levels of 2.66 +/- 0.10 log were obtained for E. coli ATCC 25922 and 2.52 +/- 0.19 log for E. coli O157:H7. In cider, inactivation levels of 2.32 +/- 0.16 log and 3.22 +/- 0.29 log were obtained for the nonpathogenic and pathogenic strains, respectively. Inactivation kinetics was characterized using the Weibull model. Turbulent treatments resulted in 5.76 +/- 0.06 log reduction in cider and 7.15 +/- 0.22 log reduction in juice, which satisfies the U.S. Food and Drug Administration requirement of 5-log reduction of E. coli. These results show promise for the use of PL for the effective reduction of E. coli in apple juice and cider.

The risk of listeriosis associated with ready-to-eat foods is a major concern in the United States. Pulsed light (PL) treatment has been effective for killing Listeria. The possibility of enhancing the antilisterial capability of PL treatment by combining PL with an additional hurdle, the natural antimicrobial nisin, was explored in this study. First, the ability of Listeria innocua to mimic the response of Listeria monocytogenes to PL treatment was demonstrated. Subsequently, a series of inoculation studies was performed in which canned sausages were surface inoculated with L. innocua as a surrogate for L. monocytogenes and then treated with a commercial preparation of nisin (Nisaplin), PL, or a combination of the two treatments. The application of a Nisaplin dip alone resulted in an immediate reduction of L. innocua by 2.35 +/- 0.09 log CFU. PL reduced L. innocua by 1.37 +/- 0.30 log CFU after exposure to 9.4 J/cm2. A total reduction of 4.03 +/- 0.15 log CFU was recorded after the combined treatment of Nisaplin and PL for 48 h at 4 degrees C. The long-term survival of L. innocua was evaluated on sausages stored at 4 degrees C. Treatment with Nisaplin and PL resulted in a 4- to 5-log reduction for two replicate studies. The combination treatment resulted in no significant microbial growth during 28 and 48 days of refrigerated storage in the first and second replicates, respectively. These results suggest that this combination treatment can be used as an effective antilisterial step in the production of ready-to-eat foods.

Pulsed light (PL) treatment can effectively reduce microbial populations in clear substrates and on surfaces, but its effectiveness varies as a function of substrate or treatment-related factors. For PL to be successfully adopted by the food industry, all factors of influence, as well as the inactivation kinetics for the microorganisms of concern, must be elucidated. In this study, the inactivation kinetics of Listeria innocua and the effect of inoculum size on PL inactivation were investigated. Stainless steel coupons (50.8 by 101.6 mm) of defined surface properties and transparent glass chamber slides (25.4 by 50.8 by 10 mm) were each inoculated with 1 ml of aqueous suspensions of L. innocua containing inoculum populations of up to 10(9) CFU. The thickness of the liquid layer in the glass slides was 1.16 mm. The inoculated substrates were exposed to PL treatment of up to 17 J/cm2 in a static PL chamber equipped with a pulsed Xenon lamp. Survivors were recovered and enumerated by both standard plate counting and most-probable-number procedures. The data indicated that in clear liquids, PL resulted in more than a 6-log reduction of L. innocua after a 12-J/cm2 treatment, regardless of the initial inoculum size. For the stainless steel surfaces, less than a 4-log reduction after a 12-J/cm2 treatment and a noticeable effect of substrate characteristics and inoculum size on inactivation were observed. The survivor curves showed pronounced tailing for all substrates used in the study. The Weibull model accurately predicted the survivor ratios for the PL treatment of L. innocua in clear liquids, with a shape and scale parameter of 0.33 and 3.01, respectively. The Weibull model resulted in significant overestimation of PL effectiveness for the stainless steel substrates, where the influence of various substrate properties and inoculum level on inactivation was significant.