The current microbiological regulatory criteria in the European Union specify a maximum Listeria monocytogenes population of 100 CFU/g allowable in ready-to-eat foods provided the product will not exceed this limit throughout its shelf life. The aim of this study was to validate the manufacturing method for traditional Greek Graviera cheese produced from thermized milk. Initial challenge experiments evaluated the fate of inoculated L. monocytogenes (ca. 4 log CFU/ml, three-strain cocktail) in thermized Graviera cheese milk (TGCM; 63 degrees C for 30 s) in the presence and absence of a product-specific starter culture (SC) in vitro. Milk samples were incubated for 6 h at 37 degrees C and then for 66 h at 18 degrees C. Experiments were conducted to evaluate the fate of a cocktail of three nonpathogenic L. monocytogenes and L. innocua indicator strains inoculated (ca. 3 log CFU/g) in Graviera cheeses commercially manufactured from TGCM+SC. Cheeses were brined, ripened at 18 degrees C and 90% relative humidity for 20 days, and stored at 4 degrees C for up to day 60 under vacuum. In TGCM, L. monocytogenes increased by ca. 2 log units, whereas in TGCM+SC L. monocytogenes growth was retarded (P < 0.05) after a ca. 1-log increase within 6 h at 37 degrees C. Populations of Listeria indicator strains did not grow in TGCM+SC cheeses at any stage; they declined 10-fold in fresh cheeses within 5 days and then survived with little death thereafter. Thus, growth inhibition but not inactivation of potent natural Listeria contaminants at levels below 100 CFU/g occurs in the core of traditional Greek Graviera cheese during fermentation, ripening, and storage.

Rindless Swiss cheese was made from a mixture of pasteurized whole and skim milk that was inoculated to contain 10(4) to 10(5) cfu of Listeria monocytogenes (strain Ohio, California, or V7)/ml. During clotting of milk, numbers of L. monocytogenes remained nearly unchanged. When the curd was heated gradually to attain the cooking temperature (50 degrees C), numbers of L. monocytogenes increased by approximately 40 to 45% over those in inoculated milk. Cooking curd at 50 degrees C (122 degrees F) for 30 to 40 min resulted in resilient curd having a pH of 6.40 to 6.45 and decreased L. monocytogenes by 48% compared with numbers of the pathogen in inoculated milk. After curd was pressed under whey, numbers of L. monocytogenes increased by approximately 52% over those in inoculated milk and reached their maxima at the end of this stage. A sharp decrease in numbers of L. monocytogenes occurred during brining of cheese blocks (7 degrees C for 30 h). The population of L. monocytogenes continued to decrease during cheese ripening. Average D values for strains California, Ohio, and V7 were 29.2, 24, and 22.5 d, respectively. Listeria was not detected (direct plating, and cold enrichment) after 80, 77, and 66 d of ripening of Swiss cheese made from milk inoculated with strains California, Ohio, and V7, respectively. Thus, Swiss cheese made in this study did not permit extended survival of L. monocytogenes.

Tyndallized samples of unfiltered skim milk and retentate (concentrated fivefold or twofold by volume) and permeate from UF skim milk were inoculated with 5.5 x 10(3) to 1.5 x 10(5) cfu/ml of Listeria monocytogenes strains California or V7 together with 4 x 10(7) to 2.3 x 10(8) cfu/ml of mesophilic lactic acid bacteria. Numbers of L. monocytogenes (McBride Listeria agar) and lactic acid bacteria (all purpose Tween agar) were determined after 0, 6, 12, 24, 30, and 36 h of incubation at 30 degrees C. Lactic acid bacteria significantly inhibited or inactivated L. monocytogenes in all three products. Inactivation was greater in permeate (6.77 orders of magnitude) than in unfiltered skim milk (3.67 orders of magnitude) or in retentate (4.21 orders of magnitude). Degree of inactivation in retentate was related to the extent of concentration. Inactivation was not complete, and L. monocytogenes survived in these products during fermentation for up to 36 h. When fermented products were refrigerated (4 degrees C), L. monocytogenes survived for 4 to 6 wk in skim milk, 3 to 5 wk in retentate, and 1 wk in permeate. At refrigeration temperature, length of survival was dependent on type of product and strain of the pathogen.

Growth of Aspergillus parasiticus and accumulation of aflatoxin B(1) in the medium that contained antifungal agents were monitored during the growth cycle of the mold. The antifungal agents tested are the food additive (antioxidant), butylated hydroxyanisole (BHA), the pesticide, isoprothiolane, and the antibiotic, nystatin. Growth of the mold was quantified using a newly developed criterion, named the growth coefficient (GC). The GC values were calculated from the growth parameters of the logistic function that fits the growth curve of the mold. At the range of concentrations of additives studied, maxima of growth inhibition were 31.3, 23.1, and 43.6% at 60 ppm of BHA, 70 ppm of isoprothiolane, and 45 units of nystatin/mL, respectively. The ability of the mold to accumulate aflatoxin B(1) in its medium [as measured by the accumulation rate constant (alpha)] In the presence of various levels of the antifungal agents was concentration-dependent. Sixty parts per million of BHA decreased the value of alpha by 71.7%, 30 units of nystatin/mL was the most effective concentration of that antibiotic and resulted in only 23.5% inhibition, and isoprothiolane at all its levels stimulated elaboration of aflatoxin B(1) by the mold.

N(alpha)-Palmitoyl-L-lysyl-L-lysine-ethyl ester dihydrochloride (PLL) has antimicrobial properties and may be useful as a food preservative. This study was conducted to see if PLL can inhibit growth and synthesis of aflatoxin by Aspergillus parasiticus. Growth of mold and accumulation of aflatoxins were monitored for up to 15 days. To compare these data with those of a known inhibitor of aflatoxin synthesis, dichlorvos was added to media, and mold growth and aflatoxin accumulation were monitored. The kinetic model of Brown and Vass that correlates growth and formation of secondary metabolites was applied to results of this study, and values for maturation time (t(m)) and aflatoxin accumulation rate constant (alpha) were calculated. Values of t(m) decreased when cultures contained PLL, whereas presence of dichlorvos resulted in a considerable increase. The lag phase of mold growth increased in the presence of PLL. The values of alpha increased with an increasing amount (up to 300 ppm) of PLL in media. Higher concentrations of PLL decreased the value of alpha. All levels of dichlorvos tested decreased the value of alpha. The aflatoxin accumulation rate constant (alpha) as a function of concentration of additive (C) followed the general equation:\documentclass{article}\pagestyle{empty}\begin{document}$$\alpha =\frac{{\alpha _m C\exp (-{C \mathord{\left/{\vphantom {C {K_i }}}\right.\kern-\nulldelimiterspace}{K_i }})}}{{C + K_a }}$$\end{document} where alpha(m), K(a), and K(i) are constants.

Nisin, 200 or 5000 Reading units/ml, was added to Aspergillus parasiticus cultures. The cultures were incubated at 28 degrees C for 3, 7 or 10 days and analyzed for mycelial dry weight, pH and accumulation of aflatoxin B1 and G1. During the first 3 days of incubation, dry weight, pH decrease and aflatoxin accumulation were suppressed by nisin, when compared with similar values for the nisin-free control. After longer incubation, differences in dry weight nd pH values decreased, whereas accumulation of aflatoxin in the nisin-containing cultures surpassed that of the control.

A rapid, economical, and reliable liquid chromatographic (LC) method is described for determination of aflatoxin M1 in milk. The method includes an improved AOAC extraction procedure, cleanup of the extract on a silica cartridge, and LC quantitation. Alternatively, a rapid column cleanup procedure can be used. Milk artificially spiked with aflatoxin M1 at 0.05, 0.1, and 0.5 ppb was analyzed using both new approaches as well as an AOAC method coupled with LC for quantitation of the toxin. Recovery of aflatoxin M1 by the first approach of the new method ranged between 93.4 and 99.1%, and for the alternative procedure between 92.4 and 96.8%. The AOAC method gave lower recovery (85.6-90.7%) of toxin, but the results from this method had a somewhat smaller standard deviation for replicate analyses than did results of the new method.

Method of homogenization (Waring blender versus stomacher), type of diluent (tryptose broth [TB] versus aqueous 2% trisodium citrate), and temperature of diluent (20 versus 40 degrees C) were compared for recovery of Listeria monocytogenes from freshly made and ripened Colby cheese. By using direct plating on McBride listeria agar, significantly higher numbers of L. monocytogenes were recovered when cheese samples were (i) homogenized for 2 min with the blender rather than the stomacher (P less than 0.01),(ii) diluted in trisodium citrate rather than TB (P less than 0.01), and (iii) diluted in diluents at 40 rather than 20 degrees C (P less than 0.05). Based on these results, a new diluent/enrichment medium was developed by adding 2% trisodium citrate to TB (TBC). Despite superior results with the blender, biosafety concerns led to use of the stomacher for homogenization of cheese samples; hence, the stomaching time was increased to 3 min. Results obtained by direct plating indicated that recovery of L. monocytogenes from Colby cheese and from curd samples taken during manufacture of brick cheese increased when samples were diluted 1:10 in TBC at 45 degrees C and stomached for 3 min, as compared with similarly treated samples diluted in TB at 25 degrees C. A similar comparison of both diluents for recovery of L. monocytogenes from cold-pack cheese food yielded bacterial counts which were not significantly different. Recovery of L. monocytogenes from cold-enriched (at 4 degrees C for up to 8 weeks) samples of Colby cheese and cold-pack cheese food was generally similar for samples homogenized in TBC or TB.

Raw whole milk was artificially contaminated to contain 1 ppb aflatoxin M1. A thin layer of milk (.1 cm) was irradiated with ultraviolet energy. In the first experiment, milk was held at 90 degrees C for 10 min, cooled to 20 degrees C, and irradiated for 30 min. Amount of aflatoxin M1 decreased equally (56.2 vs. 53.9%) in raw or preheated milk, suggesting no involvement of milk enzymes in degrading aflatoxin M1 by ultraviolet energy. Data obtained when raw milk containing aflatoxin M1 was exposed to ultraviolet energy for 15 to 60 min suggest first order kinetics for the degradation reaction. In another experiment, milk was held at 5, 25, or 65 degrees C while it was being irradiated. Aflatoxin M1 was degraded at all temperatures. Amount of toxin decreased nonlinearly when temperature at which milk was held was increased. Presence in milk of benzoyl peroxide at .002% did not change the extent to which aflatoxin M1 was degraded by irradiation. Amount of toxin, however, decreased by 89.1% in milk containing .05% H2O2 as compared with 60.7% for H2O2-free milk when both were exposed to ultraviolet irradiation for 20 min at 25 degrees C.

Probiotic lactic acid bacteria (LAB) have been shown to alleviate inflammation, enhance the immunogenicity of rotavirus vaccines, or reduce the severity of rotavirus diarrhoea. Although the mechanisms are not clear, the differential Th1/Th2/Th3-driving capacities and modulating effects on cytokine production of different LAB strains may be the key. Our goal was to delineate the influence of combining two probiotic strains of Lactobacillus acidophilus and Lactobacillus reuteri on the development of cytokine responses in neonatal gnotobiotic pigs infected with human rotavirus (HRV). We demonstrated that HRV alone, or HRV plus LAB, but not LAB alone, initiated serum cytokine responses, as indicated by significantly higher concentrations of IFN-α, IFN-γ, IL-12, and IL-10 at postinoculation day (PID) 2 in the HRV only and LAB+HRV+ pigs compared to LAB only and LAB-HRV- pigs. Peak cytokine responses coincided with the peak of HRV replication. LAB further enhanced the Th1 and Th2 cytokine responses to HRV infection as indicated by significantly higher concentrations of IL-12, IFN-γ, IL-4 and IL-10 in the LAB+HRV+ pigs compared to the LAB-HRV+ pigs. The LAB+HRV+ pigs maintained relatively constant concentrations of TGF-β compared to the HRV only group which had a significant increase at PID 2 and decrease at PID 7, suggesting a regulatory role of LAB in maintaining gut homeostasis. At PID 28, cytokine secreting cell (CSC) responses, measured by ELISpot, showed increased Th1 (IL-12, IFN-γ) CSC numbers in the LAB+HRV+ and LAB-HRV+ groups compared to LAB only and LAB-HRV- pigs, with significantly increased IL-12 CSCs in spleen and PBMCs and IFN-γ CSCs in spleen of the LAB+HRV+ group. Thus, HRV infection alone, but not LAB alone was effective in inducing cytokine responses but LAB significantly enhanced both Th1 and Th2 cytokines in HRV-infected pigs. LAB may also help to maintain immunological homeostasis during HRV infection by regulating TGF-β production.

The physical quality and functionality of shell eggs, pasteurized with heat or a combination of heat and ozone, were assessed during eight weeks of storage at 4 or 25 °C. Shell eggs were treated as follows:(1) immersion heating that mimics commercial pasteurization processes (egg internal temperature of 56 ± 0.1 °C for 32 min), or (2) a newly developed combination process comprised of heating (56 ± 0.1 °C, internal, for 10 min) followed by gaseous ozone treatment. Eggs were tested for yolk index, Haugh units, albumen pH, albumen turbidity, and percent overrun. Additionally, albumen samples were assayed for lysozyme activity and free sulfhydryl group content, and were analyzed using differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. Both processed and unprocessed eggs maintained superior quality when stored at 4 °C, as opposed to 25 °C. Pasteurization, regardless of method, led to superior maintenance of Haugh units during storage but also increased albumen opacity and decreased albumen overrun. Detrimental effects on quality markers were more severe in heat-pasteurized eggs than those treated with the ozone-based process. Pasteurization of shell eggs by either process did not affect lysozyme activity or sulfhydryl group content. Changes in protein secondary structure, as indicated by FTIR analysis, suggest that the ozone-based process is less damaging to albumen proteins than is the heat-alone process. In conclusion, heat-ozone pasteurization, by virtue of its less severe heat treatment, yields a safe final product that more closely resembles untreated shell eggs.

High-pressure processing (HPP) can reduce or eliminate microorganisms of concern in food without deteriorating product quality; however, quality benefits must justify the substantial capital investment for the utilization of this technology. HPP is particularly a beneficial preservation technology for products damaged by thermal treatments or when product quality could be improved by reformulation to raise pH or eliminate chemical preservatives. The primary objectives of this study were to determine the efficacy of HPP to protect premium ranch dressing (pH 4.4) from microbial spoilage and to assess changes in physical, chemical, and sensory attributes throughout the product's shelf life. In inoculated-packages studies, the efficacy of HPP was measured against ranch dressing spoilage organisms: Pediococcus acidilactici, Lactobacillus brevis, and Torulaspora delbrueckii. HPP treatment (600 MPa, 3 min) decreased population of P. acidilactici, the most pressure-resistant spoilage organism tested, by >or= 6.4 log CFU/g. During a shelf-life study of edible product, treating ranch dressing at 600 MPa for 5 min effectively prevented microbial spoilage throughout the storage period (26 wk at 4 and 26 degrees C). The pH and emulsion stability of ranch dressing were not adversely influenced by HPP. Extended storage of HPP product for 16 to 26 wk at 26 degrees C resulted in a decrease in consumer acceptance and significant changes in color and organic acid profile (specifically, increased pyroglutamic acid). These changes were consistent with those expected during extended storage of commercially available products. HPP may be used to produce premium ranch dressing, with defined shelf-life and storage conditions, without significantly changing product attributes.

AIMS Investigating mechanisms of lethality enhancement when Escherichia coli O157:H7, and selected E. coli mutants, were exposed to tert-butylhydroquinone (TBHQ) during ultra-high pressure (UHP) treatment. METHODS AND RESULTS Escherichia coli O157:H7 EDL-933, and 14 E. coli K12 strains with mutations in selected genes, were treated with dimethyl sulfoxide solution of TBHQ (15-30 ppm), and processed with UHP (400 MPa, 23 +/- 2 degrees C for 5 min). Treatment of wild-type E. coli strains with UHP alone inactivated 2.4-3.7 log CFU ml(-1), whereas presence of TBHQ increased UHP lethality by 1.1-6.2 log CFU ml(-1); TBHQ without pressure was minimally lethal (0-0.6 log reduction). Response of E. coli K12 mutants to these treatments suggests that iron-sulfur cluster-containing proteins ([Fe-S]-proteins), particularly those related to the sulfur mobilization (SUF system), nitrate metabolism, and intracellular redox potential, are critical to the UHP-TBHQ synergy against E. coli. Mutations in genes maintaining redox homeostasis and anaerobic metabolism were associated with UHP-TBHQ resistance. CONCLUSIONS The redox cycling activity of cellular [Fe-S]-proteins may oxidize TBHQ, potentially leading to the generation of bactericidal reactive oxygen species. SIGNIFICANCE AND IMPACT OF THE STUDY A mechanism is proposed for the enhanced lethality of UHP by TBHQ against E. coli O157:H7. The results may benefit food processors using UHP-based preservation, and biologists interested in piezophilic micro-organisms.

This study aimed to evaluate the behavior of virulent Yersinia enterocolitica (YE) during the manufacture, ripening and storage of Lighvan cheese with particular reference to strains of YE, initial inoculation level, and storage time. Three strains of YE with low (1 log cfu/ml) and high (3 log cfu/ml) inoculation levels were inoculated to raw whole ewe's milk which was then used for manufacturing of Lighvan cheese. Throughout the manufacturing, ripening and storage periods the number of YE was counted on selective media. Enumerated colonies were then confirmed by duplex PCR using ail and virF genes. Moreover, some microbial and physiochemical characteristics of the cheese samples were examined. According to the results, initial inoculation level and storage time had statistically significant (P<0.01) effects on persistency of YE, while strain type exhibited no statistically significant (P>0.01) impact on survival of the pathogen. Results showed a rapid increase in the number of YE during manufacturing, however, in the ripening and storage periods the number of YE was decreased and eventually it was eliminated in all cheese batches after 4 months of storage.

The aim of the current work was to assess the influence of two temperatures, 4°C and 24°C, on pH and water activity and their association with Brucella melitensis survival during the traditional manufacture of ripened goat cheese. Raw milk from a brucellosis-free goat herd was used for the manufacture of ripened cheese. The cheese was inoculated with 5×10(9) of the B. melitensis 16M strain during the tempering stage. The cheeses were matured for 5, 20, and 50 days at both temperatures. To assess Brucella survival, the pH and a(w) were recorded at each stage of the process (curd cutting, draining whey, immersion in brine, ripening I, ripening II, and ripening III). B. melitensis was detected at ripening stage III (1×10(3) colony-forming unit [CFU]/mL) from cheeses matured at 4°C with a pH of 5.0 and a(w) of 0.90, and at a ripening stage II (1×10(4) CFU/mL) from cheeses ripened at 24°C with a pH of 4.0 and a(w) of 0.89. The remaining stages were free from the inoculated pathogen. In addition, viable B. melitensis was recovered in significant amounts (1-2×10(6) CFU/mL) from the whey fractions of both types of cheese ripened at 24°C and 4°C. These results revealed the effects of high temperature (24°C vs. 4°C) on the low pH (4) and a(w)(0.89) that appeared to be associated with the suppression of B. melitensis at the early stages of cheese ripening. In the ripened goat cheeses, B. melitensis survived under a precise combination of temperature during maturation, ripening time, and a(w) in the manufacturing process.

The dynamics of the physicochemical characteristics of foods help to determine the fate of pathogens throughout processing. The aim of this study was to assess the behaviour of Listeria monocytogenes during cheesesmaking and ripening and to model the growth observed under the dynamic conditions of the cheese. A laboratory scale cheese was made in 4 independent replicates from pasteurised or raw cow's milk, artificially contaminated with L. monocytogenes. No growth of L. monocytogenes occurred during raw milk cheese-making, whereas growth did occur in pasteurised milk. During ripening, growth occurred in raw milk cheese, but inactivation occurred in pasteurised milk cheese. The behaviour observed for L. monocytogenes was modelled using a logistic primary model coupled with a secondary cardinal model, taking into account the effect of physicochemical conditions (temperature, pH, water activity and lactate). A novel statistical approach was proposed to assess the optimal growth rate of a microorganism from experiments performed in dynamic conditions. This complex model had an acceptable quality of fit on the experimental data. The estimated optimum growth rates can be used to predict the fate of L. monocytogenes during cheese manufacture in raw or pasteurized milk in different physicochemical conditions. The data obtained contributes to a better understanding of the potential risk that L. monocytogenes presents to cheese producers (growth on the product, if it is contaminated) and consumers (the presence of high numbers) and constitutes a very useful set of data for the completion of chain-based modelling studies.

Listeria monocytogenes CCUG 15526 was inoculated at a concentration of approximately 7.0 log(10) cfu/mL in milk samples with 0.3, 3.6, 10, and 15% fat contents. Milk samples with 0.3 and 3.6% fat content were also inoculated with a lower load of approximately 3.0 log(10) cfu/mL. Inoculated milk samples were subjected to a single cycle of ultra-high-pressure homogenization (UHPH) treatment at 200, 300, and 400 MPa. Microbiological analyses were performed 2 h after the UHPH treatments and after 5, 8, and 15 d of storage at 4 degrees C. Maximum lethality values were observed in samples treated at 400 MPa with 15 and 10% fat (7.95 and 7.46 log(10) cfu/mL), respectively. However, in skimmed and 3.6% fat milk samples, complete inactivation was not achieved and, during the subsequent 15 d of storage at 4 degrees C, L. monocytogenes was able to recover and replicate until achieving initial counts. In milk samples with 10 and 15% fat, L. monocytogenes recovered to the level of initial counts only in the milk samples treated at 200 MPa but not in the milk samples treated at 300 and 400 MPa. When the load of L. monocytogenes was approximately 3.0 log(10) cfu/mL in milk samples with 0.3 and 3.6% fat, complete inactivation was not achieved and L. monocytogenes was able to recover and grow during the subsequent cold storage. Fat content increased the maximum temperature reached during UHPH treatment; this could have contributed to the lethal effect achieved, but the amount of fat of the milk had a stronger effect than the temperature on obtaining a higher death rate of L. monocytogenes.

The coagulant retained in cheese curd is a major contributor to proteolysis during ripening. The objective of this study was to quantify residual coagulant in 9 cheese varieties by measuring its activity on a synthetic heptapeptide (Pro-Thr-Glu-Phe-[NO2-Phe]-Arg-Leu) assayed using reversed-phase HPLC. The level of residual coagulant activity was highest in Camembert cheese, probably due to its low pH at whey drainage and the high moisture content of the cheese, followed in order by Feta=Port du Salut=Cheddar>Gouda>Emmental=Parmigiano Reggiano=low-moisture part-skim Mozzarella=Mozzarella di Bufala Campana. The high cooking temperature (50-54 degrees C) used during the manufacture of Emmental and Parmigiano Reggiano cheeses and the cooking and stretching step in hot water during the manufacture of Mozzarella cheese may be the reasons for the lowest residual coagulant activity in these cheeses. The level of residual coagulant activity was higher in Feta cheese made from milk concentrated by ultrafiltration than in conventional Feta.

Because of renewed interest in specialty cheeses, artisan and farmstead producers are manufacturing surface-mold-ripened soft cheeses from raw milk, using the 60-day holding standard (21 CFR 133.182) to achieve safety. This study compared the growth potential of Listeria monocytogenes on cheeses manufactured from raw or pasteurized milk and held for > 60 days at 4 degrees C. Final cheeses were within federal standards of identity for soft ripened cheese, with low moisture targets to facilitate the holding period. Wheels were surface inoculated with a five-strain cocktail of L. monocytogenes at approximately 0.2 CFU/ cm2 (low level) or 2 CFU/cm2 (high level), ripened, wrapped, and held at 4 degrees C. Listeria populations began to increase by day 28 for all treatments after initial population declines. From the low initial inoculation level, populations in raw and pasteurized milk cheese reached maximums of 2.96 +/- 2.79 and 2.33 +/- 2.10 log CFU/g, respectively, after 60 days of holding. Similar growth was observed in cheese inoculated at high levels, where populations reached 4.55 +/- 4.33 and 5.29 +/- 5.11 log CFU/g for raw and pasteurized milk cheeses, respectively. No significant differences (P < 0.05) were observed in pH development, growth rate, or population levels between cheeses made from the different milk types. Independent of the milk type, cheeses held for 60 days supported growth from very low initial levels of L. monocytogenes introduced as a postprocess contaminant. The safety of cheeses of this type must be achieved through control strategies other than aging, and thus revision of current federal regulations is warranted.

Traditionally, Cheddar cheese is made by the milled-curd method. However, because of the mechanization of cheese making and time constraints, the stirred-curd method is more commonly used by many large-scale commercial manufacturers. This study was undertaken to evaluate quality differences during ripening (at 2 and 8 degrees C) of Cheddar cheese made by the milled-curd and stirred-curd methods, using 4 different commercial starters. Twenty-four vats (4 starters x 2 methods x 3 replicates) were made, with approximately 625 kg of pasteurized (72 degrees C x 16 s) whole milk in each vat. Fat, protein, and salt contents of the cheeses were not affected by the starter. Starter cell densities in cheese were not affected by the method of manufacture. Nonstarter lactic acid bacteria counts at 90, 180, and 270 d were influenced by the manufacturing method, with a higher trend in milled-curd cheeses. Proteolysis in cheese (percentage of water-soluble N) was influenced by the starter and manufacturing method (270 d). Sensory analysis by a trained descriptive panel (n = 8) revealed differences in cooked, whey, sulfur, brothy, milk fat, umami, and bitter attributes caused by the starter, whereas only brothy flavor was influenced by storage temperature. The method of manufacture influenced diacetyl, sour, and salty flavors.

The efficiency of combining high-pressure processing (HPP) and active packaging technologies to control Listeria monocytogenes growth during the shelf life of artificially inoculated cooked ham was assessed. Three lots of cooked ham were prepared: control, packaging with alginate films, and packaging with antimicrobial alginate films containing enterocins. After packaging, half of the samples were pressurized. Sliced cooked ham stored at 6 degrees C experienced a quick growth of L. monocytogenes. Both antimicrobial packaging and pressurization delayed the growth of the pathogen. However, at 6 degrees C the combination of antimicrobial packaging and HPP was necessary to achieve a reduction of inoculated levels without recovery during 60 days of storage. Further storage at 6 degrees C of pressurized antimicrobial packed cooked ham resulted in L. monocytogenes levels below the detection limit (day 90). On the other hand, storage at 1 degrees C controlled the growth of the pathogen until day 39 in non-pressurized ham, while antimicrobial packaging and storage at 1 degrees C exerted a bacteriostatic effect for 60 days. All HPP lots stored at 1 degrees C led to counts <100CFU/g at day 60. Similar results were observed when combining both technologies. After a cold chain break no growth of L. monocytogenes was observed in pressurized ham packed with antimicrobial films, showing the efficiency of combining both technologies.

Listeria monocytogenes is a food-borne pathogen that has been implicated in many outbreaks associated with ready-to-eat products. Listeria adjusts to various stresses by adjusting its membrane fluidity, increasing the uptake of osmoprotectants and cryoprotectants, and activating the sigma(B) stress factor. The present work examines the regulation of membrane fluidity through direct measurement based on fluorescent anisotropy. The membrane fluidities of L. monocytogenes Scott A, NR30, wt10403S, and cld1 cells cultured at 15 and 30 degrees C were measured at 15 and 30 degrees C. The membrane of the cold-sensitive mutant (cld1) was more rigid than the membranes of the other strains when grown at 30 degrees C, but when grown at 15 degrees C, it was able to adjust its membrane to approach the rigidity of the other strains. The difference in rigidities, as determined at 15 and 30 degrees C, was greater in liposomes than in whole cells. The rates of fluidity adjustment and times required for whole cells to adjust to a different temperature were similar among strains but different from those of liposomes. This suggests that the cells had a mechanism for homeoviscous adaptation that was absent in liposomes.

The antimicrobial effect against L. monocytogenes of biodegradable films (alginate, zein and polyvinyl alcohol) containing enterocins was investigated. Survival of the pathogen was studied by means of challenge tests performed at 6 degrees C during 8 and 29 days, for air-packed and vacuum-packed sliced cooked ham, respectively. Air packaging was tested with two concentrations of enterocins (200 and 2000 AU/cm2). Control air-packed cooked ham showed an increase of L. monocytogenes from 10(4) to 10(7) CFU/g after 8 days. By contrast, packaging with antimicrobial films effectively slowed down the pathogen's growth, leading to final counts lower than in control lots. Air-packaging with alginate films containing 2000 AU/cm2 of enterocins effectively controlled L. monocytogenes for 8 days. An increase of only 1 log unit was observed in zein and polyvinyl alcohol lots at the same enterocin concentration. Vacuum packaging with films containing enterocins (2000 AU/cm2) also delayed the growth of the pathogen. No increase from inoculated levels was observed during 15 days in antimicrobial alginate films. After 29 days of storage, the lowest counts were obtained in samples packed with zein and alginate films containing enterocins, as well as with zein control films. The most effective treatment for controlling L. monocytogenes during 6 degrees C storage was vacuum-packaging of sliced cooked ham with alginate films containing 2000 AU/cm2 of enterocins. From the results obtained it can concluded that antimicrobial packaging can improve the safety of sliced cooked ham by delaying and reducing the growth of L. monocytogenes.