Microbiology of a Ham-Type Product Made from Soy-Extended Cured Beef and Inoculated with Clostridium sporogenes PA3679

The microbiological stability of a new ham-type product made from soy-extended cured beef was examined under wholesale (2–4°C) and retail (5°C) refrigerated storage conditions, and during abuse-temperature holding for 24 and 48 hr at 24-25°C after inoculation with Closrridium sporogenes PA3679. No microbiological effects (P >0.05) could be attributed to the level of soy protein isolate in the injection brine (0, 5, 7.5 or 9%) on the basis of mesophilic, psychrotrophic, anaerobic and lactic bacterial counts. Samples held at 2-4°C did not exceed 10⁴ CFU/g after 4 wk for any bacterial type examined. Product shelf-life was > 3 wk at 5°C and 2 wk at 8–10°C. Inoculated PA3679 did not grow in the product during 24 or 48 hr simulated mishandling (24-2°C).     

Modified Atmosphere Packaging of Fresh, "Ready-to-use" Grated Carrots in Polymeric Films

“Ready-to-use” grated carrots were packaged in different films (oxygen permeability from 950 to 22,000 cc/m²/day/atm at 25°C) and stored at 2, 6 or 10°C for 10 days. Gaseous atmosphere in packs and the following were monitored: lactic acid bacteria, yeast counts, exudate and potassium ion released, sugars, carotene, ethanol and lactic acid. The respiration rate of the packaged carrots was measured. Films with very low oxygen permeability resulted in anaerobic respiration, high leakage of potassium, and high lactic acid bacteria. With high-permeability films (between 10,000 and 20,000 cc/m²/day/atm at 25°C), grated carrots showed aerobic respiration and retained good quality. At 10°C, in carrots packed in the most permeable film, sucrose decreased markedly during storage. The gas permeabilities required for packaging grated carrots were evaluated in relation to storage temperature.     

Inhibition of Clostridium sporogenes PA 3679 and Natural Bacterial Flora of Cooked Vacuum-Packaged Bratwurst by Sodium Acid Pyrophosphate and Sodium Tripolyphosphate With or Without Added Sodium Nitrite

Survival and growth of inoculated Clostridium sporogenes PA3679 and natural aerobic and anaerobic bacterial flora were studied in refrigerated (5°C) and subsequently temperature abused (24–25°C), cooked, vacuum-packaged bratwurst containing 0.5% sodium acid pyrophosphate (SAPP) or sodium tripolyphosphate (STPP) with or without sodium nitrite. Phosphates alone or combined with nitrite did not affect aerobic bacterial counts but resulted in reduced clostridial and anaerobic counts at 5°C. Upon temperature abuse, inhibition of all bacteria by SAPP was significant (P<0.05) for up to 48 hr and greatly enhanced by 100 ppm but not by 50 ppm sodium nitrite, whereas STPP lost its antimicrobial properties after 24 hr. Soluble orthophosphate levels had a positive correlation with bacterial inhibition in SAPP-treated bratwurst.     

Sensitivity of spores of Bacillus subtilis and Clostridium sporogenes PA 3679 to combinations of high hydrostatic pressure and other processing parameters

The combined effects of pressure, temperature, pH and the presence of nisin or sucrose laurate on the survival of spores of Bacillus subtilis 168 and Clostridium sporogenes PA 3679 were investigated. Spore populations of PA 3679 were reduced by 2.5-log₁₀ when exposed to 404 megapascals (MPa) at 25°C, pH 4.0 for 30 min, but the same treatment at pH 7.0 resulted in a <0.5-log₁₀ reduction in spore counts. Pressurization of B. subtilis spores at 70°C, pH 6.0 or 7.0 for 15 min at 404 MPa resulted in a 5-log₁₀ reduction as compared to a <0.5-log₁₀ reduction for the same pressurization treatment at 25°C. For the inactivation of spores of B. subtilis and PA 3679, the addition of nisin to the plating medium appeared to be synergistic in some instances when combined with pressurization at elevated temperatures and reduced pH. B. subtilis 168 was resistant to 0.1% sucrose laurate, but when combined at ≤6.0 pH with a 15-min treatment of 404 MPa at 45°C, a dramatic synergistic effect eliminated spore suspensions of 1×10⁶/ml.     

Effect of Heat Treatment and Selected Antimicrobials on the Shelf-life and Safety of Cooked, Vacuum-Packaged, Refrigerated Pork Chops

The shelf-life of refrigerated (2–4°C) pork chops inoculated with Clostridium sporogenes PA3679 and Staphylococcus aureus Z88 was examined in products sliced from loins cooked to 66°C (150°F), dipped in 5% polyphosphate blend, 2.5% potassium sorbate or 2% acetic acid solutions, vacuum-packaged and stored at 2–4°C. The effect of a second in-the-bag cooking step to 66°C (150°F) after vacuum packaging was also studied. Pork chops not reheated after packaging showed incipient spoilage after 15 days at 2–4°C, depending on surface treatment. The second cooking increased the shelf-life of refrigerated product to more than 60 days and reduced counts of inoculated cultures to undetectable levels. However, on exposure of the chops to simulated mishandling (24–25°C), clostridial growth was detected in all samples except those dipped in polyphosphate or acetic acid solutions.     

Fate of Clostridium sporogenes PA 3679 in Fish Sausage Formulations with Adjusted aw using Food Binders

Fish sausage from minced Spanish mackerel was formulated to a_w of 097–0.92 using egg white solids alone and in combination with nonfat dry milk, alginate and soy protein isolate, without and with nitrite added at 150 ppm. The batter was inoculated with PA 3679 spores at ca. 10⁵/g, chopped, stuffed in casing, cooked to a core temperature of 85°C, vacuum-packaged and stored at 25°C for 60 days. The test organism did not reproduce in formulations having a_w < 0.95. Total counts decreased rapidly and spore counts were nil at the end of storage. Spores of PA 3679 germinated at a_w as low as 0.924 but the cells failed to grow. Products with a_w > 0.95 spoiled. Product stability was influenced by a_w regardless of binder type and presence of nitrite.     

The effect of temperature on microbial growth in apple cubes packed in film and preserved by use of orange juice

Red delicious apple cubes were packed in fresh orange juice containing chemical preservatives (citric and ascorbic acid, potassium sorbate) and covered with plastic films of different gas permeabilities (polyethylene and EVA‐SARAN‐EVA) before storage at 4, 10 and 20 °C. The concentration of potassium sorbate in the product was optimized with respect to colour and microbial growth. Yeast and mould growth was modelled by Gompertz and linear equations to derive parameters such as lag phase, maximum microbial population and specific microbial growth or rates of decline. Activation energies for the specific growth rates were estimated from Arrhenius‐type equations and the time required to reach microbial counts of 10^6±0.2 CFU g^?1 was determined in all cases. At 4 °C, these values were longer than 25 days in all systems tested. The use of a low gas permeability film and an adequate potassium sorbate concentration extended storage life at higher temperatures.     

Effects of packaging materials,storage conditions and variety on oxidative stability of shelled walnuts

The effects of storage temperature, oxygen permeability of packaging material and variety on oxidative stability of vacuum-packaged walnut kernels were studied over a 12 months storage period. The oxidation experiments applied to two popular walnut varieties (Yalova-1 and Yalova-3) grown in Turkey. The peroxide values and hexanal contents of walnut samples significantly increased (p < 0.01) during storage at 30 °C. The highest hexanal content (4464.5–6406.9 μg/kg) were observed in Yalova-3 variety stored at 30 °C for 12 months in Polyamide/Polyethylene film pouches (oxygen permeability: 63.4 ± 0.4 mL/m²/24 h (23 °C)) with 90 μm total thickness. The effect of storage temperature and variety on lipid oxidation was found to be higher than the effect of oxygen permeability of the packaging material. It was concluded that for vacuum-packed walnut kernels in PA/PE film pouches having 63.4 ± 0.4 mL/m²/24 h (23 °C) oxygen permeability, 20 °C is sufficient to protect against oxidation for 12 months.     

Water Vapor Permeability of an Edible, Fatty Acid, Bilayer Film

A bilayer film consisting of stearic and palmitic acids as one layer and hydroxypropyl methylcellulose as the other was prepared. The permeability of this film to water vapor was tested under a variety of conditions involving film composition, temperature and relative humidity. This film exhibited permeability values (g · mil w m⁻²· day⁻¹· mm Hg⁻¹) of 0.5 at 40°C 0.3 at 25°C 1.7 at 5°C, and 6.0 at −19°C. This film would be expected to perform well at relative humidities below 90% and temperatures within the range of 40°C to -19°C.     

Selected Microbiological Properties of Kashar Cheese Samples Preserved with Potassium Sorbate

Kashar cheese, traditionally produced, is a popular dairy product in Turkey. Kashar cheese—a hard cheese—is frequently contaminated with mould. Potassium sorbate can be used for preservation of Kashar cheese. In this article, the effect of potassium sorbate on the microbiological characteristics of Kashar cheese was studied. It was found that the microbial counts at stored at 4 ± 0.1°C for 12 and 24 hours were not different from that of fresh milk samples. The means of total aerobic mesophilic bacteria (TAMB), lactic acid bacteria (LAB), coliforms, Staphylococcus aureus, proteolytic microorganisms, lipolytic bacteria, psychrotrophic bacteria and yeast-moulds in the cheese samples were determined as 4.3 × 10⁷, 2.1 × 10⁵, 3.5 × 10, 1.2 × 10, 4.5 × 10⁵, 5.6 × 10⁴, 1.7 × 10³, and 4.8 × 10⁴ cfu/g, respectively. The addition of potassium sorbate to Kashar cheese decreased the coliform and yeast-mould counts. The yeast and mould counts of cheese samples with added dry potassium sorbate were lower than that of fluid potassium sorbate.     

Whey protein isolate- and carrageenan-based edible films as carriers of different probiotic bacteria

The use of polymer blends as carriers for probiotic cells or using multi-strain probiotic culture mixture in film formulations has a high potential to maintain the stability of probiotics throughout storage. In this study, the survival of Lactobacillus acidophilus, Lactobacillus plantarum, and mixed culture (Lactobacillus spp., Lactococcus spp., and Bifidobacterium spp.) in whey protein isolate (W), carrageenan (C), and W/C blend (W to C on a wt/wt basis at 100 to 0, 75 to 25, 50 to 50, and 0 to 100) films were investigated during 30 d of storage at 4 and 25°C. The water vapor, mechanical, optical, and morphological properties of film samples were also determined. A significant decrease in total lactic acid bacteria counts of all strains (5–6 log cfu/g in reduction) for W and C films was observed during storage at 25°C, whereas blended films had 2 to 3 log cfu/g reduction. The mixed culture-incorporated films had higher cell counts during all storage temperatures. The incorporation of probiotic bacteria significantly influenced the water vapor permeability and color values of films while decreasing tensile strength and elongation at break values. This study reveals that a multi-strain mixed culture presented more chance for survival inside the polymer matrix, especially when carbohydrate- and protein-based polymers were blended.     

Diffusivity of potassium sorbate in κ-carrageenan based antimicrobial film

The diffusion of potassium sorbate incorporated into κ-carrageenan based antimicrobial film was measured at 5 s intervals using a diffusion cell. The kinetics of potassium sorbate release followed Fick's law of diffusion, as shown by diffusional exponent characteristic n-value and high correlation coefficients between experimental and theoretical data. The effects of solution pH at the film surface (3.8, 5.2 and 7.0) and temperature (5, 25 and 40 °C) on diffusion were investigated. Diffusion was found to be unaffected by adjacent solution pH in the range of values tested, but a decrease in temperature from 40 to 5 °C resulted in a reduction of diffusion coefficients from 4.24×10⁻¹³ to 1.29×10⁻¹³ m²/s at pH 5.2.     

OXYGEN TRANSMISSION RATE of an EDIBLE METHYLCELLULOSE-PALMITIC ACID FILM1

Edible coatings with low potassium sorbate permeability could be used to increase the microbial stability of food surfaces. However, such coatings could induce anaerobic food conditions if their oxygen permeability were low. the oxygen permeability of an edible emulsion film (average thickness, 55 μm), composed of methylcellulose and palmitic acid (weight ratio of 3:1), was evaluated at 24°C, atmospheric pressure, and at different percentages of relative humidity (RH). RH values in the 0–57% range had no significant effect on oxygen transmission rate (OTR); calculated OTR values ranged from 660 to 740 mL O₂ (STP)/m² 24h atm. At 79% RH, the OTR doubled to 1,500 mL O₂ (STP)/m² 24h atm. This effect correlated well with the moisture isotherm for the film which showed a low moisture content in the 0–57% RH range and a rapid increase at higher RH values. OTR values, particularly at high relative humidity, indicate no risk of developing anaerobic conditions on the food surface.     

Heat Transfer and Simulated Sterilization of Particulate Solids in a Continuously Flowing System

The heat transfer coefficients (h) between a cube and water were 239 and 303 W/m²K at 0 and 0.86 cm/s relative velocity. In 35% sucrose and 0 cm/sec, h was 146 W/m²K. A model for heat lethality in cubes during continuous sterilization which used finite difference equations for heat conduction and above values of h, revealed that hold times for 6D inactivation of PA 3679 (F₀= 7.2 min) in an isothermal fluid at 132.2°C were 1.78 and 5.2 min for 1 and 2 cm cubes when h was 303 W/m²K and 1.23 and 4.13 min when h was 2500 or higher. When h was 239 W/m²K, hold times were 2.36 and 6.02 min for 1 and 2 cm cubes. When fluid entered the hold tube at 132.2°C and particle to fluid ratio was 0.56, fluid-particle heat exchange increased hold time to 12.2 and 119 min for 1 and 2 cm cubes.     

Packaging Effects on Growth of Listeria innocua in Shredded Cabbage

Freshly shredded white cabbage was treated with citric acid and sodium erythorbate, inoculated with Listeria innocua (in lieu of Listeria monocytogenes), and packaged in 230g lots in four types of retail bags with oxygen transmission rates (OTRs) of 5.6, 1,500, 4,000, and 6,000 cc O₂/m²/24 hr, then stored 21 days at 11°C. After 14 days, L. Innocua decreased in cabbage stored in three films. After 21 days, Listeria population increased in all packages, but the increase was less (p<0.05), for cabbage packaged in film with the highest OTR (commercial film).     

Modified Atmosphere Packaging of Fresh Beansprouts

Freshly harvested beansprouts displayed a respiration rate of about 1 mmol O₂ kg⁻¹ h⁻¹ at 10°C which was strongly dependent on temperature, a 10-fold increase being observed every 16·5°C (z=16·5°C, ie Q₁₀=4·4). This commodity is also characterised by a high initial microbial load (about 10⁷ cells g⁻¹). During storage at various temperatures from 1 to 20°C, oxygen uptake rates dramatically increased with time and this phenomenon was well correlated with the development of aerobic microorganisms which reached 10⁹ cells g⁻¹ after 2 days at 20°C or 9 days at 1°C. Beansprouts were packaged in films, with permeabilities ranging from 950 to 200000 ml O₂ m⁻² day⁻¹ atm⁻¹, and stored at 8°C. Due to plant and microbial metabolism, oxygen concentrations decreased steadily within all packs until the onset of plant tissue decay. The latter occurred after 5–6 days with the least permeable films but did not occur within when the film permeability was over 100000 ml O₂ m⁻² day⁻¹ atm⁻¹. However, such films favoured brown discolouration, exudation texture and breakdown. The orientated polypropylene film (OPP) induced anoxic condition within 2 days and favoured anaerobic metabolism and necrosis of the sprouts. In all packages there was a rapid development of aerobic microorganisms and lactic acid bacteria that resulted in the accumulation of acetate and lactate and a decrease in pH. Thus, it clearly appeared that tissue decay was enhanced by microbial activity. At 8°C, 0·24 m² of film per kg of sprouts provided the optimal atmosphere composition (ie 5% oxygen and 15% carbon dioxide) when a film permeability of 50000 ml O₂ m⁻² day⁻¹ atm⁻¹ was used. These conditions allowed a shelf-life of 4–5 days.     

POTASSIUM SORBATE PERMEABILITY of POLYSACCHARIDE FILMS: CHITOSAN, METHYLCELLULOSE and HYDROXYPROPYL METHYLCELLULOSE

Edible coatings controlling preservative migration from surface to food bulk could control surface microbial growth which is often the main cause of spoilage for many food products. In this paper we examine the potassium sorbate permeability behavior of chitosan, methyl cellulose and hydroxypropyl methyl cellulose based films. to gain an understanding of the permeation process, permeability determinations were done at 5, 24, 32 and 40°C. Permeability rates followed the Arrhenius activation energy model. A lack of breaking points in Arrhenius plots indicated that no morphological changes occur within these films in the 5 to 40°C temperature range. Activation energy values were found to be independent of film composition and were affected only by the solvent embedded in the film. This behavior was confirmed by analysis of the same permeability data using a modified Stokes-Einstein equation. Methyl cellulose was the most promising diffusion barrier with a permeability constant of 3.4 and 1.4×10^?8 (mg/s cm²) (cm)/(mg/cm³) at 24 and 5°C, respectively. Electron microscopy was used to examine the morphological characteristics of these films and showed they have no visible pores or channels at magnifications up to 10,000.     

Microbiological changes in cottage cheese varieties during storage at +7°C

Studies have been made of microbiological changes in cottage cheese varieties during storage at 7°C. Commercially prepared products obtained directly from three manufacturers were at an initial pH in the range 4·6 to 5·1 and differed significantly in their content of sorbic acid/sorbate and of viable lactic streptococci. In many of the varieties that did not contain sorbic acid/sorbate multiplication occurred of Pseudomonas spp., Enterobacteriaceae and yeasts; spoilage occurred in some batches due to formation of a surface film of Pseudomonas fluorescens or of surface colonies of Sporobolomyces roseus and Trichosporon sp. at times equal to, or slightly greater than the recommended storage life. Where high numbers of viable lactic streptococci were present in varieties immediately after manufacture, no marked decrease in pH or increase in titratable acidity was observed during storage at 7°C. In varieties that contained sorbic acid at a concentration higher than approximately 500 mg kg^?1 little increase in numbers of bacteria or yeasts was observed during storage at 7°C. Decrease in quality due to separation of whey occurred in some products from each manufacturer, but no clear correlation was observed between separation of whey and pH or the number of lactic streptococci present.Bacteria of public health significance, Escherichia coli type I, Staphylococcus aureus and Vibrio spp. were not detected in these products.Fifty-nine samples produced by six manufacturers, purchased from retail outlets, were examined on the sell-by date; the results confirmed the conclusions drawn from studies during storage.     

Mathematical Modeling of Microbial Growth in Packaged Refrigerated Orange Juice Treated with Chemical Preservatives

ABSTRACT Microbial flora of refrigerated orange juice was analyzed during storage at 10 °C and the effects of the following factors were discussed: 1) the previous washing process of the orange peel, 2) the different levels of the added preservatives (citric acid, ascorbic acid, potassium sorbate, sodium benzoate), 3) the gaseous permeabilities of the packaging film. Gompertz equation was applied to model molds and yeasts growth for the different treatments and packaging conditions. The washing procedure with sodium hypochlorite extend 2–3 d the storage life of the juice (time to reach microbial counts of 10⁶ CFU/ml) in both packaging films. The use of organic acids and potassium sorbate or sodium benzoate (1.66–6.94 mM) led to storage life values > 11 d in polyethylene and > 20 d in the low gaseous permeability film, maintaining good sanitary conditions.     

Soy Protein Isolate Antioxidant Effect on Lipid Peroxidation of Ground Beef and Microsomal Lipids

Soy protein isolate antioxidant (SPIA) was separated from soy protein, fractionated, and purified. SPIA (300 or 900 ppm) was added to a ground beef model system; oxidation was initiated by adding Fe⁺²/Fe⁺³. Sealed vials were stored at 4°C for 24 hr. Oxidation products were assessed using the 2-thiobarbituric acid (TBA) test, sensory analysis, gas chromatographic separation, and mass spectrometric identification of headspace volatiles. SPIA (900 ppm) was also added to a beef microsomal protein/linoleic acid model system. Beef containing 900 ppm SPIA had lower TBA numbers, less rancid odor, hexanal, and total volatiles after 16 and 24 hr than did samples containing 300 ppm SPIA and controls.