Radiation sensitivity of selected pathogens in ice cream

Microbial contamination was investigated using ice creams with a vanilla, chocolate, and strawberry flavor commercially available in Korea. Radiation sensitivity of the food-borne pathogens was also determined by an inoculation test. Food-borne pathogens used were Listeria ivanovii, Escherichia coli, and Salmonella typhimurium. Total aerobic bacteria, moulds and yeasts, and coliforms in the ice creams ranged from 2 to 3 log CFU/g. Irradiation of 3 kGy was enough to inactivate the total aerobic bacteria for the vanilla ice cream but that of 5 kGy was needed for the chocolate or strawberry ice creams at a frozen condition (−20 °C). To inactivate (>log 6.5) the inoculated L. ivanovii, E. coli, and S. typhimurium into ice cream irradiation of 3, 1, and 0.1 kGy was needed, respectively. The D₁₀ value of L. ivanovii and E. coli was calculated as 0.71–0.77 and 0.28–0.38 kGy range for the ice cream with different flavors at −72 °C, respectively. The D₁₀ value of S. typhimurium could not be calculated in this study because even 0.1 kGy of irradiation reduced the number of S. typhimurium to undetected level. Results suggest that a low dose irradiation can improve the microbial quality and reduce the risk by the food-borne pathogens of ice cream, which has limited alternative sterilization methods due to the temperature characteristics of the products.     

Microbial and quality evaluation of green peppers stored in biodegradable film packaging

The effects of polylactic acid (PLA) based biodegradable film packaging on the microbial and physicochemical quality of green peppers (Capsicum annuum L.) were compared to the effects of low-density polyethylene (LDPE) film packaging, and perforated LDPE film packaging. Each package containing green peppers was heat-sealed and stored for 7 days at 10 °C. The microbial levels (aerobic bacteria, coliform bacteria, and yeast and moulds) and physicochemical properties such as colour, weight loss, hardness, ascorbic acid concentration, O₂ and CO₂ concentrations, were monitored during storage. Results indicated that the physicochemical properties of colour, hardness, ascorbic acid concentration, and microbial levels (total aerobic bacteria, and moulds and yeasts) did not show remarkable changes during storage period. The microbial levels in coliform bacteria were increased by less than 1 log CFU/g (0.2 log CFU/g) in the biodegradable film packaging, 2.3 log CFU/g in LDPE film package, and less than 1 log CFU/g (0.9 log CFU/g) in the perforated LDPE film package, after 7 days storage period. The results suggest that the biodegradable film with higher water vapor permeability can be used to maintain the quality and sanitary conditions (protection from microbial and insect contamination) of freshly harvested green peppers in modified atmosphere packaging.     

Effect of metal-doping of TiO2 nanoparticles on their photocatalytic activities toward removal of organic dyes

M-doped TiO₂ nanoparticles (M = Cu, Zn) were prepared by the sol–gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and UV–vis spectroscopy techniques were used to characterize the samples. Photocatalytic activities of samples for methyl orange (MO) degradation and the chemical oxygen demand (COD) were investigated. XRD results confirmed the formation of the anatase phase for the TiO₂ nanoparticles, with crystallite sizes in the range of 9–21 nm. The small crystallite size and doping ions (Cu and Zn) inhibited any phase transformation and promoted the growth of the TiO₂ anatase phase. The optical study showed that doping ions lead to an increase in the absorption edge wavelength, and a decrease in the band gap energy of TiO₂ nanoparticles. The doped TiO₂ nanoparticles in general showed higher photocatalytic activities than the pure ones. The Cu doped TiO₂ nanoparticles showed the best photocatalytic activity based on the measured COD values.     

Antimicrobial effect of acidified sodium chlorite,sodium chlorite,sodium hypochlorite,and citric acid on Escherichia coli O157:H7 and natural microflora of fresh-cut cilantro

Fresh-cut cilantro is particularly susceptible to microbial growth and, therefore, use of an effective sanitizer on this product is of great importance. The objective of this study was to evaluate the efficacy of different sanitizing treatments on reducing Escherichia coli O157:H7 populations, aerobic mesophilic bacterial, yeast and mould counts on fresh-cut cilantro. Cut cilantro was treated with sodium hypochlorite (SH) at 0.2 g L^?1 free chlorine and acidified sodium chlorite (ASC) at 0.1, 0.25, 0.5 and 1 g L^?1, along with the components of ASC, i.e., citric acid (CA) at 6 g L^?1 and sodium chlorite (SC) at 1 g L^?1. In the present study, it was found that SH inactivated, at maximum, 1–1.3 log cfu g^?1 of background or pathogenic microflora present on cut cilantro. However, reductions of more than 3 log cfu g^?1 were observed after washing with 1 g L^?1 of ASC. Moreover, when lower concentrations of ASC were used (0.25 and 0.5 g L^?1), microbial populations were reduced by about 2 log cfu g^?1. SC was as effective as ASC at 1 g L^?1 in reducing aerobic mesophilic bacteria and E. coli O157:H7 populations, although it was not as effective as ASC in reducing yeast and mould populations.     

Use of gamma irradiation for inactivation of pathogens inoculated into Kimbab,steamed rice rolled by dried laver

The effect of gamma irradiation for inactivating the pathogens inoculated into the ready-to-eat Kimbab, steamed rice rolled by dried laver, was investigated. The pathogens used were Salmonella Typhimurium, Escherichia coli, Staphylococcus aureus and Listeria ivanovii which are important for public health. The growth of four test organisms inoculated (about 10⁶–10⁷ CFU/g) into the Kimbab were sustained by an irradiation treatment during 24 h of storage regardless of the temperature at 10, 20 and 30 °C. Four pathogen inoculated into Kimbab decreased 2–3 log CFU/g by 1 kGy treatment and was not detected after 3 kGy. The D₁₀ value of pathogens inoculated into the Kimbab were 0.31–0.44 kGy among the four organisms. This study indicated that a low dose irradiation can maintain microbial safety for ready-to-eat Kimbab, steamed rice rolled by dried laver.     

Inactivation of 3-strain cocktail pathogens inoculated into Bajirak jeotkal,salted, seasoned,and fermented short-necked clam (Tapes pilippinarum), by gamma and electron beam irradiation

The objective of this study was to determine the efficacy of gamma and electron beam irradiation of the food-borne pathogens including 3-strain cocktail of Listeria monocytogenes (ATCC 19114, 19115, and 19111), Staphylococcus aureus (ATCC 6538, 25923, and 29213), and Vibrio parahaemolyticus (ATCC 17802, 33844, and 27969) in Bajirak jeotkal (8% salt), salted, seasoned and fermented short-necked clam, commercially available in the market. Irradiation (0.5, 1, 2, and 5 kGy) significantly reduced the initial microbial level not only immediately after irradiation but also during storage at 10 °C for 4 weeks (P < 0.05). No viable cells were detected at 5 kGy of irradiation at a detection limit of 10¹ CFU/g. Gamma irradiation was more effective than electron beam irradiation, and yielded D₁₀ values of 0.64, 0.63, and 0.29 kGy for L. monocytogenes, S. aureus, and V. parahaemolyticus, and those of electron beam irradiation were 0.79, 0.81, and 0.36 kGy, respectively. Results suggest that a low dose irradiation can improve the microbial quality and reduce the risk by the food-borne pathogens of Bajirak jeotkal, which has limited alternative sterilization methods due to the temperature characteristics of the products. Furthermore, in practical application, the irradiation source should be considered to obtain an effective dose for decontamination.     

Effect of gamma irradiation on Listeria ivanovii inoculated to iceberg lettuce stored at cold temperature

A low-dose gamma irradiation considerably reduced the total plate counts, psychrotrophic bacteria, lactic acid bacteria, and inoculated Listeria ivanovii on shredded iceberg lettuce. The total plate count of the lettuce irradiated at 1.0 kGy was reduced by 3.38 log₁₀ cfu/g on 0 storage day and to below the limit of detection (<2 log₁₀ cfu/g) as the cold storage was extended. Irradiation at 0.5 kGy effectively reduced the psychrotrophic bacterial counts and lactic acid bacterial counts in the lettuce to below the limit of detection (2 log₁₀ cfu/g). Irradiation at 1.0 kGy reduced L. ivanovii inoculated onto the shredded iceberg lettuce to below the limit of detection. The results showed that an irradiation at 1 kGy eliminates the bacterial contamination from the lettuce sample without any sensorial quality defect.     

Microbial profile of buffalo sausage during processing and storage

A study was made on the microbial levels of buffalo sausage during preparation and storage at 4 ± 1 °C. Microbial counts in raw minced meat were, total plate count (TPC) (log cfu/g) 5.41 ± 0.25; coliforms (MPN/g) 23.2; Staphylococcus aureus (log cfu/g) 1.57 ± 0.11; yeasts and molds (log cfu/g) 2.29 ± 0.07 and lactic acid bacteria (LAB) (log cfu/g) 0.60 ± 0.20. Sausage emulsion showed similar trend in microbial counts with minimal microbial contamination during the preparation of emulsion. Cooked buffalo sausage gave the following microbial counts: TPC (log cfu/g) 3.75 ± 0.31; coliforms (MPN/g) 0.2; LAB (log cfu/g) 0.07 ± 0.01; yeast and molds (log cfu/g) 0.72 ± 0.07. S. aureus, Clostridium perfringens and Bacillus cereus were not detected in cooked sausages. These results indicate that steam cooking for 45 min followed in the study was effective in reducing the microbial counts substantially. The investigation revealed that shelf life of cooked buffalo sausage was 31 days in either vacuum or CO₂ at 4 ± 1 °C. The results indicated that spoilage of vacuum packed cooked buffalo sausage was likely due to LAB while microflora other than LAB may be responsible for spoilage of CO₂ packed cooked buffalo sausage. The study suggests that measures such as low initial microbial counts, hygienic precautions during preparation of sausage, steam cooking for 45 min, vacuum or CO₂ packing and storage at 4 ± 1 °C would control the microbial growth and provide wholesomeness and safety to the buffalo sausage.     

Inactivation of a non-pathogenic strain of E. coli by ionising radiation

Ionising radiation is an effective method to reduce pathogenic E. coli O157:H7 in meat and poultry products. Radiation sensitivity of bacteria, however, depends on several factors. After applying an irradiation dose of 1 kGy to cultures of the non-pathogenic strain of E. coli, DSM 498, grown and irradiated in nutrient broth, reductions of 3–4 decimal units were achieved (D₁₀ = 0.27 kGy). If grown on minced turkey meat, however, reduction rates were lower (D₁₀ = 0.47 kGy). Even lower reduction rates were obtained during irradiation of frozen meat (D₁₀ = 0.72 kGy) compared to treatments at cooling temperatures (D₁₀ = 0.48 kGy). For data evaluation, both, first order reduction kinetics and the Weibull model were compared. The results emphasise the necessity to determine inactivation kinetics in food matrices of target extrinsic factors (e.g. temperature).     

Non-thermal inactivation of Escherichia coli K12 in buffered peptone water using a pilot-plant scale supercritical carbon dioxide system with a gas–liquid porous metal contactor

This study evaluated the effectiveness of a supercritical carbon dioxide (SCCO₂) system, with a gas–liquid porous metal contactor, for reducing Escherichia coli K12 in diluted buffered peptone water. 0.1% (w/v) buffered peptone water inoculated with E. coli K12 was processed using the SCCO₂ system at CO₂ concentrations of 3.1–9.5 wt%, outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Increased CO₂ concentrations and temperatures significantly (P < 0.05) enhanced microbial reduction. A maximum reduction of 5.8-log was obtained at 8.2% CO₂ and 42 °C. To achieve a 5-log reduction of E. coli K12 in 0.1% buffered peptone water, minimum CO₂ concentrations of 9.5%, 5.5%, and 5.3% were needed at 34, 38, and 42 °C, respectively. Further reductions of cells were observed after storage for 7 days at 4 °C. But storage at 25 °C increased the number of viable cells to 8-log cfu/mL after 7 days. This study showed the potential of the pilot scale SCCO₂ system with a gas–liquid porous metal contactor for microbial inactivation in liquid food.     

Different outlet for preparing nano-TiO2 catalysts for the photodegradation of Black B dye in water

Two nano-titania catalysts were prepared using two economically varying titanium precursors: titanium tetrachloride (A) and titanium isopropoxide (B). The catalysts were calcined at temperatures of 500 °C, 600 °C and 700 °C and characterized using X-ray diffraction (XRD), electron diffraction (ED), BET surface properties and high resolution transmission microscopy (HRTEM). The calcined catalysts were found to differ markedly in their physical characters and TiO₂ phases produced as well as their photocatalytic activities. The anatase titania phase diminished from 100% to 83% in TiO₂A but from 64% to zero in TiO₂B via temperature increase from 500 °C to 700 °C, due to transforming anatase to rutile. The brookite TiO₂ phase only appeared (17%) in catalyst B500. In general, the catalyst of choice is A600 by virtue of many compositional, economical and catalytic advantages.     

Efficacy of aqueous chlorine dioxide and fumaric acid for inactivating pre-existing microorganisms and Escherichia coli O157:H7, Salmonella typhimurium,and Listeria monocytogenes on broccoli sprouts

The combined effect of aqueous chlorine dioxide (ClO₂) and fumaric acid as a chemical treatment to inactivate pre-existing microorganisms was evaluated using broccoli sprouts. Broccoli sprouts were treated with distilled water, 50 ppm ClO₂, 0.5% fumaric acid, and a combination of 0.5% fumaric acid and 50 ppm ClO₂. Treatment with 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of total aerobic bacteria, yeasts and molds, and coliforms in broccoli sprouts by 2.70, 2.46, and 1.71 log CFU/g, respectively. In addition, the combined treatment of 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes inoculated on broccoli sprouts by 2.39, 2.74, and 2.65 log CFU/g, respectively, compared to the control. These results suggest that the combination of aqueous ClO₂ and fumaric acid can be useful as a hurdle for extending the shelf life of broccoli sprouts during storage.     

Effect of washing and disinfecting containers on the microbiological quality of fresh milk sold in Bamako (Mali)

The present study aimed to improve the microbiological quality of the milk, from the cow’s udder to the selling point by container washing and disinfecting. The total counts (TC), Enterobacteriaceae counts (EBC) were used as quality indicators.The results showed a significant decrease of milk flora at the selling point, from 1.6 × 10⁷ ± 1.3 × 10⁷ (control) to 4.8 × 10⁵ ± 0,8 × 10⁷ (intervention) colony forming units per ml (cfu ml⁻¹) for TC and 1.2 × 10⁶ ± 1.1 × 10⁶ (control) to 0.9 × 10⁴ ± 1.1 × 10⁴ (intervention) cfu ml⁻¹ for EBC. The study suggests that in milk production area, besides udder infection and water quality, hygiene behaviour with respect to hand washing, container’s cleaning and disinfection are the key areas that remain of relevance to milk hygiene intervention.     

Utilization of ram horn hydrolysate as a supplement for recovery of heat- and freeze-injured bacteria

Tryptic soy agar (TSA) has been widely and successfully used as a resuscitation medium for injured bacteria. The purpose of this study was to examine the use of ram horn hydrolysate (RHH) as a supplement for recovery of injured bacteria, to compare it to TSA and to evaluate its usefulness as a possible alternative supplement in microbial media. The TSA was enriched with RHH at various concentrations. 2% RHH was found to be optimal for growth of healthy bacteria. The enriched medium (TSA + 20 ml RHH in 1–l) was termed enriched tryptic soy agar (ETSA). TSA and ETSA were tested for the recovery of heat- and freeze-stressed bacteria. Four species of bacteria (Escherichia coli, Listeria monocytogenes, Salmonella typhimurium and Pseudomonas aeruginosa) were heat-treated at 55 °C in physiological saline by a capillary tube method. For the freeze-injury studies, 5 ml of the tryptic soy broth cultures were placed in a freezer at −25 °C for 7 days. The numbers of uninjured bacteria on TSA were evaluated as control. The number of viable bacteria on TSA and ETSA was determined by the pour plate method. Recovery rates of bacteria on ETSA were higher than that of TSA. The RHH appears to be a valuable supplement for microbial media.     

Application of slightly acidic electrolyzed water as a potential non-thermal food sanitizer for decontamination of fresh ready-to-eat vegetables and sprouts

The sanitization efficacy of slightly acidic electrolyzed water (SAEW) against food pathogens on selected fresh ready-to-eat (RTE) vegetables and sprouts was evaluated and compared to sodium hypochlorite (NaOCl) solution. RTE vegetables and sprouts were dip-inoculated with Escherichia coli (E. coli) and Salmonella spp. and dip-treated with SAEW, NaOCl solution for 5 min. SAEW treatment significantly (p < 0.05) reduced the total aerobic mesophilic bacteria from Chinese celery, lettuce and daikon sprouts by 2.7, 2.5 and 2.45 log₁₀CFU/g, respectively relative to un-treated. Pathogens were significantly (p < 0.05) reduced from Chinese celery, lettuce and daikon sprouts by 2.7, 2.8 and 2.8 log₁₀CFU/g (E. coli) and 2.87, 2.91 and 2.91 log₁₀CFU/g (Salmonella spp.), respectively following a SAEW treatment. SAEW and NaOCl solution showed no significant sanitization difference (p > 0.05). Results demonstrate that SAEW at low chlorine concentration and a near neutral pH is a potential non-thermal food sanitizer that could represent an alternative to NaOCl solution and would reduce the amount of free chlorine used in fresh-cut vegetables industry, since the same microbial reduction as NaOCl solution is obtained.     

Effects of gamma irradiation on the microbiological,nutritional, and sensory properties of fresh vegetable juice

The radiation pasteurization process was performed to improve the microbiological quality of fresh vegetable juice. Carrot and kale juice were irradiated and their microbiological, nutritional, and sensory properties were evaluated. The contaminating bacteria in the juices before irradiation ranged from 10⁶ to 10⁷ CFU/ml. All the aerobic and coliform bacteria in the carrot juice were eliminated by irradiation at a dose of 3 kGy, whereas about 10² CFU/ml of the bacteria survived in the kale juice irradiated at up to 5 kGy. However, the cells that survived from irradiation in the kale juice did not grow, whereas those of the non-irradiated samples reached 10⁹ CFU/ml after 3 days of storage at 10 °C. Amino acids were stable at up to 5 kGy of an irradiation. Radiation resulted in a dose-dependent reduction of the ascorbic acid content. However, the contents of the total ascorbic acid, including dehydroascorbic acid, were stable at up to 3 kGy of an irradiation. The sensory evaluation results immediately after irradiation were not different in any of the samples. At a 3-day storage, the sensory quality of the irradiated juice was adequate, while the quality of the non-irradiated control was deteriorated.     

Effect of starter cultures on microbial ecosystem and biogenic amines in fermented sausage

The microbial ecology of fermented sausages inoculated with different starter cultures (Pediococcus pentosaceus + Staphylococcus xylosus, batch A; Lactobacillus farciminis + Staphylococcus saprophyticus, batch B) was studied by culture-dependent and independent methods. The concentration of biogenic amines, pH and a_w (water activity) were followed. The starter B can inhibit indigenous bacteria effectively judged by traditional microbiological method and PCR-DGGE fingerprint. There was no statistical difference in pH between batches A and B at 2 days when substantial amounts of BAs were produced, while the amounts of histamine, putrescine, cadaverine and tyramine in batch B was lower than in batch A significantly (P < 0.001). As a result, the starter cultures which can complete, grow well and inhibit amine-positive bacteria play an important role in reducing the production of BAs during ripening of fermented sausage.     

Microbial ecology of a small-scale facility producing traditional dry sausage

The microbial ecology of a small-scale facility producing traditional dry sausage (without addition of starter cultures) was investigated at 17 control points (12 processing surfaces and equipments samples, 5 raw materials and products samples) and at different periods: winter and spring.Technological flora (lactic acid bacteria, staphylococci/Kocuria and yeast/moulds) populations were low in processing surfaces and equipments (below 10² c.f.u/cm²), but reached a level of about 10⁶–10⁷ c.f.u/g for lactic acid bacteria and staphylococci/Kocuria and about 10⁴ c.f.u/g for yeasts/moulds in the final product. Counts of enterococci were low in most of processing surfaces and equipments and increased in the batter and the sausage-1 week; but declined after 8 weeks of ripening.Differences in temperatures of the processing facility recorded in winter and in spring influenced the hygienic quality of raw materials. Pseudomonas and Coliforms populations enumerated from raw materials in spring were about 3 log₁₀ c.f.u/g superior compared to enumeration results recorded in winter. While Pseudomonas population declined remarkably in the final product, Coliforms population remained higher. Staphylococcus aureus was undetected in spring; however in winter, its population was about 2.5 log₁₀ c.f.u/g in the final product after 9 weeks ripening. One isolate originating from the stuffing machine was identified as Listeria monocytogenes. Finally, 9 presumptive Salmonella were identified as belonging to Hafnia alvei, Providencia alcalifaciens, Proteus vulgaris, P. penneri and Morganella morganii species.These results emphasize the necessity of improving the general hygienic conditions and also technological process of sausage production in this processing facility.     

Anti-Listeria innocua activity of silver functionalised textile prepared with plasma technology

Thin layers of silver particles (10–100 Å) were deposited by plasma technology on textiles mainly composed with cotton or polyester in order to obtain antimicrobial properties. The antimicrobial activity against a Listeria innocua strain (LRGIA 01) of these textiles was assessed following a protocol based on the ISO 20743-2005 standard. The number of cultivable bacteria on textiles was then monitored for 24 h. The microbial population after 24 h at 30 °C attained 10⁷ CFU g⁻¹ on control textiles while it did not exceed 10³ CFU g⁻¹ on plasma-treated textile. All plasma-treated with silver textiles were anti-Listeria (up to 7 log CFU g⁻¹ decimal reductions of L. innocua populations) and this observation was confirmed by scanning electron microscopy. These textiles could thus have potential applications in food-processing industry to control cross-contaminations by L. monocytogenes.     

Influence of food soiling matrix on cleaning and disinfection efficiency on surface attached Listeria monocytogenes

Cleaning and disinfection are essential steps in preventing contamination of foods with pathogenic and spoilage bacteria. The efficacy of cleaning and disinfection products differ depending on target bacteria and type of soiling. We evaluated the effectiveness of cleaning and disinfecting products against Listeria monocytogenes attached on food soiled inert surfaces in a laboratory model. The number of bacteria on surfaces before and after treatment was quantified using indirect conductometric measurements. L. monocytogenes attached to stainless steel surfaces in fish broth systems reached approx. 10⁴ CFU/cm². However, all cleaning and disinfection products were equally effective in this system since all bacteria were removed or killed. When the steel disks were immersed in a fish or meat emulsions, a level of approx. 10⁵–10⁶ L. monocytogenes per cm² was reached after 2–3 days at 20 °C. In this case, 2–3 log were removed or killed by alkaline cleaning products (MC103 or FC140). Direct use of a peracetic acid based disinfectant (Oxivit Active Plus) killed all bacteria when attached in salmon emulsions, whereas only 1–2 log were removed or killed in the meat emulsion system. Thus, the efficiency of cleaning and disinfection products against L. monocytogenes is strongly influenced by the food matrix.