Decimal Reduction Dose Research Articles

Evaluating UV-C Sensitivity of Calonectria pseudonaviculata in Model Buffer Solution Using a UV-C Light-Emitting-Diode System.

Calonectria pseudonaviculata, responsible for boxwood blight, produces sticky conidia that pose a contamination risk in boxwood production via cross-contamination from tools, equipment, and other resources. This study evaluated UV-C light-emitting-diode (LED) irradiation (263 to 287 nm) as a disinfection method by examining its effectiveness in inactivating conidia and determining the UV-C sensitivity. Conidial suspensions were exposed to quantifiable UV-C doses under a dynamic stirring condition. Average volumetric intensity was quantified by accounting for UV gradients and UV dose was calculated as a product of average fluence rate (mW⋅cm-2) and exposure time (s). UV-C irradiation effectively inactivated the tested pathogen following log-linear + shoulder kinetics as identified by parameters of goodness of model fit (i.e., high R2 and low root mean square error [RMSE] values). The model predicted the UV sensitivity of C. pseudonaviculata conidia as 46.6 mJ⋅cm-2 per log. A total of 2.04 log reductions of the population could be obtained by an exposure of 60 mJ⋅cm-2 of UV-C dose. The calculated decimal reduction dose (D10) was 13.53 ± 0.98 mJ⋅cm-2 (R2 = 0.97, RMSE = 0.14), inactivation rate constant (Kmax) = 0.17 ± 0.01, and shoulder length = 33.06 ± 1.81 mJ⋅cm-2. These findings indicate that UV-C irradiation could be a viable option for disinfecting tools, equipment, and possibly propagation cuttings in nurseries.

UV-C Inactivation Doses for Pathogenic and Spoilage Bacteria and Fungi Isolated from Selected Tropical Fruits and Vegetables

Food-borne microbes from sweet orange, okra and pepper were homogenized and combined based on fruit type. The homogenized mixtures of the isolates were subjected to Ultraviolet radiation using a fabricated irradiation system to determine the total viable colony count post-irradiation. This was used in calculating the decimal reduction doses for the crops, which were found to be 2.589 Jm-2, 2.556 Jm-2 and 4.133 Jm-2, for Sweet Orange, Okra, and Pepper, respectively. These doses will be helpful in the sterilization and shelf-life extension of the selected fruits and vegetables.

Effect of germicidal short wavelength ultraviolet light on the polyphenols, vitamins, and microbial inactivation in a highly opaque apple juice

AbstractThe aim of this investigation was to study the efficacy of UV‐C light emitting diode (LED) system operating at 263 nm for the inactivation of Listeria monocytogenes and Escherichia coli O157:H7. UV‐C irradiation was applied to stirred 5 ml samples, using a collimated beam LED system operating at a 263 nm wavelength. UV irradiation doses ranging from 0 to 160 mJ/cm2 were also delivered to apple juice (AJ) and polyphenols and vitamins were profiled. Liquid chromatography–mass spectrometry (LC–MS/MS) analysis was conducted to assess the stability of polyphenols or vitamins in UV‐C exposed AJ. The polyphenol and vitamin results demonstrated that UV‐C irradiation in AJs at relevant commercial UV doses induced significant reductions in the concentrations of selected polyphenols and vitamins, p < .05. Ascorbic acid was reduced to 32%, at 160 mJ/cm2 whereas 17% reduction was observed at 40 mJ/cm2. Riboflavin was observed to be relatively stable. Epicatechin and chlorogenic were significantly reduced at high exposure doses. In contrast, minor changes were observed at 40 mJ/cm2. Results show that UV‐C irradiation effectively inactivated pathogenic microbes in AJ. Inactivation levels of all organisms were proportional to UV‐C dose. The log reduction kinetics of microorganisms followed log‐linear and with higher R2 (>0.95). The decimal reduction dose (D10) values of 4.16 and 3.84 mJ/cm2 were obtained from the inactivation of E. coli and L. monocytogenes in AJ. The results from this study imply that adequate log reduction of pathogens is achievable in AJ and suggests significant potential for UV‐C treatment of other opaque liquid foods.

EFFECT OF GAMMA IRRADIATION ON GROWTH OF ESCHERICHIA COLI AND SALMONELLA SP.

Escherichia coli was still detected in treated water and Salmonella sp. filled 90% of the pathogenic bacteria content in the Wastewater Treatment Plant (WWTP) sludge. This research aimed to know the effect of gamma irradiation on the growth of E. coli and Salmonella sp. Experimental bacteria were in the form of un-raw material, bacterial isolates. The experimental method of this research gave gamma irradiation doses 1, 2, 3, 4, and 5 kiloGray (kGy) to bacterial suspensions. The isolates were cultured on Nutrient Agar (NA) and followed by cultured on Nutrient Broth (NB) to get the suspensions. The suspensions were put in microtubes for irradiation then followed by enumeration on Plate Count Agar (PCA) in Total Plate Count (TPC) based on SNI-2897-2008. This research proved that the higher dose of gamma irradiation had been given, the lower growth of bacteria (or were the higher death number of bacteria) resulted. Decimal Reduction Dose (D10) value of E. coli and Salmonella sp. were 0,3 kGy and 0,35 kGy, and totally dead by ≥ 3 kGy and ≥ 4 kGy. For further research might be conducted on raw material such as WWTP sludge, wastewater, drinking water, river water, soil water, or organic fertilizer.EFFECT OF GAMMA IRRADIATION ON GROWTH OF ESCHERICHIA COLI AND SALMONELLA SP.

Juice composition, physicochemistry, and efficacy of ultraviolet radiation against Cryptococcus albidus

To the knowledge of the investigators, this is the first report of the establishment, validation, and application of a model that quantifies the effects of relevant physicochemical properties namely, pH (2.0–8.0), soluble solids (SS, 0.0–70.0 °Brix from sucrose), insoluble solids (IS, 0.0–3.0% wt/vol cellulose), and ascorbic acid (AA, 0–1000 mg/L) on the UV-C inactivation kinetic parameter, decimal reduction dose (DUV-C), of a UV-C resistant spoilage yeast in simulated fruit juice (SFJ). Cryptococcus albidus (LJY1) was grown to mid-stationary phase and thereafter suspended in SFJs with varying combinations of physicochemical properties as determined by a Rotatable Central Composite Design. Response Surface Modelling showed that the individual linear effects of all variables significantly (P < 0.05) influenced DUV-C. Only the individual quadratic effect AA2 significantly influenced the response. The interaction effects namely, (pH × IS) and (SS × AA) also significantly influenced DUV-C. The established model overestimated the DUV-C value by 54.88 to 139.62%, which could result in overly severe predicted process schedules. However, application in the processing and finished product quality evaluations showed that the model may be used as a food processing technique for a tested real orange juice sample.

Effect of radiation processing in elimination of Klebsiella pneumoniae from food

Klebsiella pneumoniae has been considered as an important foodborne pathogen which causes severe infections that include meningitis, bronchitis, bacteremia, pneumonia, and urinary tract infections in humans and animals. It is well known to most clinicians as a cause of community-acquired bacterial pneumonia. Klebsiella is an opportunistic pathogen, that primarily attacks neonates, infants, elderly and immuno-compromised patients and therefore impose a serious, emerging public health hazard globally. Contaminated sprouts, vegetables, seafood and other animal meat products are considered as main sources of Klebsiella infection. In the current study, radiation sensitivity of K. pneumoniae MTCC 109 was determined in different food samples. The decimal reduction dose (D10) values of K. pneumoniae MTCC 109 in saline and nutrient broth at 0–4 °C were 0.116±0.009, 0.136±0.005 kGy, respectively. The mixed sprouts, fish and poultry samples were inoculated with K. pneumoniae MTCC 109 and exposed to gamma radiation to evaluate the effectiveness of radiation treatment in the elimination of K. pneumoniae. D10 values of K. pneumoniae in mixed sprouts, poultry and fish samples were found to be 0.142±0.009, 0.125±0.0004 and 0.277±0.012 kGy, respectively. Radiation treatment with a 1.5 kGy dose resulted in the complete elimination of 3.1±1.8×105 CFU/g of K. pneumoniae from these food samples. No recovery of K. pneumoniae was observed in the 1.5 kGy treated samples stored at 4 °C up to 12 days, even after enrichment and selective plating. This study shows that a 1.5 kGy dose of irradiation treatment could lead to the complete elimination of 3.1±1.8×105 CFU/g of K. pneumoniae from mixed sprouts, poultry and fish samples.

Radiation-resistant Macrococcus caseolyticus (A) isolated from radiation-processed semidried prawns.

A radiation-resistant bacterial isolate from gamma-radiation-processed (5 kGy) semidried prawns was identified as a new strain of Macrococcus caseolyticus and was designated as M. caseolyticus (A) on the basis of morphological and biochemical characterization and 16S rRNA sequencing. DNA-DNA hybridization studies with M. caseolyticus DSM 20597(T) further confirmed the isolate as M. caseolyticus. Major fatty acids present in M. caseolyticus (A) were C14:0, C16:1ω11c, and C18:1ω9c, whereas C15:0anteiso, C16:0iso, and C18:0iso were absent. The closest match for the isolate, as per fatty acid methyl ester analysis, was M. caseolyticus DSM 20597(T). However, the similarity index was significantly low (0.112), which indicates that the isolate could be a new strain of M. caseolyticus. The decimal reduction dose (D10) for M. caseolyticus (A), M. caseolyticus JCSC5402, and Staphylococcus aureus MTCC96 was 1.18, 0.607, and 0.19 kGy, respectively. This is the first report on radiation resistance of M. caseolyticus. Macrococcus caseolyticus (A) is more resistant to gamma and UV radiation stress than are M. caseolyticus JCSC5402 and S. aureus MTCC96; however, it is sensitive to heat as well as desiccation stress.

Microbiological characterization and sterilization-induced changes in the profile of the hydrophobic organic substances in Latvian balneological peat

The abundance and predominant groups of bacteria, filamentous fungi and yeasts have been studied by culture-dependent microbiological methods in peat probes obtained in two Latvian balneotherapy spa sites, Kemeri and Baldone. Unsterilized peat samples from both the sites contained 5.7–8.1 log bacterial colony-forming units (CFU) and 3.0–5.3 log fungal CFU per gram of dry peat. Isolated species belonged to Alpha-, Beta-, and Gamma-Proteobacteria, Actinobacteria, Clostridia, Bacilli and Flavobacteria as well as to filamentous fungi and yeasts. The composition of microbial population of the peat from both sites shared just four micro-organism groups (Bacillus mycoides, Burkholderia cepacia, Streptomyces spp. and Trichoderma spp.) within totally 36 groups identified. No pathogenic bacteria or fungi and no faecal pollution indicators were recovered. Decimal reduction doses for micro-organisms in peat samples and radiation sterilization doses of peat for the gamma and electron beam radiation were determined. The highest radiation resistance was observed for B. mycoides and Aureobasidium sp. Gamma-sitosterol was the most abundant hydrophobic organic compound in both peats according to GC–MS data. All the sterilization procedures increased concentration of alkanes, alcohols, and ketones and decreased the amount of fatty acids. Heat sterilization proved to be more preserving for the peat sterols than the radiation sterilization. It is concluded that the heat and radiation sterilization methods induce different changes of the profile of hydrophobic organic compounds of balneological peats, what may lead to different therapeutic effects at their application.

Effects of electron-beam irradiation on blueberries inoculated with Escherichia coli and their nutritional quality and shelf life

Fresh blueberries have become a popular new functional food because of their remarkably high levels of antioxidant phytonutrients and health benefits. However, the potential prevalence of human pathogens on blueberries has become an increased concern because they are consumed fresh. Procedures effective in decontamination and extending shelf life without affecting fruit quality are needed. Electron-beam irradiation was applied to fresh blueberries at the doses ranging from 0.5 to 3.0kGy and its effectiveness for inactivating Escherichia coli (E. coli) K-12 and extending shelf life were investigated. The decimal reduction dose, D10 values, of E. coli in cultural medium and blueberries were 0.43±0.01kGy and 0.37±0.015kGy, respectively. Irradiation reduced bacteria inoculated on blueberries from 7.7×108CFU/g to 6CFU/g at 3.13kGy and decreased the decaying of blueberries stored at 4°C up to 72% and at room temperature up to 70% at this dose. No significant effect on the total monomeric anthocyanins, antioxidant activity, and l-ascorbic acid content of blueberries was observed from irradiation at doses ≤3kGy. However, significant decreases in the antioxidant activity and l-ascorbic acid content were found in both control and irradiated blueberries after storage at 4°C for 7 and 15 d. Information obtained in this study indicates that low dose electron-beam irradiation is effective in reducing E. coli and extending shelf life while maintaining the antioxidant properties of blueberries.

Use of Low-Dose Irradiation To Evaluate the Radiation Sensitivity of Escherichia coli O157:H7, Non-O157 Verotoxigenic Escherichia coli, and Salmonella in Phosphate-Buffered Saline

Verotoxigenic Escherichia coli (VTEC) and Salmonella are major foodborne pathogens, but very little information is available on the radiation resistance of a sufficiently diverse group of these pathogens. The objective of this study was to evaluate the sensitivity of E. coli O157:H7, non-O157 VTEC, and Salmonella to a low-dose ionizing radiation treatment. Test organisms were 6 serovars of Salmonella, 5 strains of E. coli O157:H7, and 27 strains of non-O157 VTEC (representing 19 serotypes). Decimal reduction doses (D-values) for individual strains were determined in phosphate-buffered saline using an X-ray source. The viability of the bacterial cells declined with an increase in absorbed dose from 0 to 0.3 kGy. The more resistant test strains were screened at 0.5 and 0.7 kGy. All six Salmonella strains survived at 0.5 and 0.7 kGy; however, only 11 VTEC survived at 0.7 kGy. After the 0.3-kGy treatment, both E. coli O157:H7 and non-O157 VTEC had D-values with similar means and ranges (0.028 to 0.123 and 0.037 to 0.127 kGy, respectively), with no significant differences (P > 0.05). Salmonella strains had a slightly higher range of D-values (0.061 to 0.147 kGy) and a mean D-value that was significantly higher (P > 0.05) than that of both the E. coli O157:H7 and non-O157 VTEC groups.

Evaluation of mixing flow conditions to inactivate Escherichia coli in opaque liquids using pilot-scale Taylor–Couette UV unit

The pilot-scale Taylor–Couette UV unit was tested at turbulent vortices (TV), transitional (TRA) and Couette–Poisuille (CP) flow conditions to treat apple cider (pH 3.65, α=17.41cm−1), carrot juice (pH 6.31, α=52.69cm−1) and soy milk (pH 7.04, α=162.01cm−1) for inactivation of Escherichia coli ATCC 8739. The germicidal effectiveness of Taylor–Couette unit was dependent on Taylor and Reynolds numbers and flow regimes formed in the annulus. From all studied flow regimes the CP flow resulted in the lowest microbial inactivation. For instance at the flow rate of 1500ml/min and rotation of 0rpm the UV decimal reduction dose in apple cider was of 13.15±0.45mJ/cm2. On the contrary the superior E. coli inactivation was achieved at the TV flow (1500mL/min, 200rpm,), characterised by the least UV decimal reduction dose of 4.57±0.35mJ/cm2. Obtained results indicate that Taylor–Couette UV unit provided efficient mixing conditions capable of overcoming the low penetration of UV photons in opaque liquids.

Radiation Response of Bacteria Associated with Human Cancellous Bone

Cancellous bones from twenty five live tissue donors were tested for bacterial contamination and initial bioburden ranged from 4.1×10 1 to 3.1×10 3 cfu/g (average 9.0×10 2 cfu/g). Forty six representative bacterial isolates were characterized on the basis of morphological, cultural and biochemical characteristics. Staphylococcus spp. was found to be predominant contaminant in tissue samples (41.30%). To assess the radiation resistance all the bacterial isolates were exposed to 1 to 10 kGy gamma radiation from 60 Co gamma source. The radiation decimal reduction dose values (D10) and twelve log reduction values (12 D value) of the isolates were calculated. D10 values of the isolates were ranged from 0.59 to 1.20 kGy. Among the studied bacterial isolates, Streptococcus spp. was the most radioresistant isolates (D10 value 0.93-1.20 kGy) and three of the Streptococcus spp. survived up to 8 kGy. All the bacterial isolates were killed at 9 kGy. Twelve log reduction value (12D value) of the most resistant isolate was 14.4 kGy. These results indicate that standard radiation sterilization dose (25 kGy) is satisfactory for the sterilization of the cancellous bone allografts. Keywords- Bioburden, Cancellous bone, Radiation resistance, Staphylococcus, Streptococcus, Sterilization

Effects of gamma irradiation on bacterial microflora associated with human amniotic membrane.

Human amniotic membrane is considered a promising allograft material for the treatment of ocular surface reconstruction, burns, and other skin defects. In order to avoid the transmission of any diseases, grafts should be perfectly sterile. Twenty-five amniotic sacs were collected to determine the microbiological quality of human amniotic membrane, to analyze the radiation sensitivity pattern of the microorganism, and to detect the radiation decimal reduction dose (D10) values. All the samples were found to be contaminated, and the bioburden was ranged from 3.4 × 102 to 1.2 × 105 cfu/g. Initially, a total fifty bacterial isolates were characterized according to their cultural, morphological, and biochemical characteristics and then tested for the radiation sensitivity in an incremental series of radiation doses from 1 to 10 KGy. The results depict gradual decline in bioburden with incline of radiation doses. Staphylococcus spp. were the most frequently isolated bacterial contaminant in tissue samples (44%). The D10 values of the bacterial isolates were ranged from 0.6 to 1.27 KGy. Streptococcus spp. were found to be the highest radioresistant strain with the radiation sterilization dose (RSD) of 11.4 KGy for a bioburden level of 1000. To compare the differences, D10 values were also calculated by graphical evaluations of the data with two of the representative isolates of each bacterial species which showed no significant variations. Findings of this study indicate that lower radiation dose is quite satisfactory for the sterilization of amniotic membrane grafts. Therefore, these findings would be helpful to predict the efficacy of radiation doses for the processing of amniotic membrane for various purposes.

Effectiveness of radiation processing in elimination of Campylobacter from poultry meat

Campylobacter, a common poultry intestine commensal, is a well known cause of human gastric illnesses across the globe. Consumption of contaminated poultry meat is a major cause of Campylobacter related infections. In the present study, radiation sensitivity of indigenous strains of C. jejuni and C. coli isolated from poultry was evaluated. The decimal reduction dose (D 10) values of different Campylobacter isolates at 0–4 °C in saline and blood broth were in the range of 0.120–0.210 kGy and 0.170–0.234 kGy, respectively. D 10 values in chicken meat homogenate for Campylobacter were in the range of 0.110–0.190 kGy. Chicken meat samples were inoculated with C. jejuni and exposed to gamma radiation to study the effectiveness of radiation treatment in elimination of Campylobacter. Radiation treatment with a dose of 1 kGy could achieve complete elimination of 10 5 CFU of Campylobacter/g in poultry meat samples. No recovery of Campylobacter was observed, even after enrichment and selective plating in 1 kGy treated chicken meat samples stored at 4 °C up to 7 days. Present study shows that irradiation of poultry meat with 1 kGy can ensure safety of poultry meat.

Effectiveness of radiation processing in elimination of Aeromonas from food

Genus Aeromonas has emerged as an important human pathogen because it causes a variety of diseases including gastroenteritis and extra-intestinal infections. Contaminated water, sprouts, vegetables, seafood and food of animal origin have been considered to be the important sources of Aeromonas infection. In the present study, radiation sensitivity of indigenous strains of Aeromonas spp. from different food samples was evaluated. The decimal reduction dose (D10) values of different Aeromonas isolates in saline at 0–4°C were in the range of 0.031–0.046kGy. The mixed sprouts, chicken and fish samples were inoculated with a cocktail of five most resistant isolates (A. salmonicida Y567, A. caviae A85, A. jandaei A514A, A. hydrophila CECT 839T and A. veronii Y47) and exposed to γ radiation to study the effectiveness of radiation treatment in elimination of Aeromonas. D10 values of Aeromonas cocktail in mixed sprouts, chicken and fish samples were found to be 0.081±0.001, 0.089±0.003 and 0.091±0.003kGy, respectively. Radiation treatment with a 1.5kGy dose resulted in complete elimination of 105CFU/g of Aeromonas spp. from mixed sprouts, chicken and fish samples. No recovery of Aeromonas was observed in the 1.5kGy treated samples stored at 4°C up to 12 (mixed sprouts) and 7 days (chicken and fish samples), even after enrichment and selective plating. This study demonstrates that a 1.5kGy dose of irradiation treatment could result in complete elimination of 105CFU/g of Aeromonas spp. from mixed sprouts, chicken and fish samples.

Radiation resistances and decontamination of common pathogenic bacteria contaminated in white scar oyster ( Crassostrea belcheri) in Thailand

In Thailand, white scar oyster ( Crassostrea belcheri) was ranked for premium quality, being most expensive and of high demand. This oyster is often eaten raw, hence it may pose health hazards to consumers when contaminated with food-borne pathogens. As limited alternative methods are available to sterilize the oyster while preserving the raw characteristic, irradiation may be considered as an effective method for decontamination. In this study, the radiation resistance of pathogenic bacteria commonly contaminating the oyster and the optimum irradiation doses for sterilization of the most radiation resistant bacteria were investigated. The radiation decimal reduction doses ( D 10) of Salmonella Weltevreden DMST 33380, Vibrio parahaemolyticus ATCC 17802 and Vibrio vulnificus DMST 5852 were determined in broth culture and inoculated oyster homogenate. The D 10 values of S. Weltevreden, V. parahaemolyticus and V. vulnificus in broth culture were 0.154, 0.132 and 0.059 kGy, while those of inoculated oyster homogenate were 0.330, 0.159 and 0.140 kGy, respectively. It was found that among the pathogens tested, S. Weltevreden was proved to be the most resistant species. An irradiation dose of 1.5 kGy reduced the counts of 10 5 CFU/g S. Weltevreden inoculated in oyster meat to an undetectable level. The present study indicated that a low-dose irradiation can improve the microbial quality of oyster and further reduce the risks from the food-borne pathogens without adversely affecting the sensory attributes.

Electron Beam Radiation of Dried Fruits and Nuts To Reduce Yeast and Mold Bioburden

Dried fruits and nuts make up a significant portion of the commodities traded globally, and the presence of yeasts and molds on dried fruits and nuts can be a public health risk because of the potential for exposure to toxigenic fungi. Since current postharvest treatment technologies are rather limited for dried fruits and nuts, electron beam (E-beam) radiation experiments were performed to determine the doses required to reduce the yeast and mold bioburden of raisins, walnuts, and dates. The indigenous yeast and mold bioburden on a select number of commodities sold at retail ranged from 102 to 103 CFU/g. E-beam inactivation kinetics based on the linear model suggest that the decimal reduction dose required to eliminate 90% of the microbial population (D10-value) of these indigenous fungal populations ranges from 1.09 to 1.59 kGy. Some samples, however, exhibited inactivation kinetics that were better modeled by a quadratic model. The results indicate that different commodities can contain molds and yeasts of varying resistance to ionizing radiation. It is thus essential for the dried fruit and nut industry to determine empirically the minimum E-beam dose that is capable of reducing or eliminating the bioburden of yeasts and molds in their specific commodities.

Effectiveness of Radiation Processing in Elimination of Salmonella Typhimurium and Listeria monocytogenes from Sprouts

The effectiveness of radiation treatment in eliminating Salmonella Typhimurium and Listeria monocytogenes on laboratory inoculated ready-to-eat sprouts was studied. Decimal reduction doses (D10-values) for Salmonella Typhimurium and L. monocytogenes in dry seeds of mung (green gram), matki (dew gram), chana (chick pea), and vatana (garden pea) ranged from 0.189 to 0.303 kGy and 0.294 to 0.344 kGy, respectively. In sprouts made from these seeds, the D10-values ranged from 0.192 to 0.208 kGy for Salmonella Typhimurium and from 0.526 to 0.588 kGy for L. monocytogenes. Radiation treatment with a 2-kGy dose resulted in complete elimination of 104 CFU/g of Salmonella Typhimurium and 103 CFU/g of L. monocytogenes from all the four varieties of sprouts. No recovery of Salmonella Typhimurium and L. monocytogenes was observed in the radiation treated samples stored at 4 and 8°C up to 12 days. Radiation treatment with 1 kGy and 2 kGy resulted in a reduction of aerobic plate counts and coliform counts by 2 and 4 log CFU/g, respectively; the yeast and mold counts and staphylococci counts decreased by 1 and 2 log CFU/g, respectively. However, during postirradiation storage at 4 and 8°C, aerobic plate counts, coliform counts, yeast and mold counts, and staphylococci counts remained constant throughout the incubation period. This study demonstrates that a 2-kGy dose of irradiation could be an effective method of processing to ensure microbial safety of sprouts.

EVALUATION OF UV DOSE IN FLOW-THROUGH REACTORS FOR FRESH APPLE JUICE AND CIDER

ABSTRACT High absorptivity and turbidity interfere with the UV disinfection of apple cider. Three different configurations of flow-through UV reactors were evaluated to overcome this interference. Two approaches were employed: use of an extremely thin film UV reactor and increasing the turbulence within a UV reactor. Multiple-lamp UV reactors including the thin-film laminar flow “CiderSure” (8 lamps) and turbulent flow “Aquionics” (12 lamps) and annular single-lamp “UltraDynamics” reactor were studied. UV disinfection performance in laminar and turbulent flow reactors was compared by evaluation of UV dose delivery. UV fluence rate (irradiance) distribution was calculated using the multiple point source summation method. E. coli K12 was used as a target bacterium in a bioassay, and the log reduction per one pass was determined for each UV reactor. Finally, the UV decimal reduction dose (D10) was calculated by dividing the average UV fluence by log bacterial reduction per pass. Variations of the UV decimal dose were observed with various designs of UV systems. The least inactivation of E. coli K12 but the highest UV decimal reduction dose, ranging from 90 to 150 mJ/cm2, was observed in the Aquionics UV reactor in apple cider with apparent absorption coefficient (a) of 5.7 mm−1. The lower value of UV decimal reduction dose of 7.3–7.8 mJ/cm2 was required for inactivation of E. coli K12 in malate buffer and apple juice in the annular single-lamp UltraDynamics reactor. However, the decimal reduction dose for E. coli K12 in apple cider was significantly higher, about 20.4 mJ/cm2. Similar UV decimal reduction doses from 25.1 to 18.8 mJ/cm2 for inactivation of E. coli K12 were observed in the thin-film ‘CiderSure’ UV reactor in apple cider with identical absorption coefficient. Mathematical modeling of UV irradiance can improve the evaluation of UV dose delivery and distribution within the reactors.

Radiation Processing To Ensure Safety of Minimally Processed Carrot (Daucus carota) and Cucumber (Cucumis sativus): Optimization of Dose for the Elimination of Salmonella Typhimurium and Listeria monocytogenes

Minimally processed vegetables are in demand, because they offer convenience to consumers. However, these products are often unsafe because of possible contamination with pathogens, such as Salmonella, Escherichia coli O157:H7, and Shigella species. Therefore, this study was carried out to optimize the radiation dose necessary to ensure the safety of precut carrot and cucumber. Decimal reduction doses (D-values) of Salmonella Typhimurium MTCC 98 were ca. 0.164 kGy in carrot samples and 0.178 kGy in cucumber samples. D-values of Listeria monocytogenes were determined to be 0.312 and 0.345 kGy in carrot and cucumber samples, respectively. Studies of inoculated, packaged, minimally processed carrot and cucumber samples showed that treatment with a 1-kGy dose of gamma radiation eliminated up to 4 log CFU/g of Salmonella Typhimurium and 3 log CFU/g of L. monocytogenes. However, treatment with a 2-kGy dose was necessary to eliminate these pathogens by 5 log CFU/g. Storage studies showed that both Salmonella Typhimurium and L. monocytogenes were able to grow at 10°C in inoculated control samples. Neither of these pathogens could be recovered from radiation-processed samples after storage for up to 8 days.