Luke F. LaBorde

Ascorbic acid degradation in a model apple juice system and in apple juice during ultraviolet processing and storage.

UNLABELLED Ultraviolet radiation induced degradation of ascorbic acid in a model apple juice system and in apple juice was studied using a collimated beam batch UV reactor. In the model system, ascorbic acid degradation was more rapid at higher dose levels and the reaction accelerated with increasing exposure time. Ascorbic acid degradation significantly (P < 0.05) increased as the pH was raised from 2.4 to 5.5, although no difference was observed between 2.4 and 3.3. Increasing malic acid concentration between 0.1 and 1%, increased ascorbic acid degradation (P < 0.05) although there was no difference between 0.5 and 1.0%. Solution absorbance, varied by addition of tannic acid, decreased ascorbic acid degradation with increasing concentration due to absorption of UV radiation. Fructose at levels found in apple juice significantly increased ascorbic acid degradation while glucose and sucrose did not. Factors identified that accelerate ascorbic acid degradation may at least partially explain why ascorbic acid degradation occurred more rapidly in UV-treated apple juice than in the 0.5% malic acid model system. Ascorbic acid degradation continued after UV treatments during dark storage. Storage decreases were faster at higher initial UV dose levels and higher storage temperature. PRACTICAL APPLICATION The present study shows the effect of UV processing on ascorbic acid, a key vitamin found in many fruit juices. Process developers and researchers can use this study as a model for designing experiments to identify factors that influence the stability of vitamin C and other bioactive compounds during UV processing.

Influence of punctures, cuts, and surface morphologies of golden delicious apples on penetration and growth of Escherichia coli O157:H7

The ability of Escherichia coli O157:H7 to penetrate and grow within punctures, fresh-cut surfaces, and calyces of Golden Delicious apples was investigated. A three-strain cocktail of E. coli O157:H7 resistant to ampicillin was used to inoculate fresh and 48-h-old punctures, fresh-cut surfaces, and open or closed calyces. A concentric cutting procedure was used to evaluate depth of penetration within punctures and prevent cross contamination during sampling. Within 2 h, E. coli O157:H7 penetrated vertically through the fresh punctures and 3.4 mm within the underlying parenchyma. After 48 h, E. coli O157: H7 cells penetrated up to 5.5 mm within the punctures and >2.6 mm horizontally away from fresh punctures. However, 48-h-old punctures did not permit penetration beyond their boundaries. Fresh-cut surfaces permitted up to 2.8 mm penetration after 24 h. Onset of growth of E. coli O157:H7 occurred 4 to 8 h postinoculation on fresh punctures and fresh-cut surfaces with populations increasing by 3 logs after 48 h. E. coli O157:H7 penetrated within calyces regardless of the extent of opening or method of inoculation. However, E. coli O157:H7 was never recovered from the inner core of apples. Computed tomography scan imaging revealed that closed calyces effectively prevented penetration of sodium iodide solutions within the calyx cavity. Lack of solution penetration may explain why sanitizing treatments are ineffective in inactivating microbial cells within the calyx. Understanding the role of morphological differences in permitting or restricting bacterial penetration may lead to development of more effective strategies to enhance the safety of fresh horticultural products.

Incidence of Listeria monocytogenes and Listeria spp. in a small-scale mushroom production facility.

Listeria monocytogenes is a foodborne pathogen of significant concern to the agricultural and food processing industry because of its ability to grow and persist in cool and moist environments and its association with listeriosis, a disease with a very high mortality rate. Although there have been no listeriosis outbreaks attributed to fresh mushrooms in the United States, retail surveys and recalls are evidence that L. monocytogenes contamination of mushrooms (Agaricus bisporus) can occur. The objective of this study was to determine the prevalence of Listeria spp., including L. monocytogenes, in a small-scale mushroom production facility on the campus of the Pennsylvania State University in the United States. Of 184 samples taken from five production zones within the facility, 29 (15.8%) samples were positive for Listeria spp. Among the Listeria spp. isolates, L. innocua was most prevalent (10.3%) followed by L. welshimeri (3.3%), L. monocytogenes (1.6%), and L. grayi (0.5%). L. monocytogenes was recovered only from the phase I raw material composting area. Isolates of L. monocytogenes were confirmed and serotyped by multiplex PCR. The epidemiological relatedness of the three L. monocytogenes isolates to those serotypes or lineages frequently encountered in listeriosis infections was determined by multi-virulence-locus sequence typing using six virulence genes, namely, prfA, inlB, inlC, dal, clpP, and lisR. The phylogenetic positions of the three isolates in the dendrogram prepared with data from other isolates of L. monocytogenes showed that all isolates were grouped with serotype 4a, lineage IIIA. To date, this serotype has rarely been reported in foodborne disease outbreaks.

Ultraviolet-Induced Oxidation of Ascorbic Acid in a Model Juice System: Identification of Degradation Products

Degradation products of ultraviolet (UV-C, 254 nm) treated ascorbic acid (AA) are reported. Analysis by high-performance liquid chromatography-mass spectroscopy (HPLC-MS) conducted in a 0.5% malic acid model juice system (pH 3.3) demonstrated increased degradation of AA above untreated controls with concomitant increases in dehydroascorbic acid (DHA) and 2,3-diketogulonic acid (DKGA) levels. Electron spin resonance (ESR) spectroscopy studies, conducted in phosphate buffer (pH 7.0) to increase detection sensitivity, demonstrated that ascorbyl radical (AA•) formation occurs simultaneously with AA degradation. Consistent with a previous study in which UV treatments were shown to accelerate dark storage degradation, AA• radicals continued to form for up to 200 min after an initial UV treatment. Results from this study suggest that the mechanism for UV-induced degradation is the same as the general mechanism for metal-catalyzed oxidation of AA in juice.

Susceptibility of Penicillium expansum spores to sodium hypochlorite, electrolyzed oxidizing water, and chlorine dioxide solutions modified with nonionic surfactants.

The use of water flotation tanks during apple packing increases the risk of contamination of apples by spores of Penicillium expansum, which may accumulate in the recirculating water. Routine addition of sanitizers to the water may prevent such contamination. Sodium hypochlorite (NaOCl), chlorine dioxide (ClO2), and electrolyzed oxidizing (EO) water have varied activity against spores of P. expansum, and their effectiveness could be enhanced using surfactants. The objective of this study was to determine the ability of three nonionic surfactants, polyoxyethylene sorbitan monooleate (Tween 80), polyoxyethylene sorbitan monolaurate (Tween 20), and sorbitan monolaurate (Span 20), to enhance the efficacy of NaOCl, ClO2, and EO water against spores of P. expansum in aqueous suspension at various temperatures and pH conditions. The efficacy of NaOCl solutions was enhanced by the addition of surfactants at both pH 6.3 and pH 8 (up to 5 log CFU reduction). EO water and ClO2 were effective against P. expansum spores (up to 5 log CFU and 4 log CFU reduction, respectively), but addition of surfactants was not beneficial. All solutions were less effective at 4 degrees C compared to 24 degrees C irrespective of the presence of surfactants. Nonionic surfactants could potentially be used with NaOCl to improve control of P. expansum in flotation tanks, but the efficacy of such formulations should be validated under apple packing conditions.

Inactivation of human pathogens during phase II composting of manure-based mushroom growth substrate.

Commercial production of white button mushrooms (Agaricus bisporus) requires a specialized growth substrate prepared from composted agricultural by-products. Because horse and poultry manures are widely used in substrate formulations, there is a need to determine the extent to which the composting process is capable of eliminating human pathogens. In this study, partially composted substrate was inoculated with a pathogen cocktail (log 10⁶ to 10⁸ CFU/g) containing Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella. Pathogen and indicator-organism reductions were followed at temperatures that typically occurred during a standard 6-day phase II pasteurization and conditioning procedure. Controlled-temperature water bath studies at 48.8, 54.4, and 60°C demonstrated complete destruction of the three pathogens after 36.0, 8.0, and 0.5 h, respectively. Destruction of L. monocytogenes and E. coli O157:H7 at 54.4°C occurred more slowly than E. coli, total coliforms, Enterobacteriaceae, and Salmonella. Microbial reductions that occurred during a standard 6-day phase II pasteurization and conditioning treatment were studied in a small-scale mushroom production research facility. After phase II composting, E. coli, coliforms, and Enterobacteriaceae were below detectable levels, and inoculated pathogens were not detected by direct plating or by enrichment. The results of this study show that a phase II composting process can be an effective control measure for eliminating risks associated with the use of composted animal manures during mushroom production. Growers are encouraged to validate and verify their own composting processes through periodic microbial testing for pathogens and to conduct studies to assure uniform distribution of substrate temperatures during phase II.

Predominance and Distribution of a Persistent Listeria monocytogenes Clone in a Commercial Fresh Mushroom Processing Environment.

A longitudinal study was conducted to determine the prevalence of Listeria spp. in a commercial fresh mushroom slicing and packaging environment. Samples were collected at three different sampling periods within a 13-month time interval. Of the 255 environmental samples collected, 18.8% tested positive for L. monocytogenes, 4.3% for L. innocua, and 2.0% for L. grayi. L. monocytogenes was most often found on wet floors within the washing and slicing and packaging areas. Each of the 171 L. monocytogenes isolates found in the environment could be placed into one of three different serotypes; 1/2c was predominant (93.6%), followed by 1/2b (3.5%) and 1/2a (2.9%). Of 58 isolates subtyped using multi-virulence-locus sequence typing, all 1/2c isolates were identified as virulence type (VT) 11 (VT11), all 1/2b isolates were VT105, and 1/2a isolates were either VT107 or VT56. VT11 was designated as the predominant and persistent clone in the environment because it was isolated repeatedly at numerous locations throughout the study. The overall predominance and persistence of VT11 indicates that it likely colonized the mushroom processing environment. Areas adjacent to the trench drain in the washing and slicing area and a floor crack in the packaging area may represent primary harborage sites (reservoirs) for VT11. Improvements made to sanitation procedures by company management after period 2 coincided with a significant (P ≤ 0.001) reduction in the prevalence of L. monocytogenes from 17.8% in period 1 and 30.7% in period 2 to 8.5% in period 3. This suggests that targeted cleaning and sanitizing procedures can be effective in minimizing the occurrence of L. monocytogenes contamination in processing facilities. Additional research is needed to understand why VT11 was predominant and persistent in the mushroom processing environment.

Kinetics of the Thermal Degradation of Patulin in the Presence of Ascorbic Acid

Degradation of the mycotoxin patulin between 25 and 85 °C without and with added ascorbic acid was studied, and the effectiveness of linear and nonlinear models for predicting reaction rates was compared. In agreement with previous reports, ascorbic acid significantly increased (P ≤ 0.05) the rate of patulin degradation at all temperatures studied. The data for patulin degradation in the absence of ascorbic acid were adequately modeled using a zero-order linear kinetic model. However, the predictive abilities of zero and higher-order linear models were not adequate to describe the more complex reactions that likely occurred when ascorbic acid was added. In contrast, the nonlinear Weibull model adequately described the patulin-ascorbic acid reaction throughout the temperature range studied. Zero-order rate constants and Weibull scale values for each of the respective reactions followed the Arrhenius law. Activation energies of 58.7 ± 3.9 and 29.6 ± 1.9 kJ mol⁻¹ for the reaction without and with ascorbic acid, respectively, confirmed decreased patulin stability in the presence of ascorbic acid and suggested that the mechanisms for the 2 degradation reactions were different.

Microbial Survey of Pennsylvania Surface Water Used for Irrigating Produce Crops

Recent produce-associated foodborne illness outbreaks have been attributed to contaminated irrigation water. This study examined microbial levels in Pennsylvania surface waters used for irrigation, relationships between microbial indicator organisms and water physicochemical characteristics, and the potential use of indicators for predicting the presence of human pathogens. A total of 153 samples taken from surface water sources used for irrigation in southeastern Pennsylvania were collected from 39 farms over a 2-year period. Samples were analyzed for six microbial indicator organisms (aerobic plate count, Enterobacteriaceae, coliform, fecal coliforms, Escherichia coli, and enterococci), two human pathogens (Salmonella and E. coli O157), and seven physical and environmental characteristics (pH, conductivity, turbidity, air and water temperature, and sampling day and 3-day-accumulated precipitation levels). Indicator populations were highly variable and not predicted by water and environmental characteristics. Only five samples were confirmed positive for Salmonella, and no E. coli O157 was detected in any samples. Predictive relationships between microbial indicators and the occurrence of pathogens could therefore not be determined.