Joseph E. Marcy

Inhibition of pathogens on fresh produce by ultraviolet energy

Ultraviolet energy at a wavelength of 253.7 nm (UVC) was investigated for its bactericidal effects on the surface of Red Delicious apples, leaf lettuce and tomatoes inoculated with cultures of Salmonella spp. or Escherichia coli O157:H7. Inoculated samples were subjected to different doses ranging from 1.5 to 24 mW/cm(2) of UVC and enumerated on tryptic soy agar plus 0.05 g/l nalidixic acid to determine effective log reductions of microbial populations. UVC applied to apples inoculated with E. coli O157:H7 resulted in the highest log reduction of approximately 3.3 logs at 24 mW/cm(2). Lower log reductions were seen on tomatoes inoculated with Salmonella spp. (2.19 logs) and green leaf lettuce inoculated with both Salmonella spp. and E. coli O157:H7 (2.65 and 2.79, respectively). No significant statistical difference (p>0.05) was seen in the ability of UVC to inactivate a higher population of either Salmonella spp. or E. coli O157:H7 on the surface of green leaf lettuce. No significant difference was seen among the use of different doses applied to the surface of fresh produce for reduction of E. coli O157:H7 or Salmonella spp. (p>0.05). The use of UVC may prove to be beneficial in protecting the safety of fruits and vegetables in conjunction with Good Agricultural Practices and Good Manufacturing Practices.

Cyclodextrin Inclusion Complex Formation and Solid-State Characterization of the Natural Antioxidants α-Tocopherol and Quercetin

Cyclodextrin (CD) complexation procedures are relatively simple processes, but these techniques often require very specific conditions for each individual guest molecule. Variations of the coprecipitation from aqueous solution technique were optimized for the CD complexation of the natural antioxidants alpha-tocopherol and quercetin. Solid inclusion complex products of alpha-tocopherol/beta-CD and quercetin/gamma-CD had molar ratios of 1.7:1, which were equivalent to 18.1% (w/w) alpha-tocopherol and 13.0% (w/w) quercetin. The molar reactant ratios of CD/antioxidant were optimized at 8:1 to improve the yield of complexation. The product yields of alpha-tocopherol/beta-CD and quercetin/gamma-CD complexes from their individual reactants were calculated as 24 and 21% (w/w), respectively. ATR/FT-IR, 13C CP/MAS NMR, TGA, and DSC provided evidence of antioxidant interaction with CD at the molecular level, which indicated true CD inclusion complexation in the solid state. Natural antioxidant/CD inclusion complexes may serve as novel additives in controlled-release active packaging to extend the oxidative stability of foods.

Response of Salmonella and Escherichia coli O157:H7 to UV Energy

To determine the efficacy of a UV light treatment at 253.7 nm (UVC light) on microbial growth, plates containing tryptic soy agar plus 50 ppm of nalidixic acid (TSAN) were inoculated with known concentrations of five-strain cocktails of Salmonella and Escherichia coli O157:H7 and subjected to different UVC treatments. The concentration of the cocktail inoculum was determined with TSAN prior to inoculation. Serial dilutions were carried out, and inoculation levels of 10(0) to 10(8) CFU/ ml were tested for each pathogen. Multiple replications of doses of UV light ranging from 1.5 to 30 mW/cm2 were applied to different cocktail concentrations, and doses of > 8.4 mW/cm2 resulted in a 5-log reduction of Escherichia coli O157:H7, while a 5-log reduction of Salmonella was observed with doses of > 14.5 mW/cm2. Results for both organisms yielded sigmoidal inactivation curves. UVC light is effective in reducing microbial populations of pathogens on agar surfaces.

The determination of frying oil quality using a chemosensory system

Chemosensory systems are currently being introduced in the food industries for quality control and process monitoring. This study was conducted to determine the possibility of using a chemosensory system to differentiate among varying intensities of oil rancidity and investigate discrimination between good, marginal and unacceptable frying oils. Fresh, 1-day, 2-day used and discarded frying oils were obtained from a fast food restaurant in each frying cycle for 4 weeks. The oil samples were analysed using a quartz-microbalance-based chemosensory system. The discrimination between good, marginal and unacceptable frying oils with regard to rancidity was examined and the results were compared to their physico-chemical properties such as dielectric constant, peroxide value, and free fatty acid content. The different qualities of frying oils were successfully evaluated and discriminated using the chemosensory system. Good correlations (r from 0.87 to 0.96) were found between changes in physico-chemical properties of oil and the sensor signals.

Controlled release of α-tocopherol, quercetin, and their cyclodextrin inclusion complexes from linear low-density polyethylene (LLDPE) films into a coconut oil model food system.

Polymer additive migration into a food product is dependent upon numerous factors including the original concentration of the additive in the polymer, its solubility in the food, its diffusion coefficient in the polymer, its partition coefficient between the polymer and food, temperature, and time. The limited solubility of quercetin in linear low-density polyethylene (LLDPE) did not allow release from the film due to phase segregation of the quercetin in the bulk polymer. Increasing the molecular weight of α-tocopherol by β-cyclodextrin inclusion complexation can greatly reduce its diffusion coefficient in LLDPE. Ziegler–Natta and metallocene LLDPE contain different crystalline structure morphologies and diffusion path networking arrangements that allow for differences in additive release rates. Effective controlled-release packaging should combine β-cyclodextrin complexation of additives and polymer morphology control to target delivery of an optimal antioxidant concentration to achieve prolonged activity, resulting in extended shelf life foods.

Controlling light oxidation flavor in milk by blocking riboflavin excitation wavelengths by interference.

Milk packaged in glass bottles overwrapped with iridescent films (treatments blocked either a single visible riboflavin [Rb] excitation wavelength or all visible Rb excitation wavelengths; all treatments blocked UV Rb excitation wavelengths) was exposed to fluorescent lighting at 4 degrees C for up to 21 d and evaluated for light-oxidized flavor. Controls consisted of bottles with no overwrap (light-exposed treatment; represents the light barrier properties of the glass packaging) and bottles overwrapped with aluminum foil (light-protected treatment). A balanced incomplete block multi-sample difference test, using a ranking system and a trained panel, was used for evaluation of light oxidation flavor intensity. Volatiles were evaluated by gas chromatography and Rb degradation was evaluated by fluorescence spectroscopy. Packaging overwraps limited production of light oxidation flavor over time but not to the same degree as the complete light block. Blocking all visible and UV Rb excitation wavelengths reduced light oxidation flavor better than blocking only a single visible excitation wavelength plus all UV excitation wavelengths. Rb degraded over time in all treatments except the light-protected control treatment and only minor differences in the amount of degradation among treatments was observed. Hexanal production was significantly higher in the light-exposed control treatment compared to the light-protected control treatment from day 7; it was only sporadically significantly higher in the 570 nm and 400 nm block treatments. Pentanal, heptanal, and an unidentified volatile compound also increased in concentration over time, but there were no significant differences in concentration among the packaging overwrap treatments for these compounds.

Enhancement of Plant Essential Oils' Aqueous Solubility and Stability Using Alpha and Beta Cyclodextrin

Sodium benzoate has been shown to produce benzene in combination with ascorbic acid. This has led to research for safe alternatives from plant essential oils and parabens that have shown some antimicrobial activity, but many of these compounds exhibit poor solubility in aqueous solutions. Cyclodextrins can increase the solubility of many compounds. This work aimed to investigate the solubility of 23 plant essential oils and 4 parabens in water and an apple juice medium. Four of these compounds were chosen for their low aqueous solubility to determine if complexing the compound with α- and β-cyclodextrin would increase solubility. Three of the complexes were dissolved in an acidified aqueous solution and then studied in glass and polyethylene terephthalate (PET) to determine if storage material would affect the stability. Solubility of the 27 compounds in distilled water ranged from 1.6 mg/L to 2460.6 mg/L and the solubility of 18 of the compounds decreased from 2.5 to 84.7% in apple juice medium (pH = 3.4, 12-13 °Brix). Complexation with cyclodextrin dramatically increased the solubility of the compounds, up to 10-fold. Packaging material had no effect on concentration of compounds present over 7 days. Cyclodextrins were able to increase solubility of these compounds to more suitable concentrations, and may lead to viable natural alternatives to sodium benzoate.

High-pressure resistance variation of Escherichia coli O157: H7 strains and Salmonella serovars in tryptic soy broth, distilled water, and fruit juice

The effect of high pressure on the log reduction of six strains of Escherichia coli O157:H7 and five serovars of Salmonella enterica was investigated in tryptic soy broth, sterile distilled water, and commercially sterile orange juice (for Salmonella) and apple cider (for E. coli). Samples were subjected to high-pressure processing treatment at 300 and 550 MPa for 2 min at 6 degrees C. Samples were plated onto tryptic soy agar directly after pressurization and after being held for 24 h at 4 degrees C. At 300 MPa, little effect was seen on E. coli O157:H7 strains, while Salmonella serovars varied in resistance, showing reductions between 0.26 and 3.95 log CFU/ml. At 550 MPa, E. coli O157:H7 strains exhibited a range of reductions (0.28 to 4.39 log CFU/ml), while most Salmonella populations decreased beyond the detection limit (> 5-log CFU/ml reduction). The most resistant strains tested were E. coli E009 and Salmonella Agona. Generally, bacterial populations in fruit juices showed larger decreases than did populations in tryptic soy broth and distilled water. E. coli O157:H7 cultures held for 24 h at 4 degrees C after treatment at 550 MPa showed a significant log decrease as compared with cultures directly after treatment (P < or = 0.05), while Salmonella serovars did not show this significant decrease (P > 0.05). All Salmonella serovars tested in orange juice treated at 550 MPa for 2 min at 6 degrees C and held for 24 h showed a > 5-log decrease, while E. coli O157:H7 strains require a higher pressure, higher temperature, longer pressurization, or a chemical additive to achieve a 5-log decrease.

Effect of fermentation, aging and thermal storage on total glycosides, phenol-free glycosides and volatile compounds of White Riesling (Vitis vinifera L.) wines

There is growing recognition of the significance of the products of glycoside hydrolysis to varietal wine aroma. White Riesling wines were produced from four strains of Saccharomyces cerevisiae. Wines underwent conventional aging or anaerobic thermal storage (20 days at 45°C) either 2 or 40 months post-fermentation to quantify influences on total glycosides, phenol-free glycosides and selected volatiles. Glycoside and free volatile concentrations were estimated by analysis of glycosyl-glucose and gas chromatography/mass spectrometry, respectively. Thermal storage of wines 2 months post-fermentation reduced the total glycosides by an average of 33% for all yeasts and increased the concentration of free benzyl alcohol while decreasing the concentration of free linalool and geraniol. Conventional aging for 40 months reduced the total and phenol-free glycosides equally among yeasts by an average of 60%, with phenol-free glycosides averaging 80% of the total. Thermal storage of aged wines reduced the total glycoside concentration by an additional 29%. The effect of thermal storage on selected volatile phenols, higher alcohols, esters, acids, terpenes, carbonyl compounds, C-13 norisoprenoids and six-carbon alcohols was variable depending upon the component.

Nonproteolytic Clostridium botulinum toxigenesis in cooked turkey stored under modified atmospheres.

The ability of nonproteolytic Clostridium botulinum type B spores to grow and produce toxin in cooked, uncured turkey packaged under modified atmospheres was investigated at refrigeration and mild to moderate abuse temperatures. Cook-in-bag turkey breast was carved into small chunks, surface-inoculated with a mixture of nonproteolytic C. botulinum type B spores, packaged in O2-impermeable bags under two modified atmospheres (100% N2 and 30% CO2:70% N2), and stored at 4, 10, and 15 degrees C. Samples were analyzed for botulinal toxin and indigenous microorganisms, as well as subjected to sensory evaluation, on days 0, 7, 14, 28, 42, and 60. Given sufficient incubation time, nonproteolytic C. botulinum type B grew and produced toxin in all temperature and modified atmosphere treatment combinations. At moderate temperature abuse (15 degrees C), toxin was detected by day 7, independent of packaging atmosphere. At mild temperature abuse (10 degrees C), toxin was detected by day 14, also independent of packaging atmosphere. At refrigeration temperature (4 degrees C), toxin was detected by day 14 in product packaged under 100% N2 and by day 28 in product packaged under 30% CO2:70% N2. Reduced storage temperature significantly delayed toxin production and extended the period of sensory acceptability of cooked turkey, but even strict refrigeration did not prevent growth and toxigenesis by nonproteolytic C. botulinum. At all three storage temperatures, toxin detection preceded or coincided with development of sensory characteristics of spoilage, demonstrating the potential for consumption of toxic product when spoilage-signaling sensory cues are absent.