Department of Food Science and Technology

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Optimization of headspace solid-phase microextraction for analysis of wine aroma compounds
Whiton, R. S.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2000)
Headspace solid-phase microextraction (SPME) is a fast and simple sampling method for analysis of volatile compounds, but quantitation can be affected by sample matrix and sampling conditions. Sampling time and temperature are particularly important in controlling analyte response, and the effects vary for different compound classes and volatilities. Tests with model solutions containing a range of typical wine volatiles show that increasing temperature and sampling time can increase sensitivity for higher boiling polar compounds but decrease sensitivity for very volatile compounds. Sample matrix elements such as ethanol concentration can also have different effects on the responses of different compounds.
Evaluation of the phenol-free glycosyl-glucose determination
Zoecklein, Bruce W.; Douglas, L. S.; Jasinski, Y. W. (American Society for Enology and Viticulture, 2000)
Grape glycosides are, in part, an important source of varietal wine aroma and flavor. Aglycones may be aliphatic residues, monoterpenes, sesquiterpenes, norisoprenoids, or phenolic compounds. Studies were undertaken to evaluate and compare methods of isolating non-phenolic or phenol-free glycosides. Phenol free glycoside fractions were obtained by three isolation methods: the addition of polyvinylpolypyrrolidone (PVPP), isolation at pH 10.0 using C18 solid phase extraction cartridges, or isolation at pH 13.0 using Oasis(TM) hydrophilic-lipophilic balance (HLB) extraction cartridges. Glycoside separation using the Oasis cartridges reduced the phenol content of the phenol-free glycoside fractions in Chardonnay juice and wines by an average of 49.7% compared to 33.6 % using C18. The differences in the phenol concentration in the phenol-free glycoside fractions with these two methods were greater with red juices and wines. For the Cabernet Sauvignon juice and wines the phenol concentration was reduced by an average 103% and 73% using the Oasis and C18 cartridges, respectively.
How do you know if your food is safe to sell?
Boyer, Renee R. (Virginia Cooperative Extension, 2001-12-05)
When preparing foods at home to sell, you must still practice good sanitation and proper food safety techniques. Microbial growth is affected by the following six factors: Food, Acidity, Time, Temperature, Oxygen and Moisture, also known as FAT TOM. Controlling one or more FAT TOM factors prevents microorganisms from growing to dangerous levels that might make someone sick.
Measurement of 3-alkyl-2-methoxypyrazine by headspace solid-phase microextraction in spiked model wines
Hartmann, Peter J.; McNair, Harold M.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2002)
The effect of wine matrix ingredients and conditions on the headspace sampling of 3-alkyl-2-methoxypyrazines was investigated with solid-phase microextraction (SPME) and capillary gas chromatography, using a nitrogen phosphorus detector. Changes in the recovery of 3-ethyl-, isopropyl-, sec-butyl-, and isobutyl-2-methoxypyrazines from the static headspace of synthetic wine matrices spiked with 5 mug/L of each analyte were investigated and reported as a function of SPME fiber type, extraction time, and temperature. The influence of pH, ethanol, phenolics, and oak was studied. Divinylbenzene/carboxen/polyclimethylsiloxane (PDMS) SPME fibers at an extraction temperature of 50degreesC for 30 minutes with 30% (w/v) added sodium chloride resulted in the highest analyte recoveries. Although PDMS (100 mum) SPME fibers at an extraction temperature of 35degreesC for 30 minutes with 30% (w/v) added sodium chloride resulted in lower analyte recoveries, the fiber remained functional for 50 to 75 analyses after other coatings deteriorated. Changing the sample ethanol concentration from 0 to 20% (v/v) resulted in an exponential decrease in the recovered analytes. Below pH 2, there was extensive loss of the analytes in the headspace. No measurable impact on alkyl-methoxypyrazine headspace concentrations was observed with exposures to selected phenolics and to oak.
Comparison of analytical methods for prediction of prefermentation nutritional status of grape juice
Gump, B. H.; Zoecklein, Bruce W.; Fugelsang, K. C.; Whiton, R. S. (American Society for Enology and Viticulture, 2002)
Five methods for evaluating nitrogen status were compared using 70 Cabernet Sauvignon juice samples: nitrogen by o-phthaldialdehyde (NOPA), arginine NOPA, enzymatic ammonia, Formol, and high-performance liquid chromatography (HPLC). Parallel recovery studies using model solutions of various amino acids and ammonia, presented singly and in combination, were also conducted. The results from two fruit-processing methods were compared using immature and mature berries. NOPA measurements were significantly higher in mature, pressed whole berry-derived samples, compared with homogenized juice. Adjustment of formaldehyde pH prior to analysis was found to be critical to consistency of the Formol method. Average amino acid recoveries for the Formol titration ranged from 82 to 99%. Average recovery for proline was 16.9 +/- 0.4%. Ammonium nitrogen was also recovered (84 +/- 3%) in the Formol procedure. Formol results trended significantly with NOPA. The correlation coefficient between Formol and NOPA plus NH4+ was 0.87, with Formol values being higher. The average deviation between the Formol and HPLC plus NH4+ and between the NOPA plus NH4+ and HPLC plus NH4+ was 7.3%.
Quantification of glycosidase activity in selected strains of Brettanomyces bruxellensis and Oenococcus oeni
Mansfield, A. K.; Zoecklein, Bruce W.; Whiton, R. S. (American Society for Enology and Viticulture, 2002)
Brettanomyces bruxellensis and lactic acid bacteria are common microorganisms capable of modifying wine aroma and flavor. The activity of beta-glucosiclase against p-nitrophenyl-beta-D-glucopyranoside was determined in a model system for 14 strains of Brettanomyces bruxellensis yeast and 9 strains of lactic acid bacteria (Oenococcus oeni). All Brettanomyces strains and 7 Oenococcus strains exhibited enzymatic activity against this substrate. B. bruxellensis beta-glucosiclase activity was primarily intracellular; O. oeni showed some extracellular activity. Strains showing activity greater than 1000 nmole mL(-1) g dry cell mass(-1) 24 hr(-1) for Brettanomyces, or 100 nmole mL(-1) g dry cell mass(-1) 24 hr(-1) for Oenococcus, were evaluated for their effect on native Viognier grape glycosides. Neither genus was active on Viognier grape glycosides.
Evaluation of glycosyl-glucose analytical methods for various glycosides
Whiton, R. S.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2002)
The accuracy of two methods for determination of glycosyl-glucose (GG) in grapes and wine has been tested using several glycoside standards containing alkyl, benzenoid, and phenolic aglycones. The total GG method using C-18 sorbent material was found to exhibit poor recoveries of benzenoid glycosides. The recoveries for the phenol-free GG method were satisfactory for alkyl and benzenoid glycosides. In addition, an adaption of the phenol-free GG method to 96-well microplate format has been demonstrated.
Determination of ethyl carbamate in wine by solid-phase microextraction and gas chromatography/mass spectrometry
Whiton, R. S.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2002)
A method for the rapid determination of ethyl carbamate in wine by headspace solid-phase microextraction with detection by gas chromatography/mass spectrometry has been developed. The analysis parameters of fiber coating, extraction time, and sample temperature have been optimized. The optimized method of headspace sampling with a Carbowax/divinylbenzene fiber for 30 minutes has been found to be reproducible and linear from 10 to 80 mug/L, with a limit of detection of 9.6 mug/L. The method is simple, requires little operator effort, and can be automated.
The Nitty-Gritty of Food Safety. A Guide for Parents and Childcare Providers
Parra, Danielle Elizabeth; Nickols-Richardson, Sharon Michelle, 1965-; Serrano, Elena L.; Boyer, Renee R. (Virginia Cooperative Extension, 2002-12-02)
This guide illustrates for you and the children you for care ways to prevent foodborne illnesses. Follow these principles to fight bacteria - clean, separate, cook and chill. Children are never too young to learn and establish healthy practices as the safe handling of food.
Enhancing The Safety of Locally Grown Produce. On the Farm
Boyer, Renee R. (Virginia Cooperative Extension, 2002-12-06)
Explains the value of developing a food safety plan for the farm to protect profits and public health and safety.
The influence of lactose hydrolysis on the strength and sensory characteristics of vanilla ice cream
Matak, Kristen E.; Wilson, James H.; Duncan, Susan E.; Wilson, Edward J.; Hackney, Cameron Raj; Sumner, Susan S. (American Society of Agricultural and Biological Engineers, 2003)
Lactose hydrolysis was investigated as a method of producing a more extrudable ice cream product. Ice cream mixes were treated with lactase from the microbial sources Kluyveromyces lactis and Aspergillus oryzae to produce 0% to 100% lactose hydrolysis. Compression measurements and yield stress tests of frozen ice cream were both affected by the temperature of the samples. As the temperature decreased, the work required to compress the ice cream 10 mm (firmness) and the torsional shear stress both increased. There was a linear relationship between the firmness of lactose-hydrolyzed ice cream (0%, 80%, and 100%) and temperature (r(2) = 0.98, 0.99, and 0.97, respectively). The treated samples were significantly softer that? the control, but not different from each other There was a significant difference (p < 0.05) in ice cream dippability between the control samples (0% hydrolyzed) and the treatment groups (80% and 100% hydrolyzed). The control group was consistently harder to dip. Hydrolysis of lactase in the ice cream mix produced a softer, more extrudable product.
Population dynamics and effects of Brettanomyces bruxellensis strains on Pinot noir (Vitis vinifera L.) wines
Fugelsang, K. C.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2003)
Replicated, sterile Pinot noir (Vitis vinifera L.) wines were individually inoculated with one of six strains of Brettanomyces bruxellensis (Ave, M, 216, Vin 1, Vin 4, or Vin 5) at initial numbers < 50 cfu/mL. In two separate studies, population changes were monitored for 23 months, or until cell densities peaked and subsequently declined to less than or equal to 30 cfu/mL. Significant variation was noted in both growth rate and stationary phase population densities among strains. The concentration of selected volatile components was monitored using solid-phase microextraction GC/MS. Large increases in the concentration of 4-ethylphenol occurred after titers reached 2.5 x 10(5) cfu/mL. Brettanomyces-inoculated wines were found to have detectable concentrations of ethyldecanoate, isoamyl alcohol, 4-ethylguaiacol, and 4-ethylphenol, with some significant differences in their concentrations among strains. Duo-trio testing suggested sensory differences between the control and all inoculated wines and among wines inoculated with strains Ave and Vin 5, M and 216, and M and Vin 4. Consensus training analysis suggested that all Brettanomyces wines had a greater perception of earthy, smoky, spicy, and cardboard descriptors than uninoculated control wines.
Effect of fermentation, postfermentation, and postbottling heat treatment on Cabernet Sauvignon glycoconjugates
Mansfield, A. K.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2003)
In Cabernet Sauvignon must, total and phenol-free glycosides (expressed as glycosyl-glucose) rose during fermentation while skin concentrations dropped. Wines were heated postfermentation, prior to dejuicing (rising 2 to 3degreesC per day from 23 to 42degreesC, and held for one day at 42degreesC), or after bottling (at 42degreesC for 21 days) to determine the effect on total glycosides, glycosidic fractions, and anthocyanin complexing. Pre-dejuicing thermal vinification resulted in higher total (12%) and phenol-free (18%) glycosides. Large polymeric pigments rose 208% and small polymeric pigments rose 41%. Skins had lower total glycosides (-16%), and no significant difference in phenol-free glycosides. Postbottling heat treatment resulted in lower total (-15%) and phenol-free (-16%) glycosides, and increased hue (25%). Large polymeric pigments increased 62% compared to control wines.
Effects of prohexadione-calcium on grape yield components and fruit and wine composition
Lo Giudice, Danielle; Wolf, Tony K.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2004)
Prohexadione-calcium (prohexadione-Ca) was applied to field-grown Cabernet franc, Cabernet Sauvignon, Chardonnay, and Seyval to evaluate rates and timing effects on fruit yield components and on fruit and wine composition. Berries per cluster, berry weight, cluster weight, and clusters per shoot in the subsequent season were all decreased by multiple, prebloom plus postbloom, applications to Cabernet Sauvignon and Cabernet franc. Similar reductions in current season components of yield were observed with Seyval. Application (250 mg/L) to single clusters of Cabernet Sauvignon and Chardonnay at bloom, or in the one-to-two-week prebloom period decreased fruit set, whereas applications one to two weeks postbloom reduced berry weight, with no impact on fruit set. Berry weight reduction correlated to increased color intensity (420 nm + 520 nm), total anthocyanins, total phenols, and phenol-free glycosyl-glucose (PFGG) in Cabernet Sauvignon. In a separate experiment, prohexadione-Ca increased Cabernet franc must color intensity, total anthocyanins, and total phenols, despite having, minimal effects on berry weight or crop yield. Aroma and flavor triangle difference tests did not distinguish treatment differences with young Cabernet franc wines. This study of prohexadione-Ca effects on grape reproductive development illustrated that berry set and berry weight were responsive to application timing, with the one-to-two-week period after bloom most sensitive to reductions in berry weight. The concurrent effects on fruit composition were generally positive, while the full impact on wine quality remains equivocal, but worthy of further evaluation.
Effect of hydrogen peroxide and other protease inhibitors on Cryptosporidium parvum excystation and in vitro development
Kniel, Kalmia E.; Sumner, Susan S.; Pierson, Merle D.; Zajac, Anne M.; Hackney, Cameron Raj; Fayer, Ronald; Lindsay, David S. (American Society of Parasitology, 2004-08)
This study was undertaken to observe the effects of hydrogen peroxide on Cryptosporidium parvum oocysts with respect to protease activity in comparison to known protease inhibitors. In assessing the possible mechanisms of action of hydrogen peroxide, treatment effectiveness was analyzed using 3 assays and the potential roles of proteases and cations were considered. Treatment of C. parvum oocysts with hydrogen peroxide inhibited protease activity up to 50% compared with untreated controls. Treatment of oocysts with chemicals that affect sulfhydryls, including N-ethylmaleimide and dithiolthreitol, inhibited protease activity by > 90%. Treatment of oocysts with these chemicals, along with the protease inhibitors, phenylmethylsulfonyl fluoride (PMSF), ethylenediamine-tetraacetic acid, and cystatin, inhibited protease activity as well as in vitro excystation and infection in a cell culture assay. Several mechanisms may result in the successful inhibition of infection and excystation by hydrogen peroxide treatment, including: oxidation of oocyst wall proteins or lipids, chelating of cations necessary for infection, or hydroxyl radical-induced DNA damage to sporozoites, or both.
Survival of Toxoplasma gondii oocysts Eastern oysters (Crassostrea virginica)
Lindsay, David S.; Collins, Marina V.; Mitchell, S. M.; Wetch, C. N.; Rosypal, A. C.; Flick, George J. Jr.; Zajac, Anne M.; Lindquist, A.; Dubey, Jitender P. (American Society of Parasitology, 2004-10)
Toxoplasma gondii has recently been recognized to be widely prevalent in the marine environment. It has previously been determined that Eastern oysters (Crassostrea virginica) can remove sporulated T. gondii oocysts from seawater and that oocysts retain their infectivity for mice. This study examined the long-term survival of T gondii oocysts in oysters and examined how efficient oysters were at removing oocysts from seawater. Oysters in 76-L aquaria (15 oysters per aquarium) were exposed to 1 x 10(6) oocysts for 24 hr and examined at intervals up to 85 days postexposure (PE). Ninety percent (9 of 10) of these oysters were positive on day 1 PE using mouse bioassay. Tissue cysts were observed in I of 2 mice fed tissue from oysters exposed 21 days previously. Toxoplasma gondii antibodies were found in 2 of 3 mice fed oysters that had been exposed 85 days previously. In another study, groups of 10 oysters in 76-L aquaria were exposed to 1 x 10(5), 5 x 10(4), or 1 x 10(4) sporulated T. gondii oocysts for 24 hr and then processed for bioassay in mice. All oysters exposed to 1 x 10(5) oocysts were infected, and 60% of oysters exposed to 5 x 10(4) oocysts were positive when fed to mice. The studies with exposure to 1 x 10(4) oocysts were repeated twice, and 10 and 25% of oysters were positive when fed to mice. These studies indicate that T. gondii can survive for several months in oysters and that oysters can readily remove T. gondii oocysts from seawater. Infected filter feeders may serve as a source of T gondii for marine mammals and possibly humans.
Effects of high pressure processing on infectivity of Toxoplasma gondii oocysts for mice
Lindsay, David S.; Collins, Marina V.; Jordan, C. N.; Flick, George J. Jr.; Dubey, Jitender P. (American Society of Parasitology, 2005-06)
High pressure processing (HPP) has been shown to be an effective non-thermal method of eliminating non-spore forming bacteria from a variety of food products. The shelf-life of the products is extended and the sensory features of the food are not or only minimally effected by HPP. The present study examined the effects of HPP using a commercial scale unit on the viability of Toxoplasma gondii oocysts. Oocysts were exposed from 100 to 550 MPa for I min in the HPP unit and then HPP treated oocysts were orally fed to groups of mice. Oocysts treated with 550 MPa or less did not develop structural alterations when viewed with light microscopy. Oocysts treated with 550 MPa, 480 MPa, 400 Mpa, or 340 MPa were tendered noninfectious for mice. Mice fed oocysts treated with no or 100 to 270 MPa became infected and most developed acute toxoplasmosis and were killed or died 7 to 10 days after infection. These results suggest that HPP technology may be useful in the removal of T. gondii oocysts from food products.
Foodborne Pathogens. E. coli O157:H7
Boyer, Renee R. (Virginia Cooperative Extension, 2005-09-01)
What is E. coli O157:H7, it's symptoms, who and how one gets intoxicated, and the proper food handling techniques.
Common Foodborne Pathogens. Salmonella
Boyer, Renee R. (Virginia Cooperative Extension, 2005-09-01)
What is Salmonella, it's symptoms, who and how one gets intoxicated, and the proper food handling techniques.
Storage and Handling of Commercially Packaged Foods
Villalba, Abigail; Boyer, Renee R.; Bazemore, Sherry (Virginia Cooperative Extension, 2005-09-01)
Proper selection of foods at the grocery store and appropriate storage and handling practices at home are necessary to maintain the quality and safety of commercially processed foods and perishable foods. This brochure offers some guidelines to follow when buying, handling, and storing packaged foods.

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