Browsing by Author "Whiton, R. S."

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    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%.
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    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.
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    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.
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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.
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    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.