Thesis
Improving the protein precipitation assay for tannins by reformulation of the resuspension buffer
Washington State University
Master of Science (MS), Washington State University
2012
Handle:
https://hdl.handle.net/2376/102311
Abstract
The analysis of wine tannins has become more commonplace due to their important astringent properties for red wine. Various methods exist including chromatography; however protein precipitation assays have earned favor for their simplicity and strong correlation with the sensory perception of astringency. The most widely used protein precipitation method in the US for wine is a variant on the Hagerman and Butler (1980) technique, which allows for measure of both tannins and polymeric pigments (Harbertson et al. 2003). The original method called for high concentrations of sodium dodecyl sulfate (SDS) and an alkaline buffer (triethanolamine, TEA pH 9.4) to re-suspend the tanninprotein precipitate and to support the eventual colorimetric reaction with ferric chloride (FeCl3). However, recently several irregularities were found including bubble formation (presumably from the detergent SDS), a significant background drift and loss of reproducibility (presumably due to the alkaline pH). Here we proposed a possible solution: to lower the pH to neutral and to replace SDS with urea (keeping the original TEA). Forty-nine red wines, primarily made from Syrah and Cabernet Sauvignon, were tested in triplicate using the various different buffer formulations (urea/TEA pH 7, 8, 9.4, and SDS/TEA pH 9.4). With urea/TEA pH 7 the background interference was 33% lower and at pH 8 it was 23% lower compared to the original method. Besides, tannin concentration was significantly altered by the pH of the resuspension buffer in the following order: pH8 > pH7 > pH9.4. Most importantly the covariance for tannin analysis was significantly lower (p = 0.006) at pH 7 than at pH 9.4 thus altering the pH of the resuspension buffer can be used to reduce background interference and to improve the reproducibility of the analysis. Also the incubation for getting a steady background reading was possibly reduced to less than 5 minutes from original 10 minutes using urea/TEA buffer.
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Details
- Title
- Improving the protein precipitation assay for tannins by reformulation of the resuspension buffer
- Creators
- Yue Yu
- Contributors
- James F. Harbertson (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Food Science, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525176201842
- Language
- English
- Resource Type
- Thesis