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Simplified measures of copper fractions in wine: colorimetric and filtration‐based approaches
Author(s) -
Clark A.C.,
Zhang X.,
Kontoudakis N.
Publication year - 2020
Publication title -
australian journal of grape and wine research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.65
H-Index - 77
eISSN - 1755-0238
pISSN - 1322-7130
DOI - 10.1111/ajgw.12450
Subject(s) - wine , colorimetry , chemistry , fraction (chemistry) , copper , methanethiol , wine color , white wine , hydrogen sulfide , chromatography , mass fraction , filtration (mathematics) , organic chemistry , food science , sulfur , mathematics , statistics
Background and Aims Simple methods for determining Cu forms in wine do not currently exist. This study demonstrates the relevance of measuring a specific fraction of Cu in wine, and introduces simplified methods for its measurement utilising either colorimetry, or filtration in combination with routine measures of total Cu in wine. Methods and Results Electrochemically detectable Cu provided a threshold level of Cu that related directly to the accumulation of free hydrogen sulfide and free methanethiol in bottled wines. A simple colorimetric method using bicinchoninic acid was optimised to allow a rapid approximation of this fraction of Cu in white wine. By modification of the measurement conditions, an extra fraction of Cu associated with the partial release of Cu from thiols could also be quantified. The use of diatomaceous earth depth filters to isolate these fractions of Cu was also assessed. After passing red wine through the filters, the concentration of Cu in the filtrate correlated well with the electrochemically detectable Cu. Alternatively, for white wine the concentration of filtrate Cu overestimated this fraction of Cu and this was attributed to its inability to distinguish sulfhydryl‐free Cu from Cu loosely bound to thiols. Conclusions Multiple and simplified approaches have been devised to allow measurement of Cu fractions in wine. Significance of the Study These methodologies will allow an important fraction of Cu in wine to be measured with a spectrophotometer.