Kinetic and Mass Spectrometric Characterization of Anti-Greening Mechanisms of Cysteine and Glutathione in Chlorogenic Acid-Lysine Solutions
Date of Award
Master of Science (MS)
Effective decolorization methods mitigating green compound formation from alkaline chlorogenic acid-amino acid reactions can facilitate greater consumption of chlorogenic acid-rich products. While thiols show promise as decolorization agents to replace sulfites, their application has not been optimized. In this work, cysteine and glutathione were probed for their varying kinetic effects on the onset of chlorogenic acid-lysine induced greening. A six-parameter model developed from a reparametrized Weibull cumulative distribution function accurately captured the time- and thiol concentration-dependence of greening in chlorogenic acid-lysine-thiol solutions at pH 8.0 and 9.0, illustrating the pH-dependence of each thiol’s effectiveness at lowering terminal greening magnitude as well as glutathione’s prolonging of the lag time prior to greening onset due to redox coupling reactions at either pH and using 0.64-5.09 mM thiol. Subsequent mass spectrometric analyses of chlorogenic acid-lysine-thiol solutions identified the generation and consumption of aromatic and benzylic thiolyl-chlorogenic acid conjugates, as well as the formation of novel hydroxylated thiolyl-chlorogenic acid conjugate species hypothesized to arise from radical reaction mechanisms. Evidence of thiol reactions outcompeting initial dimerization reactions further emphasized the mechanisms by which greening and autoxidative browning occur in chlorogenic acid-lysine solutions. Furthermore, a 2H-1,4-benzothiazine compound was tentatively identified and associated with the increased brown color development occurring in solutions containing cysteine, which is not observed in glutathione-containing solutions. The significance of these findings include an expedient spectrophotometric approach to describing thiols’ greening mitigation in addition to more thoroughly describing the underlying thiol-CGA reactions and reaction products.
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Drucker, C. (2023). Kinetic and mass spectrometric characterization of anti-greening mechanisms of cysteine and glutathione in chlorogenic acid-lysine solutions. Master's thesis, Chapman University. https://doi.org/10.36837/chapman.000471