April 29, 2025 - Penn State Student Exchange Seminars

Fingerprinting and quantification of tannins by LC-MS/MS with ESI in-source fragmentation

Yanxin Lin

PhD Candidate

Department of Food Science

Penn State University

 SpeakerBio

Yanxin Lin is a fourth-year Ph.D. candidate in Food Science at Penn State University, working in Dr. Misha Kwasniewski's lab. Her research focuses on the analysis of aroma compounds and tannins in wine and cider using advanced techniques such as liquid chromatography-mass spectrometry (LC-MS) and gas chromatography (GC). Yanxin also gained valuable industry experience as a graduate research intern in the chemistry research division at Gallo, where she contributed to innovative projects in wine chemistry.

Abstract

Tannins are a diverse group of polyphenolic compounds, playing important roles in sensory properties, antioxidant activity, and plant defense. Despite their importance, characterizing tannins is challenging due to their structural diversity, varying polymerization, and interactions with matrix components which hinder accurate identification and quantification. In wine and hard cider, the primary tannins are categorized as condensed tannins found in grape skins and seeds, apple peels and fresh. In addition, the hydrolysable tannins such as ellagitannins, are another type of tannin mostly in wine derived from oak. Both types are essential for wine quality, influencing mouthfeel, astringency, and aging potential. However, to date tannin fingerprinting approaches lack either specificity, sensitivity, or require laborious analysis. This is due to the complexity of possible stereochemical configurations, and the varied degree of polymerization. To address this, we developed an LC-MS/MS method using electrospray ionization in-source fragmentation (ESI-ISF) for tannin fingerprinting in ciders and wines. This technique enables detailed profiling of both hydrolysable and condensed tannins by depolymerizing compounds in the ion source and analyzing their subunit-specific fragmentation spectra. The ESI-ISF method for condensed tannins has been used to fingerprint their procyanidins composition from degree of polymerization of commercial ciders. The ESI-ISF method has also been adapted into a high-throughput method for analyzing the total concentration of hydrolysable tannins in 30 different white wines and 33 different red wines and achieve high correlation (r2= 0.98) with acid hydrolysis method which requires at least four hours for sample preparation. This approach, which has already been adopted by some industry stakeholders, shows promise in expanding our ability to characterize tannins and relate their complex structure to different elements of bioactivity.

Modulation of Cu(II) reactivity toward hop-derived polyfunctional thiols by model peptides in beer 

Morgan Vincent

PhD Candidate

Department of Chemistry

Penn State University

 Speaker Bio

Morgan Vincent is a chemistry PhD candidate at the Pennsylvania State University. She earned a Bachelor of Science in Chemistry and a Bachelor of Arts in Mathematics from Seton Hill University in Greensburg, Pennsylvania. Her research focuses on the effect of copper complexation on polyfunctional thiol (i.e., flavor and aroma compounds) stability in beer. Morgan also contributes to education research projects focused on graduate student teacher identity in agriculture and student understandings of electron configurations. As a multi-award-winning educator, Morgan has taught a range of chemistry and food science courses and led workshops, including the renowned Penn State Ice Cream Short Course. Beyond academia, Morgan enjoys running, horseback riding, and cheering on her siblings at their sporting events.

Abstract

Volatile polyfunctional thiols derived from hops (e.g., 3-mercaptohexan-1-ol, 3-mercaptohexyl acetate, and 4- mercapto-4-methylpentan-2-ol) are particularly important to the aroma quality of many modern beer styles, imparting desirable aromas (e.g., passionfruit, guava, etc.). Regrettably, these volatile compounds are prone to degradation within the beer matrix, primarily through reactions with trace levels of copper, a transition metal commonly introduced via brewing ingredients and equipment. Despite the significance of this issue, thiol oxidation in beer remains underexplored, especially with respect to transition metals. In recent investigations, we used electron paramagnetic resonance (EPR) spectroscopy to probe the molecular environment of Cu(II) of a commercial pilsner and potentiometric titrations with ion-selective electrodes to assess Cu(II) binding capacities in model beer systems. Here in, we demonstrate that model ligands, such as Gly-His, oxalic acid, and L-tyrosine, can form stable complexes, thus potentially delaying the loss of the hop-derived polyfunctional thiols essential to beer aroma and quality.