Application of EEM fluorescence in combination with PARAFAC analysis to simultaneously monitor quercetin in its deprotonated, aggregated, and protein bound states

Abstract

Flavonoids, a group of naturally occurring polyphenols, attract great interest due to their many apparent health benefits including their anti-oxidant properties and anti-amyloidogenic properties. However, the behavior of flavonoids in aqueous environments can be unpredictable due to the potential formation of aggregates and hydrolysis products. A better understanding of the complex behavior of flavonoids is needed before flavonoid-based therapies can be developed. Employing excitation-emission matrix (EEM) fluorescence in combination with weighted-parallel factor analysis (WPARAFAC), a series of aqueous quercetin solutions were characterized at varying pH values and concentrations. Distinct pH and concentration-dependent fluorophores were observed with emission maxima of 540 and 600 nm, respectively. However, the excitation maxima of the two species were broad and highly overlapped ranging from 350 to 400 nm. In addition, the fluorescence of quercetin was characterized in the presence and absence of bovine serum albumin (BSA). Interaction with BSA resulted in a dramatic red-shift of the excitation maximum to 445 nm, while the emission maximum of the BSA-quercetin complex was slightly blue-shifted to 535 nm. Coupling of WPARAFAC and EEM fluorescence enabled simultaneous detection of multiple fluorescent quercetin species in solution at a wide range of conditions.

Two Statistical Tools for Assessing Functionality and Protein Characteristics of Different Fava Bean (Vicia faba L.) Ingredients

“…As this study deals with protein-rich ingredients that have been modified by process conditions, possible interactions between protein and sugars and/or polyphenols could also be expected, leading to changes in protein conformations and availability for functional requirements. Complexes of pulse proteins with phenolic compounds including hydroxycinnamic acids, flavonols, flavones and flavanols have been presented in previous reports [15,29]. The protein-tannin interaction in fava bean has also been reported to modify protein properties.…”

“…The scores from the PARAFAC m els conform to Beer's Law [14]. This combination of fluorescence and PARAFAC fo plaining intrinsic fluorescence of protein and protein interactions is gaining popul [15][16][17].…”

“…For example, cereal flours have been characterized by PARAFAC through a four-component model explaining proteins, vitamins and phenolic acids [24]. Similarly, the presence of phenolic compounds such as caffeic acid, kaempferol and quercetin and fluorophores related to sugar degradation, the Maillard reaction (hydroxymethylfurfural), and carotenoid and chlorophyll degradation have been detected and characterized by PARAFAC in other food systems [14,15,22,24,28]. As this study deals with protein-rich ingredients that have been modified by process conditions, possible interactions between protein and sugars and/or polyphenols could also be expected, leading to changes in protein conformations and availability for functional requirements.…”

“…This secondary region explains non-native protein signals from other fluorophores, including vitamins and flavonoids that are inherently present in fava bean [1,[22][23][24]. The NPR signals may also contain information on possible protein modifications from Maillard reactions and polyphenol interactions [15,25] (Figure 1). [13].…”

Four-way Self-weighted Alternating Normalized Residue Fitting Algorithm with Application for the Analysis of Serotonin in Human Plasma

“…[13][14][15][16][17][18] They aim to search for any "second-order advantage" by three-dimensional responsive data; that is, second-order calibration has better stability towards interferents as well as matrix effects. Thus, they have been brought into extensive practical applications, for example, biological matrices, pharmaceuticals, food, and environment, [19][20][21][22][23][24][25][26][27] while seeking out a way to quantify the analytes of interest, even in presence of complex background.…”