Browsing by Author "Buchweitz, Maria"

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Open Access
Analyzing bioaccessibility of polyphenols in six commercial and six traditional apples (Malus domestica Borkh.) during in vitro and ex vivo oral digestion
(2023) Kaeswurm, Julia Anna Helene; Sempio, Rebecca; Manca, Federica; Burandt, Melanie Regina; Buchweitz, Maria
Scope: Apples are an important polyphenol (PP) source. To compare the health benefits of traditional and commercial varieties, the phenolic contents and profiles as well as their release from the matrix (bioaccessibility) during oral digestion are determined. Furthermore, based on these data the proposed beneficial effect of PP on the variety specific allergenicity is discussed. Methods and results: Phenolics are quantified by HPLC‐DAD. Total phenolic contents (TPC) are in the range of 111-645 and 343-1950 mg 100 g−1 dry weight for flesh and peel, respectively. Matrix release during oral digestion is investigated ex vivo, with centrifuged and non‐centrifuged human saliva and in vitro with simulated saliva fluid (SSF). The overall bioaccessibility is similar in all digestion media, ranging between 40-80% and 39-65% of the TPC in flesh and peel, respectively. Analyzing the correlation among Mal‐d 1‐allergen‐content, unoxidized PP, and the allergenic potential for the samples reveals a negligible effect of phenolics. Conclusion: Due to higher phenolic contents in combination with a similar release, increased PP concentrations in the oral phase and an improved uptake of PP from traditional varieties are assumed. However, the proposed beneficial effect of phenolics on allergenicity cannot be confirmed.
Open Access
Impact of B-ring substitution and acylation with hydroxy cinnamic acids on the inhibition of porcine α-amylase by anthocyanin-3-glycosides
(2020) Kaeswurm, Julia A. H.; Könighofer, Lisa; Hogg, Melanie; Scharinger, Andreas; Buchweitz, Maria
An inhibitory effect on alpha-amylase and alpha-glucosidase is postulated for polyphenols. Thus, ingestion of those secondary plant metabolites might reduce postprandial blood glucose level (hyperglycemia), which is a major risk factor for diabetes mellitus type II. In addition to a previous study investigating structure-effect relationships of different phenolic structures, the effect of anthocyanins is studied in detail here, by applying an alpha-amylase activity assay, on the basis of the conversion of 2-chloro-4-nitrophenyl-4-O-ß-galactopyranosyl maltoside (GalG2CNP) and detection of CNP release by UV/Vis spectroscopy and isothermal titration calorimetry (ITC). All anthocyanin-3-glucosides showed a mixed inhibition with a strong competitive proportion, Kic < 134 µM and Kiu < 270 µM; however, the impact of the B-ring substitution was not statistically significant. UV/Vis detection failed to examine the inhibitory effect of acylated cyanidins isolated from black carrot (Daucus carota ssp. Sativus var. Autrorubens Alef.). However, ITC measurements reveal a much stronger inhibitory effect compared to the cyanidin-3-glucoside. Our results support the hypothesis that anthocyanins are effcient alpha-amylase inhibitors and an additional acylation with a cinnamic acid boosts the observed effect. Therefore, an increased consumption of vegetables containing acylated anthocyanin derivatives might help to prevent hyperglycemia.
Open Access
Multianalytical approach to understand polyphenol-Mal d 1 interactions to predict their impact on the allergenic potential of apples
(2024) Kaeswurm, Julia A. H.; Claasen, Birgit; Mayer, Pia S.; Buchweitz, Maria
Interactions between phenolic compounds and the allergen Mal d 1 are discussed to be the reason for better tolerance of apple cultivars, which are rich in polyphenols. Because Mal d 1 is susceptible to proteolytic digestion and allergenic symptoms are usually restricted to the mouth and throat area, the release of native Mal d 1 during the oral phase is of particular interest. Therefore, we studied the release of Mal d 1 under different in vitro oral digestion conditions and revealed that only 6-15% of the total Mal d 1 present in apples is released. To investigate proposed polyphenol-Mal d 1 interactions, various analytical methods, e.g., isothermal titration calorimetry, 1 H- 15 N-HSQC NMR, and untargeted mass spectrometry, were applied. For monomeric polyphenols, only limited noncovalent interactions were observed, whereas oligomeric polyphenols and browning products caused aggregation. While covalent modifications were not detectable in apple samples, a Michael addition of epicatechin at cysteine 107 in r-Mal d 1.01 was observed.
Open Access
Purification and characterization of recombinant expressed apple allergen Mal d 1
(2020) Kaeswurm, Julia A. H.; Nestl, Bettina M.; Richter, Sven M.; Emperle, Max; Buchweitz, Maria
Mal d 1 is the primary apple allergen in northern Europe. To explain the differences in the allergenicity of apple varieties, it is essential to study its properties and interaction with other phytochemicals, which might modulate the allergenic potential. Therefore, an optimized production route followed by an unsophisticated purification step for Mal d 1 and respective mutants is desired to produce sufficient amounts. We describe a procedure for the transformation of the plasmid in competent E. coli cells, protein expression and rapid one-step purification. r-Mal d 1 with and without a polyhistidine-tag are purified by immobilized metal ion affinity chromatography (IMAC) and fastprotein liquid chromatography (FPLC) using a high-resolution anion-exchange column, respectively. Purity is estimated by SDS-PAGE using an image-processing program (Fiji). For both mutants an appropriate yield of r-Mal d 1 with purity higher than 85% is achieved. The allergen is characterized after tryptic in gel digestion by peptide analyses using HPLC-MS/MS. Secondary structure elements are calculated based on CD-spectroscopy and the negligible impact of the polyhistidine-tag on the folding is confirmed. The formation of dimers is proved by mass spectrometry and reduction by DTT prior to SDS-PAGE. Furthermore, the impact of the freeze and thawing process, freeze drying and storage on dimer formation is investigated.