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Characterisation of polyphenol-protein interactions using the apple allergen Mal d 1 as an example

Subject Area Food Chemistry
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 434385225
 
Final Report Year 2024

Final Report Abstract

The interactions of polyphenols with the apple allergen Mal d 1 might explain the observed better tolerability of traditional varieties than commercial breeds by allergic patients. One hypothesis for the potentially reduced allergenic potential of traditional varieties is that an increased polyphenol content might lead to shielding or destruction of the antibody binding sites on the Mal d 1 or precipitation due to structural changes. In this project, polyphenol contents and profiles, as well as the contents of different Mal d 1 isoallergens (variants of Mal d 1 with minor structural differences) were determined in traditional and commercial apple varieties. Additionally, the release of polyphenols and Mal d 1 and their interactions under oral digestion conditions were characterized for the first time. The aim of this project was to gain a fundamental understanding of the allergenic potential of an apple variety, to identify relevant impact factors and to analyze respective parameters in the apple. The phenolic structures were identical in all apple varieties. However, there were noticeable differences in the profile and total content. Most traditional varieties were characterized by higher phenolic contents than observed for commercial cultivars. The release of polyphenols from the flesh during oral digestion depended on the individual phenolic composition, with a mean of 70%. Targeted mass spectrometry was used for the first time to quantify the Mal d 1 content and isoallergen distribution. The commercial varieties showed a clear trend towards higher allergen contents and increased expression of minor isoallergens. Therefore, the impact of storage conditions on the increase of total Mal d 1 content and changes in the isoallergen profile were investigated in detail for several commercial varieties. Various analytical methods, including isothermal titration calorimetry, saturation transfer difference-NMR, and 1H-15N HSQC-NMR experiments, were applied to investigate the interaction between apple polyphenols and r-Mal d 1 in model systems. The results revealed weak and unspecific interactions on the allergen surface. Additionally, covalent modifications of Mal d 1 by epicatechin were detected by an untargeted mass spectrometric approach, but exclusively on the cysteine residue. Browning of apples leads to the formation of oligomeric polyphenols, which in turn caused the aggregation of Mal d 1 and reduced the amount of free allergen in our experiments. These findings support the data on the release of Mal d 1 during oral digestion, as apple varieties with higher polyphenol content exhibited a lower release of Mal d 1 with increasing incubation time. The analysis of all data, including consumer reports on the allergenicity of a particular apple variety, suggests that the polyphenols present in apples have a very limited impact on the allergenic potential of the variety. Polyphenols reduced the amount of allergenic Mal d 1 only through browning. However, the absolute allergen content and isoallergen profile of an apple variety are considerably more relevant for the allergenicity of an apple cultivar. The results and methods developed in this project can aid in the advancement of hypoallergenic apple breeding, allowing the 2.5 million apple allergy sufferers in Germany to enjoy fresh apples in the future as they are an important contribution to a healthy diet.

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