Pyrrolizidine alkaloids (PAs) and tropane alkaloids (TAs) and pare plant secondary metabolites with toxic properties in human and livestock. They can enter the food chain predominantly via unintended co-harvesting of PA- or TA-containing weed plants. Moreover, by honeybees foraging nectar and pollen of such plants the plant toxins can get into honey. By means of contaminated feed they can also be transferred to milk and, subsequently, to dairy products. During processing or storage of contaminated food raw materials or foodstuff, these plant toxins may undergo certain molecular modifications, such as degradation or binding to food components, potentially affecting analytical traceability or toxicological properties of the plant toxins [1,2]. The presented project aimed to investigate the fate of toxic TAs and PAs in three food processing model systems (yoghurt fermentation, storage of honey, baking of bread) and to unveil potential transformation products.
The raw materials were spiked with standard solutions of selected PAs and/or TAs: Spiked milk was fermented to yoghurt using several yoghurt cultures and also single strains of yoghurt-producing bacteria. Honey was spiked and stored for up to four weeks. Bread was baked from flour artificially contaminated with TA standards or ground seeds of TA-containing thornapple (Datura stramonium). Non-spiked controls were produced accordingly. Samples were extracted under acidic conditions and purified using C18 SPE cartridges. Extracts were analysed by means of LC-MS/MS (targeted) and, if alkaloid levels were decreased, by UHPLC-QToF-MS (untargeted). Potential transformation products were aimed to be identified by comparing untargeted data of samples by means of multivariate analytics.
In stored honey, results showed a structure-dependant decrease of certain PA N-oxides, which prove findings of earlier studies [3]. In contrast, the contents of corresponding PAs increased only slightly. In yoghurt, PA N-oxides also showed reduced levels during fermentation, but solely when probiotic microorganisms were incorporated. In contrast to honey samples, this observation was accompanied with greatly increased levels for the corresponding PAs. Neither storing of honey nor fermentation of yoghurt showed any influence on the spiked contents of TAs, but baking of contaminated flour reduced the levels of certain TA compounds. The formation of potential plant toxin transformation products formed by the investigated processes is currently still investigated and its results will be reported. The relevance of these findings regarding the future proper assessment of toxic PAs and TAs in food will be discussed.
Literature:
[1] Kaltner F., J. Agric. Food Chem. 2022, 70, 20, 5975–5981. [2] Marín-Sáez J. et al., Food Res. Int. 2019, 122, 585-592. [3] Kaltner F. et al., J. Agric. Food Chem. 2018, 66, 20, 5221–5228
