Metabolomic profiling of botrytized grape berries: unravelling the dynamic chemical transformations during noble rot

Abstract

Botrytis cinerea, a fungal pathogen commonly known as grey mold, which under specific climatic conditions can develop into a desirable form known as noble rot. In this process the fungus penetrates the grape skin, allowing water evaporation and concentration of sugars and flavors, while profoundly affects the metabolite composition of grapes, leading to the production of unique and desirable compounds in the resulting wines. The result is a unique and complex wine with a luscious sweetness, heightened aromatics, and a distinct character. This study aimed to explore the metabolite profiles and chemical transformations associated with noble rot in grape berries from the Betsek area in the Tokaj region. Botrytized grape samples were collected monthly from August to November, covering six phases of botritization. Immediate freezing in liquid nitrogen was performed on-field to preserve sample integrity. Metabolomic analysis was conducted by cryomilling the samples, followed by extraction with methanol and ethyl acetate. The extracts were analyzed using liquid chromatography coupled with quadrupole time-of-flight mass spectrometry, utilizing both positive and negative electrospray ionization. The resulting metabolomic data was processed and statistically analyzed. A principal component analysis (PCA) was performed on the untargeted metabolomic profiles obtained from the botrytized grape samples, which revealed distinct differences between each phase of botritization. The main source of variance observed in the PCA plot was attributed to the botrytization process itself. This finding suggests that the metabolic changes occurring during the different stages of botritization significantly contribute to the overall metabolite composition of the grape berries. Results provided a valuable overview of the dynamic nature of the metabolic transformations associated with noble rot, highlighting the temporal evolution of the metabolite profiles throughout the botrytization process. Further analysis will enable the identification of specific metabolites that contribute to the unique chemical characteristics of noble rot-affected grape berries.

Acknowledgements: This research was funded by the National Research, Development and Innovation Office under the project titled “Research and development to improve sustainability and climate resilience of viticulture and oenology at the Eszterházy Károly Catholic University” with the grant number TKP2021-NKTA-16.