Online Determination of Ergosterol in Naturally Contaminated Grape Mashes Under Industrial Conditions at Wineries

In general, vinification of sound grapes is an essential requirement for the production of high-quality wines. Grape rot, mainly caused by filamentous fungi, commonly impairs perceptual quality of wine; food safety may be affected due to the formation of biogenic amines and mycotoxins. Grape rot assessment by visual examination, taste or smell remains subjective. Other methods for grape rot quantification frequently lack specify, sensitivity or reproducibility. In contrast, ergosterol represents an objective and specific marker for filamentous fungal grape rot. In our study, we approved the suitability of ergosterol as a marker for grape rot of commercially harvested grapes, delivered to wineries under normal operating conditions. A total of 177 grape samples from five grape varieties was analysed by HPLC-UV for ergosterol content. Pinot Meunier showed the highest ergosterol contents up to 11.4 mg/kg. Mean ergosterol content for all varieties amounted to 2.3 mg/kg. About 20 % of the samples exceeded the limit of 3.0 mg/kg for sound grapes, and about 3.4 % were above the limit of 6.2 mg/kg indicating rotten grapes. Moreover, near-infrared/visible (NIR/VIS) spectroscopy has been applied as a rapid tool for online determination of ergosterol under industrial conditions. Calibration models were established and validated. Validation statistics for a dependent test set were coefficient of determination of the validation (R (2) (val)) of 0.726, root mean square error of prediction (RMSEP) of 0.84 mg/kg and ratio of prediction to deviation (RPD) of 2.0. At least semi-quantitative measurements of ergosterol in grape mashes upon delivery at wineries appeared feasible, thus enabling the objective detection of grape rot. Thereby, fair and incentive quality-based payment may be enabled; quality management and food safety may be improved.