In-process quality control of wine by planar chromatography versus micro planar chromatography

High-performance thin-layer chromatography (HPTLC) methods were developed to determine glycerol, gluconic acid, amino acids and sugars for in-process quality control of wine. Twenty wine samples (Pfalz region, Germany) were diluted with methanol and used for quantitative analysis without any further sample preparation. The developed amino acid method provided quantitative and characteristic fingerprints of wine varieties. The amino acid assignments were verified by HPTLC-MS. The developed gluconic acid method was primarily used to control the threshold, indicating a Botrytis cinerea infection of grapes. However, this method also enabled the detection of further organic acids like malic, tartaric and citric acids. A glycerol method was developed for control of the grape must fermentation (spontaneous/regular) and for fraud detection (glycerol adulteration). The HPTLC results of the sugar contents in the wine samples were similar to those of the well-known Luff-Schoorl method. The combined use of these developed HPTLC methods allowed the fermentation control (e.g., alcoholic and malolactic fermentation) and the monitoring of the grapes' overall health status. Without modification, the HPTLC methods for sugar and amino acid analysis could be transferred to circular micro planar chromatography (μ-PLC), showing its potential and benefits in terms of an inexpensive alternative for wineries and distributors.