Abstract
AIM: Assess the impact of different vineyards and winemaking variables on the phenolic and volatile profiles of Pinot Blanc musts and young wines from South Tyrol.
METHODS: Grapes were harvested during September 2019 in 3 vineyards near Ora (Italy), at 450 m (MM), 550 m (K) and 800 m (V) a.s.l. Six different types of Pinot Blanc musts and young wines were studied in 3 replicates. Study A - 3 different vineyards (MM_C, K_C, V_C), but same winemaking; Study B - same vineyard (V), but 3 different vinifications: i) grapes were frozen before crushing (V_F); ii) same as V_F, but co-inoculation yeast/malolactic bacteria (V_F_ML); iii) no grape freezing, but co-inoculation yeast/malolactic bacteria (V_ML). Phenolics were analysed by HPLC-DAD and HPLC-QqQ-MS, while volatiles were investigated by SPME-HS-GC×GC-ToF-MS. Standard oenological parameters were measured using a multi-parametric analyser, alcohol distillation, pH-meter and chemical titration. The data were statistically processed with ANOVA and Principal Component Analysis (PCA).
RESULTS: Upon a dataset of 27 phenolic compounds identified in musts, a good separation among samples was achieved using PCA. The musts produced without pre-fermentative grape freezing had significantly higher amounts of catechin, gallocatechin and astilbin. Besides, the musts from the same vineyard, but with frozen grapes showed higher concentrations of ethanol, glucose-fructose, malic acid, and lower concentration of tartaric acid. 46 phenolic compounds were identified in wines. The PCA separated well the samples of Study A: caftaric acid showed the most significant difference as well as the highest relative abundance. The PCA showed that the phenolic profile of the wines of study B (V_C, V_F, V_F_ML, V_ML) clustered samples based on the pre-fermentative grape freezing. Wines made without frozen grapes were separated due to the higher phenolic concentrations. The volatile profile of wines after 1 month of storage contained 32 compounds. The PCA not only grouped samples according to the grape freezing, but it also showed that wines with no applied grape freezing were well clustered in terms of the presence/absence of malolactic fermentation in their winemaking. V_C samples were described by higher abundances of branched chain alcohols, while samples V_ML - by ethyl and phenylethyl esters.
CONCLUSIONS: The profiles of phenolics and volatiles were good discriminants of South Tyrolean Pinot Blanc wines produced under the same winemaking technology but harvested in different vineyards. In this study, the pre-fermentative grape freezing negatively affected concentrations of phenolics. The literature shows that freezing positively enhances contents only of anthocyanins and flavanol glucosides, while it negatively affects contents of phenolic acids and flavanols, that are main phenolic compound in white wines.