Chemical Traits and Microbial Population Characterization of 'Asprinio' Grape Must, a Local Vine Cultivated in Campania Region (Italy)

Abstract

'Asprinio' grape is used to produce a white wine from the Campania region, known as 'Asprinio' (DOC since 1993). A plethora of approaches was adopted to characterize the organic compounds (e.g., free amino acids and other metabolites) and microbial population (bacteria and fungi) in 'Asprinio' grape must by collecting samples from three different vineyards cultivated with the 'alberata' training system. The average free amino acid content of 'Asprinio' grape must showed quantitative variations, but no significant statistical differences were found. On average, proline was the most abundant free amino acid (~282 mg/L; 47.9%), followed by arginine (~66 mg/L; 11.5%) and glutamine (~25.2 mg/L; 4.2%). On the other hand, the total polyphenol content (TPC) of 'Asprinio' grape must was different, like their antioxidant activity, which increased when the TPC content was higher. Moreover, 1D and 2D NMR spectra highlighted the presence of high sugars amount (in particular glucose) as well as trans-caftaric acid, trans-coutaric acid, trans-fertaric acid, and the cis-isomers of these cinnamate esters. Finally, the evaluation of the microbial communities in the 'Asprinio' grape must revealed the presence of several representative bacterial phyla-mainly Bacteroidota, Proteobacteria, and Actinobacteriota-as well as various fungal genera, including Cladosporium, Hanseniaspora, Aspergillus, and Saccharomyces. Notably, these microorganisms, which contribute to the fermentation process and influence the final wine flavor, have been found in different proportions in the grape musts analyzed. Our results contribute to increasing knowledge of the 'Asprinio' grape, an indigenous vine of Southern Italy.

Keywords: Asprinio; Vitis vinifera L.; free amino acids; metagenomic analysis; nuclear magnetic resonance (NMR); white wine.

Figure 1

(a–c) Radar graphs of the average free amino acid profile of ‘Asprinio’ grape must from Alberata_A, Alberata_C, and Alberata_R samples, respectively.

Figure 2

(a) Total phenol content (TPC) and (b) antioxidant capabilities of Alberata_A, Alberata_C, and Alberata_R ‘Asprinio’ grape musts. In (a), TPC expressed as g of gallic acid equivalents (GAEs). In (b), ABTS expressed as mmol of Trolox equivalents (TEs) per liter. Values are means (±SD) of triplicate analyses (n = 3). For each bar, different letters indicate statistical significance according to Tukey’s multiple comparisons test (p ≤ 0.05).

Figure 3

¹H NMR spectra of Alberata_A, Alberata_C, and Alberata_R ‘Asprinio’ grape must samples. Chemical shifts are reported in ppm with respect to TMS.

Figure 4

¹H NMR and HMBC spectra of the partially purified fraction obtained from Alberata_R grape must samples. Data were recorded in methanol-d₄ at 500 MHz. Chemical shifts are reported in ppm with respect to TMS.

Figure 5

Structural elucidation of the main phenolics in ‘Alberata’ grape must samples. (a) Detail of the aromatic region of the HSQC spectrum; the whole spectrum can be found in Figure S2. (b) Detail of the aromatic region of the COSY spectrum; the whole spectrum can be found in Figure S3. (c) HMBC spectrum: details showing the aromatic region and the relevant correlations that allowed us to identify the main aromatic compounds. (d) Trans-cinnamate esters identified in the samples. NMR data were recorded in methanol-d₄ at 500 MHz. Chemical shifts are reported in ppm with respect to TMS.

Figure 6

Overview of dominant bacterial and fungal genera in Alberata_C (a,c) and Alberata_R (b,d), based on the high-throughput sequencing of 16S rDNA and ITS2 regions.

Figure 7

Venn diagrams of the number of shared and unique bacterial and fungal genera in the Alberata_C and Alberata_R.