Targeted metabolomics analysis based on HS-SPME-GC-MS to discriminate geographical origin of 'Muscat Hamburg' grape and wine

Monoterpenes are typical aroma components in muscat grapes and wines, closely related to its geographical origins. However, the mechanism underlying the geographical differences of monoterpenes remains to be elucidated, especially in the Chinese viticulture regions. This study investigated the diversity of six Chinese viticultural vineyards (YT, XF, SS, XX, WW and CL) in the monoterpene composition of Vitis vinifera L. cv.'Muscat Hamburg' grapes and the resulted wines. Monoterpenes were analyzed by HS-SPME- GC-MS. The total amount of free and bound monoterpenes varied dramatically between grapes of different vineyards, and their contents were obviously higher in YT region grapes. The OAVs for 18 monoterpenes of grapes from the YT vineyard were relative higher than those of other regions, and the floral odor could distinguish grapes from different regions. The total free monoterpenes were highest in the YT region wine. Concentrations of total bound monoterpenes ranged from 711.13 μg/L (XF region) to 1078.30 μg/L (CL region). A correlation analysis showed that all monoterpenes showeda positive correlation with mean relative humidity, sum rainfall, and a negative correlation with sum duration of sunshine and mean temperature. This study would provide some new insights to understand the geographical differences of monoterpenes, and the results would facilitate the effective viticultural treatment of grapes to improve the quality of the aroma.

Dynamic changes in monoterpene accumulation and biosynthesis during grape ripening in three Vitis vinifera L. cultivars

Monoterpenes are important aroma components in grapes and wines. We analyzed the free and bound monoterpene profiles and the transcript levels of terpenoid biosynthesis genes in Vitis Vinifera cvs. Muscat Hamburg, Riesling, and Sauvignon Blanc grapes at five ripening stages. Principal component analyses revealed that the three cultivars had different free monoterpene profiles at harvest and the early stage of ripening. In all cultivars, the total bound monoterpene contents were higher than the free monoterpene contents during grape ripening. The changes in monoterpene profiles in different grape varieties were correlated with the transcript levels of some VviTPS and VviGT genes. In Riesling, the VviGT14 and VviUGT88A1L1 transcript levels were related to geraniol glucoside accumulation. In Muscat Hamburg, the VviPNLGl1, VviPNLGl2, and VviPNLGl4 transcript levels were related to linalool accumulation. Understanding the dynamic changes in monoterpene accumulation and biosynthesis will allow winemakers to devise strategies to improve grape and wine aromas.