Department of Viticulture and Enology, University of California, Davis, Davis, California 95616, United States.
Food Safety and Measurement Facility, University of California, Davis, Davis, California 95616, United States.
J Agric Food Chem. 2021 Nov 17;69(45):13286-13298. doi: 10.1021/acs.jafc.1c01216. Epub 2021 Jul 2.
The isomeric nature of monoterpenyl glycosides makes unambiguous identification of intact glycosides difficult. As a result, it is challenging to relate the changes in free monoterpenol concentrations to the corresponding glycosides during wine fermentation and storage. In this study, we isolated and identified linalool, nerol, and geraniol monoterpenyl glycosides fromcv. Riesling grapes through fractionation followed by acid or enzyme hydrolysis. Changes in the composition of identified monoterpenyl glycosides and their respective free volatiles were then monitored during alcoholic fermentations of Riesling juice with four different yeast strains across two successive years. The relative concentrations of the volatiles were monitored by solid-phase microextraction gas chromatography mass spectrometry, while ultrahigh-performance liquid chromatography quadrupole time-of-flight mass spectrometry was used for intact glycosides. Glycoside hydrolysis during fermentation could be related to relative concentrations of the corresponding free aglycones. However, other sources of free monoterpenols were also observed. Differences in glycoside hydrolysis among yeast strains and across years were observed and may be related to grape maturity and/or nutrient levels.
单萜糖苷的同分异构性质使得完整糖苷的明确鉴定变得困难。因此，在葡萄酒发酵和储存过程中，很难将游离单萜醇浓度的变化与相应的糖苷联系起来。在这项研究中，我们通过分级分离，然后用酸或酶水解，从 cv.雷司令葡萄中分离和鉴定了芳樟醇、橙花醇和香叶醇单萜糖苷。然后，在连续两年的雷司令葡萄汁的酒精发酵过程中，我们用四种不同的酵母菌株监测了鉴定出的单萜糖苷及其各自游离挥发物组成的变化。通过固相微萃取气相色谱质谱联用监测挥发性物质的相对浓度，而采用超高效液相色谱四极杆飞行时间质谱法监测完整的糖苷。发酵过程中的糖苷水解可以与相应游离配基的相对浓度相关联。然而，也观察到了其他游离单萜醇的来源。还观察到酵母菌株和年份之间糖苷水解的差异，这可能与葡萄的成熟度和/或营养水平有关。
