Characterization And Origins Of The Key Odor-Active Compounds In ’Beibinghong’ Red Icewine

Volatile compounds are vital to wine quality,determining its aroma and varietal characteristic.The special vinification process contribute to icewine with unique flavor profile,including sweet,honey,dried fruit and caramel notes.In recent years,several researches have focused on identifying key odor-active compounds of icewines.However,the influence of freeze-thaw cycles on the accumulation of volatile aroma compounds in icewine grapes and icewine aroma profile was rarely reported.In this study,the differentiation of key odor-active volatile compounds between ’Beibinghong’(Vitis amurensis × V vinifera)dry wines and icewines,which were fermented from grapes harvested before and after freeze-thaw cycles respectively,was investigated by using AEDA-GC-O and HS-SPME/SPE-GC-MS.The icewines were characterized by lactones,volatile phenols,(E)-β-damascenone,phenylacetaldehyde,cis-rose oxide,diacetyl and ethyl cinnamate with higher concentrations,and the dry wines had higher concentrations of higher alcohol acetates and fatty acid ethyl esters.Aroma reconstitution experiment revealed that the overall aroma of these wines could be mimicked by aroma recombinates containing the identified aroma compounds in all cases.Quantitative descriptive analysis and PLSR analysis demonstrated that the concentration difference of these volatile compounds described above between dry wines and icewines resulted in the distinguishment of their sensory profiles,with higher intensity of fresh fruity in dry wines,and dried fruit sweet/honey/caramel and coconut aroma in icewines.The comparison of changes in volatile compounds of ’Beibinghong’ icewines during vinification process in two consecutive vintages indicated that the cell structure disruption induced by freeze-thaw cycles played an important role in the diffusion coefficient of volatiles from epicarp to pulp.The greater degree of cell structure was damaged,the more volatile compounds were diffused into juice through pressing technique.These compounds,including(E)-β-damascenone,syringol,guaiacol and cis-rose oxide,could contribute to remarkable aroma differences in icewines from two vintages.The evolution of free and glycosidically bound volatile compounds in ’Beibinghong’ grape berries throughout on-vine over-ripening and freezing processes was studied in two consecutive vintages.A striking alteration of volatile profile occurred at sub-zero temperatures.With regard to free volatile compounds,there was a decrease in the concentration of C6 compounds,terpenols and norisoprenoids and an increase of terpene oxides during over-ripening process.These changes were attributed to a series of reactions(biotransformation,oxidation and anaerobic metabolism)induced by water loss and especially freeze-thaw cycles.Then,proteome characterization of ’Beibinghong’ grape berries was performed during freeze-thaw cycles.The majority of different expressed proteins were induced at the beginning of freeze-thaw cycles.The KEGG pathway enrichment analysis showed that only a few different expressed proteins involved in volatile compound biosynthesis metabolism,mainly including fatty acid degradation,terpenoid biosynthesis and phenylpropanoid biosynthesis.The phenomena showed that the freeze-thaw cycles could affect the anaerobic metabolism and biotransformation reaction which were induced by water loss,and resulted in the accumulation of fermentation byproducts,C6 compounds and eugenol.The present study elucidated the influence of freeze-thaw cycles on the aroma profile of icewine,and revealed the origins of key odor-active compounds in icewine by investigating the changes in proteome profile and volatile compounds of grape berries during over-ripening and freezing process.Our findings could provide guidance for further research which focuses on the production mechanism of key odor-active compounds in icewine.