Effects Of Thinning On Volatile Compounds In Wine Grapes And Wines

The aroma volatile compounds in grapes and their wines of Vitis viniferal L.Cabernet Sauvignon were investigated by Headspace Solid-Phase Micro-Extraction(HS-SPME with Gas Chromatography-Mass Spectrometry (GC-MS), for revealing theeffects of crop-load and its control ways (methods of thinning) on the contents, thevarieties and their changes of volatile compounds in grapes and wines. The resultsindicated that:1. Different methods of thinning may reduce the crop-load and also can decreasethe total content of acid in grapes in different degrees, in ripend grapes, the total contentof acid in berry-thinning-50%grapes was the lowest, followed by thecluster-thinning-upper (50%); berry-thinning can obviously improve the content ofreducing sugar in grapes, while cluster-thinning made no big differences comparingwith the blank control; in contrast to cluster-thinning, the grapes of berry-thinning had ahigher sugar-acid ratio at harvest.2. In the process of maturation of Cabernet Sauvignon grapes, the content of aromavolatile compounds in grapes gradually reduced, and the varieties of these volatilecompounds also decreased. The content of C6aldehydes such as hexanal,(E)-2-hexenal,(E,E)-2,4-hexadienal was significantly decreased which resulted in the reduction of thetotal content of aldehydes. The content of alcohols was greatly increased by thesynthese of hexanol in the mature period. The varieties and contents of ketones,terpenes, esters and organic acids were all decreased, among them, β-damascenone andβ-ionone, which belong to the norisoprenoids, were not detected in ripend grapes.Under the same condition of crop-load, the different ways of thinning havedifferent influences on the aroma volatile compounds in grapes. In full matured grapes,the contents of hexanal, benzaldehyde, benzeneacetaldehyde, D-limonene and(E)-2-hexenoic acid in cluster-thinning grapes were higher than berry-thinning, whilethe contents of octanal, nonanal, decanal, nonanol,6-methyl-5-hepten-2-one,(-)-menthol and geranyl acetone were higher than cluster-thinning. In general, the totalcontent of volatile compounds in cluster-thinning grapes was higher than which inberry-thinning grapes. Among them, the cluster-thinning-50%group were showed ahigher total content of volatile compounds in grapes, followed by the blank control, thencluster-thinning-25%group and berry-thinning-50%were lower in the total content, andberry-thinning-25%was minimum. Viewed from the material composition, cluster-thinning grapes had higher content of the aldehydes and the organic acids, andberry-thinning grapes had a greater quantity of the ketone and the terpenes; under theload condition of50%, the content of the alcohols in cluster-thinning grapes was higherthan berry-thinning, while under the condition of25%of the load, berry-thinning washigher than the other.Compared with the control, under the condition of the same thinning method, withthe reduction of the load, the total content of aroma volatile compounds in full maturedgrapes all showed a trend of ‘reduced first and then increased’, among them, the mostobvious were the changes of contents of (E)-2-hexenal,(E,E)-2,4-hexadienal,β-phenylethyl alcohol and benzyl alcohol. Under the condition of the same load ofcluster-thinning, about the different position of fructification, the contents of mostvolatile compounds in cluster-thinning-lower grapes were higher than that ofcluster-thinning-upper, but there were still a few aroma volatile compounds in grape,which are important to the aroma, such as benzaldehyde, benzeneacetaldehyde,2-ethyl-1-hexanol, benzyl alcohol, β-myrcene and D-limonene, their contents incluster-thinning-upper grapes were higher than that of cluster-thinning-lower, of whichthe most remarkable were benzyl alcohol and D-limonene.3. The main aroma compounds detected in Cabernet Sauvignon wines wereisoamyl alcohol, phenylethyl alcohol, octanoic acid ethyl ester, ethyl acetate, hexanoicacid ethyl ester,2-methyl-1-propanol,1-propanol,1-hexanol, decanoic acid ethyl esterand octanoic acid. After thinning treatment on grapes, the varieties and total content ofaroma volatile compounds in thinning wines were higher than control, among them,ethyl9-hexadecenoate and citronellol were only detected in thinning wines. Theprincipal components analysis was used for constructing the evaluation model of aromaquality, and the scores of the testing wines of Cabernet Sauvignon were graded by thismodel. The results showed that, the quality of aroma of cluster-thinning-lower-50%wine was the highest, followed by cluster-thinning-lower-25%, berry-thinning-25%andcluster-thinning-upper (50%), however, berry-thinning-50%andcluster-thinning-upper-25%were the lowest. The results of sensory evaluation team andthe constructed model had a highly consistency, which stated that the evaluation modelof aroma quality is feasible and reliable. In addition, there was no evidence could showany relationship between the aroma quality score and the contents or their compositionof aroma volatile compounds in this research.