Characteristic Aroma Compounds In Table Grapes And The Effects Of Root Restriction And Plant Growth Regulators On Aroma Compounds

Since aroma is an important part of quality in table grape,numerous studies characterized its flavor.Most studies on aroma have focused on wine grapes and wines,but aroma studies in general are rare for table grapes.Aroma perception is a very complex process,which is not only affected by volatiles concentration,but also by interaction of compounds and eatting process.Meanwhile,volatiles concentration can be affected by cultivars,developmental periods and cultivation measures.Therefore,endogenous volatiles changes in table grape berries was studied by using headspace solid-phase microextraction in terms of cultivars,developmental stages and environmental factors（growth regulators and root restriction）.The role of volatiles was screened and identified by using sensory evaluation and multivariate statistical analysis,and the combination mechanism among compounds was preliminarily clarified.Finally,changes pattern of volatiles emitted from berry during ripening,cold storage and eating process,and the relationship between emissive and endogenous compounds were systematically discussed.The main results are as follows:1.20 popular table grape cultivars were selected for determination and analysis of the free aroma compounds at maturity stage,and their aroma characteristics were analyzed.C₆ compounds were the basic background volatiles,but the aroma contents of pulp juice and skin depended mainly on the levels of esters and terpenes,respectively.Most obviously,‘Kyoho’grapevine series showed high contents of esters in pulp,while Muscat/floral cultivars showed abundant monoterpenes in skin.For aroma series,table grapes were characterized mainly by herbaceous,floral,balsamic,sweet and fruity series.Combined with sensory evaluation,Shine Muscat was the most popular cultivar.We conclude that balsamic was the preferred aromatic series,andβ-ionone was the key compound.2.The aroma characteristics of 19 unfamiliar cultivars at maturity stage were studied.The fruity,floral,and sweet aromas were description by using secondary aromatic series.In combination with results from popular cultivars,we identified the aroma characters of table grape.Xiangyue and Heikuixiang emerged as the preferred table grapes according to our analysis.By comparison,the popular cultivars showed relatively fewer volatiles,but their contents were much greater than the large number of volatiles identified in the unfamiliar cultivars.3.The aroma characteristics of Shine Muscat at eight developmental stages were studied and the changes patterns of volatiles were obtained.During berry development,concentrations of volatiles was regulated by metabolic synthesis,dilution and compounds transformation.A certain amount of C₆ compounds and terpenes were present in young berries;before softening,the synthesis of compounds was slow,and their concentration was mainly affected by dilution.As a result,concentrations of terpenes decreased sharply.After softening,concentrations of compounds were mainly regulated by metabolic synthesis.Synthesis of C₆compounds on a large scale was initiated.Synthesis of terpenes on a large scale was initiated in Muscat cultivars;while for neutral cultivars,terpenes became low level or disappeared due to the inactivation of synthesis again.A large amount of esters was synthesized in mature stage,accompanied by the conversion of C6 aldehyde to alcohols.Finally,the contents of C₆ compounds and esters significantly decreased at post-maturity stage.In lipoxygenases pathway,lipoxygenase,alcohol dehydrogenase and substituted alcohols were the limiting factors.4.To study the effects of plant growth regulators on aroma compounds in berries,aroma characteristics of Shine Muscat treated with GA₃ and CPPU at eight developmental stages were analysed.Applying GA₃ and CPPU to berries could significantly regulate fruit size,sugar and acid quality,and aroma quality.Among the eight treatments,G-G+C treatment was the best choice to increase yield and sugar contents,but the best quality of sugar and aroma could not be obtained at the same time.Both GA₃ and CPPU can promote the accumulation of terpenes and have synergistic effect.The combination of GA₃ and CPPU can further improve synthesis of terpenes,but GA₃ with high concentration will play a certain inhibitory role.During berry development,terpenes function as a hub of the correlations between volatiles,and GA₃ and CPPU have little influence on the these correlations.The correlation between bound compounds is more conservative,while the correlation between free compounds is more affected by GA₃ and CPPU.In addition,GA₃ and CPPU mainly regulate the one-way ripening components,while the two-way ripening components are more conservative.Among them,17 components can be used as a marker component to judge the ripening of grape berry.5.To investigate how root restriction（RR）affect volatiles,aroma characteristics of Red Alexandria under RR at eight developmental stages were studied.For terpenes of skin in RR,accumulation peak was initiated in advance,and its contents were continuously up-regulated by changing compounds transformation.The stages with minimum and maximum difference were present in the second expansion period and late developmental stage,respectively.Finally,the concentrations of free volatiles in skin,free and bound volatiles in pulp in mature berries were significantly higher than that in the control,while the concentrations of bound volatiles in pulp was in reversal.The correlation between compounds in bound form of skin was strongest,while that in free form of pulp was the weakest.Terpenes function as a structural hub within the volatiles correlations.RR significantly regulates their correlation,resulting in increased correlation of compounds in pulp,bound and peel free states,and decreased correlation of skin.RR significantly regulated the aromatic series values of the late developmental stages,and promoted maturation stage for aroma quality.6.To investigate the change patterns of volatiles emitted from berry and its relationship with endogenous volatiles,the aroma characteristics of grape berries of Red Alexandria during the developmental stages,cold storage,and eatting process were studied by using retronasal aroma simulator.During the developmental stages,small amounts of compounds synthesized in grape berries were lost in the form of volatilization.Volatiles start to emit from one week before veraison,and the difference in qualitative was affected by the developmental stages.Rate of compounds volatilization showed type specificity and was controlled by temperature.Linalool was the main compound,and its rate increased at high temperature.The contents volatiles released in mouth,perceived by nose and produced after-odour accounted for 82.3%,70%and 5.4%of free endogenous compounds in mature berry.Mastication and saliva could promote the release of C₆ compounds;while saliva promote the release of terpenes and aldehydes in mouth.Free pulp compounds were mainly affected by cold storage,among which hexanal,（E）-2-hexenal and linalool were the key compounds correlated with the time of cold storage.