窖藏和冷藏条件下鸭梨挥发性物质及其相关基因表达分析

Comparison Analysis on Volatile Compound and Related Gene Expression in Yali Pear During Cellar and Cold Storage Condition

【目的】比较窖藏和冷藏过程中,鸭梨果实品质、呼吸速率、乙烯释放速率、电子鼻特征、挥发性物质及其相关基因表达的差异,进一步解析两种贮藏方式对鸭梨香气物质形成的影响及其机制。【方法】鸭梨采收后以窖藏和冷藏两种方式贮藏,测定贮藏期间果实硬度、可溶性固形物含量(SSC)、可滴定酸(TA)含量、呼吸速率和乙烯释放速率,使用电子鼻检测挥发性物质变化,利用气质联用色谱(GC-MS)测定挥发性物质成分及含量,利用荧光定量PCR(Real-time PCR)技术分析乙烯生成(PbACS1、PbACO2)及其信号转导(PbETR1、PbETR2、PbERS1a、PbERS1b、PbEIN3、PbERF)、挥发性物质合成(PbAAT1、PbADH2、PbADH3、PbADH5、PbHPL、PbLOX1、PbLOX8)相关基因的表达量变化情况。【结果】冷藏期间,鸭梨果实硬度变化较小,SSC上升,TA含量下降。窖藏时,果实硬度下降比较明显,但对SSC的影响较小,而TA含量增加。与冷藏相比,窖藏下果实呼吸速率较高,乙烯释放高峰提前1个月出现,且其峰值较高。电子鼻可有效区分两种贮藏方式下的挥发性物质,其中W1W、W5S、W2W、W1S这4种传感器对挥发性物质区分起主要作用;窖藏期间果实挥发性物质较多。鸭梨果皮和果肉的挥发性物质包含醛类、酯类、醇类、萜类、烷烃类等,且果皮中含量较高;窖藏果皮和果肉、冷藏果皮和果肉中分别检出36种和33种、28种和24种挥发性物质,窖藏鸭梨较冷藏时生成更多的乙酯类化合物,其中己酸乙酯、辛酸乙酯、丁酸乙酯、(E,Z)2,4-癸二烯酸乙酯等为果皮主要香味物质,己酸乙酯、丁酸乙酯为果肉主要香味物质。相关基因的表达分析表明,与冷藏相比,窖藏明显上调鸭梨果皮和果肉ACC氧化酶(PbACO2)、脂氧合酶(PbLOX1)和醇酰基转移酶(PbAAT1)相关基因的表达,下调乙烯不敏感转录因子(PbEIN3)的表达。【结论】在贮藏3个月内,与冷藏鸭梨相比,窖藏条件明显促进乙烯生成(PbACO2)和香气合成(PbLOX1、PbAAT1)等基因的表达,此时果实具有较多的香气物质种类和较高含量,表现出香味浓郁的特点。

【Objective】The aim of this study was to compare the differences of fruit quality,respiration rate,ethylene production rate,electronic nose characteristics,volatile compounds and related gene expression in Yali pear between cold and cellar storage,and to further analyze the effects of two storage methods on the formation of aroma substances and its mechanism.【Method】Postharvest Yali pear was stored in cold and cellar condition,and the fruit firmness,soluble solids content(SSC),titratable acid(TA)content,respiration rate and ethylene production rate were measured.The changes of volatile compounds during storage were measured by electronic nose,and the components and contents of volatile substances were determined by GC-MS.The expression of genes related to ethylene biosynthesis(PbACS1 and PbACO2),signal transduction(PbETR1,PbETR2,PbERS1a,PbERS1b,PbEIN3 and PbERF)and volatile compound synthesis(PbAAT1,PbADH2,PbADH3,PbADH5,PbHPL,PbLOX1 and PbLOX8)was analyzed by real-time PCR.【Result】During cold storage of Yali pear fruit,the firmness had no obvious variation,and the SSC increased,while the TA content decreased.During cellar storage,there was a remarkable decrement in firmness and increment in TA content,but there was no obvious variation in SSC.Compared with cold storage,the respiration rate was higher and the peak of ethylene production rate appeared one month earlier under cellar storage.The results showed that the electronic nose could effectively distinguish the volatile compounds of Yali pear in different storage methods.Four sensors,including W1W,W5S,W2W and W1S,played the critical role in the identification of volatile compounds,and there were more volatile substances in cellar storage.The volatile compounds,such as aldehydes,esters,alcohols,terpenes,alkanes,etc,were found in the peel and flesh of Yali pear,and which contents were higher in peel than that in flesh.36,33 and 28,24 kinds of volatile compounds were detected in peel and flesh of fruit under celler,cold storage,respectively.There were more ester compounds in cellar storage than those in cold one,among which,ethyl caproate,ethyl octanoate,ethyl butyrate,(E,Z)2,4-decadiene ester were the main aroma substances in the peel,ethyl caproate and ethyl butyrate were the main aroma substances in flesh.The analysis on expression of genes related to ethylene and aroma compound synthesis showed that the expression of ACC oxidase(PbACO2),lipoxygenase(PbLOX1)and alcohol acyltransferase(PbAAT1)genes were significantly increased,and the expression of ethylene insensitive transcriptional regulator gene(PbEIN3)was down regulated in cellar storage in contrast to cold storage.【Conclusion】Compared with cold storage,cellar storage condition promoted ethylene production and the expression of genes related to ethylene biosynthesis(PbACO2)and aroma compound synthesis(PbLOX1 and PbAAT1),thus,made more kinds and contents of aroma substances,and exhibited more rich aroma in Yali pear.