Determining Pear Fruits Volatile Aromatic Substances Based On Solid Phase Microextraction-Comprehensive Two-dimensional Gas Chromatography /Time-of-flight Mass Spectrometry

Analysis of aroma components of pear fruits was of great significance for pear fruits aromatic bred,harvested,disease prevented and stored,processed.However,aroma was volatile,fragile and its components were complex,which makes it difficult to extract and identify volatile aromatic substances.Therefore,this paper focused on the determination of volatile aromatic substances in pear by two-dimensional gas chromatography/time-of-flight mass spectrometry based on solid-phase microext-raction.In order to improve the accuracy of detection of volatile aromatic substances in pear,extraction and identification methods of volatile aromatic substances in pear were studied.(1)Volatile aromatic substances of five pears cultivars were studied by Solid-Phase Microextraction(SPME)extraction and identified by Gas Chromatography-Mass Spectrometry(GC-MS).Effects of the type of extraction head,extraction temperature and time on the extraction results were considered.SPME-GC-MS analysis conditions of volatile aromatic substances in Jinchuanxue pear and Qinsu(Pyrus bretschneideri Rehd.)were established by optimizing the SPME conditions.The optimal extraction conditions of SPME such as extraction head,extraction temperature and time were 50/30μm DVB/CAR/PDMS fiber,40℃and 40min respectively.Feasibility evaluation showed that,each substance was well linear in the range of 5-200 mg/L,the correlation coefficient R~2was more than 0.99,the minimum detection limit of each substance was less than 2.44 x 10~-33 ng.And the recovery value of the standard substances in the pear block is 89.3%-101.4%,and the relative standard deviation was 1.6%-7.9%in the addition recovery test,which satisfied the requirement of volatile aromatic substances analysis.Different types and contents of volatile aromatic substances in different pears cultivars was considered.Established conditions were applied to the determination and analysis of volatile aromatic substances in different pears cultivars,and the main volatile aromatic substances in different pears cultivars were discussed.The relative content of aldehydes and alcohols in Pyrus pyrifolia Nakai cultivars were high.The amount and relative content of esters and olefins in Pyrus ussuriensis Maxim and Pyrus communis L cultivars were high.During the refrigeration process,all kinds of volatile aromatic substances in Korla fragrant pear were affected to varying degrees.After 60 days storage,the proportion of esters decreased significantly,and the proportion of olefins,alkanes and other substances which did not contribute much to the aromatic quality of pear increased significantly.(2)Volatile aromatic substances of Nanguo pear with strong aroma were extracted by SPME and identified by Comprehensive two-dimensional gas chromatography/Time-of-flight mass spectrometry(GC×GC-TOFMS).Further optimize the conditions of temperature programming,acquisition voltage,shunt ratio and modulation period,and determine the full spectrum scanning analysis conditions of GC×GC-TOFMS.The best analytical conditions of GC×GC-TOFMS such as heating rate,split ratio,modulation period,voltage value,internal standard of 2-nonanone concentration were5°C/min,1:10,3 s,1450 V,10 mg/L respectively.Nanguo pear sample was repeated three times,and the RSD of the main volatile aromatic substances content was less than 20%,which satisfied the analysis conditions.The volatile aromatic substances of Nanguo Pear were determined using optimized GC×GC-TOFMS conditions to explore the advantages of GC×GC-TOFMS.The results of GC×GC-TOFMS were compared with those of GC-MS and GC-TOFMS.It was found that the number of volatile aromatic substances of Nanguo pear was the highest measured by GC×GC-TOFMS.A total of 133 volatile aromatic substances mainly composed of esters,olefins,alcohols and aldehydes were detected in Nanguo pear by SPME-GC×GC-TOFMS.In this paper,the method of extracting and identifying volatile aroma components was established to accurately determine it,and will provide data support for fresh food,storage and deep processing of pear fruits.