Effects of Bagging on Aroma of‘Qi xia daxiangshui’Pear Fruit

Shuwei WEI,Shaomin WANG

Shandong Institute of Pomology,Tai’an 271000,China

Responsible editor:Xiaoxue WANG Responsible proofreader:Xiaoyan WU

The pear is an important fruit and popular in the world.Currently,bagging is widely applied in pear production,which per forms excellently in terms of improving pear appearance[1-3].However,the taste of pear declines significantly simultaneously[4-6].For example,Xu et al.[7]investigated the effects of bagging on volatile substances of Ya pear and concluded that ester varieties and contents both declined,but the contents of alkanes and alcohols increased after bagging.Wang et al.[8]researched the changes of aromatic substances of bagged Xiangshui pears and concluded that it is bagging that caused the decrease of aromatic substances.

‘Qi xia daxiangshui’,a variety of pear native to Shandong,and always popular among consumers due to strong fragrance.Nevertheless,few researches are available on the effects of bagging in growth term on pear fragrance of Qixia daxiangshui pears.The research,therefore,conducted measurements and analysis on aromatic substances of Qixia daxiangshui pears by bagging and without bagging,in order to provide references for production of Qixia daxiangshui.

Materials and Methods

Test time and sites

The test was conducted in two successive years of 2012-2013.Specifically,the pears were bagged in a pear orchard in Shewopo Town,Qixia City,Shandong Province.The pears were then harvested on September 26,and measured in a center laboratory of College of Horticulture,Shandong Agricultural University two days after harvesting.

Test materials

Qixia daxiangshui was collected from Shewopo Town,Qixia City,Shandong Province.The soils were sandy soils and the orchard was well managed.The rootstock was Pyrus betulaefolia growing in 30 years.The line spacing was 6 m×6 m from north to south.

Test methods

Test designNine pear trees,with same-size crowns,growing similarly were chosen.The test arranged three test plots and every plot had a replication.The test designed bagged and non-bagged treatments and the parts of pears in the south of crown were bagged.Besides,every tree was bagged with 100 bags,and the treatment without bagging was taken as a control.After September 20,pears grew mature,and 30 pears with appropriate maturity,free from disease,insect damages,or mechanical?injuries were chosen and carried back to the laboratory for measurement with GC-MS.

Test instrumentsThe test instruments included a gas chromatography-mass spectrometer GC-MS QP2010 Plus,TurboMatrix40 HS produced from PE company,a universal pulverizer,a PE headspace bottle,aluminum-made bottle cap and a silicone rubber-made mat.

Measurement methodsThe extraction and measurements of volatile substances were conducted as per the method proposed by Tian et al.[9].Specifically,every sample contained 3-5 pear fruits and after the core was removed,the flesh was cut into pieces,with width and height both of 0.2 cm.Subsequently,5 g sample was weighed and put into a sample bottle and internal standard 3-nonanone (0.4 mg/ml)was put into the bottom of the sample bottle of 10 ml at 10 μg,sealed with teflon coated butyl rubber stopper.The extraction and measurement of volatile components were performed with Perkin ElmerTurbo Matrix 40 Trap and Shimadzu GCMS-QP2010 and by sulfur by static headspace GC-MS.

The qualitative method of volatile substances was as follows:On basis of computer retrieval,the mass spectrum diagram of unknown chemical substances matched with NIST05 spectral library and the volatile components can be determined with consideration of map interpretation and information analyzing.On the other hand,the percentage of mass of chemical compound was computed by peak area normalization and 3-nonanone was chosen as a internal standard for precise measurement.

The content of aromatic components was computed based on 1 g aromatic value,as follows:the aromatic value=the content of a chemical compound/threshhold value of aromatic substances and the components with 1 g aromatic value ＞0 were defined as aromatic components.

Results and Analysis

Effects of bagging on variety of aromatic substances of ‘Qi xia daxiangshui’pears

As shown in Table1,bagging did have effects on aromatic substances of Qixia daxaingshui pears.Specifically,the bagged pears consist of 34 aromatic substances,including 27 esters,5 alcohols,and 2 aldehydes.In control group,however,the fruits consist of 42 aromatic substances,including 33 esters,7 alcohols,and 2 aldehydes.It isobvious that because of bagging,the variety of aromatic substances reduced by 8,containing 6 esters and 2 alcohols,but the content of aldehydes maintained the same.

Table1 Effects of bagging on variety of aromatic substances of‘Qi xia daxiangshui’pears ng/g

(Continued Table1)

Effects of bagging on contents of aromatic substances of ‘Qi xia daxiangshui’ pears

As shown in Table1,bagging also had effects on contents of aromatic substances of Qixia daxaingshui pears.For the bagged pear fruits,the contents of total aromatic substance and esters declined dramatically,the content of alcohol changed little,and the content of aldehydes grew.Specifically,total content of aromatic substances of bagged pear fruits was 2 671.53 ng/g,which was 27%as high as that of control;the content of esters reached 2 530.14 ng/g,which was 26% as high as that of control; the content of alcohol was 86.06 ng/g,reducing by 0.85 ng/g compared with the control; the content of aldehydes was 23.33 ng/g,which was 138% as high as that of control.

Effects of bagging on contents of characteristic aromatic substances of‘Qi xia daxiangshui’pears

The contents of characteristic aromatic components were determined by aromatic values[9]and the results showed significant changes of characteristic aromatic components of bagged and non-bagged pear fruits.Inthe research,the bagged pear was composed of 8 characteristic aromatic components,which coincided with that of control.However,total content of the bagged pears was 2 259.00 ng/g,representing 25.96% of that of control(P＜0.01).The higher aromatic value of aromatic substances,the higher contribution made by pear fruits.Specifically,the aromatic values from high to low were ethyl hexanoate,ethyl butyrate and hexyl acetate,exceeding 3.As for bagged pear fruits,however,only the aromatic value of 2-methyl-ethyl butyrate kept over 3(Table2).

Table2 The characteristic aromatic substances of‘Qi xia daxiangshui’pears

Conclusions and Discussions

According to researches available[10-11],the effects of aromatic substances on fruit taste is closely related to the variety and content,and the taste of pear fruits with multiple aromatic substances tends to be stronger.In the research,the content of aromatic substances of bagged fruits was significantly lower compared with the control,as well as the variety of aromatic substances(Table1).Therefore,bagging is adverse to synthesis of aromatic substances,which is in consistent with the research made on Ya pear[12]and other fruits[13-16].Researches available[8]indicated that major aromatic components of ‘Qi xia daxiangshui’ included hexyl acetate,ethyl hexanoate,butyl acetate,ethyl butyrate,ethyl caprylate,and 2-methylthyl butyrate and the research proved in consistent with.Xu et al.[7]believed that the content and variety of aromatic substances of bagged Ya pear dropped because of shading and change of micro-environment of bags,of which the variety of esters declined,with which the research coincided.However,the research proved that the content of alcohol decreased and the content of aldehydes increased,possibly caused by test materials and methods.Besides,the research concluded that bagging had significant effects on synthesis of esters and aldehydes,but the content of alcohol changed insignificantly.Li et al.[17]investigated the effects of bagging on Hanfu apple fragrance and believed that bagging prevented formation of alcohol and aldehydes but advanced the formation of esters.In contrast,the research showed that bagging of Qixia daxaingshui pears prevented synthesizing of most esters and alcohols,and accelerated formation of aldehydes.Still,there were some esters whose contents kept growing,such as isobutyl butyrate,2-methyl-ethyl butyrate,butyl propionate,propyl butyrate,butyl acetate,and ethyl isobutyrate,and alcohols whose contents were increasing,such as hexyl alcohol,and (Z)-2-Hexen-1-ol,possibly caused by different test materials.

The volatile aromatic substances are mainly formed on basis of catalytic action of fruit enzymes and precursors,such as amino acid and fatty acid[18-20].Wyllie[21]researched that the supply of precursors is a limiting factor of fruit fragrance.Besides,Hauryasu believed that[22]the taste of fruits with fatty acids as a precursor is a result of synergistic effect of lipoxygenase(LOX),hydroperoxide lyase (HPL),isomerase and alcohol dehydrogenase (ADH),and smell components with monosaccharide and glucoside as precursors also catalyze with the help of some enzyme.Besides,activities of the precursors and enzymes are possibly changed by bagging,accompanied by aroma components and contents of‘Qi xia daxiangshui’,which required further exploration.

In conclusion,bagging has significant effects on the variety and content of aromatic components of ‘Qi xia daxiangshui’.For example,the variety of aromatic substances reduced compared with the control and the content declined.These indicated that bagging significantly prevents synthesizing of esters,less affects alcohols but advances synthesizing of aldehydes.

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