外源褪黑素处理对常温货架期梨果实贮藏品质的影响

Effects of exogenous melatonin treatment on storage quality of pear fruits during shelf life at room temperature

【目的】明确褪黑素处理对采后常温货架期梨果实贮藏品质的影响。【方法】以新梨7号果实为试材,设置50、100、150、200、250μmol·L^(-1)5个褪黑素浓度梯度处理,以清水处理为对照,测定了常温货架期果实失重率、硬度、可溶性固形物含量、乙烯释放速率、香气物质种类和含量等指标。【结果】从处理后5、10、15和20 d的测定结果可以看出,与对照相比,褪黑素处理减少了梨果实内水分的消耗,果实的失重率升高的幅度小,果实硬度较高,150μmol·L^(-1)褪黑素处理失重率和果实硬度与对照差异达显著水平;褪黑素处理能够使新梨7号果实的可溶性固形物含量稳定,处理20 d时,不同浓度褪黑素处理可溶性固形物含量显著高于对照;褪黑素处理新梨7号果实的乙烯释放速率均低于对照,以150μmol·L^(-1)褪黑素处理最低,较对照减少了87.05%,差异显著;不同浓度褪黑素处理对新梨7号果实香气物质种类和含量存在差异,褪黑素处理能调节果实香气种类和含量。【结论】外源褪黑素处理可延缓新梨7号梨果实失水,保持果实硬度和可溶性固形物含量,减少乙烯释放。适宜浓度褪黑素处理可调节香气物质的种类和含量,保证常温货架期贮藏品质,综合认为,150μmol·L^(-1)浓度褪黑素处理能够有效延缓梨果实的衰老,处理效果最好。

【Objective】The experiment was carried out to study the effects of melatonin at different concentrations on the storage quality of pear fruits during shelf life at room temperature after harvest,and to screen out the optimal concentration of melatonin,so as to provide references for the application of melatonin in the preservation of pear fruits.【Methods】Using Xinli No.7 as the test material,6 groups of fruits with uniform size,consistent maturity,and without decay and mechanical damage were selected.One group was soaked in water for 30 minutes as the control,and the other 5 groups were immersed in melatonin solutions at 50,100,150,200 and 250μmol·L^(-1) for 30 minutes,dried and placed on a shelf at room temperature of 20℃,and samples were taken every 5 days.Each sample was taken to determine the fruit weight loss rate,hardness,soluble solids content,ethylene release rate and other indicators.The hardness of the fruit was measured by GY-4 hardness tester,the soluble solid content was measured by the ATAGO PAL^(-1) digital sugar meter,and the ethylene release rate was measured by gas chromatography.Using a 1 mL syringe to draw air repeatedly,the sample was injected into the GC2014C gas chromatograph for determination.The fruits stored at room temperature for 15 days were chosen to determine the aroma components in the fruits.The quarter method was used to remove the core and the fruit was cut into pieces of 0.2 cm×0.2 cm×0.2 cm and mixed evenly.5 g of the sample was put into a 10 ml sample bottle and the internal standard 2-octanol(0.01644 g·L^(-1))3μL was added,which was sealed with tin foil.Heating at 40℃lasted for 30 minutes,using SPME extraction head(black)to absorb aroma after adsorption and injection analysis.The unknown compound was searched by computer and matched with the mass spectrometry library NIST17-1,NIST17-2 and NIST17-S at the same time.Various volatile components were confirmed and the content of each component was calculated.The Microsoft Excel 2010 was used to analyze the data,and SPSS16.0 statistical analysis software was used to analyze the significance of differences.【Results】Melatonin treatment had a certain inhibitory effect on the weight loss rate of pear fruits.The weight loss rates with 100 and 150μmol·L^(-1) melatonin treatments increased by 4.20%and 3.75%during storage,which were significantly different from the control.At the end of storage,the hardness of the control fruit was the lowest at 3.57 kg·cm^(-2),which was 24.20%lower than that before storage.The hardness of the fruits treated with 50,100,150,200 and 250μmol·L^(-1) melatonin was significantly higher than that of the control,respectively.The soluble solid content of the control fruit continued to rise during the early storage period,and reached a peak(14.17%)on the 15th day and then decreased rapidly,and it was 9.95%on the 20th day.The melatonin-treated fruits showed a continuous upward trend on the 20th day,respectively,compared with that before storage,increasing by 2.05%,1.22%,2.08%,-0.35%and 2.63%.The ethylene release rate of the control fruits reached a peak value of 0.073μL·kg^(-1)·h-1 on the 10th day,and the ethylene release rate was 0.062μL·kg^(-1)·h-1 at the end of storage.The melatonin-treated fruits reached the peak value on the 5th day.At the end of storage,it was 74.01%,87.05%,85.68%,77.18%and 80.72%lower than the control.The types and contents of aroma had an important influence on the flavor of the fruit.In this experiment,92 kinds of aroma substances were detected in the fruits with different treatments.The maximum of 40 kinds of aroma substances were detected in the fruits treated with 200μmol·L^(-1),followed by the control and 50μmol·L^(-1),treatment(39 types),and 100μmol·L^(-1) treatment was at least 34 types.The aroma substances commonly contained in the fruits with each treatment included Hexyl acetate,1-Hexanol,2-Methyl butanal,3-Methyl butanal,Hexanal,Heptanal,Nonanal,Decanal,(E)-2-Hexenal,2-Octanone,Toluene,o-Xylene,Dodecane,Tetradecane,and Longifolene.The lowest aroma content of the control fruit was 180.84 ng·g^(-1),and the highest(272.59 ng·g^(-1))was treated with 200μmol·L^(-1),which increased by 50.73%compared with the control.The difference in aroma content mainly came from aldehydes.The lowest one in the control was 129.03 ng·g^(-1),and the highest one was in the 200μmol·L^(-1) treatment(212.51 ng·g^(-1)),which was 64.69%higher than the control.Melatonin treatment mainly promoted the synthesis of 1-Penten-3-ol,2,2,4-Trimethyl-1,4-pentanediol diisobutyrate,1-Heptanol,Tridecanal,α-Pinene,etc..The synthesis of substances was inhibited,such as Octanoic acid,nonyl ester,1-Nonanol,2-Nonen-1-ol and 1-O-octyl-Rhamnitol.The high contents of aroma substances in the various treatments of Xinli No.7 fruits were hexyl acetate,1-hexanol,hexanal,trans-2-hexenal,toluene,o-xylene,and limonene,which accounted for 88.12%,87.95%,88.37%,91.26%,92.29%and 90.70%of the total aroma content of the fruits,accordingly to CK,50,100,150,200,250μmol·L^(-1) treatments.【Conclusion】Compared with the control,suitable melatonin treatment can effectively slow down the increase in weight loss rate and decrease in fruit hardness,stabilize the soluble solids content,inhibit the release of ethylene,delay the senescence of fruits,and significantly extend the shelf life of Xinli No.7 at room temperature.At the same time,it can significantly increase the type and content of aroma substances in the fruit of‘Xinli No.7’during shelf life at room temperature.It is generally believed that suitable exogenous melatonin treatment can improve the storage quality of Xinli No.7 fruits during shelf life at room temperature.