低压静电场对云南青梅采后贮藏品质及水分迁移特性的影响

Effect of Low Voltage Electrostatic Field on Postharvest Storage Quality and Moisture Movement Characteristics of Yunnan Green Plums(Prunus mume)

为探明电磁保鲜技术对云南青梅的保鲜效果,在4℃低温贮藏的条件下增加2.5 kV的静态电场,监测贮藏期云南青梅的色差、水分含量、失重率、pH值、丙二醛(malondialdehyde,MDA)含量等品质指标变化,同时设立常规低温保鲜组作为对照组,采用低场核磁共振技术探究贮藏末期两组青梅果实的区别。结果发现:经过25 d贮藏,处于电磁保鲜技术的云南青梅果实汁液的pH值变化范围较小;总酸含量维持在相对稳定的水平,第25天时含量为29.42 g/kg,维持可溶性固形物含量和维生素C含量;色差指标表明果实处于鲜绿色的状态,延缓硬度、还原糖含量和总糖含量的下降趋势;MDA含量较低,过氧化物酶(peroxidase,POD)酶活的第一次高峰在第15天,而对照组果实汁液的pH值增加,总酸含量下降较快,可溶性固形物含量和维生素C含量先增加后减少,色差指标表明果实开始转变为黄色;MDA含量较高,POD酶活的第一次高峰在第10天,早于电场组。与对照组相比,电场组云南青梅水分含量降低4.03%,失重率为1.90%,能保持较高的水分含量。通过低场核磁共振技术探究云南青梅的水分变化规律,由横向弛豫时间T2反演图可知电场组云南青梅中的水分更偏向于结合态,而对照组则偏向于自由态,磁共振成像(magnetic resonance imaging,MRI)图表明电场组云南青梅整体的水分含量明显高于对照组。因此,低温结合电磁保鲜技术可维持云南青梅较好的品质,减少果实中水分含量的流失,对其具有一定保鲜效果。

To investigate the effect of electromagnetic preservation technology on the preservation of Yunnan green plums,this paper added a static electric field of 2.5 kV under the condition of 4℃low-temperature stor-age to monitor the changes of quality indexes,such as color difference,moisture content,weight loss rate,pH value,and malondialdehyde(MDA)content of Yunnan green plums(Prunus mume)during the storage pe-riod.At the same time,this paper set up a conventional low-temperature preservation group as a control group and used low-field nuclear magnetic resonance technology to investigate the differences between the two groups of green plum fruits at the end of the storage period.The results showed that,after 25 days of storage,the pH value of Yunnan green plum fruit juice stored through the electromagnetic preservation technology had a small variation range,and the total acid content was maintained at a relatively stable level,with the content of 29.42 g/kg on the 25th day.The soluble solids content and vitamin C content were maintained.The color differ-ence indexes showed that the fruits were still in the state of bright green,the decreasing trend of hardness,re-ducing sugar,and total sugar was slowed down,and the MDA content was relatively low.The first peak of per-oxidase(POD)enzyme activity was 15 d.The pH value of the control group fruit juice increased,the total acid content decreased rapidly,and the soluble solids content and vitamin C content increased and then decreased.The color difference indexes showed that the fruits began to change into yellow color,the MDA content was higher,and the first peak of POD enzyme activity was on day 10,earlier than that in the electric field group.Compared with the control group,the moisture content of Yunnan green plums in the electric field group de-creased by 4.03%,and the weight loss rate was 1.90%,which were able to maintain a high moisture content.Through the low-field nuclear magnetic resonance technology,this paper investigated the variation rule of the moisture content of Yunnan green plums.The transverse relaxation time T2 inversion diagram showed that the moisture content of Yunnan green plums in the electric field group was more inclined to the bound form,while that in the control group was inclined to the free form.The magnetic resonance imaging(MRI)diagrams showed that the overall moisture content of Yunnan green plums in the electric field group was significantly higher than that in the control group.Therefore,the low temperature combined with electromagnetic preserva-tion technology can maintain a better quality for Yunnan green plums,reduce the moisture content loss in the fruits,and have a certain preservation effect on them.