Effects Of Light And Fruit Development Period On Apple Endogenous Melatonin Content

Melatonin is a kind of indole molecule that widely exists in animals, including humans,prokaryotes and plants. Melatonin has been widely concerned after found in the cow pinealgland in1958. In animals, melatonin can improve sleep quality, delay senescence, improveimmunity, prevent and treat depression et al.. Human can increased the levels of melatonin byeating foods that are rich in melatonin. Therefore, melatonin levels in the edible plantsbecame the focus of researchers. Based on apple fruit as test object, this paper developed aneffective melatonin extraction method of apple fruit, and improved the determination methodof melatonin in apple fruit by high performance liquid chromatography; studied the effects oflight on melatonin content. Besides, we analyzed the melatonin content during fruitdevelopment.The main results are as follows:1. High performance liquid chromatography with fluorescence detection （HPLC-FLD）test condition of apple fruit melatonin is: Inertsil C18ODS-3,4.6mm×250mm stainlesssteel column;50mM Na2HPO4/H3PO4buffer（pH4.5）: methanol=60:40as mobile phase;The flow rate is1ml/min; Sample size is20μL; The determination of the exciting lightwavelength of280nm, emission wavelength of348nm. Results show that melatonin in1~100ng/g FW concentration within the scope of a linear relationship, its standard curveregression equation is y=0.0023x+0.0011（R2=0.9998）, where y=peak area（mV· min）and x=melatonin concentration （ng/g FW）. The average recovery rate is87%.2. Based on test results, we found that melatonin extraction process should pay attention toseveral aspects:（a） the sample should be extracted as soon as possible after grinded intopowder, placed too long can lead to loss of melatonin levels;（b） samples must passedthrough0.22μm filter after centrifugation, and before loading, which can greatly reduce theinterference of impurity, and prolong the service life of C18column;（c） ultrasonic celldisruption can break the cytoderm, and promote the release of melatonin, is one of theimportant steps in extraction of melatonin, through the experiment, we found that the200Wand15min can make the release of melatonin effectively, and can reduce of lose of melatoninas a result of the too-long broken time;（d） C18solid phase extraction is commonly used in the process of extraction and purification methods of melatonin, but through the experiment,we found that extract of melatonin in apple fruit, there is no need for C18solid phaseextraction, leave out solid-phase extraction procedure can effectively reduce the loss ofmelatonin and obtain target peak without interference.3. Through the study, we found that, at different positions of canopy （periphery fruits andbore fruits） will affect the accumulation of endogenous melatonin in fruit. Averagemelatonin levels in the peripheral fruit peel is significantly higher than bore fruit peel. In thedifferent bearing fruit, east and south have a slightly higher melatonin levels in the apple peelthan the other two bearing apple peel. And there were no significant differences in the flesh.4. The pattern of melatonin fluctuated in bagged fruits was stable in a certain extent, whichis very similar to that of the unbagged fruits（control）. However, compared with bagged fruitpeels, control peels contains more than two times of melatonin. Curves show similar rule inflesh of bagged fruits and control.Concentration of melatonin in apple fruit peels wasobviously increased after bag removal. Melatonin peak appeared on4day after bag removal（42.46ng/g FW）, which was almost10times higher than the still-bagged fruits.Subsequently, melatonin was slightly down-regulated in followed two days, and was still6.5times of those in the bagged fruits. Concentration of melatonin in debagged fruits flesh wentup moderately, which recovered to the level of control in one day time, and then reach thepeak （14.16ng/g FW） on the3th day after the paper bag were took off. After that, the levelof melatonin shows a significant down-regulation, which even lower than those in controlflesh.5. During ‘Yuhua Early Fuji’ fruit development period, fruit weight grew rapidly after July3, and fruit volume increased rapidly in the medium-term of development. In the first stage offruit development, the apple fruit had high content of melatonin （33.79ng/g FW）. As thecuring of seed and fruit enlargement, melatonin levels droped. In early July, there is thesecond peak of melatonin content （25.61ng/g FW）. In late July to early August, melatoninlevels in fruits is low, until early September at the eve of the harvest, the level of melatoninhave rebounded to27.52ng/g FW finally.