| Corn is an important food crop.Although corn has withdrawn from the status of staple food,it still maintains stable consumption.Nowadays,people eat corn no longer for energy,but for the abundance of food,so more attention to nutrition and flavor.For the nutrition and flavor,in addition to the three major substances,there are also special nutrients such as dietary fiber,polysaccharides,vitamins and volatile organic compounds（VOCs）in corn grains,among which zeaxanthin is an important health substance,and VOCs are the main source of flavor.These components have been studied more in fresh corn at home and abroad,but less in mature corn.Especially for flavor,it seldom was reported in the past.In view of this,the present paper mainly focused on the composition and content of zeaxanthin,and VOCs in mature maize grains.The main results are as follows:1.Selection of excellent hybrid combinations and observation of important characters.Four hybrid combinations,named from Yellow No.1 to Yellow No.4,and Zhengdan 958,as control,were selected as materials.These combinations had the characteristics of high yield,stable yield and good resistance with golden yellow grain,thin peel,white axis and semi-hard grain Their were grown in locally and in Hainan for the observation of ear characters and yield performance,and for the preparation of samples that were used for detection of the content of zeaxanthin and volatile organic substances（VOCs）.The results showed that the yield of all of four combinations was more than 5%higher than that of Zhengdan 958.Yellow No.1 even increased production by more than 20%.Yellow No.2 and No.4 had good grain color.The traits that needed to be improved of four combinations were as follows:The resistance to stem rot of Yellow No.1 fluctuated in years.The grains ratio of Yellow No.2 was a little low.For Yellow No.3,its pollination needed to be improved so that to reduce the length of imaginary tip of ear,which could increase its stable yield characteristics.For Yellow No.4,what needs to be improved was to purify the parents,so as to increase the combining ability between parents.2.Detection of zeaxanthin content.The samples included four hybrid combinations,some parents,control,grains with different storage time,fresh grains after pollination 22 d of Yellow No.1 and a white waxy corn,the grains of medium orange seed.High performance liquid chromatography（HPLC）was used to detect the content of zeaxanthin.The results showed that the retention time of zeaxanthin in all samples was about 4.7 min.The peak area of zeaxanthin including lutein was much large than that of non-zeaxanthin,White waxy corn contained almost no zeaxanthin.The content in 4 hybrid combinations varied from 21 to 26mg/kg.The content of isomer in medium orange grain was higher.There was no significant difference in zeaxanthin content among the 4 combinations,but p<0.05 differences between the four combinations and the control Zhengdan 958.These results indicated that the composition of zeaxanthin in all samples was the same substance,and other isomer was little.The grain color of the four combinations was similar,and their zeaxanthin content was no difference,forming a positive correlation.After storage,the content of zeaxanthin decreased significantly.The degree of decrease was as large as up to 1/2.But there was a low-temperature vacuum-packed sample in which the content of zeaxanthin decreased little after storage for 3 years.These results suggested that zeaxanthin was easily converted and decomposed during storage,but special storage conditions could effectively prevent such loss.3.Identification and relative content analysis of VOCs in grains.The samples determined were as same as those determined for zeaxanthin.A total of 101 volatile compounds were identified by gas chromatography-mass spectrometry（GC-MS）that was supported by headspace solid phase microextraction,and"NIST 2017"spectral database searching.There were 50 to 70 volatile compounds in each variety.13 of which were the common components existing in all varieties,and 4 to 16 were unique components only existing in some varieties,which made up more than 80%of the total content.These substances mainly included that tetradecane,hexadecenoic acid,4-ethylbenzaldehyde,2-ethylbenzoate methyl ester,3,4-dimethylacetophenone,dibutyl phthalate,amyl valerate,2-methoxy-4-ethylenophenol,dimethylpyrazine,etc.Most of these substances were aromatic.Two components with high content of peak area over 10~7 level,n-dodecane and tert-butanol,were considered as important volatile compounds in samples.The relative total content of volatile substances in the samples ranged from 36.660 mg/kg to 68.001 mg/kg.The content of Yellow No.1,Yellow No.2 and Yellow No.1 fresh grains was at high level,while that of Yellow No.3,Yellow No.4and Zhengdan 958 was at medium level,and the difference between them was at P<0.01 level.The detection results of content of aroma substances in the samples of different storage time showed that it was the highest in the newly harvested grains.It lost about 1/5 when grains were stored naturally for one year;and it lost nearly 1/3 when grains-powder were stored naturally for 1 year.But vacuum packing,5℃low temperature storage for 3 years,its loss is slight.These observations and analysis indicated that the 4 hybrid combinations,from Yellow No.1 to Yellow No.4,which had characteristics of high yield and high content of zeaxanthin and aroma substances,could be used as high quality edible corn varieties.For the content of zeaxanthin,there was no difference among 4 hybrid combinations,but for the content of volatile aroma substance,the difference existed among them,meaning that in maize varieties it was possible to combine both characteristics of high yield with high content of volatile aroma substances.The content of zeaxanthin and aroma substances in corn grains or powder decreased rapidly during storage,but vacuum packing and low temperature storage could effectively reduce this decrease.These results provided valuable experimental data for better understanding the edible quality and effective storage of corn productions. |
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