The Development And Properties Of Starches From Vitreous And Floury Endosperms Of Maize Kernels

The endosperm is the main component of maize kernel,and contains vitreous and floury endosperm,locating in the exterior and interior of the kernel,respectively.Both vitreous and floury endosperms are rich in starch.According to the proportion of vitreous and floury endosperm in kernel,maize kernels are divided into popcorn,flint maize,dent maize,and floury maize.The properties of starches from different types of maize have been reported,however,those from vitreous and floury endosperms in the same kernel are reported little,and there also are some disagreements about them.Especially,it is unclear for the developmental reasons for the differences of starch properties of vitreous and floury endosperms.In this study,the mature maize kernels with different endosperm textures were first used to investigate the morphological characteristics and starch properties of vitreous and floury endosperms in the same kernels.The developing kernels were used to reveal the developmental reasons for the above differences.The main findings are as follows:1.Morphological characteristics of vitreous and floury endosperms in maize kernel.The mature kernels from conventional dent maize inbred line Zheng 58(Z58),flint maize inbred line Mo 17,and popcorn inbred line SK were used as materials in this study.The transverse and longitudinal sections of whole kernels were prepared with resin semi-thin section method,and used to in situ observe and analyze the morphological characteristics of vitreous and floury endosperm.The results showed that the shapes and size of endosperm cells were significantly different among different regions of kernel,but has no correlation with the texture of vitreous and floury endosperms.The vitreous endosperm contained smaller spherical starch granules with loose arrangement and larger polygonal starch granules with close arrangement,existing in sub-aleurone cells and starchy endosperm cells,respectively.The floury endosperm had only spherical starch granules with loose arrangement.The protein content gradually decreased from the outer vitreous endosperm to the inner floury endosperm.The abundant protein in vitreous endosperm tightly encloses the starch granules,while the protein in the floury endosperm is scattered in the space between the starch granules and around the cell walls.The contents and distribution of protein in maize endosperm determine the texture of kernel2.Physicochemical properties of starches from vitreous and floury endosperms from the same maize kernels.Two dent maize inbred lines Z58 and KA103 and three flint maize inbred lines Mo17,B73 and QA502 were used as materials in this study.The vitreous and floury endosperms were separated from mature kernels,and their starches were extracted.The morphological,structural and functional properties of starches from vitreous and floury endosperms were investigated and compared using the morphological observation method,physicochemical measurement,and spectrum analysis technologies.The results showed that the average granule size of starch granules from vitreous endosperm was larger than that from floury endosperm.The vitreous endosperm starch had higher amylose content and damaged starch content,while floury endosperm starch had higher relative crystallinity and lamellar peak intensity.The floury endosperm starch had higher gelatinization temperature and enthalpy and higher resistance to enzyme hydrolysis than the vitreous endosperm starch.However,the gelatinized and retrograded starches from vitreous and floury endosperms had similar digestion properties.The principal component analysis based on the starch property parameters exhibited that starches from vitreous and floury endosperms had significant differences in their physicochemical properties.3.Development of starches in vitreous and floury endosperms of maize kernel.The conventional dent maize inbred line Z58 and flint maize inbred line Mo 17 were used as materials in this study.The developing endosperms were used for morphology observation,starch property measurement,transcriptomic analysis,gene expression level detection,and enzyme activity assay to reveal the development reasons for the different properties of starches from vitreous and floury endosperms.The results showed that the insufficient nutrients and the strong anoxia effect in inner endosperm influenced the development and accumulation of starch,resulting that the inner endosperm had small spherical starch granules with loose arrangement,and the outer endosperm had large polygonal starch granules with tight arrangement.With the development of endosperm,the amylose content gradually increased in the inner and outer endosperm starches.The high expression level and enzyme activity of pyruvate orthophosphate dikinase and large starch granules in outer endosperm increased the amylose content of outer endosperm starch.During endosperm development,the relative crystallinity and lamellar scattering peak intensity of inner and outer endosperm starch decreased gradually,but the outer endosperm starch had lower relative crystallinity and lamellar scattering peak intensity than inner endosperm starch at the late development stage.The different properties of starches in inner and outer endosperms were related to the granule size and amylose content of developing starch.The above results showed that the texture of vitreous and floury endosperm of maize kernel was related to the content and spatial distribution of storage protein,and had no significant relationship with shape and size of endosperm cell and starch granule.The properties of starches from vitreous and floury endosperms in the same kernel showed significant differences due to the differences of starch size and amylose contents.The insufficient nutrients and the strong anoxia effect of inner endosperm were the main developing reasons for small size and loose arrangemen of starch granules in floury endosperm.The high expression and activity of PPDK in outer endosperm increased the amylose content of starch in vitreous endosperm.This study would enrich the knowledge of starch development and properties,provide the theoretical basis for the cultivation and utilization of maize cultivars with different endosperm textures,and be helpful for the applications of vitreous and floury endosperms and their starches in food and nonfood industries.