| Starch is semi-crystalline granules composed of amylose and amylopectin.The amylopectin forms A-or B-type crystallinity.Starches are classified into A-,B-and C-type according to their crystalline structures.A-and B-type starches contain only A-and B-type crystallinity,respectively,while C-type starch contains both A-and B-type crystallinity.A-and B-type starches have simple structure and have been studied widely;however,C-type starch has complex structure and is seldom studied.The properties of C-type starch are affected by plant sources,growth environments,starch granule sizes,and allomorph distributions.The kernels of Chinese chestnut(Castanea mollissima Bl)contain C-type starch.Although the effects of different varieties of Chinese chestnut and their growing conditions on the properties of C-type starch have been reported,there are few studies on the properties of C-type starches and their different-sized granules from different varieties of Chinese chestnut under the same growing condition.Especially,it is unclear for the effects of different allomorph distributions on the properties of C-type starches.In this study,different varieties of Chinese chestnut under the same growing condition were used as materials.Their starch properties were investigated,and the effects of granule size on the starch properties were studied.The properties of C-type starches with different allomorph distributions were compared in Chinese chestnut,sweet potato Ipomoea batatas,and Apios fortunei.The main results are as follows:1.Properties of C-type starches from different varieties of Chinese chestnut.In this study,9 Chinese chestnut varieties under the same growing condition were used as materials.Starches were isolated from mature kernels,and their morphological,structural and functional properties were investigated and compared using the morphological observation,physicochemical measurement,and spectrum analysis technologies.The results showed that the dry kernels of Chinese chestnut had starch contents from 42.7 to 49.3%.Starches from 9 Chinese chestnut varieties had similar morphologies and exhibited round,oval,ellipsoidal,and polygonal shapes with a central hilum and smooth surface.The starches of 9 Chinese chestnut varieties showed bimodal size distribution,the particle size range of small and large granules was 0.5?1.5 ?m and 1.5?25 ?m,respectively,and had apparent amylose contents from 23.8 to 27.3%.They all exhibited the same C-type starch,but had similar relative crystallinity,ordered degree,and lamellar structure.The gelatinization onset,peak,and conclusion temperatures ranged from 60.4 to 63.9?,from 64.8 to 68.3?,and from 70.5 to 74.5?,respectively,among 9 starches;and the peak,hot,breakdown,final,and setback viscosities ranged from 5524 to 6505 mPa s,from 3042 to 3616 mPa s,from 2205 to 2954 mPa s,from 4378 to 4942 mPa s,and from 1326 to 1788 mPa s,respectively.The rapidly digestible starch,slo wly digestible starch,and resistant starch ranged from 2.6 to 3.7%,from 5.7 to 12.7%,and from 84.4 to 90.7%,respectively,for native starch,and from 79.6 to 89.5%,from 1.3 to 3.8%,and from 7.1 to 17.4%,respectively,for gelatinized starch2.Physicochemical properties of large and small starch granules from Chinese chestnut.Large and small granules were separated from C-type starches of 4 Chinese chestnut varieties.The effects of granule size on starch properties were investigated using physicochemical measurement and spectrum analysis technologies.The results showed that large and small starch granules of four Chinese chestnut varieties had similar amylose contents from 17.7 to 20.2%,and showed C-type crystallinity.Among four Chinese chestnut varieties,the large granules had relative crystallinity from 19.2 to 20.3%,ordered degree from 0.686 to 0.706,and lamellar peak intensity from 233.2 to 267.1,but small granules had relative crystallinity from 16.2 to 18.2%,ordered degree from 0.635 to 0.663,and lamellar peak intensity from 201.6 to 213.1.The gelatinization peak temperatures ranged from 62.6 to 65.7?in large granules but from 60.3 to 61.7? in small granules,and the enthalpy variation did from 12.5 to 13.7 J/g in large granules but from 10.1 to 11.7 J/g in small granules.Both large and small granules showed biphasic hydrolysis.Though small granules had significantly higher hydrolysis rate than large granules,but they had similar total hydrolysis extent during whole hydrolysis.The granule size had significantly positive relationships with relative crystallinity,ordered degree,lamellar peak intensity,and gelatinization temperature and enthalpy,but was negatively correlated to the hydrolysis rate.3.Physicochemical properties of C-type starches with different allomorph distributions.C-type starches with different allomorph distributions were chosen from Chinese chestnut,A.fortunei and sweet potato.Their gelatinization properties and enzymatic hydrolysis were investigated using differential scanning calorimetry(DSC),hot stage microscopy,and enzymatic hydrolysis analysis.The results showed that Apios fortunei starch contained both A-type and B-type starch granules with gelatinization temperature range from 61.5 to 84.4?.The DSC curve had two peaks with low and high gelatinization temperature,corresponding to B-type granule and A-type granule,respectively.The enzyme hydrolysis showed two phases,at the fast hydrolysis stage,the hydrolysis rate of A.fortunei starch was higher than that of sweet potato and Chinese chestnut starches,but at the slow hydrolysis stage,the hydrolysis rate of A.fortunei starch was lower than that of sweet potato and Chinese chestnut starches.Sweet potato starch had A-type,B-type and C-type starch granules with gelatinization temperature range from 51.9 to 84.2?.The DSC curve had three peaks with low,mediate,and high gelatinization temperature,corresponding to B-type granules,C-type granules,and A-type granules,respectively.The enzyme hydrolysis showed two phases,at the fast hydrolysis stage,the hydrolysis rate of sweet potato starch was lower than that of A.fortunei starch and higher than that of Chinese chestnut starch,while at the slow hydrolysis stage,the hydrolysis rate of sweet potato starch was higher than that of A.fortunei starch and lower than that of Chinese chestnut starch.The A-and B-type crystallinities of Chinese chestnut starch were located in the same starch granule with gelatinization temperature range 60.8 to 72.7?.The DSC curve showed a single gelatinization peak,and A-and B-type crystallinities were gelatinized simultaneously.The enzyme hydrolysis showed two phases,at the fast hydrolysis stage,the hydrolysis rate of Chinese chestnut starch was lower than those of A.fortunei and sweet potato starches,while at the slow hydrolysis stage,the hydrolysis rate of Chinese chestnut starch was higher than those of A.fortunei and sweet potato starches.The above results showed that C-type starches from different Chinese chestnut varieties had significantly different physicochemical properties.The large and small granules of Chinese chestnut C-type starch exhibited the same crystalline structure and similar amylose content,but the granule size had significant effects on starch physicochemical properties.The allomorph distributions of C-type starch influenced its properties and utilization.This study not only could enrich the knowledge of C-type starch,but also provide references for the processing and utilization of Chinese chestnut kernels and their starch. |
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