Properties And Allomorph Distribution Of C-type Starch From Root Tuber Of Apios Fortunei

Starch is the main energy storage material in higher plants,and also is the main source of human energy.It is widely used in food and non-food industries.The starches from different plant sources have different structural and functional properties,leading to their different utilizations.Plant starches are classified into A-,B-and C-type according to their crystalline structure.C-type starch consists of A-and B-type crystallinity,and is commonly found in the plant seeds,tubers,and rhizomes.Previous studies are mainly focused on A-and B-type starches,but there are few reports on C-type starches,especially their properties and allomorph distribution.The less research has seriously hindered the understanding and utilization of C-type starch resources.In our previous study,the starch was isolated from the root tuber of Apios fortunei Maxim,belonging to the family Leguminosae,and identified as a C-type starch.’In this study,the structural and functional properties of A.fortune starch were investigated and compared with maize A-type starch,potato B-type starch and pea C-type starch.The allomorph distribution of A-and B-type crystallinities in A.fortune C-type starch was analyzed using many methods.This study could provide important reference for the utilization of root tuber starch of A.fortunei,but also enrich the knowledge of plant C-type starch.The main results were shown as following:1.Properties of C-type starch from root tuber of A.fortunei.The dried root tuber contained about 75%starch.The starch had spherical,polygonal,and ellipsoidal granule shapes with central hila.The granule size ranged from 3 to 30 μm.The starch had 35%amylose content,and exhibited C-type crystallinity with 25.9%relative crystallinity and 9.55 nm lamellar thickness.The starch showed two separated gelatinization peaks with the first peak temperature of 68 ℃and the second peak temperature of 75.6℃.The swelling power and water solubility at 95℃were 28.73 g/g and 10.77%,respectively.The starch had peak viscosity of 1689 mPa s,hot viscosity of 1420 mPa s,and final viscosity of 2103 mPa s.The rapidly digestible starch,slowly digestible starch,and resistant starch were 6.04%,10.96%and 83%in native starch,83.16%,15.23%and 1.61%in gelatinized starch,and 87.13%,8.87%and 3.99%in retrograded starch,respectively.The A.fortunei starch had a monophasic hydrolysis pattern,and its hydrolysis rate coefficient was significantly higher than that of potato starch and lower than maize starch.2.Allomorph distribution of C-type starch from root tuber of A.fortunei.The two groups of starch granules with different gelatinization temperatures were in situ observed in A.fortunei C-type starch using a polarized microscope in combination with a hot stage.The differential scanning calorimetry analysis showed that the C-type starch was composed of A-type and B-type starch granules.The A-type starch granules accounted for about 54.5%of the total granule number.The A-and B-type starch had high and low gelatinization temperature,respectively.The gelatinization peak temperature of the separated A-type starch granules was similar to the second gelatinization peak temperature of C-type starch.The separated A-type starch and native starch had similar granule shape,size distribution,amylose content,and short range ordered structure.The above results indicated that the A-and B-type allomorphs of C-type starch from A.fortunei were distributed in the different starch granules.This allomorph distribution pattern was different from the previous reports.