| Arenga pinnata flour(APF)produced in Guangxi province,enjoying a good reputation at home and abroad,has been deeply popular among consumers due to its therapeutic,nutritional and health effects.As one of the main components of APF,Arenga pinnata starch(APS)plays a key role in its processing quality.The relationships between the inner structure,especially its fine structure,and the physicochemical properties of APS are unclear and there were few researches at present,which has limited the further research and development of APF.Therefore,this paper was aim to determine the physicochemical properties of APS with different particle sizes,characterize their granular structure,crystal structure and molecular ordered structure and analyze the relationships.The granular structure of APS was characterized by SEM,CLSM and AFM,and the crystal structure and molecular ordered structure were characterized by ATR-FTIR,SAXS and solid 13C CP/MAS NMR.Meanwhile,HPSEC and FACE were used to analyze the molecular structure and fine structure of the graded APS.This study focused on explaining the role of APS fine structure in its physiochemical properties.The expectation was to build a molecular model of APS or to provide a theoretical basis for existing molecular models.Meantime,the study was revealed the relationship between the multi-scale structure and physicochemical properties of APS,which could provide a theoretical basis for modification and functionalization of APS and technical support for new processing technology of APS.The main results were as following:(1).Granules of APS had no significant hollows,the edge was smooth,the granules were intact and the radius distribution range is large.The large particles of APS(APS-L)were elliptical.The surface is smooth(surface roughness(Sa=0.365 nm).The average particle volume diameter was 45.18?m,the small particles of APS(APS-S)were round,the surface is rough(Sa=1.906 nm),the average particle volume diameter was 26.82?m.The Maltese cross are clear and bright of both granules.umbilical point was at one end of the oval in APS-L,while APS-S was center of circle.The crystallinity of APS-L(18.2%)was higher than that of APS-S(14.5%).Compared with the APS-S,the APS-L could clearly see the light-dark alternating characteristics of the natural starch,with lower amorphous,double helix and higher single helix content,and the helix structure was more closely arranged,the contents of amorphous,double helix and single helix were 15.8%(39.3%),4.8%(8.3%)and 79.4%(52.4%),respectively.(2).The thermodynamic properties of two kinds of APS with different diameters were significantly dissimilar.The enthalpy of gelatinization of APS-L(24.1 J/g)was significantly higher than that of APS-S(17.8 J/g),suggesting that the thermal stability of APS-L was better.In addition,APS-L showed higher peak viscosity(3774.5 cp)and stronger anti-swelling and trough,and,breakdown value.Also,the peak time(the time to reach the peak viscosity)decreased from 5.16 min(APS-L)to 4.20 min(APS-S).The gel of APS has the characteristics of solidity,which was typically solid gel and gel network structure of APS-S was stronger and more elastic.(3).The branching model of APS amylopectin was established.Branched chains of APS amylopectin were highly branched,mainly composed of short chain and medium-long chain,almost without long chain and super-long chain.The relative contents of DP?12 and DP13-24 in APS-L amylopectin were40.47%and 40.16%respectively,which were higher than those of APS-S amylopectin(39.69%and 37.97%).The unit chain length distribution is characterized by that internal chain length of B2 chains(20.0 DP,21.5 DP)and the average number of branches per cluster(15.1,16.0)of the APS-L are smaller.However,the intra-cluster branch distance of the larger particles(3.0 DP)was larger than that of the APS-S(2.6 DP).The chain length of B1b and B2 of APS-S amylopectin was longer than that of APS-L,but the situation of B1a is opposite.In addition,based on the basic biosynthesis process,the branching model was further validated by fitting the FACE length distribution into two mathematical models,which expressed the chain length distribution with parameters reflecting the activity of related enzymes.The results showed that the?(i)values of APS-L and APS-S were 68.4×10-3and 80.5×10-3,respectively,and the?(ii)values were 4.95×10-3and 12.9×10-3,respectively.The sum of?(?)and?(?)values of APS-L was 118.3×10-3,and that of APS-S was104.9×10-3,the proportion of A chain and B1 chain of APS amylopectin in branched starch was higher than that in small starch.(4).The rheological properties of amylopectin with different granular sizes were different after treated with three kinds of debranching enzymes,but the pastes of amylopectin with weak gelatinous viscoelasticity changed with frequency.Pullulanase and isoamylase were more complete than?-amylase in large granular amylopectin,the molecular weight distribution of small granule amylopectin was wider after enzymolysis,and it was more sensitive to isoamylase,the molecular weight distribution of large amylopectin was narrower than that of small amylopectin,but the?-1,6 glycosidic bond of large amylopectin hydrolyzed by pullulanase was more complete. |
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