Research On Water Adsorption Characteristics And Starch-Water Molecular Heterogeneous System Of HuaQiao Chestnut

As the newly-developed and locally grown chestnut of Hunan Province in recent years,HuaQiao chestnut is an improved variety of typical starchy chestnut which has broad prospect in development and utilization.This paper takes HuaQiao chestnut as the research object to study its water adsorption characteristics,starch particle morphology structure and physics and chemistry characteristics,the effect of water on starch gel properties and the number of phase transition of water molecules on the gel structure.The main results are as follows:1.The water adsorption characteristics of HuaQiao Chestnut flour is strong:as temperature and water activity increases,the moisture absorption rate of chestnut flour and the equilibrium water content also increase accordingly;the MSI is "J" type and belongs to type III isotherm.Huaqiao chestnut powder also contains fat and other hydrophobic substances,resulting in the force of the solid surface on the adsorbed molecules is less than the force between the adsorbed molecules.Therefore,the moisture adsorption characteristics of chestnut flour are mainly affected by starch.Within the Aw range of 0.11-0.92,the fitting effect of five commonly used mathematical models on MSI are as follows:Peleg>GAB>Smith>Halsey>Oswin model,so the Peleg model describes the best-fitting model for the adsorption process.According to this,the absolute safe storage moisture of chestnut flour at 20?,30?and 40? conditions is 11.04%,10.40%,9.95%,relatively safe storage moisture is 13.71%,12.15%,11.56%.When the water content of chestnut flour exceeds 20%,moisture is easily removed.2.The starch particles of HuaQiao Chestnut exist in the form of single-stranded starch and are spherical,elliptic and pear-shaped.Its long axis is 4-22 ?m and minor axis is 2-14 ?m."Maltese cross" and growth ring structure are observed on the surface.The degree of crystallinity is 28.20%,belongs to C type crystal,the amylopectin content is as high as 63.79%,and the branch/straight chain ratio is 2.748.The gelatinization process is a typical two-stage expansion process and is restricted expansion starch.With the increase of the number of freeze-thaw cycles,the moisture extraction rate gradually decreased and the structure was loosely spongy.The moisture extraction rates after 1-3 times of freeze-thaw cycles are 49.19%,42.94%and 37.24%respectively.HuaQiao Chestnut starch has the phenomenon of thixotropy and shear thinning as well as the fluid index of lower than 1.It's a pseudoplastic fluid and its storage modulus is significantly greater than the loss modulus(P<0.05),which both increase as the angular frequency increases.Its loss tangent is less than 1 and presents as a typical weak gel rheological dynamic system.During the process of gelatinization and gel formation,the elasticity is greater than the viscosity,indicating that it is an elastic solid.3.With the increase of the concentration,the gel roughness of HuaQiao Chestnut starch increases,and the network structure of gel become more compact.As the concentration increased from 5%to 10%,the elasticity of the gel increased significantly(P<0.05),but the elasticity did not show big growth as the concentration increased from 10%to 30%.With the increase of concentration,the deep bound water and weakly bound water in the gel increased from 0.23%and 0.58%to 8.3%and 6.3%respectively,while the free water decreased from 99.2%to 85.4%.In the Fourier infrared spectrogram,there are absorption peaks derived from stretching vibrations of hydroxyl(-OH)and aldehyde groups(C=O),as the concentration increases,the peak position does not change and the peak height gradually decreases.The concentration has a significant effect on the rheological properties.As the concentration increases,the fluid index decreases while the consistency coefficient and dynamic modulus increase.Water makes the pseudoplastic behavior more obvious and shear thinning more prominent.4.The phase transition of water molecules makes the starch gel structure of HuaQiao Chestnut dehydrated and shrank.As the number of phase transitions increases,the pore size in the gel structure becomes smaller and rearrangements occur.The phase transition of water molecules does not contribute much to the formation of new crystal structures,and the crystal structure becomes CB type crystals.With the increase of the number of phase transformation treatments,the degree of crystallinity increased from 2.97%to 12.78%.And after 7 times of transition phases,the crystallinity decreased to 5.712%.With the increase of transition phase,hydroxyl(-OH)red shift occurred;while alcohol hydroxyl and the C-O in the C-O-C occur blue shifts and the peak position remain un-shift after 3 times and 4 times transition,but the peak height increase.