Effect Of Annealing Period On The Properties And Retrogradation Of Pueraria Lobata (Willd.) Ohwi Starch

Annealing?of starch?is known as a hydrothermal treatment of physical modification that changes the structure and properties of starch by improving its crystalline perfection and strengthening the interaction between starch chains.The extent of different changes is influenced by the types of starch and by the arrangement of amorphous and crystalline areas.In this paper,Pueraria lobata?Willd.?Ohwi starch was subjected to annealing treatment at 50°C for 1 h,3 h,6 h,12 h,24 h in 1:2 starch to water ratio?w/v?.Modern instrumental analysis was used to study the influence of annealed Pueraria lobata?Willd.?Ohwi starch on the glass transition temperature?T_g?,moisture distribution and movement,crystal property,digestibility and the retrogradation properties.The main conclusions are as follows:1.Annealing times of 0,1,3,6,12,and 24 h were employed to determine the effects on the T_g of the starch using differential scanning calorimetry?DSC?with the support of ¹H low field NMR,polarized light microscopy and ¹³C CP/MAS NMR.The T_g values of the starch increased with increasing annealing times.The ¹H low field NMR results showed that the T₂ relaxation time decreased and starch–water interactions increased as the annealing time increased.Based on polarized light microscopy,the starch crystal structure was not destroyed after annealing,but the relative crystallinity percentage increased slightly according to the ¹³C CP/MAS NMR results.2.The native Pueraria lobata?Willd.?Ohwi starch had 62.10%rapidly digested starch?RDS?,35.39%slowly digested starch?SDS?and 2.51%resistant starch?RS?.Compared with native Pueraria lobata?Willd.?Ohwi starch,annealed starch had higher contents of SDS and RS,but the relative content of RDS of starch after annealing showed a tendency of decrease.3.The effect of annealing on the the retrogradation of Pueraria lobata?Willd.?Ohwi starch during storage was demonstrated by Using Differential Scanning Calorimetry?DSC?.The results suggested that gelatinization enthalpy increased significantly,aging enthalpy decreased obviously,and then the degree of retrogradation reduced as the annealing time increased.The degree of retrogradation of native Pueraria lobata?Willd.?Ohwi starch stored at 4°C for 1 day and 10 days were 32.95%and 37.41%,respectively.The degree of retrogradation of Pueraria lobata?Willd.?Ohwi starch annealed after 24 h stored at 4°C for 1 day and 10 days were 19.58%and 19.46%,respectively.The ¹H low field NMR results showed that the relative content of water molecules after retrogradation showed a tendency of decrease as the annealing time increased.4.The effects of annealing times on the texture properties of Pueraria lobata?Willd.?Ohwi starch were investigated by texture analyser.The results indicated that the gel strength of the annealed starch gel was higher than that of the native one,but elasticity of annealed starch was lower than that of the native one.As annealing time increased from 12h to 24 h,gel strength increased significantly.