Study On The Starch Physicochemical Properties In Pueraria And Six Other Chinese Medicinal Materials

As the special kind of plant, there were abundant of starches in the fruit or bulbof some Chinese medicinal materials (CMM). Based on the previous research,starches were isolated from Pueraria lobata (Willd.) Ohwi (PLO) and Puerariathomsonii Benth.(PTB). Three kinds of modification methods (enzyme hydrolysis,acid hydrolysis and heat-moisture treatment) were applied to preparing modifiedstarches. Native and modified Pueraria starches were then characterized by scanningelectron microscope (SEM), X-ray diffraction (XRD) and differential scanningcalorimetry (DSC) on purpose of providing reference and instruction for rationalutilization of CMM.The research indicated that the amylose (AM) content and water-bindingcapacity (WBC) of Pueraria starches decreased after enzyme hydrolysis and acidhydrolysis accompanied by the increase of transparency. Moreover, acid hydrolysisshowed stronger effects on the AM content and transparency of starch, while theWBC was more influenced by enzyme hydrolysis. SEM results revealed that nativePLO starches appeared elliptic while PTB was mostly polygonal in shape. Similarmechanisms were observed in the process of enzyme hydrolysis and acid hydrolysis.The exterior of starch granules were firstly attacked and cracks or scales were formedon the surface, and then the interior of granules were corroded. Finally, starchgranules were disintegrated and conglutinated to large lumps. XRD patterns revealedthat both of PLO and PTB starches were classified as C-type crystallization. Afterenzyme hydrolysis or acid hydrolysis, the degree of crystallinity decreased. Thecrystalline type did not change in the acid hydrolysis, however, the PTB starch turnedfrom C-type to A-type after enzyme hydrolysis. DSC results showed that after enzymehydrolysis the thermal parameters of Pueraria starches reduced, which resulted in theincrease of thermoplastic property. However, the effects of acid hydrolysis on thethermal properties were not regular obviously.Heat-moisture modification indicated that micro-structures of Pueraria starchesdid not alter in the treatment. With the moisture content increasing, thecrystalline structure of Pueraria starches damaged more seriously, which may lead tolower degree of crystallinity. Moreover, decrease in WBC as well as increase intransparency was observed. Compared to native starches, the digestibility of Pueraria starches enhanced significantly after treatment and the resistant starch contentsreduced evidently.Research on CMM starches suggested that the properties of starches apparentlydiffered from each other owing to different biological sources and growingenvironments. Stephania tetrandra S. Moore.(STM) starch displayed excellenttransparency, whereas high WBC was observed for Paeonia lactiflora Pall.(PLP) andCurcuma phaeocaulis Val.(CPV) starch. SEM results indicated that Euryale feroxSalisb.(EFS) starch was classified as small granule starch, which existed in theform of aggregates. Similar micro-structures were observed for Alisma orientalis(Sam.) Juzep.(AOJ), STM, Paeonia suffruticosa Andr.(PSA) and PLP starch,which were mainly spherical or elliptical in shape. CPV starch possessed the highestproportion of small irregular granules as well as the largest variation in particle size.Except the PSA starch with C-type pattern, all the other CMM starchesdisplayed typical A-type pattern. In addition, PSA and PLP starches were moreeasily to gelatinization, which showed better thermoplasticity.