Study On The Mechanism Of Amylase Hydrolysis Of Rice Amylopectins

Starch is an important carbohydrate in human staple food,and its digestive properties to a large extent affect the body's blood sugar levels.The digestion rate of starch is related to starch granule size,amylose content and amylopectin branching structure and so on.The digestion of starch largely depends on the amylopectin branching structure.Therefore,in order to study the effect of the internal branch structure of amylopectin on the digestibility of rice starches,the relationship between the structural characteristics of waxy-rice amylopectin(WRA)and normal rice amylopectin(NRA)and amylase hydrolysis mechanism was discussed in depth based on building blocks(smallest,tightly branched units)of amylopectin.The main results are as follows:1.Structural analysis of building blocks showed that compared to NRA,the structures of building blocks from WRA are mainly expressed in the following parameters:longer chain length,larger chain number,longer inner chain length,higher degree of polymerization,longer interblocks chain length,smaller branching degree and smaller ratio of short B chain to long B chain.Also,the chain length between the WRA and the NRA tended to be in the form of a Haworth conformation.2.When alpha-amylase from porcine pancreas was used alone,the degree of hydrolysis of NRA was much higher than that of WRA at any one time.While alpha-amylase was combined with glucoamylase from Nepeta,the degree of hydrolysis of WRA was also lower than that of NRA,and the degree of hydrolysis is slowly decreasing.3.Based on building blocks,compared to WRA,NRA had a shorter chain length,shorter number of B-chain,smaller branching,smaller distance between branch points.In general,building blocks from NRA was smaller conduciving to the attack on the role of the site.So,NRA was subjected to more completly enzymatic hydrolysis.4.Gelatinized waxy-rice amylopectin(GWRA)was more sensitive to enzyme than WRA,while gelatinized rice amylopectin and NRA had little difference in sensitivity to enzymes.5.LOS analysis showed that the hydrolysis process of waxy-rice amylopectin and normal rice amylopectin was divided into two phases(the rapid phase and the slow phase).The enzymatic process was discontinuous,and the rapid phase was longer than 30 min and then decreased to slow phase.At the rapid phase,the k value of NRA was greater than the k value of WRA regardless of using?-amylase alone or AA/AMG.The k value of GNRA was similar to the k value of NRA,but the k value of GWRA was higher than that of WRA which indicated that the effect of gelatinization on the degree of hydrolysis of waxy-rice amylopectin was greater than that of normal rice amylopectin,and waxy-rice amylopectin was less sensitive to enzymes.The fast phase of the C_?value was always lower than the slow phase of the C_?value,and the C_?value of WRA and NRA were low.6.The results of SEM showed that whether the hydrolysis of WRA using?-amylase alone or?-amylase and glucoamylase,the form of amylopectin residues was layered,but the hydrolyzed NRA precipitates were massive and visible holes.7.In the analysis of high performance liquid phase(HPLC),it was concluded that:when the WRA,GWRA,NRA and GNRA were hydrolyzed by?-amylase,the maltose,maltotriose,maltotetraose and maltohexaose were preferentially produced,and the rate of glucose formation was the lowest.Only the WRA hydrolyzate contained oligomeric oligosaccharides with a degree of polymerization greater than 7.However,while WRA,GWRA,NRA and GNRA were hydrolyzed with?-amylase and glucoamel,glucose increased the fastest rate.This suggested that?-amylase and glucoamylase played a synergistic role in the hydrolysis process.