Study On The Influence Of Guar Gum On The Digestibility Of Tapioca Starch

With the improvement of living standard, some chronic disease, which is closely related to people’s diet, has become a risk factor to our health. Decreasing the starch digestion in human body is crucial and beneficial to prevent and control the chronic disease. Body’s postprandial glucose is closely related to starch digestibility. Once starch digestibility is reduced, the rate of starch digestion and absorption could slow down and postprandial glucose of the diabetic can keep stable. Thus, the combination of guar gum and starch has some superior properties to their application in food industry. Guar gum, a soluble dietary fiber, shows a potential that guar gum can reduce starch digestibility. Therefore, this research is aimed to study the influence of guar gum on the in vitro digestibility of tapioca starch. Digestibility difference was explained by studying effects of guar gum on starch physicochemical properties, and enzyme kinetics of pancreatic amylase and amyloglucosidase were discussed by adding guar gum. The main results were present as follows:Firstly, combination ratios(0:100, 1:90, 1:80, 1:70, 1:40, 1:30, 1:20(w/w)) of guar gum and tapioca starch were chosen in this study. Englyst method was used to evaluate the starch digestibility. The results showed that tapioca starch digestibility was changed by guar gum. Starch hydrolysis degree of combinations(1:90, 1:80) was improved by guar gum. While starch hydrolysis degree was negatively correlated with guar gum content, when ratio was increased more. As for combination 1:20,the total amount of slowly digestible starch and resistant starch was 37.51%, which was 19.99% more than that of combination 0:100.Secondly, the starch digestibility affected by guar gum was discussed on the base of physicochemical properties of combinations. Rapid viscosity analyser and fourier transform infrared spectrometer analysis results indicated that guar gum interacted with starch through hydrogen bonding. Interaction force strength of combination 1:80 was weakest, and combination 1:20 was strongest. Low- field nuclear magnetic resonance analysis showed that combination 1:80 had the most amount of free water and combination 1:20 had the most amount of bound water. The observations of scanning electron microscopy and fluorescence microscopy showed that guar gum with higher mobility resulted in more porous and loose fracture morphology in combination 1:80, which was benefit for enzymes to erode starch. In addition, microstructure of starch turned denser when guar gum content increased. Fluorescence microscopy showed that guar gum was around starch, functioning as a barrier, retarded hydrolysis process of combination 1:40 and 1:20.The effects of guar gum on enzyme kinetics and secondary structure of pancreatic amylase were investigated. A modified method was chosen to determine starch digestibility of combinations by using pancreatic amylase replacing mixed enzymes. Molecular weight distribution of remaining starch was measured after enzymolysis for 1 min. The result indicated that guar gum had an obscure inhibition on pancreatic amylase in combination system. Molecular weight distribution of remaining starch digested by pancreatic amylase was similar to that of remaining starch digested by mixed enzymes, which meant pancreatic amylase was closely related with the initial hydrolysis rate. Michaelis-Menten model displayed guar gum was a noncompetitive inhibitor topancreatic amylase. The inhibition rate of pancreatic amylase could reach to 27.59%. C ircular dichroism analysis found that secondary structure of pancreatic amylase was changed by guar gum. Enzyme’s rigid was reinforced and flexibility was weakened. Pancreatic amylase guided the digestion process. The initial enzymolysis rate would reduce more, when guar gum content increased more.In addition, the effect of guar gum on enzyme kinetics of amyloglucosidase and secondary structure of enzyme protein were investigated. The same experiment on pancreatic amylase was also done on amyloglucosidase. The result showed that hydrolysis efficiency of amyloglucosidase was nearly not affected by guar gum. Both enzyme kinetics study and circular dichroism analysis indicated guar gum did not affect the enzyme activity and secondary structure of amyloglucosidase. Guar gum didn’t affect the synergistic effects between pancreatic amylase and amyloglucosidase.In conclusion, combinations’ physicochemical property was affected by guar gum, and the enzyme activity of pancreatic amylase was inhibited by guar gum. The two impact factors together caused difference of tapioca starch digestibility.