|M.Sc Student||Hila Wolf|
|Subject||The Effect of type III Resistant Starch Crystallite|
Structure on its Prebiotic Properties
|Department||Department of Biotechnology and Food Engineering||Supervisor||Dr. Shimoni Eyal|
This research explores the relation between the structural properties and prebiotic behavior of the different polymorphs of RSIII. Understanding this relation is critical for the development of RS with improved prebiotic properties. One of the goals of this research was to improve procedure for producing different polymorphs of RSIII. In order to accomplish this goal we have first melt the starch and then re-crystallized it either at a high temperature or at low temperature. For all types of starch being used, the polymorph type was determined by the crystallization temperature. Regardless of chemical composition or crystalline structures of the native starch, retrogradetion at low temperature led to the formation of polymorph-B, whereas retrogradation at high temperature led to a mixture of polymorphs, mostly polymorph-A. Polymorph-A has a dense unit cell, and contains very few bound water molecules, whereas polymorph-B is less dense and includes more water molecules. Despite these differences, there were no differences in the thermal stability between the two polymorphs. All the thermograms showed endothermic peek at 140-1700C, which is a characteristic of amylose crystals melting. As this peak describes melting of both polymorphs, their thermal stability seems to be very similar.
The enzymatic digestion of different RSIII polymorphs was characterized by digesting the different polymorphs with a-amylase, b-amylase, pancreatin, and amyloglucosidase. Polymorph-A was digested faster then polymorph-B and the extent of hydrolysis (% w/w) was higher. Hydrolysis of hydrated samples, showed no difference between A and B. Pancreatin and a-amylase exhibit highest digestion rate, significantly higher than b-amylase and amyloglucosidase.
Fermentation of RS polymorphs was studied in anaerobic cultures of microbiota from fecal samples. The bacterial growth was measured in a medium containing A or B polymorphs as the sole carbon source. Similar growth was observed in cultures containing either A or B polymorphs. The production of butyrate, acetate, and propionate was higher in cultures grown on polymorph-A. The production of butyric acid has an important role in colon health.
When measuring the total anaerobic bacteria in the fermentation, there was no significant difference between fermentation containing polymorph-A and fermentation containing polymorph-B. A possible explanation is that each polymorph encourages the production of different culture. In order to establish this hypothesis T-RFLP analysis was performed. The results suggest that when using polymorph-A as the sole carbon source, different bacterial strains eventually dominated the culture, when compared to cultures grown in present of polymorph-B.