Physicochemical Properties Of Cassava Starch And Preparation Of Cassava Resistant Starch

Resistant starch (RS) is defined as the total dietary starch that does not digest in the small intestine and can be fermented in the large intestine. Cassava starch is chosed as the material of this study, because it is more plentiful and cheaper than other starches. The physicochemical properties of cassava starch and cassava RS were comparatived investigated and then preparation of cassava RS was conducted by the method of autoclave and twin screw extrusion.Studying the physicochemical properties of cassava starch showed:The granules size, smooth surface and crystal structure (A-type) of cassava starch were similar with those of corn starch. The shape of most cassava starch granules was truncated oval and those of most corn starch were polyhedral. Cassava starch had the lower nitrogen content and lipid content, higher swelling power and solubility, higher paste clarity and paste viscosity, lower gelatinization temperature and weaker freeze-thaw stability than corn starch. All of results showed that cassava starch had better processability than corn starch.The preparation processes of cassava RS by autoclave method and twin screw extrusion method were determine, and the results are as follow:The optimal preparation conditions of cassava RS by autoclave method were determined: starch slurry concentration 10%, autoclave at 121℃for 45 min and retrogradation at 4℃for 24 h, resulted in the cassava RS yields increased by 12.32%. This result showed that cassava RS content had increased significantly by autoclave method.The optimal preparation conditions of cassava RS by twin screw extrusion method were determined:water content of raw material 40%, die temperature 130℃, screw speed 25, feeding rate 20 and retrogradation at 4℃for 24 h, resulted in the cassava RS yields increased by 6.14%. This value was lower than the cassava RS yields (12.32%) obtained from autoclave method.The physicochemical properties of cassava RS were studied and the results as follow:The granule surface of cassava RS was rough and its shape was polygon or irregular; Compared with raw cassava starch, cassava RS had the higher water holding capacity, similar emulsification ability, negligible viscosity and higher thermostability. Both of the raw cassava starch and cassava RS were made of amylose and amylopectin; There was no new absorption peak shown in the infrared spectrum of cassava RS, which indicated cassava RS belonged to the physical modified starch; Crystallization structure turned into B-type from A-type of the raw cassava starch. Meanwhile, some new crystalline regions were produced and the crystallinity was increased. This indicated the higher crystalline and the higher RS content.Taking cassava starch as raw material to produce cassava RS is a very promising deep processing mode, because not only did cassava have lower price and better processability, the cassava RS had better processability and particular physiological properties. However, the casava RS yields is relatively low and it still can not be industrialized. Consequently, how to increase the cassava RS yields remains to be further studied.