In this work the occurrence of resistant starch (RS) in normal corn and banana (naturally resistant) starches was studied and also the effects of conditioning moisture, storage temperature and time on the formation of RS in normal corn starch. The physico-chemical characteristics of the RS from corn and banana were also studied, including the molecular structure. The proximate composition data showed that the percentage of RS is not related to the chemical composition of the granule. Banana starch showed granules with a certain polyformism, and a B x-ray diffraction pattern. The dextrins from this starch showed a linear fraction with DP 34 resistant to sequential action of <FONT FACE="Symbol">b</font>-amylase and/or pulullonase. The pasting characteristics indicated that the high RS content observed in this starch, could not be explained by the physical structure which maintains the granule. The normal corn starch showed polyhedral shapes. Exclusion gel chromatography of the residues obtained after <FONT FACE="Symbol">b</font>- amylase and/or pulullonase hydrolysis, did not show a fraction with DP 34, although the pasting properties indicated a higher granule cohesivity than that of the banana starch. The hydrothermal treatment almost triplicated the RS content (7.15%) of the corn starch, because of the formation of more cohesive structures inside the granule. The retrograded corn starch, with 7.15% RS, was constituted of porous fragments and a C type diffraction pattern. On the other hand, the non significance of storage time on the formation of RS in conjunction with the absence of a fraction with DP 34, suggested the participation of amylose in this resistant structure.
Starch-structure; Corn; Banana
