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The RS content of extruded samples was affected by FM content,SS, and storing at 4 C for 24 h, but no significant interaction effectof FM and SS on RS content was observed. Increasing FM led tohigher RS levels. Similar observations were previously reportedfor extruded phoenix flour from regular barley grain by Vasanthan,Gaosong, Yeung, and Li (2002) and for extruded pastry wheat flourby Kim et al. (2006). Lower SS provided extruded samples withhigher RS content compared to samples extruded at higher SS. Thisresult was probably a result of relatively lower starch degradationdue to less shear rate at lower SS conditions. Previous studies alsoreported that lower SS in extruded corn and mango produced higherlevels of RS (Gonzalez-Soto et al., 2006). Also the longer residencetime at 200 rpm might have been responsible for a higheropportunity in amylose chain association and thus RS formation.Amylose content is generally an important factor that increasesRS production during extrusion cooking (Huth, Dongowski, Gebhard,& Flamme, 2000). At high moisture content, RS may beformed and increased at high amylose level, probably by a retrogradationtendency with the formation of strong intermolecularhydrogen bonds in the amylose fraction (Gonzalez-Soto, Mora-Escobedo, Hernández- Sánchez, Sánchez-Rivera, & Bello-Pérez,2007). A strong correlation between amylose content and RS couldbe found in this study (Table 3). Storing at 4 C for 24 h further increasedRS by 2.43–17.12%. Also Huth et al. (2000) reported thatextrusion cooking parameters and subsequent storage affectedthe generation of RS content in extruded barley flour. They observedthe highest RS formation of up to 6% in extruded barleyflours after extrusion cooking at higher FM (approximately 20%),a mass temperature of 150 C, and SS of 200 rpm, followed byfreeze-storage at 18 C for 7 days.Compared to native flour, all extruded samples had very low RScontent after extrusion cooking. Extrusion cooking caused a significantreduction of RS content by 91.5–98.1%. Any correlations toamylose or any increase in RS content in the extrudates is thereforequite low comparing with its initial amounts. In general, nativestarch granules from green banana contain very high initialamounts of RS2. However, RS2 is susceptible to be lost by thermalprocessing (Menezes et al., 2011). Gonzalez-Soto et al. (2007)found that the starch granules of native banana observed by Xraydiffractometry were found in a C-type crystalline pattern, amixture of the A- and B-type, which makes them easily susceptibleto enzymatic hydrolysis after gelatinization. An X-ray pattern of
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