Physicochemical and morphological properties of resistant starch type 4 prepared under ultrasound and conventional conditions and their in-vitro and in-vivo digestibilities.

In the present work, cross-linked resistant starch (RS4) was prepared under sonication and conventional conditions at various levels of pH (9-12) and cross-linker concentration (sodium trimetaphosphate/sodium tripolyphosphate 99:1, 5-15%). It was found that phosphorous and resistant starch content was generally increased by increasing the cross-linker concentration, pH and application of sonication. The damage to the surface of sonicated granules was revealed by scanning electron micrographs. The presence of cross-linked phosphorous groups was demonstrated by FT-IR results through the appearance of a new peak at wave numbers of 1248-1252 cm that was more conspicuous in sonicated cross-linked samples. Sonicated cross-linked starches showed higher gelatinization temperatures and lower degrees of crystallinity, while no changes was detected in terms of A-type crystalline pattern. The development of viscosity was diminished prominently by the extreme cross-linking reactions in both sonicated and conventional cross-linked starches. The least glycemic index value was obtained for sonicated cross-linked starches which was negatively correlated to their higher RS content measured in-vitro. These results provide novel information on the preparation of cross-linked resistant starch under sonication conditions.