The influence of bound water on the FTIR characteristics of starch and starch nanocrystals obtained from selected natural sources

Starch is a natural polymer consisting of amylose and amylopectin. The amylopectin region of starch contains crystalline structures known as starch nanocrystals. These starch nanocrystals can be extracted by acid hydrolysis of the respective native starches. Morphology, the degree of crystallinity and yield of starch as well as the amount of starch nanocrystals obtained, depends on the botanical origin of the source used. The starch nanocrystals thus obtained has been shown to enhance the properties of several polymeric packaging materials incorporated with the same. In this study, an attempt is made to obtain starch nanocrystals from a few natural sources like rice (Oryza sativa), ragi (Eleusine coracana), wheat (Triticum astivum), and sorghum (Sorghum bicolour) by acid hydrolysis of the isolated starches using sulphuric acid. A comparative evaluation of morphological, spectral, and thermal characteristics of the native starches as well as starch nanocrystals isolated from them is carried out. Detailed examination of FTIR, DSC, and TGA data indicate that more bound water is interacting with starch compared to starch nanocrystals, thereby influencing its spectral and thermal characteristics.