Sonochemical effect on the degree of substitution of octenyl-succinic anhydride into waxy rice starch nanoparticles and study of gastro-intestinal hydrolysis using INFOGEST in vitro digestion method

Abstract

Octenyl succinylation of starch nanoparticles has been proven to be effective in a variety of food industry applications such as fat replacement, thickening agents, emulsion formation, and delivery of bioactive compounds. In this study, waxy rice starch was debranched with pullulanase to obtain short glucans, which were then modified with octenyl succinic anhydride (OSA) to obtain amphiphilic short glucans (ASG) using high (400 W) and low (200 W) ultrasonic power intensity at 30 and 60 cycles. Developed ASG were characterized by nanoparticle size (ca. < 50 nm), surface hydrophobicity and gastro-intestinal stability. Ultrasonic intervention progressively increased the degree of substitution (DS) of OSA into hydrolysed starch. A significant molecular exchange between starch and OSA was confirmed with shoulder peak at 1.07 ppm by 1H NMR, and 1560 and 1727 cm−1 peaks in FTIR spectral image, and broad band at 1260 cm−1 by Raman spectroscopy. The XRD analysis confirmed the change in crystalline structure, and the emergence of new peaks at 2θ angles of around 5.81° which represent the development of B-type structure following pullulanasehydrolysis, and minor peaks at 13.92° and 19.83°, which imply the production of Vh type structures in ASG. Gastro-intestinal hydrolysis of starch after modification was analyzed in a sequential digestion process using INFOGEST method. The gastro-kinetic studies unveiled the reduction in the digestibility constant in the oral-gastric phase, with significantly enhanced value of kinetic constants in the intestinal phase, proving a sustained gastro-intestinal stability. The OSA-modified starches with greater DS havemore rigid and compact surface structure, which provides superior protection against biochemical conditions in the stomach fluid.