The impact of high hydrostatic pressure treatment time on the structure, gelatinization and thermal properties and in vitro digestibility of oat starch

As a non-thermal processing technology, high hydrostatic pressure (HHP) can be used for starch modification without affecting the quality and flavour constituents. The effect of HHP on starch is closely related to the treatment time of HHP. In this paper, we investigated the impacts of HHP treatment time (0, 5, 10, 15, 20, 25, 30 min) on the microstructure, gelatinization and thermal properties as well as in vitro digestibility of oat starch by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, 13C NMR and differential scanning calorimeter. Results showed that 5-min HHP treatment led to deformation and decreases in short-range ordered and double-helix structures of oat starch granules, and further extending the treatment time to 15 min or above caused the formation of a gelatinous connection zone, increase of particle size, disintegration of short-range ordered and double-helix structures, and crystal structure change from A type to V type, indicating gelatinization occurred. Longer treatment time also resulted in the reduction in both the viscosity and the stability of oat starch. These indicated that HHP treatment time greatly influenced the microstructure of oat starch, and the oat starch experienced crystalline destruction (5 min), crystalline disintegration (15 min) and gelatinization (> 15 min) during HHP treatment. Results of in vitro digestibility showed that the rapidly digestible starch (RDS) content declined first after treatment for 5 to 10 min then rose with the time extending from 15 to 30 min, indicating that longer pressure treatment time was unfavourable to the health benefits of oat starch for humans with diabetes and cardiovascular disease. Therefore, the 500-MPa treatment time for oat starch is recommended not more than 15 min. This study provides theoretical guidance for the application of HHP technology in starch modification and development of health foods.