Investigation of Morphological, Structural, Rheological and Digestibility Characteristics of Common Buckwheat Starch Modified via Physical and Chemical Methods

The present study investigated the impact of different physical and chemical modifications on starch extracted from the Pakistani cultivar of common buckwheat (Fagopyrum esculentum Moench). The physical modifications included annealing (ABS), which was performed at 50°C for 24 h, and heat-moisture treatment (HBS) was done at 110°C for 16 h. The chemical modifications involved citric acid (CA) crosslinking (non-conventional) and phosphorous oxychloride crosslinking (conventional). CA was added at a level of 10% (CBS10) and 30% (CBS30), whereas phosphorous oxychloride (POCl3) was used at a concentration of 0.05% (PBS0.05) and 0.1% (PBS0.1), respectively. Native buckwheat starch (NBS) was found to have an A-type polymorphic structure with polygonal granules in the range of 3.18–14.55 μm. The pores with a diameter ranging from 217 to 324 nm were also present on the surface of starch granules. Rheological analysis revealed that all starches were elastic in nature, with phase angles ranging from 3.06° to 9.15°, with the highest being exhibited by the HBS. The percent crystallinity measured through X-ray diffraction was observed in the order of PBS0.1 > HBS > PBS0.05 > ABS > CBS10 > NBS > CBS30, suggesting an increase in crystallinity after physical and chemical modifications, except for CBS30. Moreover, all modifications were observed to reduce the digestibility of buckwheat starch. The resistant starch (RS) content observed the following order: PBS0.1 > PBS0.05 > CBS30 > ABS > CBS10 > HBS > NBS.