The role of alkali in sweet potato starch-Mesona chinensis Benth polysaccharide gels: Gelation, rheological and structural properties.

According to the Chinese traditional black jelly production process, a critical step to ensure the quality of jelly is to add alkali to it. In this study, the effects of sodium carbonate (NaCO) and sodium bicarbonate (NaHCO) on the pasting, rheological, textural, and structural properties of sweet potato starch (SPS)-Mesona chinensis Benth polysaccharide (MCP) gels were evaluated. Adding NaCO at low concentration reduced the final viscosity (FV) of SPS-MCP gels, whereas adding it at a high concentration increased the FV. Adding NaHCO can increase the FV of SPS-MCP gels in a concentration-dependent manner. Rheological results indicated that adding NaHCO at a low concentration decreased the storage modulus of SPS-MCP gels, whereas adding it at a high concentration increased the storage modulus. The storage modulus of SPS-MCP gels increased with increasing concentration of NaHCO. The addition of NaCO and NaHCO improved the textural properties of SPS-MCP gels and decreased the water mobility. Infrared results indicated that adding alkali can enhance the hydrogen bonding between SPS and MCP. Scanning electron microscopy results suggested that alkali can reduce the size of gels, and make the structure more compact.