Differential roles of C-3 and C-6 phosphate monoesters in affecting potato starch properties

The effects of starch phosphate monoester content (SPC), namely C-3 (C3P) and C-6 phosphate monoesters (C6P), on the starch properties were investigated using four potato starches with varied SPC/C3P/C6P and two non-phosphorylated maize starches with a similar range of amylose content (AC) as controls. The starch property results showed that a higher SPC is associated with lower turbidity, storage and loss modulus after storage, and water solubility, but higher swelling power (SP) and pasting viscosities. These findings suggested that SPC inhibited molecular rearrangement during storage and starch leaching during heating, and enhanced swelling and viscosities due to increased hydration and water uptake caused by the repulsion effect of phosphate groups and a less ordered crystalline structure. Increased SPC also resulted in lower resistant starch (RS) content in a native granular state but higher RS after retrogradation. Pearson correlations further indicated that SPC/C3P/C6P were positively correlated with peak (r2 = 0.925, 0.873 and 0.930, respectively), trough (r2 = 0.994, 0.968 and 0.988, respectively), and final viscosities (r2 = 0.981, 0.968 and 0.971, respectively). Notably, SPC, mainly C3P, exhibited a significantly positive correlation with SP (r2 = 0.859) and setback viscosity (r2 = 0.867), whereas SPC, mainly C6P, showed a weak positive correlation with RS after retrogradation (r2 = 0.746). However, SPC had no significant correlations with water solubility, turbidity and rheology properties, which were more correlated with AC. These findings are helpful for the food industry to select potato starches with desired properties based on their contents of SPC, C3P, or C6P.