Effect of phosphorylation techniques on structural, thermal, and pasting properties of pulse starches in comparison with corn starch

Abstract

The impact of three phosphorylation techniques on structural, thermal, and pasting properties of faba bean (FB) and field pea (FP) starches were investigated in comparison with regular corn (RC) starch. Phosphorylation was performed using the following three methods: a) POCl3-aqueous: 1–2% phosphorus chloride (POCl3, v/w) in aqueous slurry at 25 °C; b) STMP-semidry: 2–4% sodium trimetaphosphate/sodium tripolyphosphate (STMP/STPP 99:1. w/w) in a semidry state at 130 °C; and c) STMP-aqueous: 5–12% STMP/STPP (99:1. w/w) in aqueous slurry at 45 °C. The native and crosslinked starches were characterized using a rapid visco-analyzer (RVA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). STMP-semidry showed the highest reaction efficiencies as indicated by degree of crosslinking (DC) followed by STMP-aqueous and POCl3-aqueous, while the POCl3-aqueous was the most efficient crosslinking method for altering the pasting properties (RVA) in all starches. The influence of STMP-semidry on thermal stability (DSC) was more pronounced in pulse starches, while RC starch was influenced more by POCl3-aqueous. STMP-aqueous with higher chemical concentration showed relatively lower thermal stability than STMP-semidry and POCl3-aqueous. XRD and ATR-FTIR spectra confirmed that crosslinking resulted in the loss of crystallinity. The influence of POCl3-aqueous on the disruption of crystalline structure was more pronounced in FB and FP than in RC; while STMP-aqueous had less influence on the crystalline structure of pulse starches; STMP-semidry disrupted the B-type polymorph in C-type pulse starches. This study provides a foundation for a better understanding of the structure-crosslinking-functionality relationships of pulse starches and promotes novel applications of pulse starches in food industry.