Amylase resistance of corn, faba bean, and field pea starches as influenced by three different phosphorylation (cross-linking) techniques

The objective was to study the effect of cross-linking on in vitro amylase resistance of regular corn (RC), faba bean (FB), and field pea (FP)starches in their native and gelatinized states, by three different phosphorylation methodologies. Phosphorylation was carried out by the following three methods: a) POCl3 -aqueous: 1-2% phosphoryl chloride (POCl3, v/w) in aqueous slurry at 25 degrees C; b) STMP-semidry: 2-4% sodium trimetaphosphate/sodium tripolyphosphate (STMP/STPP 99:1, w/w) in a semidry state at 130 degrees C; and c) STMP-aqueous: 5-12% STMP/STPP (99:1. w/w) in aqueous slurry at 45 degrees C. The modified starches were characterized for morphology, phosphorus content (% P, w/w), degree of crosslinking (DC) and amylase resistance (AR). Phosphorylation imparted minor differences in the starch granular morphology. The %P and DC of modified starches increased with increasing chemical concentration. The % P (0.01-0.19%, w/w) significantly differed with starch sources (FP > FB > RC) and the method of phosphorylation (STMP-semidry > STMP-aqueous > POCl3-aqueous). However, the DC did not follow the same trend as % P, where POCl3-aqueous showed the greatest. The POCl3-aqueous method had a greater impact than both STMP methods on AR with decreasing rapidly digestible starch (RDS) levels and increasing resistant starch (RS) levels in ungelatinized starches. In gelatinized starches, all three phosphorylation methods increased AR. These changes were more pronounced with STMP-semidry. The results showed that crosslinking by three phosphorylation techniques had a significant influence on AR of starch, and the correlation between AR and DC was different among starch types (r = 0.627-0.910) and phosphorylation methodologies (r = 0.590-0.799).