31P-nuclear magnetic resonance spectroscopic analysis of phosphorus in oat and barley β-glucans

Abstract

Oat and barley β-glucans were isolated from their respective concentrates that were prepared through a novel technology, containing total phosphorus at 0.920 and 0.170%, w/w, respectively. The highest purity of oat and barley β-glucans achieved was 97 and 90%, w/w (db), respectively. Purified oat and barley β-glucans contained 21.8 and 54.1%, w/w, respectively, of the total phosphorus present in the corresponding β-glucan concentrates. On a weight basis, the total phosphorus content in purified oat and barley β-glucans was 0.201 (degree of substitution (DS)=0.011) and 0.092% (DS=0.005), respectively. 31P NMR of both types of β-glucans showed the presence of inner C-6 carbon bound phosphomonoesters and an unknown form of phosphorus, possibly phospholipids and/or phosphoproteins. In addition to these phosphorus forms, barley β-glucan sample contained pyrophosphate for which the origin was unknown. Although a substantial amount of phytate phosphorus (0.745 and 0.103%, w/w, for oat and barley, respectively) was present in both types of β-glucan concentrates, this form of phosphorus was absent in the purified β-glucan as evidenced by 31P NMR data. Aqueous extractability of oat β-glucan from purified sample at 37 °C was 6.6-fold higher than that of barley β-glucan at the same temperature. This may partly be attributed to the presence of more (46%) negatively charged phosphorus substitution in oat β-glucan than in barley.