Studies on the physicochemical properties of inulin and inulin oligomers

Inulin, Raftiline® ST, Raftilose® P and oligofructose in aqueous solutions were investigated at 2.5, 5, 10, 15, 17.5, 20 and 25 g of solute in 100 g of water by physicochemical measurements in order to obtain molecular weights, reducing activities, apparent specific volumes, isentropic apparent specific compressibilities, and 1H-NMR pulse relaxation times (T1 values). Molecular weights have been found to range from 340 to 4620 g mol−1. Raftilose® P is the only sample which shows reducing capacity and may be expected to be susceptible to the Maillard reaction. Apparent specific volumes lie within the sweet range 0.60–0.64 cm3 g−1 and increase with degree of polymerisation (DP); this behaviour describes increasing displacement of water as molecular weight increases. Isentropic apparent specific compressibilities increase as concentration of solute, molecular weight and DP increase, showing reduced solute–water affinity. T1 values decrease with increasing molecular weight and concentration as a result of increased order of protons and reduced water mobility.