Physicochemical properties of serish root (Eremurus spectabilis) fructan as affected by drying methods

Abstract

The fructans, inulin and oligofructose, are relatively unique functional food components because of their chemical nature and the combination of their physiological and nutritional effects that affect gastrointestinal functions. In the present study, the physicochemical properties of dried serish root fructans prepared by application of freeze drying, spray drying, vacuum drying and oven drying at 80 and 105°C were evaluated. The oven-dried and freeze-dried fructans seem to be more hygroscopic than the spray and vacuum oven-dried fructans. The oven-dried sample at 105°C showed the least water solubility among all samples. Fructan contents, purities, and the degree of polymerisation for dried serish fructan samples were 85-87, 79-80 and 13-14%, respectively. The drying method affected the microstructure of the fructan particles leading to differences in their physical properties (particle size, shape, zeta potential, colour and solubility). The colour analysis suggested that the successive combination of spray drying and freeze drying methods had the least negative effect on appearance among the drying treatments. As evidenced by the X-ray diffractograms, the oven and spray-dried samples exhibited amorphous structures, while the freeze and vacuum drying of serish fructans tend to produce semi-crystalline dried products. Differential scanning calorimetry showed that Freeze-drying gave the highest onset and mid-point melting temperatures, whereas oven and spray drying showed the lower melting enthalpy than the freeze dried and vacuum dried samples. FT-IR spectral analysis showed no major structural differences in fructan samples produced by various drying treatments.