抄録
Two gum arabic samples of high (GA-H) and low molecular weight (GA-L) were used in this study to investigate the effect of high pressure homogenisation. The effect of pressure homogenisation on gum arabic solutions and ultimately adsorption of the gum on to oil droplets has not previously been reported. In this study, the effect of high pressure homogenisation on gum solutions was monitored using the GPC-MALLS technique, which enabled the oil adsorbed component to be measured. Moreover, the relation between the stability of the emulsion and the pressure homogenisation treatment was evaluated. Gum arabic solutions were treated by dispersion or high pressure (1 or 3 pass at 25, 50, 75, 150 MPa). No significant changes were observed following dispersion treatment while a decrease in molecular weight and AGP content was confirmed by high pressure homogenisation a behaviour which was similar for both GA-L and GA-H solutions.
The droplet size distributions of the emulsion were determined initially, then the emulsion was treated for 3 and 7 days at 60℃ in order to accelerate the evaluation of stability. The results show a droplet size of 1 micron or greater is formed, with only a small fraction adsorbed on to oil droplet following this dispersion treatment only. The amount of adsorbed component increased with high pressure homogenisation , and was accompanied by lower droplet sizes but these decreased when the pressure increased to 150 MPa. High pressure homogenisation had a pronounced effect on the amount of adsorbed component and droplet size in GA-L but not on GA-H. The number of passes at a given pressure resulted in a reduction in initial droplet size and decreased amount of adsorbed component.
A decrease in molecular weight and AGP content was observed with gum arabic solutions treated by high pressure (75 MPa) compared with 25 MPa or 50 MPa. However, emulsions made with GA-L and GA-H which when treated with 75 MPa were found to be more stable compared with those treated with 25 MPa and 50 MPa. It is concluded that the stability of the emulsions is related not only to the amount of adsorbed component but also to the conformational and de-aggregation changes induced by high pressure homogenisation. It is, therefore, necessary to properly select the pressure homogenisation conditions to obtain stable emulsions.
