The treatment of aqueous gum arabic solutions with ultraviolet radiation

Aqueous solutions of gum arabic have been photolysed with UV light from a low-pressure mercury lamp (maximum emission at 254 nm). The survival of the bacteria present was monitored as a function of fluence and it was found that a fluence of similar to 450 J/m(2) reduced the bacterial concentration in a 200 g/dm(3) gum arabic solution which has a 254 nm absorbance of 0.8 by 90%. The size of the fluence required for 90% bacterial reduction is much larger than that needed for transparent (at 254 nm) solutions, where a fluence of 250 J/m(2) typically reduces the bacterial load by four orders of magnitude. Low-angle laser light-scattering measurements indicate that photolytic degradation of the gum arabic occurs, although with an extremely low efficiency, a fluence of 8 x 10(5) J/m(2) being required to produce an average of one 'degradative' chain break per molecule. Gel permeation chromatography confirmed the low sensitivity of gum arabic to UV-induced degradation, there being no significant increase in the fraction of low-molecular-weight material after an essentially 'sterilizing' fluence of 3.9 x 10(3) J/m(2). On photolysis, the absorbance (220-350 nm) of gum arabic solutions increases; for a given fluence the increase is larger when oxygen is present. The emulsifying ability of photolysed gum arabic was tested using orange oil; no difference was detectable between photolysed (3.9 x 10(3) J/m(2)) and untreated controls.