A novel xyloglucan gum from seeds of Afzelia africana Se. Pers.: Some functional and physicochemical properties

Abstract

Afzelia gum (AzG) is a nonstarch polysaccharide extracted from the seeds of Afzelia africana Se. Pers. Some physicochemical and thermal properties of the polysaccharide have been determined and compared with those of hydroxypropylmethyl cellulose (HPMC). The isothermal swelling characteristics show that AzG and HPMC are hydrogels. The swelling of AzG unlike that of HPMC is pH responsive as characterized by its swelling profile and mean swelling time (MST) in different pH buffer solutions. The thermograph of AzG shows four characteristic peaks. Three endothermic peaks and an exothermic peak, while that of HPMC is characterized by two peaks, an endothermic peak and an exothermic peak. The moisture sorption characteristic of HPMC and AzG show that both polymers are moderately hygroscopic. The equilibrium moisture uptake of AzG was greater than that of HPMC at low (21-47)
relative humidity (RH); at higher (75-100) RH, the equilibrium moisture uptake was considerably higher for HPMC. The gel clarity of AzG and HPMC were pH responsive. AzG produced similarly lower gel clarity in pH 4 and pH 9 solutions its highest clarity was in pH 7 solution. The reverse was the case for HPMC dispersions. The results of the various properties evaluated indicate that AzG has potential as pharmaceutical.
Key words: Afzelia gum, gel clarity, hydroxypropylmethyl cellulose, moisture sorption, swelling isotherm, thermal properties