Effects of calcium concentration and cooling rate on gelation of gellan gum

Abstract

The effects of calcium concentration and cooling rate on the gelation of deacylated potassium gellan gum, a commercially available food additive, were investigated by circular dichroism spectroscopy, dynamic mechanical testing, compression testing, syneresis observation and scanning electron microscopy. Aqueous solutions of 0.15% gellan gum were adjusted to pH 3.8 in the presence of various concentrations of calcium after heating at 90?. Gellan gum gels were then set under slow or rapid cooling rates from 80? to 10?. Gellan gum solutions with 6.5mM calcium showed higher saturated storage modulus values when cooled at the slow rate, as compared to rapid cooling from 40? to 10?. In agreement with these results, gellan gum gels set under slow cooling exhibited high breaking strength and fine structure. On the other hand, gellan gum solutions with 26mM calcium showed higher saturated storage modulus values when cooled at the rapid rate, as compared to slow cooling from 40? to 10?. Gellan gum gels set under rapid cooling exhibited high breaking strength and fine structure. Gellan gum texture was smooth at 6.5mM calcium, irrespective of cooling rate, but was rough at 26mM calcium. These results suggest that cooling rate has different effects on the gelation behavior and gel structure of gellan gum depending on calcium concentration.