The effect of sugars on low acyl gellan gels

V Evageliou1, M Mazioti1, G Tseliou1, I Mandala1 and M Komaitis1

1Department of Food Science and Technology, Agricultural University of Athens, 75 Iera Odos, 11855, Athens, Greece

Low acyl gellan is a biopolymer that finds many applications in the food science. It is able to gel on cooling in the presence of cations. Several sugars or their mixtures are used by the food industry in order to achieve the desired properties in sweetness and in texture. Their presence affects both the formation and the mechanical properties of various polysaccharides’ gels. In the present study, the effect of sucrose, glucose, fructose and inulin on the gelation of 0.5 wt% low acyl gellan in the presence of potassium chloride (100 mM) was investigated by large deformation compression experiments. The sugar concentration varied from 0-15 wt%. Samples prior to compression were refrigerated at 5°C for 24 hrs. True stress and true strain at failure along with Young’s modulus were calculated from each compression curve. Stress and strain at the break point are indicative of the network’s strength and elasticity, respectively, and Young’s modulus is related to the network firmness. Glucose showed no contribution to the gellan network strength, as the moduli for all studied concentrations were almost identical with the sample with no sugar present. On the other hand, fructose and sucrose enhanced the strength of the network with sucrose being slightly more effective, whereas the presence of inulin led to gels with decreased strength. Regarding firmness, the general trend was that fructose and sucrose are practically not changing the firmness of the resulting gellan gels, whereas glucose and, even more, inulin showed a major drop in the modulus. Moreover, for all concentrations and all sugars studied, the values of strain remained almost unchangeable showing that the addition of cosolutes had little effect on the deformability of the resulting gels. It is very interesting that the above mentioned observations depended solely on the presence and type of each sugar and not in its concentration.