COMPARISON OF THERMAL AND VISCOELASTIC PROPERTIES OF 4 WAXY STARCHES AND THE EFFECT OF ADDED SURFACTANT

The waxy starches used in this investigation (maize (WM), barley (WB) and two rice starches RD4 and IR29) showed different gelatinization temperatures (GT) and enthalpies (DELTAH(G)) measured with differential scanning calorimetry (DSC). The differences in GT and DELTAH(G) could only partially be related to X-ray crystallinity. The high GT waxy starches WM and RD4 retrograded to a greater extent measured with DSC and the order of increased retrogradation agreed well with the order of X-ray crystallinity of the retrograded waxy starches. The melting temperature (T(C)) of the retrograded waxy starches in contrast to GT was very similar for all starches. This indicates that the temperature of the glass transition (T(g)) of the amorphous regions in the starch granules controlled the onset GT and perhaps also the extent of retrogradation. Addition of cetyl trimethyl ammonium bromide (CTAB) decreased the extent of retrogradation more than 45% compared to the melting enthalpy (DELTAH(C)) of the waxy starches without CTAB addition. The rice starch RD4 was most affected by the CTAB addition, and the WM starch the least. The viscoelastic behaviour in the temperature interval 25-90-degrees-C of 12%(w/w) gels differed between the waxy starches. The WB starch gels showed the highest storage modulus (G') value and the lowest phase angle (delta), i. e. strongest and least viscous gels. The WM starch gels showed the lowest G' value and the highest delta. The rice starches were in between with the RC4 starch (high GT) showing higher G' value and lower delta than the IR29 (low GT). The viscoelastic parameters changed only slightly with increased temperature. The addition of CTAB to the waxy starch gels changed the viscoelastic behaviour of the stronger and less viscous starch gels of the WB and RD4 as their G' value decreased and delta increased with increased temperature. The effect on WM and IR29 was only small.