Effect of konjac glucomannan on syneresis, textural properties and the microstructure of frozen rice starch gels

Repeatedly frozen and thawed rice starch gel loses quality. This study investigated how incorporating konjac glucomannan (KGM) in rice starch gel affects factors used to measure quality. When rice starch gels containing 0-0.5% KGM were subjected to 5 freeze-thaw cycles KGM reduced the % syneresis and moderate increases in gel hardness. SEM of freeze-thaw gels showed starch gel with KGM had smaller pores and less well-defined surrounding matrices than those without KGM. Moreover, CLSM of unfrozen gels without KGM showed densely aggregated swollen starch granules while those in gels with KGM were more evenly distributed. Furthermore, starch pastes with KGM showed higher viscosities than paste without KGM suggesting KGM inhibited granule association. These results suggest that KGM retards rice starch gel retrogradation induced by freeze-thaw treatment and that KGM is effective in preserving quality in freeze-thaw rice starch gels. (C) 2010 Elsevier Ltd. All rights reserved.