Functional properties of hydroxypropylated, cross-linked, and hydroxypropylated cross-linked tuber and root starches

Functional properties of some underexploited tuber and root starches (true yam, gourd yam, taro, lotus, and sweet potato) were investigated before and after hydroxypropylation, cross-linking, and hydroxypropylation and cross-linking using potato starch as the reference. Low swelling ability, poor viscosity development but high shear stability, gel hardness, and resistance to enzyme hydrolysis was observed in starches from true yam and gourd yam. The extent of retrogradation was also highest in these two starches. Most of the functional properties of lotus starch were similar to those of potato starch. Hydroxypropylation to a molar substitution level of approximate to 0.1 increased the swelling factor and susceptibility to (alpha-amylase hydrolysis but decreased acid tolerance of paste viscosity, retrogradation, gelatinization parameters, gel hardness, and shear stability. Cross-linking decreased the swelling factor and amylose leaching, and increased shear stability and resistance to enzyme and acid tolerance. Cross-linking had very little influence on gelatinization and retrogradation properties but a larger effect on pasting properties. Increased or decreased peak viscosities and gel hardness values were noted for different cross-linked starches. Cross-linking of hydroxypropylated starches increased commonly desirable functional properties providing a wider range of potential applications.