Endothermic Transitions of Acid-Modified Tapioca Starches; Annealing and Freeze-Thaw Stability Study

Napaporn Atichokudomchai¹, Saiyavit Varavinit¹ and Pavinee Chinachoti²

¹Department of Biotechnology, Faculty of Science, Mahidol University, Thailand

²Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA

ABSTRACT

Acid-modified tapioca starches obtained by hydrolysis of native tapioca starch with 6% hydrochloric acid (w/v) at various reaction time was found to increase in line with relative crystallinity while amylose content decrease when increase hydrolysis time. . Annealing and freeze-thaw stability of the acid-modified starches were studied using Differential Scanning Calorimetry (DSC). For annealing study, as the hydrolysis time increased, the effect of annealing on narrowing and shifting the endothermic peak to a higher temperature were decreased. Endothermic transition of annealed 48-h acid-modified tapioca starch showed a narrow peak and a broad small shoulder, corresponding to the melting of the least stable crystalline regions and the isolated crystalline regions, respectively. This effect was less pronounced on annealed 192-h and annealed 768-h acid-modified tapioca starches. These results indicated that annealing leads to more homogeneous crystallites and this is enhanced when the material contains more amorphous and homogeneity domains. For freeze-thaw stability study, the melting endotherm of recrystallized amylopectin became larger with increasing hydrolysis time. The first detectable endotherm of native tapioca retrograded gel was observed after 5 cycles, while all acid-modified retrograded gels showed the melting endotherm after only 1 cycle. Increasing hydrolysis time may increase the proportion of the short chain amylopectin, which was suitable for the formation of double helixes, resulting in the increase in the enthalpy and the higher retrogradation rate of the gel.