Abstract:
The importance of amylopectin structure in relation to the functional properties of starch have been of increasing interest in recent years. In this thesis, thermal properties and digestibility of starches form 7 botanical sources including maize, wheat, rice, quinoa, sweet potato, Maori potato and New Zealand yam were studied. The starches of Maori potato had the highest enthalpy change of gelatinisation (∆HG), and maize starch had the highest gelatinisation transition temperature. For retrogradation properties, the Parera which is one of the genotypes of Maori potato, exhibited the highest degree of retrogradation, whereas the quinoa and wheat starches showed an obviously lower retrogradation rate than other samples. Consequently, the wheat and BQO (one of the genotypes of quinoa) had a faster digestion rate than other samples, and the Parera was highly resistant to enzymatic hydrolysis. Pearson correlation analysis revealed that these differences of starch functional properties were related to their structure of amylopectin. In particular, the enthalpy changes of gelatinisation (∆HR) and retrogradation (∆HG) were negatively correlated to short unit chains of amylopectin (DP 6-12), while being positively correlated to long unit chains (DP >25). Some internal parts of amylopectin are closely related to the functional properties of starch. For instance, the short B-chains of β-limit dextrin (e.g., BSmajor- and B1-chains) were negatively correlated with peak temperature and conclusion temperature of retrogradation, but the long B-chains (e.g., B3-chains) were positively correlated to these retrogradation parameters. The external chain lengths (ECL) of amylopectin and B-chains of β-limit dextrin (e.g., BSmajor-, B1- and B3-chains) co-determined the retrogradation and digestibility of starch. In addition, the digestion rate of starch gel had a significant negative correlation with their retrogradation thermal parameters.