Novel potato starch : new structure and beneficial qualities

Sammanfattning: This thesis presents a simplified method for determining the internal molecular structure of whole starch without prior amylopectin isolation. The structure of potato and barley whole starches, the thermal properties of starch from potato lines with different genetic backgrounds and the relationship between molecular structure and functional properties of starch were examined in the thesis. The internal B-chain distribution and building block composition of amylopectin were characterised effectively by degrading starch into β-limit dextrins (β-LDs), α- limit dextrins (α-LDs) and building blocks. Great variations in internal structure were observed for starches from different plant sources and genetic backgrounds. The general composition of intermediate and large building blocks and the proportion of fingerprint B-chains (Bfp-chains), in size order, were determined for starches with decreasing amylose content. Thermal properties (gelatinisation and retrogradation) of potato starches were investigated using differential scanning calorimetry. Amylopectin lines with a high degree of mutations in multiple genes showed a broader gelatinisation temperature range and lower enthalpy of gelatinisation and retrogradation. Various internal structure parameters were found to affect the thermal properties of potato starch. A dense structure of building blocks led to higher gelatinisation temperatures and enthalpy, while retrogradation was found to be favoured by more large building blocks and many short internal chains. The high-amylose potato line T-2012 was shown to have higher levels of resistant starch and dietary fibre than the parental variety after cooking. The level of resistant starch increased further after one extra day of cold storage. T-2012 had a very large fraction of long outer amylopectin chains and intermediate-sized inner amylopectin chains, and more intermediate and large building blocks, than the parental potato. The unique amylopectin structure of T-2012 starch favoured formation of recrystallised amylopectin that did not split as easily as ordinary potato starch and was resistant to enzyme digestion.