Melting the secrets of gelatinisation temperature in rice

Abstract. Gelatinisation temperature (GT) is oneof thekey traitsmeasured inprograms for breeding rice (Oryza sativaL.). It is commonly estimated by the alkali spreading value (ASV), and less commonly by differential scanning calorimetry (DSC). Using a diverse set of germplasm, it was determined that DSC values associate poorly with ASV, are not correlated with amylose content but correlate with cooking time. Rice varieties are traditionally grouped into three classes of GT based onASV: high, intermediate and low.However, the distribution ofDSCvalues of 4000 samples shows only two classes: high and low. Large differences in the distributions of chain lengths synthesised by starch synthase IIa (SSIIa) support the two classes as themajor grouping, twohaplotypes associatingwith each peak. EachpeakofDSCvalues spanned10C.The chain lengthdistributionof the amylopectinmolecules fromvarieties at theupper boundaryof eachpeak showed significantlymore chains that span both the crystalline and amorphous lamellae of a cluster than varieties at the other end of that distribution. Improved varieties, classified as intermediate GT byASV, belong to both of the classes defined byDSC, implying that some enzyme, other than SSIIa is involved in intermediate GT