The effect of ripening temperature on rice (Oryza sativa) grain quality was evaluated by assessing starch structure and gelatinization, pasting, and cooking properties. As the ripening temperature increased, the amylose content and number of short amylopectin chains decreased, whereas intermediate amylopectin chains increased, resulting in higher gelatinization temperatures and enthalpy in the starch. These results suggested that an increase in cooking temperature and time would be required for rice grown at higher temperatures. A high ripening temperature increased the peak, trough, and final viscosities and decreased the setback due to the reduction in amylose and the increase in long amylopectin chains. With regard to starch crystallinity and amylopectin molecular structure, the highest branches and compactness were observed at 28/20 °C. Rice that was grown at temperatures above 28/20 °C showed a deterioration of cooking quality and a tendency toward decreased palatability in sensory tests.

The strengths of hydrogen bonding interaction between formamide (FA) and thioformamide (TFA) were investigated at the B3LYP level with the 6-311G(d,p), 6-31+G(d,p), and 6-311++G(2d,2p) basis sets. The 18 minimum energy structures of FA-FA, TFA-TFA, and TFA-FA dimers were examined. The average strength of the OCN-H---OdC, SCN-H---SdC, OCN-H---SdC, and SCN-H---OdC hydrogen bonds at the B3LYP/6-311++G(2d,2p) level was -6.1 ( 0.3, -5.0 ( 0.1, -4.8 ( 0.3, and -7.3 ( 0.4 kcal/mol, respectively, when the basis set superposition error (BSSE) was corrected. The results show that TFA is a good hydrogen bond donor but a poor hydrogen bond acceptor as compared to FA. For the OC-H---OdC, SC-H---SdC, OC-H---SdC, and SC-H---OdC hydrogen bonds, the average strength has been predicted to be -2.2 ( 0.3, -2.2 ( 0.2, -1.0 ( 0.3, and -3.1 ( 0.3 kcal/mol, respectively. It is remarkable that the thioformyl hydrogen atom of TFA has a strong hydrogen bonding ability as compared to that of FA. The abilities of the hydrogen bond donor have a good correlation with the proton affinities of the deprotonated anion.

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