Thermal properties of buckwheat proteins as related to their lipid contents

The thermal properties of buckwheat proteins (BP) as related to their lipid contents were studied using differential scanning calorimetry (DSC). BP samples with three levels of lipid content (2.5%, 6.5% and 17.8%, w/v) were obtained by selecting different extraction and de-fatting techniques. In the DSC thermograms of all BPs, there were two observable endothermic peaks with similar denaturation temperatures of about 80 and 102 °C, corresponding to the 8S and 13S globulins, respectively. The enthalpy changes (ΔH) of buckwheat globulins are also unaffected by the presence of lipids (2.5–17.8%), however, the width at half peak height (ΔT1/2) presenting the cooperativity of the transition from native to denatured state was related to the lipid content. DSC analyses in the presence of some protein perturbants (e.g., urea, SDS and DTT) showed that the structure of buckwheat globulins (especially 13S globulins) are mainly maintained by hydrogen bonding and hydrophobic interactions, and the presence of lipids may disturb the hydrophobic interactions of these globulins. The disulfide bonds only pay an important role in those globulins with high (17.8%) or low (2.5%) lipid contents. These results suggest that the presence of lipid affect the thermal properties of buckwheat globulins, especially the ability to resist the denaturant-induced denaturation, and a suitable amount of lipids be favorable for the maintenance of native protein conformation of 13S globulins.