Abstract The role of water and hematite (Fe2O3) on the stability of ovalbumin-based model paint layers was investigated by means of DSC and FTIR. The aim of this research is to improve our understanding on the stability of paint layers based on proteinaceous media, assessing the water content and the pigment presence effects. Pigments may play a fundamental role in determining the structure of proteins in paint layers, thus affecting the possible interactions among proteins and the external environment, including humidity. Previous studies revealed that hematite affects the secondary structure of OVA in paint layers, although no experimental evidence of hematite/OVA covalent bonds has been reported in the literature. In this paper we investigate the synergic effect of water and hematite on OVA structure and stability. DSC analyses coupled with FTIR measures on protein hydration revealed that below 30 % of humidity the amount of water strongly influence the protein structure and stability: the less the water content, the higher the protein stability. Furthermore, our results suggest that a water phase separation occurs in the presence of hematite for which, in water-limiting condition, the hematite’s hydration shell becomes almost negligible if compared to the bulk water available for the protein hydration because of the high protein-water affinity. Accordingly, the protein phase humidity is higher than the sample’s nominal value. Paints at the same overall humidity exhibit different protein hydration state following the pigment/binder ratio, and in turn different resistance to damages throughout aging.

中文翻译：

---

卵白蛋白-赤铁矿“蛋彩画”涂料的 DSC：水和颜料对蛋白质稳定性的作用

摘要 通过DSC和FTIR研究了水和赤铁矿(Fe2O3)对卵清蛋白基模型漆层稳定性的影响。这项研究的目的是提高我们对基于蛋白质介质的油漆层稳定性的理解，评估水含量和颜料存在的影响。颜料可能在决定油漆层中蛋白质的结构方面发挥重要作用，从而影响蛋白质与外部环境（包括湿度）之间可能的相互作用。先前的研究表明，赤铁矿影响涂料层中 OVA 的二级结构，尽管文献中没有报道赤铁矿/OVA 共价键的实验证据。在本文中，我们研究了水和赤铁矿对 OVA 结构和稳定性的协同作用。DSC 分析结合 FTIR 对蛋白质水合的测量表明，低于 30% 的湿度对蛋白质结构和稳定性有很大影响：水含量越少，蛋白质稳定性越高。此外，我们的结果表明，在赤铁矿存在的情况下会发生水相分离，在限水条件下，如果与可用于蛋白质水合的大量水相比，赤铁矿的水合壳几乎可以忽略不计，因为高蛋白质-水亲和力。因此，蛋白质相湿度高于样品的标称值。在相同的总湿度下，随着颜料/粘合剂的比例不同，涂料表现出不同的蛋白质水合状态，进而在整个老化过程中对损坏的抵抗力也不同。