Influences and potential mechanisms of zein-fucoidan nanoparticles loaded with and without curcumin on casein before and after thermal treatment

This study aims to investigate the influences and potential mechanisms of zein-fucoidan nanoparticle (ZFNPs) loaded with and without curcumin (Cur) on casein (CN) before and after thermal treatment. It was found that the addition of ZFNPs into CN solution slightly promoted its fluorescence. However, significant fluorescence quenching of CN was observed after heating when Cur-loaded ZFNPs (CZFNPs) and free Cur were added. We speculated that Cur released from CZFNPs during heating might access the hydrophobic sites in the interior of CN to interact with tryptophan (Trp) residues, like free Cur. Obviously conformational changes of CN caused by released Cur was stronger than that caused by ZFNPs. FTIR spectra revealed that the influences of CZFNPs on the secondary structure of CN also resulted from both ZFNPs and the loaded Cur molecules. Additionally, with the addition of CZFNPs, ZFNPs and Cur, the average particle size of CN increased before heating but decreased after heating. Although they exhibited a same trend, the CN solutions with ZFNPs and CZFNPs were more homogeneous systems from this aspect. Last but not least, DSC curves showed that the presence of ZFNPs during heating did not alter the thermal stability of CN. Nevertheless, CZFNPs and Cur led to a reduction in the denaturalization temperature of CN, indicating that they were just simply mixed with CN in the solutions rather than bind to CN through covalent bonds. The results obtained in this work may provide theoretical guidance for the application of nano delivery systems in functional foods and beverages.