Functional, conformational, topographical, and antioxidative properties of convectively- and freeze-dried sunflower protein and hydrolysate: a comparative investigation

This study focused on the influence of convection (at 40 °C and 50 °C) and freeze drying on functionality, structural properties and antioxidant potential of sunflower meal protein (SPm) and hydrolysate (SPHm). Likened to the respective convectively-dried isolates, lyophilized SPm and SPHm showed higher dispersibility and water binding efficacy, but lower oil binding efficacy (buttressed by surface hydrophobicity results) (p < 0.05). The alterations in sulfhydryl clusters and disulfide bridges due to convection drying (under varied temperatures) implied limited unfolding of SPm and SPHm structure and reduction in intermolecular interactions. Moreover, fluorescent intensity and deconvoluted Fourier transform infrared (FTIR) spectroscopy illustrated that convectively-dried (CD) preparations, considerably CDSPHm, possessed more flexible/movable secondary structures over freeze-dried isolates. Topographical study indicated that dehydrated SPHm-s had irregular small particles with partly destroyed/splitted micropores, suggesting disruption in the noncovalent bonds between SPHm-s molecules. Furthermore, isolates from the freeze drying process, notably lyophilized hydrolysate, showed higher antioxidative (DPPH scavenging, ABTS and reducing power) potential over the convectively-dried samples, supported by the analysis of amino acids composition. The current investigation could help the pharmacological and/or food industry to develop new therapeutic product and/or functional food from lyophilized isolates.