Expanding the pH‐Shift Technique for Sequential Extraction of Intact Proteins and Sulfated Polysaccharide From Fish Heads: A Novel Biorefinery Approach

The pH-shift technology was successfully expanded for the sequential recovery of proteins and sulfated polysaccharides (SPs) from rainbow trout heads. Adjusting the pH of the remaining process water after protein recovery at their isoelectric point to 8 enabled precipitation and recovery of SPs with the aid of ethanol at both alkaline and acid process versions and named SP-11.5 and SP-2.5, respectively. The mass yield of SPs recovered using the alkaline process version was 3.25%, nearly double that of SP (1.75%) from the acid version. SP-11.5 contained higher levels of carbohydrates (61.22%), proteins (13.29%), and sulfates (12.13%) compared to SP-2.5. FTIR, DSC, and XRD analyses showed no significant differences in the structural properties of the recovered SPs as a function of the pH-shift process version. However, SP-11.5 exhibited better antioxidant activity in DPPH, ABTS, and metal chelating tests and superior antibacterial properties against <i>Listeria monocytogenes</i> and <i>Escherichia coli</i> than SP-2.5. This study suggests that the pH-shift process can be effectively extended for sequential extraction of both protein isolates and SPs from fish by-products for a multiple product biorefinery where the alkaline version outperformed.