Tuning the pH-shift protein-isolation method for maximum hemoglobin-removal from blood rich fish muscle

• Alkaline pH-shift version could remove considerably more Hb compared to the acidic version.
• Protein precipitation at pH 6.5 improved Hb removal during alkaline and acid processing.
• Adding phytic acid to the first supernatant of the alkaline version yielded 93% Hb removal.
• Combining one prewash with phytic acid at pH 5.5 followed by pH-shift increased Hb removal.

A main challenge preventing optimal use of protein isolated from unconventional raw materials (e.g., small pelagic fish and fish by-products) using the pH-shift method is the difficulty to remove enough heme-pigments. Here, the distribution of hemoglobin (Hb) in the different fractions formed during pH-shift processing was studied using Hb-fortified cod mince. Process modifications, additives and prewashing were then investigated to further facilitate Hb-removal. The alkaline pH-shift process version could remove considerably more Hb (77%) compared to the acidic version (37%) when proteins were precipitated at pH 5.5; most Hb was removed during dewatering. Protein precipitation at pH 6.5 improved total Hb removal up to 91% and 74% during alkaline and acid processing, respectively. Adding phytic acid to the first supernatant of the alkaline process version yielded 93% Hb removal. Combining one prewash with phytic acid at pH 5.5 followed by alkaline/acid pH-shift processing increased Hb removal up to 96/92%.