Value added fish by-products - Nordic Innovation

(Iceprotein), fish protein hydrolysate (MariPep C, Danish Fish Protein), homogenized fish
protein and dried collagen peptide (Faroe Marine Biotech). Evaluation was made on weight
loss, viscosity (Brabrander® and Bohlin), pH, chemical composition (protein, water, salt) and
molecular weight distribution of proteins (SDS-PAGE).
The FPH had the lowest water content and the highest protein and salt content (3.6%±0.1%).
There was no significant difference found in chemical composition between the other fish
protein solutions. Results obtained with SDS-PAGE showed how the fish protein solutions
differ in molecular weight distribution. The FPH and the gelatin solutions contained a higher
proportion of smaller protein units while the other fish protein solutions contained a higher
proportion of larger protein units and even myofibrils. The FPH had a wide molecular weight
distribution from 2-212 kDa, while the gelatin contained no molecules bigger than ~66 kDa.
Weight loss of the fish protein solutions indicates the ability of the soluble proteins to retain
water, i.e. a high weight loss of the protein solutions can indicate that their ability to retain
water is low. The FPI showed the lowest weight loss, while there was no significant
difference between the other solutions. Studies have shown that increased pH, above pI, can
increase water holding capacity (Wagenknecht & Tuelsner 1975; Thorkelsson 2007). The FPI
was significantly more alkaline (9.28±0.1) compared with the other fish protein solutions,
which can explain the difference in weight loss. According to Fennema (1990), the mean
isoelectric point (pI) of the myofibrillar proteins are about pH 5-6. Minimum water holding
capacity, swelling and protein solubility of meat has been observed around the pI, but it
increases again with either decreasing or increasing pH value.
The lowest viscosity was obtained for the FPH which may be correlated to considerable
smaller protein units. Viscosity can be limiting factor with regard to injection ability of the
protein solutions and may affect how well they are retained within the fish muscle.
3.5.2 Comparison of the effect of injected protein solutions on fillet properties
A couple of studies were performed where fresh and lightly salted cod fillets were injected
with fish protein isolate (FPI: from Iceprotein) and fish protein hydrolysate (FPH: MariPep C
from Danish Fish protein). The influence of the FPI, homogenized fish protein (HFP: from
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