Characterization of peptide fractions from salmon (Salmo salar) rest raw materials towards identifying biologically active fractions
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Over 150 million tons of fish are produced globally each year of which 25% are discarded. The 25% contain huge amounts of protein rich fish rest raw materials. These proteins can be isolated via enzymatic hydrolysis, which can improve nutritional, sensory and functional properties. The main aim of this thesis has been to characterize peptide fractions from a protein hydrolysate powder (ProGo) from Atlantic salmon (Salmo salar) towards identifying biologically active fractions. The hydrolysates were membrane filtered, giving two fractions (permeate smaller than 4000 Da, retentate larger than 4000 Da). The permeate was also freeze-dried. Another objective in this thesis was to see how changes in processing conditions affected the composition and properties of ProGo. Four batches, two from before and two from after the changes, were compared. This study has shown that ProGo is suited as nutraceuticals due to a high amino acid content containing all essential amino acids, indicating a clean product with high nutritional value. ProGo may also be suitable as a functional ingredient due to complete solubilization in water at degree of hydrolysis ~11%. The molecular weight distribution (main fraction below 6500 Da) and high levels of acid-soluble peptides (~60%) indicate that the hydrolysate contains small peptides that may exert bioactivity. The high content of small peptides and hydrophobic amino acids (~50%), as well as low amount of free amino acids favors for antioxidant activity. High levels of glycine indicate that ProGo can possibly enhance the iron uptake. The hydrolysates also showed good in vitro ACE-inhibitory activity with increasing effect as the concentration of the FPH increased. The FDP exhibited stronger inhibitory effect than the FPH at the same concentrations. The old and new batches had similar DH (10.9 ± 0.42 - 11.9 ± 1.98 %), amount of water-soluble (101 ± 1.49 - 115 ± 3.75 %) and acid-soluble peptides (54 ± 0.76 - 62 ± 1.52 %), amino acid content (871 ± 169 - 1008 ± 74 mg/g FPH) and composition, amount of free amino acids (16 ± 0.68 18 ± 0.47 mg/g FPH), and molecular weight distribution. This implies that changes in processing conditions did not affected the FPH. However, batch Old 1 showed a general higher ACE-inhibitory activity than batch New 1. In conclusion, the results of this thesis indicate that ProGo is suited as nutraceuticals due to high nutritional value and a high content of small peptides which may exert bioactivity. These peptides remain to be identified, extracted and further investigated. Hence, more multidisciplinary research is needed to potentially expand the application of ProGo to pharmaceutical and food processing/preservation industries.