Abstract
The hydrolytic and cost efficiencies of five endopeptidases (Alcalase 2.4L, Corolase 7089, Neutrase 0.8L, Promod 671L and Protex 7L) to hydrolyze Atlantic salmon by-products were compared at standardized activity levels based on a casein assay. The substrate was characterized prior to the hydrolytic experiments (pH=6.5, t=50 °C) to obtain substrate--specific constants for nitrogen to protein mass (in g) ratio, i.e. conversion factor fN=5.23 and total amount of peptide bonds (htot)=9.3 mmol per g of protein. At low enzyme activity to substrate ratio, all enzymes were equally efficient in hydrolyzing the substrate. At highest enzyme activity to substrate ratio, Protex 7L, Alcalase 2.4L and Promod 671L gave higher degree of hydrolysis (DH=14.2-14.6%) than Corolase 7089 (13.2%) and Neutrase 0.8L (11.6%) after 120 min of hydrolysis. No differences were observed in protein recovery (yield of solubilized protein) relative to DH. Determination of DH was followed by the pH-STAT and o-phthaldialdehyde methods. Based on pH-STAT data, response surface regression models were established based on the combined effects of hydrolysis time and enzyme activity to substrate ratio on DH and protein recovery. The modelling approach was combined with enzyme cost to identify the most cost-efficient enzyme (Protex 7L).
Highlights
The world fisheries and fish farming industries generate large amounts of by-products with possible food and feed applications [1]
Atlantic salmon by-product-specific values for total amount of peptide bonds and nitrogen-to-protein conversion factor deviate from the commonly used and underline the importance of substrate characterization in order to achieve a precise estimation of protein content and degree of hydrolysis (DH)
At low enzyme activity to substrate ratio all enzymes were efficient in hydrolyzing the substrate
Summary
The world fisheries and fish farming industries generate large amounts of by-products with possible food and feed applications [1]. All by-products from the fish filleting industry are food grade after the primary processing and represent raw material with a high protein level, including all essential amino acids and other valuable compounds [3,4,5]. A promising industrial food utilization of fish filleting by-products is through the manufacture of water-soluble protein hydrolysates, using exogenous enzymes. The development and availability of industrial food-grade proteases has opened up new possibilities for production of fish protein hydrolysates from these resources [6,7,8] with applications within the food and nutraceutical market [5].
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