Nutritional Value and Bioactive Properties of Enzymatic Hydrolysates prepared from the Livers of Oncorhynchus keta and Oncorhynchus gorbuscha (Pacific Salmon)

  • cc icon
  • ABSTRACT

    Calculated chemical scores (computed in relation to the FAO/WHO reference protein) for salmon liver protein hydrolysates indicated that all amino acids (other than methionine and threonine) were present in adequate or excess quantities; thus, the raw liver material is a good source of essential amino acids. The hydrophobic amino acids contents in hydrolysates prepared from Oncorhynchus keta and O. gorbuscha were 38.4 and 39.1%, respectively. The proportion of released peptides exceeding 500 kDa was reduced when hydrolysates were treated with the commercial enzyme Alcalase, although proportions in the following MW ranges were elevated: 100–500 kDa and <50 kDa. The optimal conditions for enzymatic hydrolysis were as follows: pH 7.0, 50℃, and a reaction time of 1 h. Of the different proteases tested, Alcalase was the most efficient for production of salmon liver hydrolysate with the highest 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity. The hydrolysates prepared from salmon liver had a balanced amino acid composition. The liver protein hydrolysates contained low molecular weight peptides, some of which may be bio-active; this bio-active potential should be investigated. Inhibition of the DPPH radical increased with increased degree of hydrolysis (DH), regardless of protease type. DPPH radical scavenging abilities, antithrombotic effects and α-glucosidase enzyme inhibition effects of O. keta liver hydrolysate increased in a dose-dependent manner. Thus, salmon liver hydrolysate may be useful in functional food applications and as a source of novel products.


  • KEYWORD

    Oncorhynchus keta , Oncorhynchus gorbuscha , Salmon liver hydrolysate , Hydrolysis degree , DPPH (1 , 1-Diphenyl-2-picrylhydrazyl) radical

  • Introduction

    Pacific salmon are widely distributed in Far Eastern waters, where they are an important protein resource for the human population. Local consumers greatly appreciate commercially prepared salmon meat that is available in fresh and in frozen forms. The annual catch of salmon in the Far East is 400,000–500,000 ton.

    By-products of salmon, including viscera, skin, head, liver, bones and roes, that are produced by seafood processing plants amount to >20% of total raw fish weight. They are usually processed into low-value products, such as animal feed, fish meal and fertilizer; some are discarded and cause water pollution.

    To meet an increasing demand for better utilization of limited natural resources and reduction of environmental pollution by fish processing, modern technologies have been developed to produce a broad spectrum of food ingredients and industrial products. Enzyme technology is now available for protein recovery from waste products in the processing of salmon or underutilized species. The protein concentrates produced in this manner have generated considerable industrial interest. Hydrolysis may be used to improve or modify the physicochemical, functional, and/or sensory properties of native proteins without losing nutritional value (Kristinsson and Rasco, 2000). Protein hydrolysates from waste fish products have been produced worldwide (Chalamaiah et al., 2012). These include Pacific whiting solid wastes (Benjakul and Morrissey, 1997), and Atlantic salmon (Kristinsson and Rasco, 2000) and tuna livers (Ahn et al., 2010). Je et al. (2009) used enzymatic hydrolysis functions of commercial proteases, such as Flavourzyme, Alcalase, Protamex, and Neutrase, to produce protein hydrolysates from skipjack tuna liver, a fish by-product that is used to produce fish meal and animal feed, or discarded as processing waste.

    Hydrolysis technology could also be used for better utilization of salmon livers. Our starting premise was that by developing an appropriate technology we would be able to produce a functional and nutritional ingredient giving added value to the hydrolysates of salmon. Thus, we investigated the optimum conditions, nutritional value and functionalities of enzymatic hydrolysates using salmon Oncorhynchus keta and Oncorhynchus gorbuscha liver as a raw material.

    Materials and Methods

      >  Materials

    The livers of frozen Pacific salmon (Oncorhynchus keta and O. gorbuscha) caught in Far Eastern waters were pretreated and analyzed at the National Fisheries Research and Development Institute (NFRDI), Republic of Korea and at the Pacific Scientific Research Fisheries Centre (TINRO Center), Vladivostok, Russia. We used the food-grade proteases Alcalase, Neutrase, Protamex, and Flavourzyme, all of which were produced by Novozymes Biopharma A/S (Bagsværd, Denmark) (Table 1).

      >  Extraction of proteins

    The livers were homogenized for 3 min in cold (5℃) distilled water (1:1 ratio; w/v) using a homogenizer (Ika 25T basic, IKA-Works, Wilmington, NC, USA) operating at 8000 rpm. The protein extract was adjusted to pH 7.0 using 2 N NaOH, and centrifuged at 5000 rpm for 20 min (H-3FR centrifuge, Kokusan Denki, Shizuoka, Japan) to separate the lipid layer from residues. The middle layer of centrifugate containing proteins was separated and adjusted to pH 4.0 using 0.1 N HCI, and then held in a cold room (4℃) for 30 min. The suspension was centrifuged at 7,000 rpm for 20 min. The protein precipitate was dissolved in distilled water and adjusted to pH 7.0 using 2 N NaOH. The suspension was centrifuged at 7,000 rpm for 20 min. We used the protein isolate suspension (pH 7.0) as a substrate for the proteases. The protein concentration in the protein isolate suspension was 638 mg/mL.

      >  Solubility