Nutritional and Sensory Properties of Protein Hydrolysates Based on Salmon (Salmo salar), Mackerel (Scomber scombrus), and Herring (Clupea harengus) Heads and Backbones.

Protein hydrolysates based on salmon, mackerel, and herring heads and backbones were produced, and the sensory properties of the hydrolysates were evaluated by a highly trained sensory panel. The nutritional content of the products was evaluated, and the hydrolysates contained all the amino acids inherent to the raw material, including considerable levels of connective tissue amino acids glycine, proline, and hydroxyproline. Hydrolysates based on herring were the most flavor intense, whereas hydrolysates based on salmon were deemed more palatable. In this work, choice of fraction (heads vs. backbones) and enzyme had minor effects on sensory and nutritional properties, indicating that choice of raw material species was the major factor for flavor development in the produced protein hydrolysates. There were large variations in protein content and amino acid composition in the raw material fractions, but as expected, only minor variations were found in the final products.

Reduction in flavor-intense components in fish protein hydrolysates by membrane filtration.

Enzymatic protein hydrolysates based on side stream materials from the fish-filleting industry are increasingly explored as food ingredients. However, intense sensory properties, and high salt contents, are often a limiting factor. Most of the sensory attributes, such as fish flavor and salty taste, can be ascribed to low-molecular-weight, water-soluble components, whereas bitterness is associated with small hydrophobic peptides. In this study, protein hydrolysates based on head and backbone residuals from Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) were produced using two different enzymes. The effects of micro- and nanofiltration on the chemical composition, protein recovery, and sensory properties of the final products were investigated. The choice of raw material and enzyme had negligible effects, whereas nanofiltration caused a considerable reduction in metabolites, ash, and the intensity of several sensory attributes. The intensity of bitterness increased after nanofiltration, indicating that small peptides associated with bitter taste were retained by the membrane. Total protein yield after microfiltration was 24%-29%, whereas 19%-24% were recovered in the nanofiltration retentate. PRACTICAL APPLICATION: Enzymatic protein hydrolysates can be included in food products to increase the protein content, and as a nutritional supplement and/or functional ingredient; however, unpalatable and intense flavors limit applications. This study investigated the use of membrane filtration to improve flavor quality and reduce salt content in fish protein hydrolysates. Although some protein loss is unavoidable in micro- and nanofiltration, this study demonstrates the production of fish protein hydrolysates with >90% protein and peptide content, which is suitable for inclusion in foods.

Emulsion and Surface-Active Properties of Fish Solubles Based on Direct Extraction and after Hydrolysis of Atlantic Cod and Atlantic Salmon Backbones.

The focus on natural foods and "clean" labeled products is increasing and encourages development of new biobased ingredients. Fish solubles derived from downstream processing of side stream materials in the fish filleting industries have potential as emulsifiers based on their surface-active and emulsion stabilizing properties. The aim of this study was to evaluate and compare emulsion properties and critical micelle concentration (CMC) of direct protein extracts and protein hydrolysates based on fish backbones, and to identify associations between molecular weight distribution and process yield with the studied physicochemical properties. Protein extracts and enzymatic protein hydrolysates were produced based on two raw materials (cod and salmon backbones), two enzymes with different proteolytic specificity, and varying hydrolysis time. Emulsion activity index (EAI), emulsion stability index (ESI) and CMC were measured and compared with casein as a reference to protein-based emulsifiers. Protein hydrolysis was found to have negative impact on EAI and CMC, likely due to generation of small peptides disrupting the amphiphilic balance. The direct protein extracts had comparable EAI with casein, but the latter had superior ESI values. Protein hydrolysates with acceptable EAI could only be obtained at the expense of product yield. The study emphasizes the complexity of physicochemical properties of protein hydrolysates and discusses the challenges of achieving both good surface-active properties and high product yield.

Sensory Assessment of Fish and Chicken Protein Hydrolysates. Evaluation of NMR Metabolomics Profiling as a New Prediction Tool.

Nuclear magnetic resonance (NMR) metabolomics profiling was evaluated as a new tool in sensory assessment of protein hydrolysates. Hydrolysates were produced on the basis of different raw materials (cod, salmon, and chicken), enzymes (Food Pro PNL and Bromelain), and hydrolysis time (10 and 50 min). The influence of raw material and hydrolysis parameters on sensory attributes was determined by traditional descriptive sensory analysis and 1H NMR spectroscopy. The raw material had a major influence on the attribute intensity and metabolite variation, followed by enzyme and hydrolysis time. However, the formation of bitter taste was not affected by the raw material. Partial least-squares regression (PLSR) on 1H NMR and sensory data provided good models (Q2 = 0.55-0.89) for 11 of the 17 evaluated attributes, including bitterness. Significant metabolite-attribute associations were identified. The study confirms the potential prediction of the sensory properties of protein hydrolysates from cod, salmon, and chicken based on 1H NMR metabolomics profiling.