Considerable amounts of fish processing byproducts are discarded each year. By developing enzyme technologies for protein recovery and modification, production of a broad spectrum of food ingredients and industrial products may be possible. Hydrolyzed vegetable and milk proteins are widely used food ingredients. There are few hydrolyzed fish protein foods with the exception of East Asian condiments and sauces. This review describes various manufacturing techniques for fish protein hydrolysates using acid, base, endogenous enzymes, and added bacterial or digestive proteases. The chemical and biochemical characteristics of hydrolyzed fish proteins are discussed. In addition, functional properties of fish protein hydrolysates are described, including solubility, water-holding capacity, emulsification, and foam-forming ability. Possible applications of fish protein hydrolysates in food systems are provided, and comparison with other food protein hydrolysates where pertinent.

Fish Protein Hydrolysates: Production, Biochemical, and Functional Properties

Antioxidative activity and functional properties of protein hydrolysate of yellow stripe trevally (Selaroides leptolepis) as influenced by the degree of hydrolysis and enzyme type

Proteins play an important role as macromolecular surfactants in foam and emulsion-type food products. The functioning of proteins in these applications is determined by their structure and properties in the adsorbed layers at air-water and oil-water interfaces. In addition, because typical food proteins are mixtures of several protein components, interaction between these components in the adsorbed layer also impacts their ability as surfactants to stabilize dispersed systems. In this paper, recent progress in our understanding of the molecular mechanisms involved in the formation and stability of protein-stabilized foams and emulsions has been reviewed.

Protein Stabilization of Emulsions and Foams

Proteins are increasingly being utilized to perform functional roles in food formulations. Common food proteins possess good functional properties including solubility, gelation, emulsification and foaming. The functional properties of proteins are impaired near their pl (isoelectric point), as is the case in most acidic foods. Enzymatic modification of food proteins by controlled proteolysis can enhance their functional properties over a wide pH range, and other processing conditions. Choosing the right proteolytic enzyme, environmental conditions for hydrolysis and degree of hydrolysis is crucial for enhancing the functional properties of proteins. Understanding the molecular properties required for protein functionality and the development of strategies to achieve them are critical for developing and utilizing modified protein ingredients. Numerous reports on enhancing the functionality of food proteins by limited proteolysis have been published, some of which are reviewed in this article.

Enhancing the functionality of food proteins by enzymatic modification

No changes in actomyosin Ca 2+ -, Mg 2+ -, or Mg 2+ -Ca 2+ -ATPase activities were observed during iced storage of Pacific whiting fillets, but Mg 2+ -EGTA-ATPase increased with a loss of Ca 2+ -sensitivity. Surface hydrophobicity of actomyosin increased substantially within 2 days, but not total sulfhydryl (SH) content. During longer storage, the SH content decreased gradually, but surface hydrophobicity remained constant. Autolytic degradation products increased in fish muscle with storage time. Myosin heavy chain (MHC) was degraded by 45% within 8 days, but no noticeable difference was observed in actin. Results indicated that autolysis may be the main cause of physicochemical changes in Pacific whiting muscle proteins during iced storage.

Physicochemical changes in Pacific whiting muscle proteins during iced storage

Heat-denatured whey protein isolate was hydrolyzed with trypsin, α-chymotrypsin, Alcalase or Neutrase to 2.8, 4.3, 6.0 or 8.0% degree of hydrolysis. Hydrolysates were fractionated by ultrafiltration and freeze-dried. Protein content of retentates showed little variation but permeates differed with enzyme. Surface hydrophobicity increased with hydrolysis but was not linear except for α-chymotrypsin. Ultrafiltration increased solubility and the permeates and retentates had better solubility than hydrolysates. Retentates had higher emulsifying activity index than hydrolysates while permeates did not form stable emulsions. Permeates formed stable foams but hydrolysates and retentates showed poor foaming characteristics. Specificity of the enzyme, and degree of hydrolysis influenced the functional properties of the peptides. Fractions generated by trypsin, at all levels of hydrolysis generally had higher solubility, emulsifying properties and foaming properties. Permeates from Alcalase hydrolysis had the best foam capacity but low foam stability.

Functional properties of hydrolysates from proteolysis of heat-denatured whey protein isolate.

Vanilla ice cream with 8, 13 or 18% sucrose and 10, 14 or 18% butterfat was evaluated by descriptive analysis (DA) with 15 judges, instrumental texture measurements (ITM), and hedonic rating with 146 consumers. Increased sugar caused higher vanilla, almond, buttery, custard/eggy, sweetness, fatty, creamy, doughy and mouthcoating characteristics, and lower coolness, ice crystals, melt rate (ITM) and hardness (ITM). Increased fat caused higher buttery, custard/eggy and sweet flavor, fatty, creamy, doughy and mouthcoating texture, and lower color, ice crystals and melting rate (DA). Acceptability was positively related to the vanilla, creamy, fatty and milky characters, and negatively related to color, ice crystals and ITM hardness.

Sugar and Fat Effects on Sensory Properties of Ice Cream

Effect of sugar and fat on the acceptability of vanilla ice cream

Whey protein isolate was denatured at 85°C, pH 4.6 for 30 min to produce heat denatured whey protein isolate (HDWPI) which was hydrolyzed with trypsin, chymotrypsin, Alcalase or Neutrase to 2.8, 4.3, 6.0 or 8.0% degree of hydrolysis (DH). Analysis of freeze-dried fractions revealed a linear increase in primary amino groups, non-protein nitrogen and ash contents. Polyacrylamide gel electrophoresis showed that high and intermediate molecular weight peptides were converted to lower molecular weights with progress of hydrolysis. Differences in proteolysis patterns were observed with different enzymes. The time required to achieve equivalent hydrolysis at 1, 2, 3 or 4% enzyme/substrate ratio varied with the type of enzyme and DH.

Hydrolysates from Proteolysis of Heat-denatured Whey Proteins

AHSTRACT: Casein was hydrolyzed by trapsin to 5% degree of hydrolysis, and the hydrolysare was fractionated by ultrafiltration. While sereening for the best emulsifying properties, the retentate fraction was systematically fractionated by ammonium sulfate precipitation, ion exchange, and reverse-phase high-performance liquid chromatography (HPLC). Residue from 30% ammonium sulfate saturation yielded 3 fractions on anion exchange chromatography. Preparative reverse-phase HPLC was used to isolate 4 peptides with good emulsilying properties for characterization. Computational methods were used to complement amino acid sequencing, and the peptides were identified as origioating from α casein (f167-208), β-casein (f48-63), and (f129-84), A 4th peptide couid not be conclusively identified. Properties of the emulsifying peptides are discussed.

D. Panyam

Papers

Functional properties of hydrolysates from proteolysis of heat-denatured whey protein isolate.

Sugar and Fat Effects on Sensory Properties of Ice Cream

Effect of sugar and fat on the acceptability of vanilla ice cream

Hydrolysates from Proteolysis of Heat-denatured Whey Proteins

Emulsifying Peptides from the Tryptic Hydrolysis of Casein