Barbara A. Rasco

Fish Protein Hydrolysates: Production, Biochemical, and Functional Properties

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.

Chemical composition and protein digestibility of poultry by-product meals for salmonid diets

Abstract Poultry by-product meal (PBM) is a potential substitute for a portion of the fish meal typically used in salmonid feeds. The nutritional value of commercial PBM as a fish meal replacement will depend primarily upon the quality and quantity of protein in a particular PBM batch. The purposes of this study were to quantitate the chemical variability in samples of PBM obtained from several manufacturers in North America, and to determine the digestibility of PBM protein by salmonids using one in vivo and three in vitro methods. The range in dry weight proximate composition among PBM samples was 55–74% for protein, 10–19% for lipid, and 11–23% for ash. Of the three in vitro methods for predicting in vivo protein digestibility, a method using trout pyloric ceca enzymes was the most sensitive and was more closely correlated to in vivo results than the other in vitro methods examined. We found significant differences in chemical composition and protein digestibility of PBM samples obtained from different manufacturers, illustrating the range of protein quality in PBM products that fish feed manufacturers will encounter in the marketplace.

Kinetics of the hydrolysis of Atlantic salmon (Salmo salar) muscle proteins by alkaline proteases and a visceral serine protease mixture

Abstract The hydrolytic efficiency of an extract of serine proteases from cultured Atlantic salmon ( Salmo salar ) pyloric caeca and four commercially available alkaline proteases (Alcalase 2.4L, Flavourzyme 1000L, Corolase PN-L and 7089) on salmon muscle mince were compared (pH 7.5, T =40°C) at the same activity level based upon Azocoll results. Alcalase 2.4L had the highest activity per g on the Azocoll substrate compared with the other enzymes. When the enzymes were added to the salmon muscle system at the same Azocoll activity level Corolase 7089 hydrolyzed the salmon muscle protein most efficiently reaching 14.4% degree of hydrolysis (%DH) within 180 min. The pyloric caeca extract (PCE) was also highly efficient (14.1%DH), followed by Flavourzyme 1000L (7.5%DH), Corolase PN-L (6.7%DH) and Alcalase 2.4L (5.6%DH) under the same reaction conditions. The reaction kinetics for each enzyme preparation was determined at different Azocoll activity units to evaluate cost effectiveness of using each enzyme in a commercial process. Alcalase 2.4L was the most cost-efficient.

Estimation of protein digestibility—II. In vitro assay of protein in salmonid feeds

Abstract The in vitro digestibility of protein in various salmonid feeds was determined by pH-stat using enzyme fractions from trout pyloric ceca. Data were compared with in vivo digestibility and growth of fish by linear regression analysis. Results indicated that there were good agreements between the degree of hydrolysis of most feed samples and growth of fish. The pH-stat method is not suited for feed samples that have been partially hydrolyzed during their preparation.

Preparation and nutrient analyses of lactic acid bacterial ensiled salmon viscera

Abstract The objective of this study was to define a procedure for converting salmon viscera into a co-dried product that could evetually be the major protein ingredient in dry salmonid feeds. A lactic acid bacteria fermented silage, and for comparative purposes, a sulfuric acid silage were prepared from salmon viscera ( Oncorhynchus nerka and Oncorhynchus gorbuscha ). Both ensiled products were separately co-dried with poultry by-product meal in a final ratio of 1:1 ( w/w ) on a dry weight basis. Nitrogen levels of the co-dried products were 9 to 1 1%, sufficiently high to be the main protein source in dry feeds for salmonids. Methionine was the limiting amino acid in the co-dried products. Protein fractionation by size exclusion chromatography of samples obtained on the first and fourteenth day of ensilage showed that proteins were hydrolyzed to low molecular weight proteins, peptides, and amino acids. The co-dried products had low numbers of aerobic bacteria and low water activity, which would enhance storage stability. Formation of high levels of thiobarbituric acid reactive substances in freeze-dried silage was inhibited by the addition of 0.025% ( w/w ) ethoxyquin to the silage prior to drying.

Application of immunochemical assays to food analysis

Immunochemical assays are powerful bioanalytical techniques with application to several areas in food science, including food analysis, microbiology, nutrition, food safety, food quality, and process control. In principle, immunochemical techniques can be applied to the analysis of any compound, with only one specific antibody needed that can be obtained either from laboratory animals or, when available, from commercial sources. A well-designed immunochemical assay can detect targeted compounds at levels as low as 10(-12) M. Immunochemical techniques require little or no sample pretreatment, making these analytical procedures relatively rapid. The initial cost of developing an immunoanalytical assay may be high, but when the procedure is well established, the cost per test is often a fraction of that for other analytical methods. For these reasons, immunoanalytical assays provide an attractive alternative for the food analyst who requires either inexpensive qualitative screening tests or reliable quantitative methods with a high degree of sensitivity. This review concentrates on the use of enzyme immunoassay to address analytical problems in food chemistry and the analysis of various food components.

Parvalbumins in fish and their role as food allergens: A review

(1993). Parvalbumins in fish and their role as food allergens: A review. Reviews in Fisheries Science: Vol. 1, No. 1, pp. 1-26.

Iron, calcium, zinc, and phytic acid content of yeast-raised breads containing distillers' grains and other fiber ingredients

Abstract A comparison was made between the total and soluble iron, calcium, zinc, and phytic acid content of yeast raised breads, each containing approximately 13% total dietary fiber (TDF, as is basis) as either white wheat bran, white wheat distillers grains, barley fiber (brewers spent grains), soy fiber, or oat fiber. Substitution level of the fiber ingredients into the breads varied from 12 to 23% flour replacement (w/w) depending upon the TDF content of the fiber ingredient. The phytic acid content was highest in the wheat bran and oat fiber breads (24 mg/100g and 27 mg/100g, respectively). When formulated on an equal TDF basis, the level of soluble mineral in the fiber ingredient was not predictive of the level of soluble mineral in the bread. The highest amount of soluble calcium was found in the control and white wheat distillers grain breads, 167 and 146 μg/g, respectively. The highest amount of soluble iron was found in the soy fiber bread (31.6 μg/g) and the greatest amount of soluble zinc (5.3 μg/g) was found in the wheat bran bread.