Asbjørn Gildberg

Fish silage: A review

Based on a review of various production principles of fish silage, this paper discusses the prospects of introduction of this method, as an alternative to fish meal, to utilize low value fish and waste products, particularly in developing countries. The paper covers the biochemistry, microbiology, and nutritional aspects of fish silage, as well as production technology and economy.

A new process for advanced utilisation of shrimp waste

Abstract A high quality chitosan for application in cosmetics can be produced from the processing waste of Northern shrimp ( Pandalus borealis ). A major fraction of the shrimp waste is protein tissues, which are normally wasted during conventional chitosan preparation. The present work shows that the shrimp waste proteins can be hydrolysed by a commercially available protease (Alcalase) and recovered as a protein hydrolysate with a high content of essential amino acids, before the scales are processed to chitosan. The Alcalase treatment had no adverse effect on either yield or quality of the chitosan. By this new method the total recovery of Kjeldahl nitrogen was 68.5% as compared with only 12.8% by the conventional method. In addition, a concentrate of astaxanthin was recovered in the sediment after centrifugation of the crude protein hydrolysate. This concentrate may be a valuable supplement in the feed to salmonid fishes.

Aspartic proteinases in fishes and aquatic invertebrates

1. The literature on molecular properties and physiological role of aspartic proteinases in fishes and aquatic invertebrates has been reviewed. 2. Pepsins have not been detected in invertebrates, and apparently cathepsin D, as well as other cathepsins, act both as digestive and lysosomal enzymes in many of these animals. The molecular properties of invertebrate cathepsin D correspond with cathepsin D in fishes and mammalians. 3. Fishes with a true stomach have pepsinogen secretion. Fish pepsins have higher pH optimum and are less stable in strong acid conditions than mammalian pepsins. They are very efficient at low temperatures, but less thermostable than mammalian pepsins. 4. Many fishes have two significantly different pepsins: Pepsin I and Pepsin II, which digest haemoglobin at a maximal rate in the pH ranges 3-4 and 2-3 respectively. Usually the pI of Pepsin I is in the range 6.5-7, whereas pI of Pepsin II is about 4. 5. Fish Pepsin I and cathepsin D have very similar molecular properties, and a hypothesis proposing that cathepsin D is the ancestor enzyme of aspartic proteinases in higher animals is presented.

Isolation of acid peptide fractions from a fish protein hydrolysate with strong stimulatory effect on atlantic salmon (Salmo salar) head kidney leucocytes

Abstract Medium size (3000 d > Mw > 500 d) peptides from a hydrolysate of emptied stomachs from Atlantic cod (Gadus morhua) were fractionated on an S-Sepharose cation exchange chromatography column. Four distinctly separated acid peptide fractions were used in in vitro stimulatory experiments with head kidney leucocytes from Atlantic salmon (Salmo salar). All four acid peptide fractions promoted strongly elevated oxidative burst reactions in the leucocytes after 2 and 7 days of incubation at concentrations from 1 to 25 μg/ml. The stimulation was equally good, and in most cases better than the stimulation achieved with similar concentrations of lipopolysaccharides from the fish pathogen Aeromonas salmonicida. Visual inspection and pictures of peptide stimulated cells showed strongly enhanced vacuolisation and formation of long stretched out pseudopodes after 7 days of incubation. Acid peptide fractions from fish protein hydrolysate may be useful as adjuvants in fish vaccine and as an immune stimulant in fish feed.

Utilisation of cod backbone by biochemical fractionation

The backbone fraction obtained from industrial processing of Atlantic cod (Gadus morhua) yields about 15% of the whole fish weight. Due to a high content of muscle and bone proteins, it is a valuable raw material for further processing. In the present work minced backbones were subjected to gentle hydrolysis by proteinases to solubilize muscle proteins before the pure bone fraction was heat extracted to recover gelatine and a solid residual fraction containing protein and calcium. Five enzyme preparations were compared: the bacterial enzymes Alcalase, Neutrase and Protamex and preparations of pig and cod trypsins. Best recoveries of protein hydrolysates were obtained with the bacterial enzymes, but these hydrolysates were more bitter than the hydrolysates obtained by tryptic digestion. The gelatine extracted had relatively low molecular weight and may be suitable for technical applications or as a neutraceutical. Apparently the solid residual fraction was mainly collagenous structures containing little calcium.

Catalytic properties and chemical composition of pepsins from Atlantic cod (Gadus morhua)

1. Three pepsins were purified from the gastric mucosa of Atlantic cod (Gadus morhua). 2. The enzymes, called Pepsin I and Pepsin IIa and b, had isoelectric points 6.9, 4.0 and 4.1, respectively, and digested hemoglobin at a maximal rate at a pH of approximately 3. 3. They resembled bovine cathepsin D in being unable to digest the mammalian pepsin substrate N-acetyl-L-phenylalanyl-3,5-diiodo-L-tyrosine. 4. Specificity constants (kcat/Km) for the cod pepsins were lower than for porcine pepsin, and they expressed higher substrate affinity and physiological efficiency at pH 3.5 than at pH 2. 5. The cod pepsins are glycoproteins, and their amino acid composition resembles that of porcine cathepsin D more than that of porcine pepsin. 6. The N-terminal sequence of Atlantic cod pepsins is substantially different from that of porcine pepsin. This indicates a significant evolutionary gap between fish and mammalian pepsins.

Purification and characterization of pancreatic elastase from Atlantic cod (Gadus morhua)

1. A pancreatic elastase from Atlantic cod (Gadus morhua) has been purified and characterized. 2. The enzyme is a very basic protein with an approximate mol. wt of 28,000. 3. The cod elastase has higher elastin specificity than porcine elastase, and it is inhibited by soybean trypsin inhibitor, which has no effect on porcine elastase. 4. The cod elastase expresses a higher turnover number (kcat) and catalytic efficiency (kcat/Km) than porcine elastase, but it is less thermostable.

CHITOOLIGOSACCHARIDES STIMULATE ATLANTIC SALMON, SALMO SALAR L., HEAD KIDNEY LEUKOCYTES TO ENHANCED SUPEROXIDE ANION PRODUCTION IN VITRO

Chitosans and chitooligosaccharides stimulated Atlantic salmon, Salmo salar L., head kidney leukocytes in vitro to produce elevated levels of superoxide anion. Both soluble and insoluble chitooligosaccharides were stimulatory 2 and 7 days after addition. Protein-chitooligosaccharide conjugates were also stimulatory in vitro both at 2 and 7 days after addition. Deacetylation seemed to be of little importance for the stimulatory capacity. High concentrations of the 80% deacetylated chitosan/chitooligosaccharides were toxic to the leukocytes as judged by reduced reduction of nitroblue tetrazolium and morphology.

Solubility and enzymatic solubilization of muscle and skin of capelin (Mallotus villosus) at different pH and temperature

Abstract 1. 1. The breaking strength of capelin skin increases in the pH range from 6 to 10. 2. 2. Digestive enzymes in capelin degrade protein in the native skin at pH below 6, but not at neutral or alkaline conditions. 3. 3. The digestive enzymes release proteins with high molecular weight when acting on muscle tissue at neutral pH. 4. 4. Adjusting the pH to 4 facilitates a chemical/enzymatic dissection of skin and myocommata and simultaneously minimizes solubilization of muscle protein.

Characteristics and Composition of Pepsins from Atlantic Cod

Three pepsins have been purified from the gastric mucosa of Atlantic cod (Gadus morhua). The enzymes were denominated Pepsin I and Pepsin IIa and IIb. Pepsin I is a 35.5 kDa neutral protein (pI 6.9), whereas Pepsin IIa and IIb are 34 kDa acidic proteins (pI 4.0 and 4.1, respectively). Apparently, all three pepsins are glycosylated. The cod pepsins resemble bovine cathepsin D in being unable to hydrolyze N-acetyl-L-Phenylalanyl-3,5-diiodo-L-Tyrosine, a dipeptide used as substrate for mammalian pepsins. With hemoglobin as a substrate, they expressed lower catalytic efficiency than porcine pepsin. The apparent substrate affinity of the cod pepsins was substantially higher at pH 3.5 than at pH 2. N-terminal sequence analyses of cod pepsins indicate a significant evolutionary gap between fish and mammalian pepsins. A comparative evaluation of the results obtained indicate that fish pepsins may constitute an intermediate stage in a genetic evolution from cathepsin D to mammalian pepsin.