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Role of chemistry and biotechnology in value-added utilization of shellfish processing discards.

With over a million tonnes of shellfish waste being discarded annually, this potential resource of value-added proteins, chitin, and minerals must be fully utilized

The seafood processing industry produces large amounts of shellwaste which have traditionally been hauled into the ocean or dumped in-land [1]. However, environmental restrictions and a better understanding of potential value of processing discards for a variety of applications has resulted in efforts to find uses for these materials. Coupled with the above problem, there has been a growing interest in natural ingredients which are readily available from shellfish discards.

Processing by-products from shellfish are made up primarily of protein residues from body sections such as heads and carpace, as well as minerals and chitin which constitute the exoskeleton of crab, shrimp and lobster [2]. In addition, it is possible to recover minor components such as carotenoid pigments, flavourants and enzymes from the waste. While flavourants can be readily recovered from the cook water or the proteinaceous materials, enzymes such as chitinase, alkaline phosphatase, hyaluronidase and [Beta]-N-acetyl glucosaminidase may be isolated from the thaw water of frozen raw shrimps [3], and potentially from other shellfish species.

Chitin and chitosan

Chitin is a natural biopolymer with 2-deoxy-2-acetaminoglucose monomers linked together via a [Beta]-1,4 linkage. Chitosan is referred to the deacetylated (to different degrees) form of chitin [4]. Manufacturing of chitosan may be carried out by boiling of chitin in concentrated sodium hydroxide solutions or incubating at 25-30 [degrees] C for a period of 1-30 days in 30-65% NaOH solutions [5].

The chemical structures of chitin and its monomer N-acetyl-D-glucosamine as well as chitosan are shown in Figure 1. Chemically, chitin is analogous to cellulose except that the 2-hydroxy substituent in the glucose unit of cellulose is replaced by a 2-acetylamino group. Meanwhile, chitosan possesses varying levels of free amino groups which are capable of strong H-bonding and ionic interaction.

The global annual production of crustacean discards, on a dry weight basis, is estimated at 1.44 million metric tons [6]. The content of chitin in shellfish discards is between 20 and 50% of the total dry weight. Thus a minimum of 200,000 metric tons of chitin could potentially become available. Currently only a few thousand tons of chitin are produced annually. Table 1 summarizes the content of chitin in shrimp and different sections of crab processing discards. Other major components of the waste are proteins and minerals.
Table 1. The content of chitin in shrimp and crab processing

Species (Segment) Chitin, % dry weight

Shrimp (Head and Carapace) 17.0 [+ or -] 0.3
Crab (Backs) 22.3 [+ or -] 0.5
Crab (Claws) 23.7 [+ or -] 0.3
Crab (Legs) 32.3 [+ or -] 0.1
Crab (Shoulders) 26.9 [+ or -] 0.1
Crab (Tips) 27.9 [+ or -] 0.2
Table 2. Some applications of chitin and its derivatives.

Area of Application Examples

Food - Clarification of wine and juice
 - Dietary fibre and edible films
 - Protein flocculation
 - Removal of tannins
 - Chromatography

Agriculture - Coating for delayed ripening of fruits
 - Seed coating
 - Nutrient control release
 - Nematode treating
 - Animal feed

Water Treatment - Food processing
 - Potable drinking water
 - Removal of dyes
 - Removal of metals, pesticides and PCBs
 - Sewage treatment

Additive - Inhibition of oxidation
 - Thickener
 - Stabilizer
 - Texture modifier
 - Slow-release additive support

Biomedical - Hypocholesterolemic effect
 - Wound care
 - Eye bandage
 - Drug delivery
 - Biomaterials
 - Dental applications

Cosmetics - Moisturizers
 - Thickener in low pH products
 - Film formers
 - Emulsifiers
 - Anti static
 - Hair and skin care

Biotechnology - Enzyme immobilization
 - Cell immobilization
 - Encapsulation
 - Filter aid
 - Protein recovery

Textile/Paper - Coatings
 - Dyeability
 - Fibres
 - Wet strength
 - Retention aid

The process by which chitin is produced may be summarized in the flowsheet of Figure 2. Different unit operations involved are grinding of the shells to a uniform reduced size followed by the removal of proteins and minerals. The latter two steps may be easily interchanged [7]. However, in commercial practice, generally proteins are first extracted by using a base. The demineralization is achieved using a dilute hydrochloric acid solution. Although the resultant calcium chloride may be used in the pulp and paper manufacturing, the dehydration process required for its recovery is commercially unattractive. Another potential applications of calcium chloride as a 30% solution is as a dust control agent for spraying on mud roads. It should be noted that minerals and chitin in dehydrated, deproteinized shellwaste are present in nearly equal amounts.

The deproteinized and demineralized shells contain mainly chitin with less than 10% moisture and 2% ash. The degree of deacetylation may vary between 10 and 20%. In order to assure high quality of chitin, it is necessary to acquire fresh shells and to adequately control reaction time and temperature as well as the concentration of reagents involved. Highest molecular weight chitin with lowest ash content obtains a better market value since the quality of chitin derivates, such as chitosan, is primarily dictated by the quality of the starting material.

Chitin is insoluble in almost every common organic solvent and in acidic, basic and neutral aqueous solutions. However, chitosan is insoluble in dilute adds and in aqueous solutions. Production of chitosan follows simple unit operations of deacetylation, washing and drying [ILLUSTRATION FOR FIGURE 2 OMITTED]. The quality characteristics of chitosans depend, to a large extent, on the degree of deacetylation of the macromolecule. The crude chitosan may be further purified by dissolution in a suitable acid solution followed by filtration and precipitation by pH adjustment. Chitosan derivatives with different functionalities may be prepared in order to address specific needs of the under industries.
Table 3. Distribution (% of total) of xanthophylls in shrimp and
crab processing discards.

Carotenoid Shrimp Crab(a)

Astaxanthin 3.95 [+ or -] 0.19 21.16 [+ or -] 1.15
Astaxanthin monoester 19.72 [+ or -] 0.19 5.11 [+ or -] 0.23
Astaxanthin diester 74.29 [+ or -] 0.38 56.57 [+ or -] 1.60
Astacene Nil 3.26 [+ or -] 0.47
Leutein Nil 8.24 [+ or -] 0.30
Zeaxanthin 0.62 [+ or -] 0.05 4.64 [+ or -] 0.76
Unidentified Nil 0.22 [+ or -] 0.05

a Soft-shelled crab shells contained 2.66% canthaxanthin. Shrimp
shells contained 14.7 mg xanthophylls/100 g and soft- and
hard-shelled crab shells contained 11.9-13.9 mg xanthophylls/100
g dried matters.

Table 2 summarizes some of the numerous applications of chitinous materials in different areas of food, agriculture, cosmetics, textile, paper, biomedical, biotechnology, water treatment and removal of radioactive and poisonous metals [8,9,10,11,12,13]. Although different applications of chitin derivatives have received considerable attention, the market realities with respect to competition from alternative materials and supplies may prove challenging.

A novel approach for utilization of chitinous materials was recently examined in our laboratories. N,O-Carboxymethylchitosan (NOCC) was prepared in a laboratory scale or obtained from Novo Chem. Inc. (Halifax, NS). It was noted that NOCC and its lactate, acetate and pyrrolidine carboxylate salts were able to prevent cooked meat flavour deterioration over a nine-day storage period at refrigerated temperatures. The mean inhibitory effect of NOCC and its aformational derivatives at 0.05-0.3% addition level in the formation of oxidative products as reflected in 2-thiobarbituric acid reactive substances was 46.7, 69.9, 43.4 and 66.3%, respectively. The mechanism by which this inhibition takes place is thought to be related to chelation of free iron which is released from hemoproteins of meat during heat processing. This would in turn inhibit the catalytic activity of iron ions.


The compound N-acetylglucosamine (NAG) is the monomer of chitin. It has been reported that NAG has anti-inflammatory effect and may possess interesting characteristics. Although chemical preparation of NAG is feasible, a commercially attractive process for its production would be much desirable. Therefore, consideration of reaction conditions under high pressure may prove beneficial. Use of NAG in different synthetic applications may also be of interest to biochemists.

Carotenoids and carotenoproteins

A minor, but important class of compounds in crustacean processing discards is carotenoids. Carotenoids in seafoods are oxygenated forms of [Beta]-carotene referred to as xanthophylls. They may be extracted from shellfish using appropriate solvents. Carotenoproteins from processing discards of shellfish have also been isolated using enzyme-assisted separation techniques [14]. Figure 3 illustrates the chemical nature of some of the important xanthophylls found in shellfish processing discards. A close scrutiny of the results summarized in Table 3 indicates that Astaxanthin diester is the major carotenoid component found in the processing discards of shrimp and crab [4]. Unesterified astaxanthin and astaxanthin monoester were present in smaller amounts, followed by astacence, leutein and zeaxanthin.

Carotenoids from shellfish discards may be extracted into a vegetable or marine oil at a ratio of 1:2 (v/w) at 60 [degrees] C for 30 min [7]. The oil may be reused to enrich it with carotenoids. Such oils may be used in the formulation of feed for salmonid fish species. Recent studies have indicated that extracted carotenoids are assimilated in the flesh and skin of Arctic char (Salvelinus alpinus) without undergoing any major chemical changes [15,16,17,18].
Table 4. Essential amino acids of shrimp and crab shellwaste
proteins (g/100g protein).

Amino acid Shrimp Crab

Arginine 6.13 [+ or -] 0.07 6.66 [+ or -] 0.02

Histidine 2.24 [+ or -] 0.09 3.58 [+ or -] 0.01

Isoleucine 5.78 [+ or -] 0.13 2.67 [+ or -] 0.02

Leucine 7.01 [+ or -] 0.02 5.14 [+ or -] 0.02

Lysine 6.58 [+ or -] 0.07 2.51 [+ or -] 0.07

Methionine 2.41 [+ or -] 0.08 1.93 [+ or -] 0.00

Phenylalanine 5.13 [+ or -] 0.07 5.98 [+ or -] 0.01

Threonine 4.14 [+ or -] 0.20 4.74 [+ or -] 0.02

Tryptophan 1.19 [+ or -] 0.07 0.78 [+ or -] 0.01

Valine 5.95 [+ or -] 0.06 7.07 [+ or -] 0.10
Table 5. Amino acid composition of water extractable flavourants
from shrimp shell.

Amino acid flavourant

Alanine 6.30 [+ or -] 0.04
Arginine 6.54 [+ or -] 0.04
Aspartic Acid + Asparagine 6.61 [+ or -] 0.03
Cysteine 0.55 [+ or -] 0.01
Glutamic Acid + Glutamine 10.05 [+ or -] 0.12
Glycine 13.91 [+ or -] 0.02
Histidine 1.73 [+ or -] 0.02
Hydroxyproline 0.25 [+ or -] 0.03
Isoleucine 3.16 [+ or -] 0.01
Leucine 4.84 [+ or -] 0.01
Lysine 4.57 [+ or -] 0.04
Methionine 0.55 [+ or -] 0.01
Phenylalanine 2.85 [+ or -] 0.01
Proline 7.76 [+ or -] 0.07
Serine 3.89 [+ or -] 0.09
Taurine 3.99 [+ or -] 0.11
Threonine 3.29 [+ or -] 0.01
Tryptophan 0.44 [+ or -] 0.01
Tyrosine 1.91 [+ or -] 0.02
Valine 4.43 [+ or -] 0.05

* Adapted from reference [1].

Proteins and flavourants

Proteins in shellwaste may be isolated by extraction into a 5% hot sodium or potassium hydroxide [19]. The resultant proteins generally have an amino acid composition similar to those in the starting material (see Table 4); however, care must be exercised to prevent the formation of lysinoalanine in the resultant product. It is also possible to extract the flavourants from cook water of crab or from processing discards by extraction into hot water prior to deproteinization (Table 5). The resultant material may then be subjected to ultrafiltration/concentration and dehydration.

Enzyme-assisted proteolysis may be used to extract proteins with flavour-enhancing effects from shellfish processing discards. In all cases the products obtained included carotenoid and/or carotenoproteins. Potential use of shellfish protein hydrolyzates in surimi-products as protein fortifying agents and to enhance moisture retention in products and as flavour enhancers as well as in aquaculture feed formulations is being examined in our laboratories.


Most of the catch of shrimp (Pandalus borealis) is frozen as raw, whole blocks. At the processing plants, the frozen blocks are thawed by circulating spraying water. The resultant waste water contains a number of digestive enzymes. The waste water may be collected and clarified using ferric chloride and concentrated by ultra-filtration employing a molecular weight cut-off of 10,000 Daltons. A simplified scheme for production of enzymes from shrimp that water is given in Figure 4. The enzymes hyaluronidase, [Beta]-N-acetyl glucosaminidase, chitinase and alkaline phosphatase are recovered in the retentate with a yield of 65-100% and with 1786% increase in specific activities [3].


As the supply of raw material from aquatic resources is shrinking and trends towards production of acquacultured species develop, full utilization of marine processing by-products and underutilized species becomes more urgent. Coupled with environmental restrictions, efforts for value-added utilization of natural ingredients from shellfish by-products is expected to proceed at a faster pace in the coming year.


Financial support from the Department of Fisheries and Oceans and the Natural Sciences and Engineering Research Council of Canada is acknowledged.


1. Shahidi, F. Seafood processing by-products. In Seafoods: Chemistry, Processing Technology and Quality. F. Shahidi and J.R. Botta (Eds). Blackie Academic and Professional, Glasgow, pp.320-334, 1994.

2. Shahidi, F. Protein from seafood processing discards. In Seafood Proteins. Z.E. Sikorski, B.S. Pan and F. Shahidi (Eds). Chapman & Hall, New York, pp.171-193, 1994.

3. Olsen, R.L., Johansen, A. and Myrnes, B. Recovery of enzymes from shrimp waste. Process Biochem. 25:67-68, 1990.

4. Shahidi, F. and Synowiecki, J. Quality and compositional characteristics of Newfoundland shellfish processing discards. In Advance in Chitin and Chitosan. C.J. Brine, P.A. Sanford and J.P. Zikakis (Eds). Elsevier Applied Science, London and New York, pp.617-626, 1992.

5. Alimuniar, A. and Zainuddin, R. An economical technique of producing chitosan. In Advances in Chitin and Chitosan. C.J. Beine, P.A. Sanford and J.P. Zikakis (Eds). Elsevier Applied Science, London and New York, pp.627-632, 1992.

6. Skaugrud, [Phi]. and Sargent, G. Chitin and chitosan: Crustacean biopolymers with potential. In Proceedings of the International By-Products Conference. Anchorage, Alaska, pp.61-69, 1990.

7. Shahidi, F. and Synowiecki, J. Isolation and characterization of nutrients and value-added products from snow crab (Chinoecetes opilio) and shrimp (Pandalus borealis) processing discards. J. Agric. Food Chem. 39: 1527-1532, 1991.

8. Brzeski, M.J. Chitin and chitosan - putting waste to good use. INFOFISH International 5: 31-33, 1987.

9. Knorr, D. Use of chitinous polymers in food - A challenge for food research and development. Food Technol. 38(1):85-97, 1984.

10. Knorr, D. Recovery and utilization of chitin and chitosan in food processing waste management. Food Technol. 45(1):114-122, 1991.

11. Michihiro, S. Watanabe, S., Kishi, A., Izume, M. and Ohtakara, A. Hypocholesterolemic action of chitosans with different viscosity in rats. Lipids 23:187-191, 1988.

12. No, H.K. and Meyers, S.P. Crawfish chitosan as a coagulation recovery of organic compounds from seafood processing streams. J. Agric. Food Chem. 37:580-583, 1989.

13. Pandya, Y. and Knorr, D. Diffusion characteristics and properties of chitosan coacervate capsules. Process Biochem. 26:25-81, 1991.

14. Simpson, B.K. and Haard, N.F. The use of proteolytic enzymes to extract carotenoproteins from shrimp wastes. J. Applied Biochem. 7:212-222, 1985.

15. Shahidi, F., Synowiecki, J. and Penney, R.W. Pigments in salmonid fish meat. Meat Focus International 1:319-320, 1992.

16. Shahidi, F., Synowiecki, J. and Penney, R.W. Pigmentation of Arctic char (Salvelinus alpinus) by dietary carotenoid. J. Aquatic Food Prod. Technol. 2:99-115, 1993.

17. Shahidi, F., Synowiecki, J. and Penney, R.W. Chemical nature of xanthophylls in flesh and skin of cultured Arctic char (Salvelinus alpinus, L.). Food Chem. 51:1-4, 1994.

18. Synowiecki, J., Shahidi, F. and Penney, R.W. Nutrient composition of meat and uptake of carotenoids by Arctic char (Salvelinus alpinus). J. Aquatic Food Prod. Technol. 2(3):37-59, 1993.

19. Shahidi, F., Synowiecki, J. and Naczk, M. Utilization of shellfish processing discards. In Seafood Science and Technology. E.G. Bligh (Ed.) Fishing New Books. Oxford, pp.300-304, 1992.

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Fereidoon Shahidi, MCIC, is a Professor at the Department of Biochemistry, Memorial University of Newfoundland, and is President and CEO of PA Pure Additions, Inc., both in St. John's, NF.
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Title Annotation:shellfish waste
Author:Shahidi, Fereidoon
Publication:Canadian Chemical News
Date:Sep 1, 1995
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