Chemistry Reference
In-Depth Information
Exopeptidases, especially aminopeptidases, are ubiquitous, but less readily available as
commercial products, since many of them are intracellular or membrane bound. Based on
the nature of the catalytic site, proteinases are further classified into four categories: acid or
aspartate proteinases, serine proteinases, thiol or cysteine proteinases or metalloproteinases.
3
The enzymes in the different classes are differentiated by various criteria, such as the nature
of the groups in their catalytic sites, their substrate specificity, their response to inhibitors or
by their activity/stability under acid or alkaline conditions.
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10.2.1 Applications of proteases
Proteases are by far the most studied enzymes for industrial bioprocessing. For the fishery
industry, proteases are used as processing aids for many products. These include recovery of
pigment and flavouring compounds, production of fish protein hydrolyzates, viscosity
reduction, skin removal and roe processing.
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10.2.1.1
Carotenoprotein extraction
Various methods have been devised to recover carotenoid or carotenoprotein from crustacean
wastes as a potential source of red/orange pigments for use in feed of farmed fish and shellfish.
Extraction of shell waste with oil
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reduces ash and chitin levels and achieves a good recovery
of pigment. However, this method suffers the disadvantage of yielding a product devoid of
protein, thereby decreasing the stability of the carotenoid to oxidation and failing to recover
a valuable nutrient. Since about one-third of the dry matter in crustacean shell waste is
protein, an enzymatic process has been developed to extract and recover the protein along
with the carotenoid in its native carotenoprotein from crustacean waste. Proteolytic enzymes
were used to recover carotenoprotein from shrimp
8
and crab.
9
About 80% of the protein
and 90% of the astaxanthin pigment from shrimp processing waste can be recovered as an
aqueous dispersion after trypsin hydrolysis. Cano-Lopez
et al
.
10
reported that using Atlantic
cod trypsin from pyloric ceca in conjunction with a chelating agent (EDTA) in the extraction
medium increased the efficacy in recovering both protein and pigment from crustacean
wastes. This method has facilitated the recovery of as much as 80% of astaxanthin and
protein from shrimp processing wastes as carotenoprotein complex. Ya
et al
.
11
recovered
carotenoprotein from lobster waste by using trypsin from bovine pancreas. The product
obtained was found to contain higher protein and pigment content than those of untreated
lobster waste and was devoid of chitin and ash. Recently, Klomklao
et al
.
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also recovered
carotenoprotein from black tiger shrimp waste by using trypsin from bluefish pyloric ceca.
The product contained higher protein and pigment content than those of untreated black tiger
shrimp waste and had low contents of chitin and ash (see Table 10.1). A lower yield of protein
(60-70%) and pigment (35-50%) is recovered in the carotenoprotein fraction when protease
with broad specificity is used rather than trypsin. Chakrabarti
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isolated carotenoprotein from
tropical brown shrimp shell waste by enzymatic process including trypsin, papain and pepsin.
Trypsin yielded the maximum recovery of carotenoid (55%) when hydrolysis was conducted
for 4 h at room temperature. Pepsin and papain showed about 50% recovery during the
same period. The yield of protein paste isolated with trypsin was highest. Protein-associated
astaxanthin is more resistant to oxidation
8
and is deposited in the skin and flesh of rainbow
trout more efficiently
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than free pigment. Use of this process by industry is promising due
to a less costly source of trypsin than from the currently available process.
