Enzymes in fish processing - Enzymes in Food Technology - page 213

Table 10.1 Proximate composition of black tiger shrimp shell and carotenoprotein recovered with or
without bluefish trypsin (reprinted from Ref. [12]).

Carotenoprotein a

Compositions (% dry
weight basis) Shrimp shell Control Bluefish trypsin-aided

Crude protein 30.88 ± 0.76 59.95 ± 0.02 70.20 ± 0.11

Crude fat 3.93 ± 0.79 14.91 ± 0.15 19.76 ± 0.25

Ash 29.98 ± 0.75 17.89 ± 1.12 6.57 ± 0.18

Chitin 32.89 ± 1.55 5.40 ± 0.01 1.50 ± 0.10

a Values are mean

± standard deviation from triplicate determinations.

10.2.1.2 Fish sauce

Fish sauce is a traditional fermented fish product, which is used as an important source of
protein in Southeast Asia. Fish sauce is a clear brown liquid with a salty taste and mild fishy
flavour. The product is basically made from a mixture of fish and salt with a weight ratio
of 3:1. This mixture is allowed to ferment for more than 6 months at 30-35 ◦ C for complete
hydrolysis and flavour development. 15 During fermentation, endogenous enzymes slowly
degrade the fish tissue in the presence of 20-30% salt to form a clear liquid with a high
content of free amino acids and excellent flavour. The fermentation, which proceeds until
the desired product is obtained, is time consuming, requires a large storage capacity and is
therefore costly. To reduce this capital investment, it is desirable to accelerate the fermentation
process. Addition of exogenous proteases to the fermentation can accelerate the process.
However, flavour characteristics of the finished product are normally inferior to the traditional
product. Plant enzymes were the first to be used. Papain from unripe papaya, bromelain
from pineapple stems and ficin from figs have all been used. These enzymes are cysteine
proteases, most active under weak acid conditions. Fish sauce recovery was obtained after 2-3
weeks of the fermentation process. Best results were obtained using bromelain preparations,
but the characteristic flavour of the finished product was inferior to the traditional one.
This accelerated method is used today in commercial fish sauce production in Thailand. 16
The enzymes recovered from fish have also been successfully used as seafood processing
aids including the acceleration of fish sauce fermentation. Chaveesuk et al . 17 reported that
supplementation with trypsin and chymotrypsin significantly increased protein hydrolysis
of fish sauce. Fish sauce prepared from herring with enzyme supplementation contained
significantly more total nitrogen, soluble protein, free amino acid content and total amino
acid content, compared to fish sauce without added enzyme. 17 By supplementing minced
capelin with 5-10% enzyme-rich cod pyloric ceca, a good recovery of fish sauce protein
(60%) was obtained after 6 months of storage. 18 Additionally, Klomklao et al . 15 reported that
fish sauce prepared from sardine with spleen supplementation contained greater contents of
total nitrogen (see Fig. 10.1), amino nitrogen, formaldehyde nitrogen and ammonia nitrogen
than did those without spleen addition throughout the fermentation. Therefore, the addition
of spleen can accelerate the liquefaction of sardine for fish sauce production.

10.2.1.3 Seafood flavouring

Seafood flavours are in high demand for use in products like artificial crab and fish sausage.
Proteolytic enzymes can aid the extraction of flavour compounds from shells and other