A simple and effective method is suggested to improve the quality and shelf-life of commercial whole dried thelly prawns (Metapenaeus dobsoni). Treatment of whole prawns in 10% brine containing 0.1% citric acid for 20 min followed by drying in sun yield a product having good physical, chemical and organoleptic characteristics. Retardation of fungal incidence, reduction in total volatile nitrogen (TVBN) and improvement in flavour are some of the advantages of the treatment. The treated product has a shelf-life around 30 weeks compared to 20 weeks for untreated control and 7 weeks for commercial sample

Balachandran, K.K.

Joseph, A.C.

Prabhu, P.V.

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A. C. JOSEPH, K. K. BALACHANDRAN aid P. V. RABHU 
Central Institute of Fisheries Technology, Cochin - 682 029 
A simple and effective method is suggested to improve the quality and slaelflife of 
commercial whole dried thelly prawns (Metapenaeus dobsoni). Treatment of whole 
prawns in 10 % brine containing 0.1 % citric acid for 20 min followed by drying in sun 
yield a product having good physical, chemical and organoleptic characteristics. 
Retardation of fungal incidence, reduction in total volatile nitrogen (TV N) and impro-
vement in flavour are some of the advantages of the treatment. The treated product 
has a shelflife around 30 weeks compared to 20 weeks for untreated control and 7 weeks 
for commercial sample. 
Dry prawn pulp was a major item of export 
from India until mid fifties when it gave way 
to products processed employing modern 
technologies of freezing and canning. 
However, whole dried prawns, processed 
mostly out of small thelly (Metapenaeus 
dobsoni) remained a popular item of com-
merce, catering mainly to the interior markets 
within the country. The internal demand 
for the product is steadily increasing. 
The commercial whole dry prawn is not 
of satisfactory quality. The relatively high 
moisture accelerates the deterioration in 
physical, chemical and organoleptic quali-
ties during storage. Considering the volume 
of trade of this commodity and its steady 
increase it was felt necessary to work out a 
technique to improve its quality and shelf-
life. The principle of lowering water acti-
vity by the use of humectants like sodium 
chloride and the subsequent retardation of 
quality deterioration are made use of in this 
method. 
?Aerials and Methe s 
In the initial studies cleaned fresh thelly 
prawns (M. dobsoni) after treatment with 
salt solutions of different concentrations 
were dried in sun and compared its quality 
with control (untreated). Though the treated 
samples had better-shelf life and organole-
ptic qualities compared to those of the con-
trol its appearance was not appealing parti-
cularly because of bleaching of the natural  
colour of dried prawns. Attempts were 
made to rectify this problem by incorpora-
ting permitted chemicals in the salt solution 
used for the treatment. Of several trials 
made, one with 10 % sodium chloride and 
0.1 % citric acid in water was found more 
effective and this was employed in the subse-
quent studies. 
Fresh thelly prawns (M. dobsoni) of 
average count 1200/kg procured from market 
were used for further studies. The material 
was repeatedly washed with potable water 
to remove the adhering dirt. It was divided 
into two portions. One portion was dipped 
in a solution containing 10 % salt and 0.1 % 
citric acid in the ratio 1 :1 (w/v) in water for 
20 min. The other portion was dipped in 
potable water for the same period. Both 
the samples were then drained and dried in 
sun separately spreading over cemented 
floor for a total period of 7 h. They were 
allowed to cool and packed separately in 
200 gauge polythene bags and stored at 
ambient temperature. Samples were drawn 
at definite intervals and were analysed for 
physical, chemical and organoleptic chara-
cteristics after removing the head. A sample 
of commercial dry prawns of the same spe-
cies and almost of the same size grade pro-
cured from market was also similarly stored 
and analysed for the above characteristics. 
Moisture, ash and sodium chloride were 
determined according to A AC (1975). 
Total volatile basic nitrogen (TVBN) was 
Vol. 25, 1988 
3 I Its es 11Z (I Discuss io  
118 	 A. C. JOSEPH, K. K. BALACHANDRAN AND P. V. PRABHU 
determined by the method of Conway (1947). 
For assessing the organoleptic quality a 10 
point hedolic scale, 10 being very good; 0 
being bad and 4 being just unacceptable 
taking into consideration the changes in 
odour, texture and flavour of the samples 
fried in refined groundnut oil, was used 
(CIDA/FAO/CECAP, 1977). 
Chemical characteristics of commercial 
as well as experimental samples during 
storage are given in Table 1, and their phy-
sical observations and organoleptic score 
are given in Table 2. The initial moisture 
content of the commercial sample was very 
high compared to that of experimental sample. 
During storage it increased gradually absor-
bing the atmospheric moisture. The TVBN 
content of commercial sample increased 
sharply during storage probably due to 
rapid deterioration of the sample because 
of high moisture content and the accom-
panied bacterial as well as enzymatic degra-
dation. This was supported by the physical 
observations and organoleptic scores of the 
samples. The sample developed slight 
ammonical odour after 5 weeks' storage and 
intense ammonical odour and incidence of 
fungus after 7 weeks. Ash and sodium 
chloride contents of the commercial and 
untreated samples were more or less the same 
ie 12.4 & 11.17 and 1.72 & 1.63 % (DWB) 
respectively while treatment increased these 
values to 16.35 and 5.59 (DWB). 
The yields of whole dried prawns after 7 h 
drying were 26.5 % in the case of untreated 
sample and 28 % in the case of treated sample. 
The slight increase in the latter case was due 
to the gain in weight because of absorption 
of salt during the treatment. The moisture 
contents of both experimental samples were 
almost same after drying. During storage 
it increased gradually in both the cases just 
as in the case of commercial samples. After 
15 weeks storage increase in moisture was 
very sharp i treated sample compared to 
that of untreated sample probably due to the 
hygroscopic nature of the absorbed salt. 
The TV is N content of the untreated sample 
was higher than that of treated sample ini-
tially. During storage it showed a gradual 
increase in both; but in the treated sample 
the rate was far less compared to that 
untreated sample. The ash and sodium 
chloride contents of the treated samples were 
higher than those of untreated sample due 
to the presence of sodium chloride. The 
physical observation and organoleptic score 
of experimental sample fully supported their 
chemical changes during storage. After 15 
weeks the untreated sample lost its original 
colour and texture due to fungal attack and 
increase in moisture. After 20 weeks the 
sample became organoleptically unacceptable 
as shown by its organoleptic score. On the 
other hand, the treated sample was in acce-
ptable condition even after 25 weeks storage 
as indicated by its physical and organoleptic 
characteristics. The only problem noticed 
in this case was slight softening of its texture 
Table 1. 
Storage 
period 
Changes in chemical characteristics of commercial and experimental samples 
Moisture % 
	
TV N mg/100 g (DWB) 
weeks 1 2 3 1 2 3 
0 23.63 15.67 15.43 147 163 116 
5 27.65 17.45 17.51 187 221 146 
7 29.88 659 
10 17.60 17.71 231 149 
15 18.64 19.05 240 155 
20 19.42 20.00 267 176 
25 20.86 25.72 318 237 
30 25.40 250 
1 — commercial sample; 2 — untreated control; 3 — treated sample; DWB — Dry weight basis 
FISHERY TECHNOLOGY 
6 8 
5 7 
5 7 
4 6 
3 5 
— — 4.5 
IMPROVEMENT IN QUALM a Y 
 
F D lb TED PRAWNS 
 
S 119 
 
Table 2. Changes in physical characteristics and organoleptic score of commercia and experi-
mental samples 
Physical 
characteristics 
Organoleptic 
score 
2 3 1 9 3 
rick red colour, 
firm texture 
rick red colour, 
firm texture 
6 8 9 
f 5 7 8 
2 
Stsrage 
period 
weeks 
0 
5 
7 
1 
Brick red colour, 
slight soft texture 
Reddish brown 
colour, soft texture, 
ammonical odour 
Reddish brown 
colour, spongy 
texture, incidence of 
fungus and insects, 
very strong 
ammo ical odour 
30 
eddish brown 
colour, firm texture, 
Pale reddish brown 
colour, slight soft 
texture, incidence 
of fungus 
Pale brown 
colour, spongy 
texture, off odour 
eddish brown 
colour, firm texture 
lb eddish brown 
colour, slight 
soft texture 
Reddish brown 
colour, soft texture 
Reddish brown 
colour very 
soft texture 
Pale brown colour 
spongy texture 
20 
25 
10 
15 
1 - commercia sample; 2 - untreated control; 3 - treated sample 
due to increase in moisture but it was not 
reflected ii its organoleptic chatacteristics. 
At the end of 30 weeks its quality was on the 
border line of acceptability as judged by its 
overall physical appearance and organole-
ptic score. In general the treatment improved 
the overall quality of whole dried prawns 
considerably in addition to extending its 
shelf-life. The post-process loss encountered 
in commercial whole dried prawns can be 
prevented to a great extent by this method. 
The authors are thankful to Shri M. R. Nair, 
irector, Central Institute of Fisheries Technology, 
Cochin for the permission to publish the paper. 
References 
AOAC (1975) Official Methods of lnalysis 
(Horwitz, W., Ed) 12th edn., Associa-
tion of Official Analytical Chemists, 
Washington 
Conway, E. J. (1947) Microdiffusion Ana-
lysis, Revised edn., d. Van Nostrant 
Co. Inc., New York 
CIDA/FAO/CECAP (1977) A collection 
of Analytical Methods and Testing Pro-
cedures for the Assessment of Fish and 
Shellfish Quality, p. 10, FAO, Rome 
Vol. 25, 1988 


Improvement in quality and shelf-life of whole dried prawns

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Improvement in quality and shelf-life of whole dried prawns

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