White pomfret fillets packed under aerobic conditions had a limited shelf life of 8 days as against 10 days for samples packed under vacuum and stored at 0-2°C. Irradiation and subsequent storage of the fillets under vacuum at 0-2°C exhibited shelf lives of 30, 50 and 60 days for radiation doses of 0.1, 0.3 and 0.5 Mrad respectively in contrast to aerobically packed fillets which showed only 20, 35 and 50 days of storage life for the same levels of radiation doses and developed yellow discolouration and rancid odours

Gaonkar, S.G.

Kamat, S.V.

Kumta, U.S.

Aquatic Commons

ST ES 0 F 
Ill. STO E IES OF ITE 
ET (STROMATEUS CINEREUS) FILLETS 
S. V. KAMAT, S. G. GAONKAR AND U. S. KUMTA 
Biochemistry & Food Technology Division, Bhabha Atomic Research Centre, Trombay, Bombay~ 85 
White pomfret fillets packed under aerobic conditions had 
a limited shelf life of 8 days as against 10 days for samples 
packed under vacuum and stored at 0~2°C. Irradiation and sub-
sequent storage of the fillets under vacuum at 0-2°C exhibited 
shelf lives of 30, 50 and 60 days for radiation doses of 0.1, 
0.3 and 0.5 Mrad respectively in contrast to aerobically packed 
fillets which showed only 20, 35 and 50 days of storage life for 
the same levels of radiation doses and developed yellow discolou-
ration and rancid odours. 
INTRODUCTION 
White pomfrets (Stromateus cinereus), 
a choice fish variety, constitute 2-3% of 
the total marine fish catch in India 
(Venkataraman et al 1968). Serious pro-
blems of handling, processing and storage 
of the fish are encountered during glut 
seasons. Due to prevailing inadequate 
facilities for freezing of the fish and 
transportation of the frozen product, only 
a small percentage of available white porn-
frets are preserved for slack season by 
freezing. It has been observed, however, 
that the acceptability of the frozen fish 
decreases progressively on account of the 
textural alterations (Sawant and Magar, 
1961) and development of a characteristic 
yellow discolouration on the skin surface 
(Pawar a11d Magar, 1966; Kamasastri eta! 
VoL IX No 1 1972 
1967). Ice storage is therefore mainly 
adopted for limited preservation and to 
meet the consumers' demand. However, 
due to indifferent methods of handling 
and processing, besides prevailing unhygi-
enic conditions, the fish stored and tran-
sported in ice are prone to rapid micro-
bial spoilage. Reckoning the limitations 
of the conventional methods, the advan-
tages of radiation pasteurisation process 
have been examined for augmenting the 
shelf life of white pomfret in 'as is' form. 
/ 
Earlier studies (Kamat and Kumta, 
1972) have shown that white pomfret pro-
vides a system susceptible to radiation-
induced oxidative changes, skin tissue being 
more sensitive than the muscle. Pre-
packaging under vacuum, however, effec-
tively suppressed the oxidative changes in 
25 
'K a mat, GaonfZar & 'Kumia: 'Radiation pasteurisation of medium fatty fisfi. 
the fish, both on irradiation and during 
subsequent storage at 0-2°C. 
The present paper describes a radia-
tion pasteurisation process for white pom-
fret based on control of i) microbial 
spoilage reactions by low dose irradiation 
and ii) oxidative changes by maintenance 
of anaerobic conditions during irradiation 
and subsequent storage. Storage properties 
of radio-pasteurised fish have been evaluated 
in terms of organoleptic, biochemical and 
microbiological parameters. 
EXPERIMENTAL 
Preparation of fish samples: 
Fresh white pomfrets ( Stromateus 
cinereus) available from local market were 
brought to laboratory in crushed ice. The 
fish were then washed clean with tap water 
before and after evisceration, cut into 
fillets and stored in ice until used. 
Experiments relating . to the assess-
ment of freshness indices -organoleptic score 
(0. S.), total bacterial count (TBC), trime-
thylamine nitrogen (TMAN) and total 
volatile basic nitrogen (TVBN) - were 
carried out with three different lots of 
10-12 fish each. Duplicate samples were 
used for each assay. The average values 
on three lots of fish have b~en reported 
in the text. 
Packaging of fish: 
The fish fillets (approx. wt. 50 g; 
12.5 em. X 5.0 em. X 2.0 em.) were packed 
under vacuum in polycel pouches after re-
peated flushings with nitrogen gas and eva-
cuations. The pouches were further sealed 
under vacuum in metal cans in order to 
maintain strict anaerobic condition during 
storage. Another lot of the fillets packed 
under aerobic condition served as a control. 
Irradiation: 
The fish fillets were irradiated with 
· 0.1, 0.3 and 0.5 Mrad at the dose rate 
26 
of 0.3 Mrad I hr in Food Package Irradia-
tor IR11 (100,000 curies, Coso source). 
During irradiation temperature was main-
tained at 0-2°C (melting ice). ·The unirra-
diated samples served as the controls. 
Storage: 
All irradiated and unirradiated fish 
samples were stored at 0-2°C in crushed ice. 
Quality evaluation: 
Organoleptic score (0. S.): The sensory 
scoring was done on a reference scale, 
based on changes in colour, odour and 
appearance, as adopted by Miyauchi et al 
(1964). 
Chemical analysis: The total volatile basic 
nitrogen (TVBN) and trimethylamine 
nitrogen (TMAN) were analysed using 
TCA (8 %) extracts of the fish homogenates 
(10%), according to the methods of Farber 
and Ferro (1956) and Bethea and Hilling 
(1965) respectively. 
Bacteriological analysis: Total aerobic 
count was determined by the conventional 
pour plate technique using TGY- agar 
(Mavinkurve et al 1967). Plates were 
counted after incubation at 30°C for 48 hr. 
RESULTS AND DISCUSSION 
Storage characteristics of unirradiated white 
pomfret fillets: 
Table I incorporates data on storage 
properties, assessed in terms of 0. S., 
TMAN, TVBN and TBC of the unirra-
diated white pomfret fillets packed under 
vacuum or aerobic conditions and stored 
at 0-2°C. The fish fillets packed under 
aerobic condition had a limited shelf-life 
of 8 days as against 10 days for the 
samples packed under vacuum. The ter-
minal spoilage of the unirradiated fish was 
marked by development of putrid odours 
coincident with precipitous decline in O· S. 
and sharp rise in the initial levels of 
TBC ( 1 x 105 /g), TMAN (0.5 mg%) and 
FISHERY TECHNOLOGY 
'Kamat, 9aonfar & 'Kurnta: 'Radiation pasteurisation of medium fatty fisft 
TABLE I 0. S. AND FRESHNESS INDICES OF UNIRRADIATED FILLETS PACKED 
UNDER VACUUM AND AEROBIC CONDITIONS 
Indices Days Aerobically packed Vacuum packed 
0. S. 
TMAN: mg% 
TVBN: mg% 
TBC per gm 
l 
8 
12 
15 
1 
8 
12 
15 
1 
8 
12 
15 
1 
8 
12 
15 
10 
7 
1-2 
0.5 
l.9 
6.0 
8 
27 
37 
1.5 X 105 
2.2x 107 
8.4 X 108 
10 
7 
3-4 
0.5 
L6 
2.3 
3.6 
:8.5 
9.5 
18.0 
.:28.5 
I X IQ5 
9 X IQ5 
3 X 10 6 
6.9 X 107 
The unirradiated fillets packed under vacuum and aerobic conditions were stored at 0-2oc. At 
intervals during storage, the quality of samples was examined in terms of TMAN, TVBN. TBC 
and 0. S. 
TVBN (8 mg%). Putrefactive activities 
due to psychrophilic microorganisms are 
known to occur in ice stored fish, con-
comitant with synergistic action between 
weak and rapid spoilers (Lerke et al 1965, 
Shewan, 1961). The net result of micro-
bial reactions is the formation of putrid 
odours and undesirable appearance of the 
fish. Several amines and sulphur com-
pounds have been ic:entified as malodourous 
in spoiling fish (Tomiyasu and Zenitani, 
1 957). End r:roducts of bacterial meta-
bolism have been examined for their use-
fulness as freshness indices (Farber, 1961). 
Storage characteristics of radiation pasteu-
rised white pomfret fillets: 
Evidence obtained from organoleptic, 
chemical and bacteriological evaluation 
demonstrates dose dependent storage be-
VoL IX No 1 1972 
haviour of radio-pasteurised white pomfret 
fillets. Figures 1 and 2 describe the 
storage properties, assessed in terms of 
0. S., TMAN, TVBN and TBC values 
of white pomfret fillets irradiated under 
aerobic and anaerobic condition respecti-
vely and stored at 0-2°C. 
Irradiation and subsequent storage 
under vacuum showed dose dependent ex-
tension in shelf-life of the fish fillets without 
causing any loss in desirable quality of 
the product. Thus, the fish samples expo-
sed to 0.1, 0.3 and 0.5 Mrad had the 
shelf-life of 30, 50 and 60 days respecti-
vely at 0-2°C. The terminal spoilage 
patterns of these fillets varied as a ,fun-
ction of radiation dose. The fillets irra-
diated at 0.1 Mrad spoiled with develop-
ment of putrid odours like the unirradiated 
27 
'Kamat, 9aonliar & 'Kumta: Radiation pasteurisation oft medium fatty fisii 
...... · ·o UNIRRAOtATED 6-----4. 0·3MI"ad 
~O·SMrad 
STORAGE PERIOD. DAY$ 
Fig. L Freshness indices of aerobically iuadia~ 
ted white pomfret fillets. White pom-
fret fillets were irradiated at 0.1, 0.3 
and 0.5 Mrad under aerobic conditions 
and stored at 0-2°C. The 'Unirradiated 
samples served as ocntroli At intervals 
during storage, quality of the fish sam-
ples was assessed in terms of 0. S. 
TMAN, TVBN and TBC. 
fish. The fillets exposed to 0.3 Mrad 
did not develop putrid odours but were 
considered to be spoilt when they produ-
ced sweetish type of odours. No spoilage 
could, however, be detected in samples 
treated with 0.5 Mrad throughout the sto-
rage period of 60 days investigated. Pelroy 
and Eklund (1966) noted that petrale sole 
fillets irradiated at 0.2, 0.3 and 0.4 Mrad 
had a spoilage pattern that was significantly 
different from that of non-irradiated fillets 
and the fillets exposed to 0.1 Mrad. 
Treatment of fresh water fish with 0.3 and 
0.6 Mrad was also observed to alter the 
spoilage patterns usually found in untreated 
fish (Kazanas, 1966; Kazanas et al 1966). 
This was attributed to selection of micro-
bial groups resulting from irradiation. 
Fish samples irradiated and stored un-
der vacuum also showed suppression in the 
levels of TMAN, TVBN and TBC (Fig 2). 
28 
- UNIRRADIATED 
o--------..o 0·1 M rod 
...,____,. 0·3 M ra d 
o--o O·SM rad 
40 50 60 
STORAGE PERIOD, DAYS 
Fig. 2: Influence of vacuum packing on fre-
shness indices of white pomfret fillets. 
White pomfret fillets pre-packed under 
vacuum were irradiated at 0.1, 0.3 and 
O.fi Mrad and subsequently stored at 
0~2°C. Similarly packed unirradiated 
fillets served as control. At intervals 
during ·storage, quality of fish samples 
were assessed in terms of 0. 8 .. , T;1,1AN, 
TVBN and TBC. 
Significant rise in the levels of TMAN 
TVBN and TBC occurred in the fillet~ 
irradiated with 0.1 Mrad after a lag period 
of 8 days while this period was extended 
to about 20 days for 0.3 and 0.5 Mrad 
treated fish samples. Low levels of 
TMAN and TVBN exhibited by white 
pomfret samples appeared to be due to 
suppression of microorganisms responsible 
for the formation of th~sc indices. Some 
of the predominant microorganisms of fish 
and meat have been examined for their 
spoilage potential in terms of their ability 
to produce VRS, TMAN and TVBN. 
Studies of Alur et al (1970) showed that 
P.vulgaris and Pseudomonas species pro-
duced large amounts of TMA and TVB 
in Bombay duck homogenate stored at 10 
or 0°C. Mavinkurve et al (1967) noted 
that Micrococci species, the major radia-
tion survivor, did not produce TMA from 
FISHERY TECHNOLOGY 
'Kamat, 9aonl'wr & Kumta: Radiation pasteurisation of medium fatty fisft 
sterilized Bombay duck drip. Inability of 
certain microorganisms to produce TMA 
has also been reported from other studies 
(Castell and Anderson, 1948; Tarr, 1938). 
In contrast to vacuum packed fillets, 
the fish samples packed under aerobic condi-
tion were prone to development of rancid 
odours on irradiation at 0.5 Mrad, while 0.3 
and0.5Mradtreated samples developed a cha-
racteristic yellow discolouration by 20th and 
10th day of storage respectively. Aerobically 
packed fillets exposed to 0.1, 0.3 and 0.5 
Mrad showed extended shelf-life of 20, 
35 and 50 days respectively (Fig. I). How-
ever, this extension of shelf-life was signi-
ficantly less than that exhibited by correspon-
ding vacuum packed fish samples. Our 
results corroborate with the findings of 
Spinelli et al (1965) on petrale sole. Han-
sen and Jorgensen (1967) and Ampola 
(1969) observed that vacuum packaging of 
ocean perch fillets not only inhibits radia-
tion-induced oxidative changes but also 
enhances the effect of irradiation in exten-
ding the shelf-life of fish. Such comple-
mentary effects of vacuum packaging have 
also been reported by Connors et al (I 964, 
1966). Licciardelo (1967) suggested that 
the low biochemical activity of surviving 
microorganisms may be due to comple-
mentary effect of vacuum packaging. 
Selection of radiation dose: 
Although the evidence is not nrecise 
enough it has b~en suggested from inoculum 
pack studies of Eklund et al (1969) that 
radiation doses over 0.3 Mrad may increase 
potential hazard for Clostridium botulinum 
species in the fish like cod, halibut, English 
sole, Dover sole and petrale sole fillets 
stored in the temperature range of 3 .3 °C 
to l0°C. It was suggested that at lower doses 
of radiation where terminal spoilage could 
be distinguished in terms of putrid odours, 
the samples could be rejected before toxin 
production takes place. To define shelf-
life from the olfactory rejection of the 
VoL IX No I 1972 
samples, a radiaton dose of 0.1 Mrad for 
white pomfret would be more suitable for 
pasteurisation, since the terminal spoilage 
pattern of these fish samples was similar 
to that of the unirradiated fish. At this 
dose level, under anaerobic condition, ex-
tended shelf-life of 35 days for the fish 
is adequate enough for transportation of 
the product. Microbial safety as deter-
mined by the procedures of Eklund et al 
(1969) based on mouse lethal dose tests 
have shown (unpublished data) that there 
was no evidence of toxin formation in the 
irradiated white pomfret fillets stored 
at 0-2°C. 
SUMMARY 
A radiation pasteurisation process in-
tegrating low dose irradiation with vacuum 
packaging is described for white pomfret, 
based on suppression of oxidative changes 
in the fish fillets stored at 0-2°C. Orga-
noleptic, chemical and bacteriological ana-
lysis indicated that the unirradiated fish 
fillets packed under aerobic or anaerobic 
conditions and stored at 0-2°C, spoiled 
within 8 and 12 days respectively. Dose 
dependent extension in shelf-life was, how-
ever, exhibited by the irradiated fish. 
Anaerobically packed fish fillets exposed 
to radiation doses of 0.1, 0.3 and 0.5 
Mrad showed extended shelf-life of 35 
' 50 and 60 days respectively without under-
going any loss in quality attributes of 
colour, odour or texture. The fish samples 
packed under aerobic condition were, how-
ever, prone to development of rancid 
odours on irradiation (0.5 Mrad) and 
yellow discolouration (0.3 and 0.5 Mrad) 
during storage and also exhibited lesser 
extension in shelf-life when compared to 
anaerobically packed fish. 
REFERENCES 
Alur, M. D., Lewis, N. F. and Kumta, 
U. S. 1970. Ind. J. Expt. Biol., 48. 
Ampola, V. G., Connors, T. J. and Ron-
29 
Kamat, 9aon~ar & Kumta: 'Radiation pasteurisation of medium fatty fist! 
sivaili, L. J. 1969. Food Techno!., 
23, 357. 
Bethea, S. and Hilling, F. 1965. J. A. 0. 
A. C., 48, 73 L 
Castell, C. H. and Anderson, G. W. 1948. 
J. Fish Res. Bd. Canada, 7, 378. 
Connors, T. J. and Steinberg, M. A. 1964. 
Food Techno!., 18, 1057. 
Connors, T. J. and Steinberg, M.A. 1966. 
Ibid., 20, 1357. 
Eklund, M. W. and Poysky, P. T. ln 
'Proceedings of Panel on irradiation of 
foods of marine origin', Vienna, 
Dec. 1969. 
Farber, L. 1961. In 'Fish as Food', 
Academic Press, N. Y. Vol. IV, pp. 
66-126. 
Farber L. and Ferro, M. 1956. Food 
Techno!., I 303. 
Hansen, P. and Jorgensen, B. V. 1967. 
In Microbiological problem:S in food 
preservation by Irradiation', IAEA, 
Vienna, p. 133. 
Kamasastri, P. V., Doke, S. N. and Rao, 
D. R. 1967. Fish Techno!., 4, 78. 
Kamat, S. V. andKumta, U. S. 1972. Fish 
Techno!., 9 ( 8. 
Kazanas, N. 1966. Appl. Microbial., 
957. 
Kazanas N., Emerson, J. A., Seagran, H. L. 
and Kempe, L. _L 1966. Ibid., 261. 
30' 
Lerke, P., Adams, R. and Farber, L 1965. 
Ibid., 13, 625. 
Licciardello, J. J., Ronsivalli, L. J. and 
Slavin, J. W. 1967. J. Appl. ·Bact., 
30, 239. 
Mavinkurve, S. S., Ganga!, S. V. Sawant, 
P. L. and Kumta, U. S. 1967. J. 
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Miyauchi, D., Eklund, M., Spinelli, J. 
and Stoll, N. 1964. Food TechnoL 
18, 928, 
Pawar, S. S. a nd Magar, N. G. 1966, 
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Pelroy, G. A. and Eklund, M. W. 1966, 
Appl. Microbial. 921. 
Sawant, P. L. and Magar, N. G. 1961. 
J. Food Sci. 26, 253. 
Shewan, J. M. 1971. In "Fish as Food~, 
G. Borgstrom, ed., Academic Presses: 
N. Y., Vol I, p, 487. 
Spinelli, J., Eklund, M., Stoll, N. and 
Miyauchi, D. 1965. Food Technol, 
19, 1016. 
Tarr, H. L.A. 1938. Nature, 142, 1078. 
Tomiyasu, Y. and Zenitani, B. 1957. 
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Venkataraman, R., Solanki, K. K. and 
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fiSHERY TECHNOLOGY 


Studies on radiation pasteurisation of medium fatty fish 3. Storage properties of white pomfret (Stromateus cinereus) fillets

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Studies on radiation pasteurisation of medium fatty fish 3. Storage properties of white pomfret (Stromateus cinereus) fillets

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