Canning operations suitable for packing mackerel (Rastrelliger kanagurta) in the form of skinless and boneless fillets in oil were studied and the process standardised. The technique of lye peeling for skin removal could be successfully applied. The storage life of the final product was tested over a period of one year and found to be quite comparable to other similar fish products

Parashuram, P.

Rai, B.S.

Saralaya, K.V.

Aquatic Commons

IES 
ll 
NNI G 
I 
F 
Oil 
EREL 
K. V. SARALAYA, P. PARASHURAM* & B. S. RAI 
College or Fisheries, University or Agricultural Sciences. Mongo/ere: 
Canning operations suitable for packing mackerel ( Rastr-
elliger kanagurta) in the form of skinless and boneless fillets in oil 
were studied and the process standardised. The technique of 
lye peeling for skin removal could be successfully applied. 
The storage life of the final product was tested over a period 
of mie year and found to be quite comparable to other 
similar fish products. 
INTRODUCTION 
Several species of Atlantic and Pacific 
mackerels are widely used as raw material 
for canning (Jarvis, 1943). The Indian 
species ( Rastrelliger kanagurta), though 
smaller in size, is quite suitable for pro-
cessing by canning. It forms a substantial 
proportion of our marine landings,· the 
majority of which is fished on the west 
coast. At present this fish is canned in 
one or two pieces, with skin and bone, 
in round sanitary cans using brine, refined 
oil or tomato sauce as packing medium. 
A 'curry' has also been fJrmulated as an 
alternate filling medium (Rai, Saralaya and 
Parashuram, 1971). This paper reports the 
development of a new product of superior 
quality in an attractive and more convenient 
form. In this improved form the product 
is expected to have better acceptability and 
also export potentiaL 
MATERIALS AND METHODS 
Mackerel obtained from commercial 
catches were used in fresh, iced or frozen 
condition. Double refined deodorised 
vegetable oil was used as filling medium 
and quarter dingly can (Anon., 1967) as 
container. 
Fish canning procedures described by 
Broek (1965) were followed in this work. 
The fish were deskinned by lye peeling in 
hot sodium hydroxide solution, washed 
thoroughly and cooked in steam in auto-
claves or retorts. They were then cooled 
* Present address: Plant Manager, Karnataka Fisheries 
Development Corporation, Ullal, Mangalore. 
120 Fish. Techno!. 
8aralaya, Parasfwram & 'Rai: 
to room temperature, cleaned and filleted. 
The fi11ets, after trimming, were packed 
into plain quarter dingly cans either long-
itudinally or across the cans by placing 
them in the can in two layers with their 
flat inner surface facing the· bottom and 
top of the container. For this style of 
packing, two or two and a half fillets in 
each layer were generally sufficient for 
one can. The cans were then filled with 
hot (80-85°C) double refined groundnut 
oil to make up to the ad0pted l 06 g. 
net weight, and about 2 g. of powdered 
table salt were added to each can to give 
the necessary salty taste and to provide a 
safety margin in the net weight. The 
filled cans were exhausted in steam with 
lids on for about 10 min. at 100°C, and 
then promptly double seamed while still 
hot. These were then adequately proce-
ssed by retorting, cooled in water, wiped 
dry and stored at room temperature. The 
various operations were standardised by 
several trials. The product was tested at 
regular intervals for about an year after 
production and its acceptability and shelf 
life were ascertained. Microbiological 
examinations at various stages, from raw 
material to finished product, were also 
c:.mducted to determine the efficiency of 
op~rations at different stages of processing. 
RESULTS AND DISCUSSION 
Mackerel in the fresh, iced or frozen 
condition may be used for canning by 
this method .. However, it was found that 
frozen fish in semithawed condition, be-
. ing firmer than either fresh or iced fish, 
were more convenient for lye peeling, 
handling and preparation. On the other 
hand, fillets prepared out of fresh fish 
were prone to breaking easily during 
processmg. 
VoL ll No. 2 1975 
Canning of macfwrel fillets 
Relation of fish size to canning yield 
Table I shows the relationship between 
fish size and the final yield of fillets 
obtained, as percentage of fish weight. 
It can be seen that mackerel of size around 
100 g. round weight give the maximum 
yield when canned as fillets in quarter 
dingly cans, because of minimum wastage 
in cleaning and trimming. Incidentally this 
size group forms the majority of commer-
cial catches. 
Deskinning 
'Lye peeling' of the skin, unlike 
manual peeling or peeling by other methods, 
has been found to be very convenient in 
the case of small fish like mackerel, since 
the method removes the skin neatl_yr with-
out disturbing the meat fibres, resulting 
in a smooth and even surface. Peeling loss 
can also be minimised by carefully con-
trolling the lye concentratiOn, temperature 
and dip time. The effects of different lye 
treatments are summarised in Table H. 
It was found that peeling effect was better 
when higher concentrations of alkali or 
longer dip durations were applied. Con-
sidering the peeled condition of the fish 
peeling loss and breakage of meat in the 
fillets, dipping the fillets in boiling 1% 
sodium hydroxide so1ution for one minute 
in the case of mackerel of normal s1ze 
and for one to two minutes in the 
case cf extra large fish, was fc und to be 
optimum. 
The figures in this table refer to 
frozen thawed fish samples. But even 
fresh fish samples when subjected to lye 
treatments showed similar trends. 
Statistical analysis of the results showed 
that there was significant difference in 
121 
8arra!aya, 'Parasfturam & 'R.ai: Canning of macfierel fillets 
TABLE I 
Influence of fish SIZe on fillet length and canning yield. 
Length of fillets Final cann-
Sample Length of fish Weight of fish obtained ing yield 
No. (em.) (g.) (em.) (%weight of fish) 
]_ 19_0 67.0 9.3 22.4 
2 19.4 88.0 9.5 24.2 
3 19.8 89.1 10.2 28.7 
4 20.3 96.9 10.3 29.9 
5 20 4 100.0 10.5 32.0 
6 21.1 111.8 10.9 28.9 
1 21.5 116.0 10.6 28.1 
8 22.5 133.0 u.s 29.8 
TABLE II 
Effect of lye treatments on mackerel used for canning as fillets. 
Average ini- Loss in Meat 
Lye treatment given tial weight peeling & breakage Peeled condition 
%NaOH Dip time of fish washing (% ofNo. 
(g.) (%of fish weight) of pieces) 
0.5 88.7 2.2 0 UP 
1.0 89.4 5.0 0 UP 
0.5 2.0 83.6 8.6 6.7 l/3UP, 2/3 GP 
3.0 88.3 13.2 60.0 2/3GP, l/30P 
5.0 88.5 18.6 66.7 OP 
0.5 86.6 2.0 13.3 UP 
LO 86.0 8.6 13.3 GP 
1.0 2.0 84.7 12.1 66.7 2/3GP, 1/30P 
3.0 81.8 15.9 80.0 OP 
5.0 79.3 27.5 100.0 OP 
0.5 84.7 3.7 0 UP 
1.0 88.1 7.0 20.0 GP 
2.0 2.0 92.9 14.8 66.7 l/3GP, 2j30P 
3.0 85.7 17.8 80.0 OP 
5.0 87.2 25.2 100.0 OP 
0.5 88.2 4.7 33.3 l/3UP, 2/3GP 
1.0 87.1 6.3 53.3 OP 
3.0 2.0 81.7 16.5 93.3 OP 
3.0 90.9 23.1 100.0 OP 
5.0 94.9 31.8 100.0 OP 
Note:- UP- Under peeling; GP - Good peeling; OP - Over peeling. 
122 Fish. Technol. 
8aralaya, Parasfluram & 'Rai: Canning of nwc~erel fillets 
TABLE III 
Influence of washing on lye peeled fish. 
Control, dipped in 
boiling water for 1 min. 
Lye treated, dipped in 
boiling 1% NaOH for 1 min. 
Samples pH of surface pH of meat pH of surface pH of meat 
by paper by meter by paper by meter 
After treatment and dip 
washing in tap water. 6.45 
After washing in running 
water for 5 min. 6.35 
-do- 10 min. 6.30 
-do- 15 min. 6.25 
-do- 20 min. 6.25 
Note:- Initial pH of fish surface: 6.25 
peeling effect with changes in either alkali 
concentration or dip time. But the diff-
erence between fresh fish and frozen fish 
samples was not significant at 5% and 1% 
levels. 
It is necessary that washing the fish 
after lye peeling be sufficient to remove 
all traces of alkali from the fish, so as 
to avoid pH changes and other adverse 
effects of alkali on taste, flavour, can 
corros·on, etc. in the finished product. 
The influence of washing the lye treated 
fish over different durations is shown in 
table III. It can be seen that the fish 
treated with 1% alkali for one min. loses 
all the alkali, both on the surface and 
in the meat, when washed in running water 
for 20 minutes. 
Precooking, cooling and filleting 
The peeled and washed fish were 
cooked and cooled as in the case of can-
mug tuna (Lassen, 1965). Cooking the 
VoL 12 No. 2 1975 
6.35 7.50 6.65 
6.23 7.25 6.38 
6.28 6.90 6.38 
6.18 6.40 6.23 
6.30 6.25 6.20 
and of fish meat: 6.30 
fish in steam at 100°C for 20 mm. and 
cooling overnight in racks served the 
purpose adequately. The total reduction 
in weight due to cooking and cooling was 
around 30% of the fish weight. 
In cleaning and separating the fillets 
from bones, it was found that thin bam-
boo strips could be used with great advant-
age. The belly side of the fillets was cleaned 
by gentle washing; but dipping fillets in 
water for any length of time was avoided 
to prevent moisture intake. Care was 
necessary in these operations which were 
manually performed, so as to obtain the 
fillets whole and unbroken. The fillet 
ends were trimmed by sharp knives, to 
give lengths of 9.5 - 10.0 em. for length-
wise packing and 6.5- 7.0 em. for breadth-
wise packing in quarter dingly cans. The 
trimming losses were around 6 to 8% of 
fillet weight. The yield of trimmed fillets 
was around 30 to 32% of the original fish 
weight in the optimum size group (Table I). 
123 
Saralaya, Parasliuram & Rai: Canning of mac~erel fillets 
TABLE IV 
Microbial fluctuations m the canning of mackerel fillets. 
Stage of operation Sample Total plate Mesophilic Thermophilic 
count/g. spores/g. spores/g. 
Raw material a 5 X lOS 0 0 
(round fish) b 7 X lOS 5 0. 
Lye peeled & a 5 X 10!! 0 0 
washed fish b 5 v lOS 0 0 .1\. 
Precooked fish a 0 0 0 
b 1 X 10 0 0 
Fish after overnight a 3.2 X 105 0 0 
cooling b 7.2 X 104 0 0 
Packed meat, after a 3.5 X 105 10 0 
cleaning & filleting b 3.5 X 105 0 0 
Final canned a 0 0 0 
product b 0 0 0 
Note:- Sample (a) : iced fish; sample (b): frozen fish. (Values are average) 
TABLE V 
Thermal processes used or recommended for mackerel canned in oil, 
in containers of different sizes. 
Product 
Mackerel in oil 
(full size with 
skin & bone) 
Mackerel in oil 
(half size with 
skin and bone) 
Pacific mackerel 
fiUets in oil 
Indian mackerel 
fillets in oil 
124 
Can used 
No. 1 TaU 
(301 X 409) 
8 oz. can 
(301 X 206) 
Square 5A can 
Quarter 
dingly can 
Mininum 
dimension 
for heat 
penetration 
37 mm. 
(radius) 
27 mm. 
(half height) 
14 mm. 
(half height) 
9mm. 
(half height) 
Retmt Temp-
pressure erature 
pst oc 
10 115 
115 
8 112 
8 112 
(Recommended) 
Process 
time 
min. 
90-100 
70-75 
75 
40 
Fish. T echnol 
Saralaya, Parasfturam & 'Rai: Canning of macfierel fillets 
TABLE VI 
Results of product examination by 'cut-out' test and 'panel' tests. 
Test 
Cut-out 
Test 
Charateristic of the product 
Net weight of contents (g.) 
Drained weight of solids (g.) 
% of water in drained liquid 
Can vacuum by piercing gauge 
(em. of Hg) 
pH of contents 
Canned fi.Hets made of 
Iced mackerel 
112.5 
82.2 
37.5 
6-16 
(Mean : 9.25) 
6.28 
frozen mackerel 
114.9 
80.1 
34.6 
6-17 
(Mean: 9.8) 
6.30 
General appearance on opening the can 
Colour of meat 
Good 
Good 
Acceptable 
Good 
Good 
Acceptable 
Good 
Good 
Acceptable 
Good 
Good 
Acceptable 
Panel 
Test 
Flavour 
Taste 
Texture of fillets 
Can condition (internal) with special 
reference to S-discolouration. 
Exhausting. 
Exhausting in steam was necessary 
since filling with hot oil alone could not be 
relied upon to give sufficient vacuum 
in the can, as the fillets we-re cold-packed 
in this method. The ten minute exhaust 
with lid on was found to give 9-10 em. of 
vacuum in the fina1 product, which is 
quite adequate, with reference to I. S. I. 
specifications, which require that for cans 
other than round there should be positive 
vacuum. 
Microbiological evaluation and process 
requirement 
Microbiological examinations showed 
that lye peeling and pre-cooking reduced 
the total count of organisms initial]y present 
whereas overnight cooling and further 
handling of the fillets ·caused increases. 
VoL ll No. 2 1975 
However, the final processing of the filled 
cans for 40 minutes at H 2°C (8psl) was 
found to be adequate for obtaining a 
product that was commercially sterile. The 
fluctuations in bacterial load are shown 
in Table IV. The thermal' process recomm-
ended for this product has been compa-
red with other processes employed for si-
milar products in other containers (TableV). 
Evaluation of product quality and shelf life 
The canned mackerel fillets stored at 
ordinary temperatures, when subjected to 
regular cut-out tests and panel tests, were 
found to be satisfactory with respect to 
all the characteristics significant for canned 
fish products. The summary of results of 
these tests, conducted upto one year after 
production, is presented in table VI. 
125 
8aralaya, 'Parasliuram & 'Rai: 
Of the six organo!eptic characteristics, 
four have been judged as 'good' and two 
as 'acceptable' on a four point scale (ex-
cellent, g;od, acceptable and not acceptable). 
The presence of sulphide discolouration at 
certain points on the can interior, as 
found in the tested samples, were not so 
intense as to render the product unaccep-
table. 
The quality of the product was found 
to be consistent upto one year after pro-
duction of the canned fillets. There was 
no deterioration either in texture, colour, 
flavour or taste. 
ACKNOWLEDGEMENT 
The authors wish to express their 
indebtedness to Sri. H. P. C. Shetty, 
Director of Instruction for his valuable 
suggestions in preparing this paper. Our 
thanks are also due to Mr. G. E. Samuel 
and Mr. V.S. Reddy, Instructors, who helped 
us in some experiments during their tenure 
126 
Canning of mac~erei fillets 
in the College, and to Mr. K. S. Udupa 
for his assistance in the statistical analysis 
of the results. 
REFERENCES 
Anon. 1963. Indian Standard: Specification 
for mackerel canned in oil. IS: 2420. 
Indian Standards Institution, New 
Delhi. 
Anon. 1967. Indian Standard: Speczfication 
for seamless rectangular fish tins. IS: 
4638. Indian standards Institution, 
New Delhi. 
Broek Van Den, C. J. H. 1965. Fish as 
Food; Vol. 4. Academic Press, 
London, p. 138. 
Jarvis, N. D. 1943. Principles and methods 
in the canning of fishery products. 
Research report, U. S. Fish Serv., 1: 
_199. 
Lassen, Sven. 1965. Fish as Food; Vol. 4. 
Academic Press, London, p. 225. 
Rai. B S., K. V. Saralaya & P. Parashuram. 
1971. Indian Food Packer; 25, 2 : 19. 
Fish. Techno!. 


Studies on cannning of mackerel fillets in oil

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Studies on cannning of mackerel fillets in oil

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