Chemical Changes and Visual Appearance of Indian

Shad (Tenualosa ilisha) During Ice Storage

Musleh UDDIN *, Md. Naim UDDIN **, Munehiko TANAKA *

and Md. KAMAL **

* Laboratory of Food Processing, Department of Food Science and Technology, Tokyo University of Fisheries
Konan, Minato, Tokyo 108-8477 Japan
** Department of Fisheries Technology, Bangladesh Agricultural University
Mymensingh-2202 Bangladesh

This study was conducted to evaluate the quality changes of fresh Indian shad Tenualosa ilisha
during ice storage in a polystyrene insulated box for 24 days. Chemical and visual analyses were
carried out every 4th day. Moisture contents decreased significantly from the 16th day of
storage. Total crude protein and ash content slightly decreased throughout the period of study.
Non-protein nitrogen (NPN) and free fatty acid (FFA) values increased gradually. A positive
relationship was observed between the pH and solubility of the fish myofibrillar proteins where
solubility decreased greatly (70% to 41%) as the muscle pH of the stored fish decreased. Both
chemical analyses and visual appearance examination showed that the quality of Indian shad was
in acceptable condition up to the 19th day of ice storage. Results from chemical analyses were
well correlated with basic visual appearance.
(Received Jun, 7, 1999; Accepted Aug. 18, 1999)

Indian shad Tenualosa ilisha constitutes the development scheme to give maximum benefit to
largest single fishery of Bangladesh. Its annual the producers, retailers and consumers. Most of the
catch accounts for nearly 40% of the total inland studies on maintaining quality of fish in ice have
fish harvest of the country.1) It is a fatty fish and been made on fish from cold and temperate waters,

hence highly perishable. Not only Bangladesh but particularly cod and herring groups. Comparatively
also other Southeast Asian countries handle and little information has been published on spoilage of
transport fish mainly in traditional wooden or fish from tropical waters, but there are some
bamboo boxes with an inside lining of gunny bags, indications that fish from warmer waters will
sawdust, or a thin layer of ice. But unfortunately, stay fresh longer. 2) Usually a simple storage
neither method of icing is standardized with experiment under suitable containers with
respect to quality, amount, size and thickness of ice improved handling has been performed to reveal
used nor with respect to containers and the the proper storage period. 3)
insulating materials used in the container. An Considerable information has been available on
essential prerequisite in maintaining the quality of the organolepti changes and shelf-life of various
fish during handling, storage, transport and fish species during storage under chilled
marketing is to identify how long particular temperature. CONNEL4) reported that the shelf-life
species in the catch can be preserved. Once this of some species of cod could be maintained in ice
information is available for a particula rfish up to 18 days. GUPTA et al. 5) studied the shelf-life
species, it can be helpful to take up any of milk fish in ice storage with daily replacement
 of ice and maintaining the temperature of fish at load (numbers and kinds) in gunny and

0•Ž. They found that the fish were acceptable up polyethylene.1) It is, therefore, important to see the

to 18 days. PERIGREEN et al. 6) studied the storage chemical changes and visual appearance under the

characteristics of common murrel Channa striatus similar storage condition. The chemical changes

in ice (fish and ice ratio 1 : 1). Organoleptically the and visual appearance taking place in ice stored

fish were acceptable for 9 days. BANDYOPADHYAY Indian shad in a polystyrene insulated box are

et al. 7) suggested that both Catla catla and Labeo presented in this paper.

filbriatus could be stored in ice for 18 days in an

Materials and Methods
acceptable condition for human consumption.

Very little information is available on Samples and experimental design

biochemical changes of Indian shad during ice Fresh Indian shad Tenualosa ilisha of more or

storage, whereas there are a several studies that less uniform size (average body weight: 850g) were

have been reported on other fishes. VARMA et al. 8) procured in a lot from the fishermen at Meghna

reported on the biochemical changes in different near Chandpur, Bangladesh. The fish were put into

varieties of iced fish during transportation in ice immediately after the catch and brought to the

second hand thermoclined tea-chests from Varaval fish landing center at Chandpur. The fish were

to Bombay and Delhi. The moisture content packed in layered ice (1:1, w/w) in a polystyrene

increased for all the varieties except for eel and insulated box (80cm•~70cm•~50cm) 3cm thick and

hilsa. Total volatile nitrogen (TVN) increased in transported to the Bangladesh Agricultural

all cases, but the maximum increase was observed University, Mymensingh. Every individual fish was

in seer fish. In regard to quality changes, weighed and labelled. They were packed in

MUSLEMUDDIN et al. 9) reported that the solubility crushed commercial block ice in a ratio of 1:1 (w/

of hilsa myofibrillar proteins decreased from an w) in a polystyrene insulated box (80cm•~70cm•~

initial value of 65% to about 18% in 75 days of

storage at -7•Ž to -10•Ž. The iodine value dropped the bottom to drain out melting water. Stowage in
from 79.0 to 56.0 and the peroxide value increased the boxes consisted of a bottom layer of about 5
from 3.5 to 35.0 during the same storage period. cm of crushed ice and then layers of fish sprinkled
The total volatile base nitrogen (TVBN) value with ice and a top layer of ice again of about 5 cm.
increased from 24mg to 82mgN/100g meat. They Fresh crushed ice was added in each of the two
also reported that the iodine value decreased boxes every morning equal in quantity to replace
from 87.0 to 65.0 and the acid value increased that which was lost due to melting water. Sampling
significantly from 4 to 19 when the fish were stored was done every fourth day.
in ice for 10 days. Visual appearance evaluation
A variety of chemical compounds or groups of Sensory methods were used for visual
compounds accumulate in post-mortem fish flesh. appearance evaluation of fish. The grading system
These compounds are intermediates or end using a score for the characteristics of fish was
products of biochemical changes occurring in the followed according to EC freshness grade for
muscle of fish after they died or result from the herring with some modification 3) to judge the
action of exogenous bacterial enzymes released by quality of the fish as described in Tables 1 and 2.
the proliferating bacteria on muscle metabolites. Panelists consisted of 8 graduate students and 4
The amounts formed can be used as an index of faculty members (4 females and 8 males) for the
spoilage. The bacteriological changes of Indian sensory evaluation.
shad in three types of insulating containers were Proximate analyses
evaluated in iced condition and fish kept in the Proximate composition was analyzed according

polystyrene insulated box showed lower bacterial

to the methods given in A. O. A. C. 10) with some
 Table 1 Grading of fresh fish

Table 2 Guidelines for visual appearance evaluation of Indian shad

modification as described below. All deter- Measurement of muscle pH

minations for each sample were replicated three pH value of muscle homogenate was measured

times. Moisture content of 5 g sample was by using a pH meter (Model HM-30 V, Toa

determined by drying in an oven at 105•Ž until a Electronics Ltd., Tokyo). The muscle homogenate

constant weight was obtained. The loss of moisture was prepared by blending 10 g of minced meat

was calculated as percent moisture content. The with 40 me of chilled distilled water.

standard macro-Kjeldahl method was followed for Solubility

the determination of crude protein. About 2g of Two g of fish meat was homogenized with 20 ml

communited sample was employed for the Kjeldahl of 1 M KCl plus 100 mM phosphate buffer (pH 7.0)

procedure. A factor of 6.25 was used for using a homogenizer. The homogenate was

converting the total nitrogen to crude protein allowed to stand at a refrigerated temperature

content. Lipid content was determined by (4•Ž) overnight. The suspension was then

extracting a given quantity of samples with centrifuged for 30min at 900xg in cold condition.

petroleum ether in a Soxhlet apparatus for 16 to 18 The protein in the supernatant was determined by

hours. Ash content was determined by igniting the the Biuret method.11)

sample in a muffle furnace at 550•Ž for 4•`6 hours. Estimation of total non-protein nitrogen (NPN)

Total NPN of TCA extracts of fish tissue was

 Table 3 Changes in visual appearance of Indian shad during ice storage in a

polystyrene insulated box

determined according to the standard macro- daily organoleptic examination. On the basis of the

Kjeldahl technique reported by KONOSU et al.12) scores, the fish were found to be in acceptable

Estimation of free fatty acid (FFA) condition for 20 days in ice before becoming

Fish oil extracted from Indian shad by the Folch inedible.

reagent (chloroform-methanol in the ratio of 2: The changes taking place in the organoleptic
1, v/v) was used for determination of FFA quality during the storage period could roughly be
according to the method described in A. O. A. C.10) divided into 6 phases corresponding to 0, 0 to 4, 4
to 8, 8 to 12, 12 to 16, and 16 to 20 days in ice. In
Results and Discussion
phases 1 and 2 the fish were very fresh with a
Changes in the visual appearance (organoleptic species-specific taste and natural flavor and odor.

quality) of Indian shad during ice storage are At this stage the fish had characteristics of

presented in Table 3. The quality of fish was excellent quality. In phases 3 and 4 there was slight

graded using a score from 1•`5. The grades were deterioration apart from a slight loss of natural

defined in terms of the total number of defects or flavour and characteristic odor but no off-flavors.
demerit points. A score of less than 2 points was In phase 5 there were signs of early spoilage with
considered excellent. A score of 2 to less than 5 slight off-flavors. The off-flavor was slightly sour,

points was judged as good or acceptable, while 5 sickly sweet, or fruity. During phase 6, the fish

points was considered to be bad or rejected. The began to taste stale, its appearance and texture

changes in the quality of fish were assessed by started to show obvious signs of spoilage, and the
 Table 4 Proximate analysis (%) of Indian shad during ice storage in a polystyrene
insulated box

Fig. 2 Changes in non protein nitrogen (NPN) and free

Fig. 1 Relationship between the changes of
fatty acid (FFA) content of Indian shad during ice
solubility (%) and pH of Indian shad during ice
storage.
storage.

gills and belly cavity had an unpleasant smell and artisanal containers. They suggested that a fish-ice
became unacceptable on the 20th day of storage. ratio of 4:1, 2:1, and 1:1 could preserve the shelf
Similar organoleptic changes were reported for life of fish up to 72 h, 120 h, and 144 hours,
cod fish during ice storage studies. 13) respectively. In the present study the quality
The above results indicated that a polystyrene changes of hilsa fish transported by bamboo basket
insulated box was more effective in preserving the and polyethylene were not investigated. However,

quality of ice stored Indian shad in comparison to the results in this study suggested that the shelf
bamboo baskets and wooden boxes with a, life of icestored Indian shad in a polystyrene
smaller amount of ice required to keep the fish insulated box can be increased to 19 days.
noted. 14) On the other hand, HYE et al. 15) reported The results of the proximate composition of ice
that a polyethylene container was most suitable stored fish are presented in Table 4. Moisture,
and had the best insulation effects than different protein, lipid, and ash content were 67.69, 17.10, 13.
 Food Preservation Science VOL.25 NO.6 1999

28, and 1.55%, respectively for 0 day iced fish flesh. stored in ice. There was a clear trend of
Usually, the sum of moisture and lipid content of increasing NPN content with the lapse of storage
the fish is approximately 80%. 16) Moisture content period but the values were within an acceptable
decreased from 67.69% to 64.50% after 20 days of limit set for fresh fish as reported by TARR. 24) For
storage. This may be explained by the loss of teleost fish, the recommended value of NPN
moisture from the body as exudated or may be the varied from 9.2 to 18.3% of the total nitrogen while
result of production of volatile compounds. the fish had acceptable quality. A similar increase
Protein content remained almost unchanged during in FFA value was also observed during storage.
the storage period while a slight variation in lipid Free fatty acids probably do not contribute much
content was observed. This can be explained by to undesirable flavor in the fish muscle itself, while
individual variation since lipid content varies from they are more readily oxidized and produce rancid
fish to fish and even within the same fish odour. However, the value was within the limit of
depending on size, sex, age and feeding. 16) Decrease 2 to 10 recommended for fresh fish as acceptable
in ash content was also noted. The loss of quality 24) which also corresponded to organoleptic
moisture during storage of the chilled product may quality of the fish.
also occur due to the evaporation of moisture
Conclusion
from the surface which depends on many factors

such as geometric shape, chemical composition of Both chemical analyses and visual appearance

the product, type of packing, storage temperature, examination showed that the quality of Indian

and relative humidity. 17) In the present study, the shad was in acceptable condition up to the 19th day

samples were stored in ice without packaging. It of ice storage. Results also revealed that a

can be assumed that the fish might be exposed to polystyrene insulated box was more effective in
atmospheric temperature during storage which preserving the quality of ice stored Indian shad in
leads to evaporation of moisture from fish body comparison to bamboo baskets, wooden boxes, or
surface. other traditional methods. The smaller amount of

Changes in the solubility and pH of myofibrillar ice required to keep the fish was also noted.

proteins are used as an index of the extent of

muscle protein denaturation and hence of textural References

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