Lupine Publishers | Scholarly Journal of Food and Nutrition
Abstract
Cooking techniques were applied on
Mullet fish (Mugil cephalous) steaks. Raw Mullet fish steaks were stored at
-180C for 180 days to study the changes in the proximate composition during
storage period. The proximate composition of raw Mullet fish was affected by
cooking techniques. Moisture contents decreased in fried and grilled mullet
steaks while protein, fat and ash contents were significant increase in cooked
mullet steaks. The loss of moisture in fried samples amounted to the highest
levels, also the protein and fat value was proportionally high. The raw and
cooked Mullet fish showed a gradual decrease in their contents of moisture,
protein and fat as affected by frozen storage period and cooking method while
ash contents were increased. Mullet fish steaks maintained their nutritional
value until the end of the storage period.
Keywords: Frying; Grilling; Mullet Fish Steaks; Freezing; Proximate
Composition
Introduction
Fish is highly nutritious, rich in
micronutrients, minerals, polyunsaturated fatty acids and proteins, and
represents a valuable supplement in diets lacking these nutrients, essential
vitamins and minerals. In many countries, especially developing countries, the
average per capita fish consumption may be low, but, even in small quantities,
fish can significantly improve the quality of dietary proteins by complementing
the essential amino acids that are often present only in low quantities in
vegetable-based diets1. Preservation provides a long shelf‐life for fish and
fish products. Preservation can be defined as the storage of excess fish when
they are abundantly caught or produced so they can be consumed as if fresh in
times when food is scarce or when transported to long distances. Preservation
affects food in two ways:
I. it keeps the original freshness
and properties of fish;
II. it changes the original
properties of the food and creates new product.
The main purpose of both of these is
to prevent spoilage, especially by microorganisms. Several preservation methods
have been developed, some of them providing a longer shelf‐life than others.
The choice of a preservation method depends on the product, properties of the
product, availability of energy, the storage facilities, and the costs of the
method. It is sometimes necessary to combine methods. Proximate chemical
composition generally means percentage composition of basic constituents such
as moisture, proteins, fats, carbohydrates and minerals. In recent times, the
importance of fishery products as a source of nutrients including high quality
proteins, unsaturated lipids, a number of vitamins, and minerals has been
realized. Several fishery items have attracted the attention of nutritionists
and dieticians as a source of therapeutically important polyunsaturated fatty
acids [2]. In the freezing process, the temperature degree lowers to under the
freezing point. In this case, most of the water to turn into ice. The freezing
point passed on the total soluble solid or substances dissolved in the fluid of
the tissue [3]. Fish is processed in different methods such as frying and
grilling and roasting. These methods improved the hygienic quality by
inactivation of pathogenic microorganisms and enhanced the digestibility and
bio-availability of nutrient in the digestive tract [4]. In Egypt, Mullet fish
is usually processed by various cooking methods, such as grilling and frying,
before consumption. Thermal processing techniques are widely used to improve
eating quality and safety of food products and to extend the shelf life of the
products [5]. During cooking process, some physical and chemical changes take
place which either impair or improve the nutritional value of food. Therefore,
digestibility is increased because of protein denaturation in food while, the
content of thermo labile compounds, vitamins or polyunsaturated fatty acids is
often reduced [6]. The aim of current study was to follow up the changes which
occur in chemical composition of mullet fish steaks by frying and grilling
technique during frozen storage period.
Methods and Data
Sample
Preparation
Ten kilogram of fresh Mullets fish
(Mugil cephalous) were obtained from one of the fishermen in Wadi El-Rayan
Lake, Fayoum Governorate in February 2016. They had been transported in ICE-BOX
to the laboratory of Fish Processing Technology, National Institute of
Oceanography and Fisheries (NIOF), Fayoum Governorate, Egypt. In laboratory,
whole fish were immediately beheaded, gutted and cut into steaks then washed
gently with tap water. Steaks samples were divided into four groups. One of
them was cooked by frying and grilling methods in the same day of the
acquisition of the fish, corresponding to 0 day. The other samples were packed
in polyethylene bags with oxygen permeability, stored at -18˚C for six months
in domestic freezer, and removed for analysis after 60, 120 and 180 days to
cooked.
Experimental
Design
The different ingredients included;
sunflower oil, table salt, wheat flour, wheat bran, garlic, black pepper, cumin
and red pepper were obtained from the local market at Fayoum, Egypt.
Cooking
Techniques (Table 1)
Raw
Mullet Fish Steaks
Raw Mullet fish steaks were packed
in polyethylene bags and stored in deep freezer at -18˚C for 180 days. Samples
were withdrawn periodically at intervals of 60 days for analysis and to prepare
the fried and grilled fish steaks.
Analytical
Methods
4.5.1.Proximate Chemical
Composition: Moisture, crude protein, crude fat and ash contents were
determined according to [7]. Total carbohydrates were calculated by difference
method using the following equation: Total carbohydrates =100% - (% protein + %
fat + % ash + % moisture) [8].
Statistical
Analysis
Chemical composition data were
analyzed statistically using SPSS 16.0 for windows (SPSS Inc., Chicago, USA).
least significant difference test (LSD) at (P ≤ 0.05) and Standard Error (Mean
± SE) were calculated.
Results and Discussion
Effect
of Cooking Techniques on Mullet Fish Steaks
The effects of frying and grilling
cooking technique on the proximate composition (moisture, protein, lipid, ash
and carbohydrates) of Mullet fish are presented in Table 2. Moisture content of
raw, fried and grilled steaks of Mullet fish were 71.45±0.83%, 60.23±1.28% and
64.72±1.73%, respectively. There was significant (p < 0.05) loss in the
moisture content of raw fish due to the cooking process by frying and grilling.
It was observed that moisture content was decreased by 11.22 % in the fried
steaks and 6.73 % in the grilled samples. This observation agreed with
El-Sherif et al. [9] for fried Tilapia fish as well as for some fish species
[10]. The protein content in raw Mullet fish was significant increased
(P<0.05) in the fried and grilled Mullet steaks. Increasing protein content
in the cooked fish samples (fried and grilled) due to the water loess during
cooking. Protein contents were19.4±0.81, 23.77±0.44 and 22.65±1.15% in raw,
fried and grilled Mullet steaks, respectively. Similar data showed that
deep-fried fish had the highest protein value comparing other cooking methods
[10, 11].
Data given in Table 2 showed that
total lipids in raw, fried and grilled Mullet samples were 7.41±0.81,
13.45±0.26 and 10.2±1.15%, respectively. These values were differing
significantly (P<0.05). The higher lipid content of fried Mullet fish than
grilled steaks is mainly due to the absorption of oil and losing moisture
during frying process [12]. Ash contents were 1.46±0.27, 2.05±0.29 and
1.98±0.57 in raw, fried and grilled fish steaks, respectively (Table 2). The
differences of ash content higher of fried steaks is due to more loss of
moisture took place during deep frying cooking comparing with grilling method
[11]. The carbohydrates contents of cooked fish steaks showed similar
observations. The changes found in the chemical composition of Mullet fish
cooked by frying and grilling were similar to several studies carried out in
other fish species included Sea bass [10-14].
Effect
of Cooking Techniques on Pre-frozen Mullet Fish Steaks
The effect of frozen storage on
moisture, protein, fat, and ash contents of Mullet fish steaks post-cooked by
frying and grilling were studied. The obtained results are tabulated in Tables
3-7.
Moisture
Table 3 showed the effects of
storage at -18°C and cooking technique on the moisture contents of raw Mullet
fish as well as Mullet fish steaks cooked by frying and grilling. The initial
moisture contents of raw, fried and grilled fish samples were 71.45±0.84,
60.23±1.28 and 64.72±1.73 %, respectively. The differences were a gradual
decreasing in their contents of moisture as affected by frozen storage period
and cooking technique. After two months of storage, moisture contents of raw,
fried and grilled fish samples were 70.60±2.07, 59.04±0.6 and 63.45±1.41,
respectively. As the storage period extended, the moisture content considerably
decreased. At the end of six months storage, moisture of raw, fried and grilled
fish samples decreased down to 69.1±2.88, 57.64±1.52 and 60.91±0.525%,
respectively. Moisture losses in raw, fried and grilled samples were estimated
by 2.35, 2.59 and 3.81%, respectively after six months of frozen storage. The
loss of moisture of the pre-frozen fish samples could be attributed to the
sublimation of ice in frozen storage and the loss of drip during thawing
process in addition to water loss due to heat during frying and grilling
processes [15]. Similar findings were reported for other species of fish such
as Sea bass fillets [16], Carp fish cutlets [17], Tilapia fillets [18], Labeo
rohita [19] and Catla fish cutlet [20].
Protein
Table 4 showed that effect of
storage periods at -18°C and cooking technique on protein contents of raw and
cooked Mullet fish products. Protein contents of raw, fried and grilled samples
at time zero were 19.4±.81, 23.77±.44and 22.65±0.1.15 %, respectively. The
results indicated that protein contents of raw (uncooked) and cooked Mullet
fish samples gradually decreased during storage. As shown in Table 5 after six
months of frozen storage protein contents of raw, fried and grilled cooked
Mullet fish samples decreased to 18.5±2.59, 22.9±.52 and 21.8±1.6%,
respectively. Protein decreases were estimated by 2.35, 2.59 and 3.81 % in raw,
fried and grilled fish samples, respectively in related to the initial protein
content of raw unfrozen sample. Protein loss during frozen storage of fish products
had been studied and several mechanisms were suggested to explain this behavior
[21] reported that the changes in protein content during frozen storage may be
due to the loss of some volatile nitrogenous compounds during frozen storage
and protein hydrolysis by enzymes which enhanced the loss of water soluble
nitrogen with separated drip [19] attributed protein loss observed during
frozen storage of (Labeorohita) to the leaching effect on amino acid and
water-soluble protein during thawing, process.
Fat
Storage changes in fat content of
raw and cooked Mullet fish samples were periodically determined at intervals of
two months during frozen storage at -18°C and the results obtained are given in
Table 5. Fat content of raw as well as the fried and grilled samples
immediately after cooking process were 7.41±.81, 13.45±.26 and 10.2±1.15%,
respectively. During storage, fat content slightly decreases down to 7±.58,
13.15±1.24 and 9.95±.548 %, respectively at the end of 180 days storage. The
losses in fat contents of Mullet fish samples at the end of storage period were
calculated by 5.53, 2.23 and 2.45 % in raw, fried and grilled samples,
respectively. In a study made by Gandotra et al. [19] on (Labeo rohita) fish
during frozen storage for 21days at -12 ± 2°C the losses in lipids were 5.44,
15.80 and 22.27% after 7, 14 and 21 days of storage. Similar results reported
by Arannilewa et al. [22], [18,23]. The decreasing in fat content might be due
to oxidation and hydrolysis of lipids which result in the formation of some
volatile compounds as aldehydes and ketones [19].
Ash
Changes in ash content of raw and
pre-frozen cooked Mullet fish samples during frozen storage at-18°C for 180
days are presented in Table 6. The raw and cooked Mullet samples showed gradual
increasing in their contents of ash during frozen storage. The initial ash
contents of raw, fried and grilled samples were 1.46±.27, 2.05±.29 and
1.98±.57%, respectively. Ash content gradually increased during frozen storage
up to 4.55±.32, 5.61±.69 and 6.49±.75% at the end of storage period,
respectively. Similar observation was found during frozen storage of some fish
products 19. 23 reported that ash content of fish sausage made from Catfish and
Tilapia increased during storage at -18°C for 120days. The increase in ash
contents of fish products during frozen storage might be attributed to the loss
recorded in protein and fat content which reflected the increasing found in ash
contents. On the other hand, some studies showed a decreasing in ash content of
fish during frozen storage which was attributed to the drip loss during thawing
process [19].
Carbohydrate
The carbohydrate of raw and cooked
Mullet fish products during frozen storage were in Table 7. Carbohydrates of
raw and cooked Mullet fish sample were determined by difference and therefore
the change of it might be due to the change of other constituents mainly as a
result of added spices.
Conclusion
Proximate composition of Mullet fish
steaks showed significant differences between cooked and raw samples and during
frozen storage. The loss of moisture in fried samples amounted to the highest
levels; also, the protein and fat value was proportionally high. Mullet fish
showed a gradual decrease in their chemical composition contents. Mullet fish
steaks maintained their nutritional value until the end of the storage period
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