Abstract
Introduction
The Food and Agriculture Organization 1 reported that fishery products have increased in the last 2 decades as healthy seafood. The fish feed composition affects the nutrient composition and nutritional quality of fish. The effect of feeding on different nutrients and their effect on further processing are included in this report. This study also presents that slaughtering with special care is necessary in getting rid of spoilage microbes and making further processing easy. Other factors include the environment, primary processing steps, and packaging. 2 Fish provide high content of fat and n−3 fatty acids as a health benefit for people's nutrition. 3 The physiological changes of fish affect the nutrient composition of different fish species. 4 Monterio et al 5 reported that wild fish is desirable for people's nutrition. Fish, as a high source of animal protein, provides approximately 30%-80% of diet protein. 5 The nutritional quality of fish can be affected by the feed composition, food availability in the ecosystem, species, water quality, and processing and storage methods. Fish must be processed and stored to reduce rate of spoilage because it is perishable when caught. The chilling, smoking, salting, freezing, drying, and fermentation processes are used by producers.6,7 The lowest moisture content and higher values of nutrients in the oven-dried sample indicate that they are affected by dehydration.8,9 Fish generally contain very little carbohydrate, vitamins, and minerals, but has high moisture content. Most fish species contain a maximum of 80% moisture, 26% protein, and 13% fat. The oil contents vary with age, species, size, and season. Fish that are high in oil are called fatty or oily fish, whose dry matter may contain a maximum of 30% oil, while those that are low in oil are called white fish. 10 Other research results indicated that cooking had a considerable effect on the proximate composition. Changes in the protein and ash contents of dry matter are significant for all cooking methods. The increase in the fat percentage of the fried samples was significant, except for the samples cooked by other methods. 11
However, due to its pH being close to neutral, fish is highly perishable, has a high water activity, is rich not only in unsaturated fatty acids, but also in free amino acids, and exhibits active autolytic enzymes causing microbial and oxidative degradation. Among the traditional methods of preservation, heat treatment can lead to changes in appearance, texture, and taste in addition to affecting the nutritional value. Refrigeration, in turn, can slow its deterioration, but limit the shelf life to 7-14 days, while freezing increases the shelf life, but can lead to adverse changes in the nutritional value, such as cholesterol oxidation. 12 Therefore, the aim of this research is to investigate the compositions of protein, fat, moisture, energy, and ash of raw rainbow salmon processed under different processing methods.
Scientific Hypothesis
The nutritional quality of processed fish depends on the method and conditions of processing, initial quality of fresh fish, and preservation of fish nutrients after processing.
Material and Methodology
This research work was carried out at 2022 at the Fisheries Laboratory of University, Iran. The fish were caught in Behbahan, Iran and transferred to the laboratory as fresh fish with crushed ice.
Chemicals
All chemicals were purchased by Behbahan Company in Iran and of analytical-grade quality
Animals and Biological Material
This research work was carried out at 2022 at Fisheries laboratory of Behbahan Khatam Alanbia University of Technology, Iran. It has a scientific name of Oncorhynchus mykiss. The sunflower oil used in the frying method is non-volatile oil pressed from sunflower seeds (Helianthus annuus).
Instruments
Charcoal, water, meter, scale, oven, electric furnace, Chinese container, Petri dish, distilled water, homogenizer, and pH meter were used in this research.
Laboratory Methods
The 5 cooking methods of boiling, freezing, thawing in hot water, thawing in oven, and frying were used in this research.
Description of Experiment
Sample Preparation
The fish was filleted with a knife, and the fillets were weighed by a scale. The weight of the fillets was 281.3 kg. The fillets were divided into 6 parts: A, B, C, D, E, and F.
Design of Experiment
Four rainbow samples weighing 1023.7, 759.5, 612.7, and 902.1 g, with an average length of 39.5 cm and an average width of 8 cm, were randomly purchased from a local market (Behbahan, Iran). They were kept in ice and immediately transported to the laboratory within 1 h. The head scales and guts were separated, and the fillets were prepared. The net weight of the fillets was 281.3 g, and the yield of fillets was 49.91%.
Upon arrival at the laboratory, the fish sample was washed and cut into pieces. The head and wastes were removed, and the pieces were thoroughly washed again with distilled water. The pieces (100 g) were separated into 6 parts. One of the 6 divisions was set apart as control (fresh); one was boiled; and the others were frozen, fried, and thawed in oven and hot water. Common procedures for fish preparation for table consumption were followed.
The fillets were divided into 5 groups. The first group was a control, which was not cooked, and the other 4 groups were used for each of the processing methods. In the first method, the fillets were cooked in oil in an oven for 20 min. In the second method, they were boiled in water for 20 min. In the third method, they were frozen in the freezer for 1 week. In the fourth method, they were cooked in an oven for 110 °C for 30 min after being thawed from a frozen state or thawed from a frozen state in warm water for 20 min. No ingredient or additive was added for cooking. Bones were removed from the samples, but the skin was not. The fillets were then mashed, and the moisture content was immediately determined. The dried samples (after the moisture content determination) were ground using mortar and pestle, then wrapped in aluminum foil and polyethylene bags. The samples of each group were homogenized in a food blender and then analyzed. Each sample was analyzed in triplicate.
Macronutrient Composition Analysis
AOAC 9 standard methods were adopted for the analyses of samples to measure the fat crude, crude protein ash, and moisture contents.
Measurement of pH of Samples
To measure the pH of samples, 5 g of each sample was mixed with 30 ml of distilled water. The mixture was homogenized by stirring. We used a digital pH meter to measure the pH.
Measuring Raw Energy of Samples
The energy values in kcal were determined using equations and measured by Atwater method.
Samples analyzed: 90 samples.
Repeated analyses: All chemical analyses were conducted in triplicate.
Experiment replication: Two times.
Statistical Analysis
The analyses were performed in triplicate, and all data were expressed as means. All data were analyzed with SPSS software version 16.0. One-way analysis of variance was used to determine significant differences between different groups at a confidence level of P < .05.
Results and Discussion
The moisture content ranged from 72.50% for fresh fish to 19.50% for frozen fish, while the fat content ranged from 8.09% for fresh fish to 64.47% for frozen fish. The ash content was in the range of 4.82%-5.82%, while the protein content was 10.47%-13.59%. The cooking methods resulted in a variation in the nutrient composition. However, no significant variation was observed in the fried and boiled samples, except for samples frozen and thawed, which recorded significantly changed fat and moisture contents.
The moisture contents in the fish species was in ranges previously reported by other researchers.13–15 The moisture content generally decreased with the processing, and the decrease was more pronounced and significant in the fried and frozen samples than in the other processed samples. The fat content increased as a result of processing, and this increase was more pronounced in the fried, frozen, and thawed samples.
The ash content of fish decreased with the processing, although this decrease did not follow a particular order and was probably due to loss of some water-soluble and heat-sensitive minerals during processing. The protein content of the samples slightly decreased after processing, which was significant because fish is generally consumed as a source of protein; therefore, it is very important that processing methods do not negatively affect the protein content or quality. The processing techniques here did not lead to a reduction in the protein content.
Fish processing is carried out for the preservation of nutritious compounds and prevention of spoilage such that its shelf life is prolonged. The best method of preserving fish in the present study, which preserved the freshness of fish, was quick freezing. The thawing method in oven had the highest energy value of fish, such that the moisture level of fish was low; its fat was high; and its pH was at an optimal level. Because the moisture of fresh fish was high, and its fat was low, its energy level was less. Thawing in hot water and boiling methods were found in the next stages of the preservation of fish nutrients.
The proximate composition of the samples of raw and processed fish is shown in Table 1 and Figure 1. The composition of raw fish was similar to the findings of the other researchers. 16 Changes in the protein and ash contents were significantly found for all processing methods (P < .05). The fat content in the fried, frozen, and thawed samples significantly increased (P < .05). In a previous report, the difference in the water content between the fresh and processed rainbow trout was significant. 16 The fat was absorbed by fish through frying and also increased dry matter. Unlusayin et al 16 and Steiner-Asiedu et al 17 reported similar findings. The highest increase in the amount of dry matter was observed in fried and cooked in water samples. Water losses during frying and boiling and thawing in oven and thawing in hot water resulted in a higher fat content than raw fish. This is consistent with findings of Toth-Markus et al 18 that fried fillets had significantly higher fat than raw fillets.
Mean nutrient composition (%) for the whole and Oncorhynchus mykiss species of fish processed using different methods.
Proximate Compositions (Dry Weight Basis), Energy, and pH Values of Raw and Processed (Oncorhynchus mykiss).
Values are means ± SD. Different letters in the same column indicate a significantly different p-value (P < .05).
The frozen fish sample had the highest nutritional value, with a maximum of 80.5% dry matter (Figure 2), while the sample thawed in oven preserved nutrients better than that thawed in hot water (Figure 3).
The dry material (%) for the whole and Oncorhynchus mykiss species of fish processed using methods of frying, boiling, and freezing.
Mean dry material (%) for the whole and Oncorhynchus mykiss species of fish processed using methods of thawed in oven and thawed in hot water.
Table 1 shows that in frozen fillet, the percentage of dried matter was the highest due to the high amount of organic and mineral matter in frozen fish. This was followed by fish that had been defrosted in an oven and hot water, and then fried fish.
The increase in the processing time and the loss of moisture lead to the denaturation of protein. The fat content increases in all methods, with a decrease in the water content as fat plus water content of flesh equal to 80%. 19
The premier value of moisture was noted in the raw samples, while the reduction of moisture was observed in the fried sample. It was also found that the moisture content decreased in the method of cooking, except for boiled fillets. In the present study, these differences were found comparable to those stated by Aberoumand and Karimian-Khosroshahi et al.20,21 In this study, the fried samples' moisture content was the lowest recorded in fish. The main factor for moisture loss by frying produced a higher protein content in fried fish compared to uncooked fish. The intensification in the ash, protein, and fat contents obtained in the cooked fillets was justified by lessening moisture. Same patterns were observed in the present study, where the fried samples tended to increase their protein, ash, and fat contents after removal of moisture.
The moisture content of fried fish was significantly low with a value of (28.74% ± 1.43) (Figure 1) compared to boiled fish (30.4% ± 1.02). This may be due to the evaporation of water by the high heat of oil. The low amount of moisture in fried fish compared to boiled fish might have contributed to the high protein content in fried fish. The decrease in the moisture content in fried fish was also described as a change that makes protein and fat contents significantly increase in fish fillet. The direct contact with oil in high temperature might contribute in extraction of minerals from fried fish. The high protein recorded in fried fish might be due to the lesser time taken in frying compared to boiling. This high protein in fried fish was also reported by Aberoumand and Ziaei Nejad. 22 It is clear that protein decreased in the frozen samples. In this study, frozen storage reduced the protein content in frozen fish. Several workers similarly observed that protein and moisture decreased with the frozen storage. 23
According to researchers in the literature, it is not possible to give valid information for the best thawing method. For instance, thawing at room temperature was widely practiced in small businesses, but it is not recommended due to the risk of microorganism development. Excessive water loss, bad odor, and taste may occur in refrigerator thawing due to slow thawing and bacterial growth over time. In principle, seafood should be thawed as quickly as possible. Faster and more advantageous thawing methods are possible for large facilities, and oven thawing is one of them. 24
The pH might be used as an indicator of the extent of microbial spoilage in fish. The increase in pH may be due to the increase in the accumulation of ammonia compounds mainly caused by increased microbial activities. The increase in pH can also cause an increase in volatile compounds due to the decomposition of nitrogenous compounds by endogenous or microbial enzymes. These results are in line with the present study results. The pH is an index, which is important in the evaluation of the product quality. The decrease in crude protein in fish during processing could be due to the slow denaturation of crude protein to more volatile compounds, such as total volatile bases, trimethyl amine, hydrogen sulfide, and ammonia. These findings were in line with the present study results. The decrease in protein in fillet could be due to reduction in salt and water soluble or because of autolytic degradation combined with endogenous enzymes and bacteria. The decrease in the protein content was probably due to the leaching of soluble components, especially water proteins and urea as fresh fish spoils in storage. 25
Thawing loss is mainly due to protein denaturation and mechanical losses caused by ice crystallization as one of the most important indicators for evaluating the quality of fish meat, 26 which was agreed with the present study results.
The proximate composition of fish meat was combined to form a nutritional profile, which is the first indication of the commercial standards of fish required by food regulations. The analyzed amount of moisture, protein, fat and ash of fish is very important for consumers, producers, and scientists from different perspectives. In addition to knowing the nutritional value of fish, it helps understand its better processing and storage and regular evaluation of the physiological state of fish from the perspective of fisheries. Today, proper knowledge about the approximate composition of fish was increasingly used in various fields, and knowing the chemical composition of fish helps nutritionists determine available sources of high-protein and low-fat food sources for human consumption and helps food scientists determine food sources with high protein foods with high nutritional value. Information about the proximate composition of a species helps determine its nutritional value in terms of the energy units compared to other species. It also helps processing technologists to determine optimal processing and storage conditions to maintain the fish quality as much as possible. 27
Water constitutes a major part of the fish body. Through it, the transfer of various nutrients and the transfer of chemical energy and several cytoplasmic reactions are carried out. For most fish species, the moisture content generally varies between 60% and 80%. The percentage of water also serves as a good indicator of the relative amount of protein, energy and fat. 28 Aberoumad and Pourshafi 29 confirmed that moisture acts as an excellent indicator of relative energy and fat and protein content and shows an inverse relationship with them. This means that the percentage of water was less; protein and fat were more; and the energy density of the fish was higher. Fish protein has high nutritional value and beneficial effects on people's health. Depending on the texture and quality of fish meat, fish protein is considered as the best source of protein in developing countries. The protein content of fish can be used as a vital tool in evaluating the physiological standards of fish. The quantity and quality of fish also affect their protein requirements because a higher protein content in the fish body is equal to a higher protein requirement for fish growth, and vice versa. 27 Fat is considered the third major component in fish muscle and is generally reported to range from 6% to 20%. The lipid content in fish is considered as a good indicator of future survival and reproductive potential in some fish stocks and considered as the most critical food stock. Fat indices are also used as a means of describing the relationship between fat and water contents. 27
Fresh O. mykiss
Frozen O. mykiss
Fried O. mykiss
Ash comes fourth in terms of quantity. Its amount varies from 0.5% to 5% of the total weight of the fish body, and it acts as an important source of nutrients for fish and as the most reliable method for detecting the mineral composition of fish. It is considered because it represents the total mineral content of the sample. It has been reported that the total mineral content in wet muscle generally ranges from 0.6% to 1.5% of the total fish body weight. Muscles and bones act as an excellent source of non-consumable minerals, and approximately 65% of minerals are stored in the skeleton. 27 The limitations of this research are that the fishing season for this type of fish is short, and the storage and preservation of fish for people's consumption are not sufficient. Therefore, it is not possible to perform all methods of fish processing. Consequently, although each processing method shows distinct advantages, their comparative analysis shows that no single approach is superior in all respects. The effectiveness of each method depends on the specific application conditions and types of seafood products, which require careful optimization to ensure the best results. The choice of fish and the part of the sample did not affect the experimental results. There are some basic links between different fish processing treatments. For different experiments, the fish sampling methods are the same. Measuring changes at different time points was not in the design.
Conclusion
All fresh and processed fish are good sources of protein. The highest level of protein was determined in the fried sample. Some samples, such as frozen and thawed in oven, were characterized by a relatively high fat content. Frozen, thawed in hot water, and thawed in the oven samples had the best energy and nutritional values. The frozen and thawed samples in the cooking processes showed reduced water content, which helped increase relative the concentration of nutrients, including crude ash, crude protein, and fat contents.
Footnotes
Acknowledgments
The authors would like to thank Behbahan Khatam Alanbia University of Technology.
Data Availability Statement
The datasets used and/or analyzed during the current study are available from the corresponding authors upon reasonable request.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by Behbahan Khatam Alanbia University of Technology, Behbahan, Iran.
Statement of Informed Consent
Informed consent was obtained from all subjects involved in study.