Development of Low fat fried fish by using a protein based edible coatin

CHAPTER 2 Literature Review2.1. Fried Food Consumption and Average Intake of Dietary Fat
In the past three decades, obesity or being overweight has been cited as a growing public health concern, primarily due to its prevalence among younger people. Among the various factors that contribute to the health problem attributing to obesity, a persistent dietary pattern that influences the increasing epidemic and shifts away from healthier options is the consumption of fried foods. When people fry their food in oil, the food absorbs the oil while losing water as lipids are exchanged with the frying oil. The amount of oil being absorbed would depend on the type of food and the conditions for frying. Additionally, fried food undergoes pyrolytical decomposition in its surface layers, leading to the formation of heterocyclic amines. Lastly, once the fried food absorbed the oil, degradation products like polymers and polar compounds from the cooking oil is formed, the food is believed to cause cancer, endothelial dysfunction, and hypertension (Cahill et al., 2014; Guallar-Castillon et al., 2007).
Dietary fats are important because they affect taste perception and are applicable in numerous food technology processes. Drawing from a nutritional perspective, dietary fats are significant for various health-related aspects and the best possible functioning of the body. First, dietary fats are great sources of energy and serve as the structural building blocks of the body that transport fat-soluble vitamins, included in important physiological processes, and optimal growth and development (Aranceta & Perez-Rodrigo, 2012).

According to the USDA dietary guideline for Americans as of 2010, the daily recommended fat intake for adults is 44-78 fat grams and less than 10% of calories in saturated fatty acids. However, the consumption of trans-fat is discouraged.
It is clear that food authorities suggest that it is safe for adults to consume a daily total dietary fat between 20 and 35 %E that come from dietary fat sources. Moreover, it is important to mention that fat has numerous essential biological functions and, as a result, its total consumption may not be lower than 15 to 20 %. Low-fat diets (≤20%E) may negatively affect blood lipids by lowering HDL and increasing triglycerides. It may potentially result in an inadequate intake of essential fatty acids. The upper limit for fat intake intends to guarantee that people do not consume excessive daily calories as fat because it is the most energy-dense macronutrient (Aranceta & Perez-Rodrigo, 2012).
Many healthcare professionals advise against too much fat intake due to its detrimental effect on health and development of illnesses or diseases. In one study, the researchers found that the consumption of fried food promotes obesity in Spain wherein traditional cooking involves frying with oil. They discovered that obesity was common in participants who have high energy intake from fried food (Guallar-Castillon et al., 2007). Frying with oil changes the fatty acid composition of food raises energy density and lowers water content. Although frying undeniably makes food tastier and aromatic, eating fried foods on a regular basis encourages obesity because of increased fat intake and energy density (Cahill et al., 2014; Guallar-Castillon et al., 2007).
2.1.1. Consumption of Deep-fat fried fish in the U.S. and rest of the world.
According to the yearly National Oceanic and Atmospheric Administration’s (NOAA) Fisheries of the U.S. Report, a majority of Americans have increased their seafood consumption up to 15.5 pounds of fish and shellfish per individual as of 2015 (U.S. Department of Agriculture, 2017). Meanwhile, according to Kearney’s (2010) study, “Seafood consumption is set to continue to rise towards 2050 at a faster rate than any other food category”. In response, the U.N. Food and Agriculture Organization (UN-FAO) claims that populations in developing nations are most likely to be dependent on fish as an integral part of their everyday diet in contrast to the populations residing in more developed nations. As of 1995, fish provide more than 7% of animal protein for people in North and Central America; 9.2% for those in Europe; 17.4% for people in Africa; 26.2% for people in Asia; and 22% in China and low-income food-deficit countries. Likewise, the popularity of fish in the world population’s diet is 16.4% (U.N. Food and Agriculture Organization, n.d.).
Upon the recommendation of the American Heart Association, people can eat fish at least twice a week as an inclusive part of a healthy diet. Most fish are low in saturated fat and are a good source of vitamins like D (i.e. herring and salmon) and B2, protein, minerals (i.e. iron, zinc, magnesium, iodine, and potassium), calcium, phosphorus, and omega-3 fatty acids (i.e. salmon, trout, sardines, herring, mackerel, canned light tuna, and oysters) that optimize consumers’ health. Fish can lower a person’s risk of heart attack, stroke, autoimmune diseases like type-1 diabetes, prevent asthma in children, improve sleep and mental conditioning, and slow down macular degeneration affecting the vision in old age and reduce the rates of cognitive decline and neurodegenerative disease (Pearson & Dutson, 2013).
Depending on the type of fish one consumes, they are likely to benefit from polyunsaturated fatty acids, proteins, oils, vitamins, and minerals. Fish from saltwater are rich in omega three fatty acids that are considered heart friendly. Besides, fish from saltwater contain high levels of iodine. Fish are rich nutritional foods; the only nutrients they lack are carbohydrates, and vitamin C. Fatty acids found in fish are important nutritional elements for people keen on a healthy diet. Contemporary lifestyles have made society vulnerable to cardiovascular diseases, hence the need to get the fatty acids in the diet (Young, 2009).
Mohanty (2014) asserts that proteins in fish provide both essential and non-essential amino acids. Amino acids are crucial and indispensable properties in the process of biosynthesis. Biosynthesis is the process responsible for growth in children and replacement of protein in grown humans. The existence of hormones in the human body is dependent on amino acids. Amino acids are essential molecules in the metabolic process, and they also serve as building blocks of proteins. Amino acids regulate gene expression in humans hence their indispensable nature (Mohanty, 2014).
Whiting fish (Merlangius merlangus) is chosen because of its sweet taste and high nutritious value (it feeds of shrimps and crabs) thus supplies the human body with important nutrients. The nutrients include a small amount of fat and proteins. For instance, a 3-ounce of fish served contains approximately 15 grams of protein and 1 gram of fat, which is considered healthy for the human body. The fish also contain omega-3 fatty acids. The omega-3 fatty acids are essential to the body. They are known to prevent heart diseases and reduce chances of heart attack. Also, whiting fish is a source of important minerals. They include magnesium, estimated at 18 mg, 40 mg of calcium, 200 mg of potassium, and 190 mg of phosphorus per 3-ounce fish serving. Lastly, it is rich in vitamins, especially vitamin B, D and A (Mahaffey, 2004). Particularly, it contains 85 per 1000 milligrams (mg) per 3-ounce serving. All these minerals are important for the human body, which makes whiting fish a healthy food. Although fried fish is generally perceived as a healthier option than fried meat, many studies have discovered that fried fish can also attribute to the higher risk and development of some diseases. Recent news reports reveal that fried fish can cause a series of health problems. In one study published in the journal of Circulation, the researchers reveal that consuming fried fish for a minimum of once a week was correlated with a 48 % higher chance of developing heart failure and diabetes though another study deems these findings inconclusive (Xun & He, 2012; Wallin et al., 2012). Therefore, it is important to reduce the fat uptake in fried foods like fried fish.2.2. Mechanisms of Fat Uptake in Deep-Fat Fried Foods
There are various mechanisms that affect the oil uptake in fried foods. These mechanisms involve an evaluation of the primary product structure, different interchanges that occur between the product and the heating medium, and variations of food product and oil properties. In particular, these mechanisms include water escape, capillary pressure (porosity), adherence and drainage of oil, and vapor condensation and vacuum effect (Brannan et al., 2014).
2.2.1. Factors Affecting Fat Absorption in Deep-Fat Frying
Various studies have attempted to improve the process of frying food by controlling and reducing the final fat content of fried food products. For example, by changing the physical and chemical properties of oil, the mechanisms of oil absorption predict that the more the water or moisture is removed from the surface during the frying process, the more the oil is absorbed by the food (Brannan et al., 2014).
Frying factors include oil temperature and frying time, vacuum frying (that decreases oxygen concentration and frying temperature), and post-frying conditions like the cooling condition after food are removed from the frying medium – these factors determine oil distribution, the food’s structure, and flavor properties (Brannan et al., 2014). Many studies have determined, the larger the water amount or moisture is stored in the food’s surface, the higher the amount of oil is absorbed (Pettit, 2014). This mechanism is due to the water vapor escaping from the crust and substrate, which then produces voids into which oil enters. As a result, the more water there is, the more voids are created, and an increased oil uptake ensues (Pettit, 2014).
2.3. Intrinsic variables influencing fat uptake
Examples of intrinsic variables include the substrate type, the content of moisture, porosity formation, and surface area (Pettit, 2014). Capillarity effect influences the liquid drawn or moisture released when the adhesive intermolecular forces found between the moisture and the food are stronger than the cohesive intermolecular forces found in the liquid. This leads to a difference in pressure in-between the two sides of the curbed interface according to the Laplace law. Also, the lower the contact angle is between the product’s surface and the oil, the stronger the adhesion forces and the higher the oil uptake becomes (Brannan et al., 2014). Therefore, water removal and intensity serve as factors for oil uptake since they modify or control the amount of oil being absorbed during frying. For example, in Pettit’s 2014 study, it was discovered that the amount of oil absorbed by fried food is identified by high moisture content of food, particularly the crust. The author explains that the larger the water amount stored in the food surface is, the larger the amount of oil is absorbed, which is better explained by the water replacement theory (Pettit, 2014). Therefore, it is important to dry fish before frying to reduce the amount of oil uptake.
In another study, researchers used battered and breaded chicken fritters as their sample that was tested for both moisture and lipid content. The researchers used a post-breeding dip composed of 11% dried egg white solution and were compared to an un-dipped control. It was discovered that the control or undipped fritters lost 62.2% moisture during frying while 37.8% remaining moisture was lost due to moisture innately happening in the chicken that was vaporized and escaped through the crust’s pores. Thus, it was assumed that the low water amount that vaporized from the chicken was responsible for the oil inhibiting effect that was associated with the moisture found on the surface of the battered and breaded chicken (Pettit, 2014). Additionally, Pettit (2014) explains that “substrates that have a larger surface area absorb more oil. Oil absorption increases linearly as surface area increases. Surface roughness creates a larger surface area and also increases the oil absorption. The density of the food has also been related to oil uptake. This could be because density has been correlated to porosity. The portion of the food that determines the amount of oil absorbed is the crust. It is well known that almost no oil is absorbed into the core of the food”.
2.3.1. Extrinsic variables are influencing fat uptake.
Examples of extrinsic variables that influence oil absorption of food during the frying process include frying time, the temperature of the cooking oil, oil composition, ingredients that prevent oil absorption, and the amount of oil drained after frying (Pettit, 2014). For example, when food is fried, it undergoes water evaporation whereby spaces are created, which are then entered by the cooking oil. The food product stays at an estimated temperature of 100 ºC for as long as there is moisture to evaporate. While the moisture evaporates, a crust is formed. In short, frying food involves the process of heat transfer from the heated oil to the food; mass transfer of water from the inside of the food product to the exterior then to the oil; and mass transfer of oil into the food product (Huse, Mallikarjunan, Ngadi, Chinnan, & Phillips, 2009). Additionally, due to the high temperature and steam, the oil used for frying also undergoes certain changes in its chemical composition.
Furthermore, studies conducted on actual frying process found that the process itself can be modified to help lessen oil absorption. Some hypothesize that using an external head gas like nitrogen may limit or lower fat absorption in breaded chicken products while others reveal no significant difference in the oil absorption of fried food products in a certain pressure fryer in comparison with those fried with nitrogen wherein the latter technique tends to increase oil content on fried food. Also, another study effectively lowered reduced oil uptake by frying the food under vacuum pressure (Huse et al., 2009; Mah, Prince, & Brannan, 2009).
2.4. Batter and Breading in Deep Fat Fried Foods
There are different kinds of breading and batter systems. The flour-dredge breading is done by bringing or soaking the food in buttermilk and then tossed in seasoned flour before frying. This leads to a crunchy, dark brown crust. Another common type of breading is the standard bread-crumb breading whereby the food is dredged in flour, then dipped in beaten eggs, and then dredged in dried breadcrumbs. It is very simple and will form a crisp, solid, airtight crust that can easily absorb sauces. However, the standard breadcrumbs can become soft quickly and, thus, also causes a fast breakdown of oil. Another typical type of bread is the Panko bread-crumb breading that is similar to the standard breadcrumbs but instead uses panko that is a type of breadcrumbs that have a wide surface area, making crisp coatings (Lopez-Alt, 2017)
With regards to batters, a common type is the beer batter where the food is first seasoned with flour mixture composed of leavened flour, beer, and egg that makes a thick batter similar to pancake batter. The purpose of adding the beer is to brown the crust beautifully while the bubbles from the beer aid in keeping the batter light. Lastly, another common batter is the cornstarch thin, tempura-style batter that uses high-starch but low-protein flour (i.e., wheat flour, cornstarch) and mixed with ice-cold water (or soda water), and egg (optional) that are mixed quickly to create a lumpy batter where the food is dipped immediately and fried quickly (Lopez-Alt, 2017).
The presence of breading and battering affect the amount of oil that it absorbs when fried. For example, one study found that fish sticks coated in batters significantly slowed down or held back fat movement into the fish (Falguera, Quintero, Jimenez, Muñoz, & Ibarz, 2011). This is supported by another study whereby the researchers declared that higher reduction of oil in fried food products is expected along with better understanding of the mechanisms of oil absorption related to process parameters (Brannan et al., 2014). For example, pieces of evidence show the conditions after removing food from the fryer affects fat uptake by properly shaking and draining the food and frying at the correct duration and temperature.
Additionally, Mah et al. (2009) stated that batters reduce fat uptake along with altering frying techniques and medium. Therefore, batter and breading lower fat uptake and water loss during the process of frying (Falguera et al., 2011; Mah et al., 2009; Brannan et al., 2014). On the other hand, Stastny, Keith, Hall, and Garden-Robinsons’s (2014) explained that breading and deep-frying increase the fat content of foods, which increases a person’s risk of obesity and chronic diseases. Some of the attempts to reduce fat content and oil uptake in deep-fried food products include adding fiber, coating with hydrocolloids like starchy gum coatings, dipping in sugar or salt solutions, coating with cellulose derivatives, or vacuum frying and flash-frying (Stastny et al., 2014).
2.4.1. Starches
The batter also avoids water evaporation from the food product. To lower the oil content and increase the retention of moisture of food products during frying, gums and proteins or modified starches like microcrystalline cellulose (MC) or cellulose derivatives are used in the batters (Chen, Chen, Chao, & Lin, 2009). When starch granules swell and become gelatin-like, the batter creates a barrier between the food and the oil that decreases the possibility of oil absorption into foods while frying. For example, different degrees of cross-linked tapioca starches were used in one study that was able to lower oil absorption by 17 % because it limited starch granule disintegration. Also, water content increased and resulted in reduced batter pick-up, cooked yield, and oil uptake (Gamonpilas et al., 2013).
Cornstarch is used in the battering system for deep fried food and products. Cornstarch has several components for breading and batter systems. In particular, the cornmeal dough is directly browned to make corn chips (Gönenç & Us, 2018). Corn flour has a low content of zein proteins, low molecular weight proteins with β-sheet and α-helical structure ((Tycko, Savtchenko, Ostapchenko, Makarava, & Baskakov, 2010). Besides, Cornstarch has about 13.4 g of dietary fiber per 100g of the cornflour and is almost all pure starch. However, there are limitations in using corn-starch in battering systems: when added to the sauce corn-starch creates a glossy appearance when thickening, besides lacking good taste. Moreover, corn-starch lowers fat uptake. Consequently, there is a need to replace con-starch as the main ingredient to enhance the quality of the product as well as reducing the fat absorption (Newman, Petri, Grüll, Zebeli, & Metzler-Zebeli, 2018).
2.4.1.1. Sweet potato starch versus cornstarch
Sweet potato, (Ipomoea batatas), belongs to family Convolvulaceae and is among the world’s most important and undermined tubers. Sweet potato starch is usually extracted by grinding and wet separation techniques. The size of its starch granule differs from less than 1 μm to over 100 μm. These sweet potato starch granules come in round, oval, and polygonal shapes. Sweet potato starch can be modified through either physical or chemical techniques, depending on how it is intended to be used in traditional products.
Moreover, the sweet potato is rich in dietary fiber, vitamins, and minerals. Also, it has antioxidants; phenolic acids, β-carotene, tocopherol, anthocyanin, and ascorbic acid (Kim, Lee, Lee, & Lee, 2002). Besides edible coating in sweet potato, it has a wide variety of additives which include antioxidants and antimicrobial. Unlike the corn-starch, sweet potato has an edible coating and a lower fat uptake. In conclusion, the sweet potato coating in the battery system reduces TBARS (2-thiobarbituric acid reactive substance), melanosis, and microbial growth Alotaibi & Tahergorabi (2018). Also, the use of sweet potato will cut loses of shrimp meat besides maintaining the quality of the fried food.
In contrast to sweet potato starch, cornstarch is not a necessarily great source of vitamins or protein alone. This is because cornstarch only includes small amounts of essential minerals. Lastly, as for its chemical composition, cornstarch is in general approximately 27% amylose polymer, and the remaining are amylopectin. Also, there are certain possible impurities that the milling of corn kernels may leave behind, such as fiber, gluten proteins, and oils and fats. Additionally, cornstarch is a non-Newtonian liquid that has eccentric properties intended for sheer thickening caused by polymer forms of starch. It is a huge macromolecule with a molecular weight of 692.65802 grams/moles. Based on cornstarch’s chemical structure, it can function as a form of a binding substance (Ding, 2017).
Finally, when comparing between sweet potato starch and corn starch, the thermal properties of starch influences oil uptake in fried foods. Cornstarch has the highest onset temperature (63.19 ºC), which is followed by sweet potato and potato starches. Although the addition of starch in batters can lower the oil content in fried food, the extent of this decreased oil uptake depends on the amylase. Sweet potato starch has a lower level of amylase compared to the cornstarch. Therefore, since starch granules with higher contents of amylase offer a better barrier preventing oil from being absorbed into the food product (Zhang, Yang, Ji, & Ma, 2014).
2.4.2. Proteins
The use of traditional batter and breading for fried food is common and one of the contributors to low-fat uptake (Perera, 2011). Because of this, innovations are made to make lessen the fat uptake during deep frying. One of the most popular materials used to create alternative batter or breading for food is protein-based material. This is because protein-based coatings are great for reduction of oil absorption (Mah, Price, & Brannan, 2008).
Mah, al (2008) conducted a study to test the oil reduction property of whey protein isolate through using it as post breading dip. The results of the study showed that whey protein isolate is a great material to be used for fat uptake reduction when cooking deep-fried.
2.4.3. Gums
Gum is another substance used as batter coating or breading food because of the many beneficial properties that they possess. Some of the known beneficial properties are in decreasing the heat transfer and decreasing the oil absorption. Sahin, Sumnu, and Altunakar (2005) tested these properties through coating chicken nuggets with various gums, HPMC, guar gum, xanthan gum, and gum Arabic, before deep-frying. The results presented HPMC and xanthan gums to promote reduced oil absorption compared to other gums and control (no gum coating).
A follow-up study was conducted by Akdeniz, Sahin, and Sumnu in 2006 to test the oil-reducing property of gums on deep-fried carrots further. The team used a combination of guar gum and xanthan gum as batter coating. The study was able to yield a maximum of 53% oil reduction on the deep-fried carrots with less moisture loss.
In 2008, Garmakhany, Mirzaei, Nejad, & Maghsudlo (2008) analyzed the effect of hydrocolloids in reducing the oil uptake and sensory attributes of some deep-fried potato chips. Carboxymethylcellulose, xanthan gum, and guar gum were used as a source of hydrocolloids. The minimum fat content was found from chips coated with CMC, xanthan, and guar compared to the other samples.
2.4.4. Bread Crumbs
Breadcrumbs are common coating ingredients for fried food. This is because breadcrumbs provide the desired texture and crispiness in fried foods (Rosbottom, 2012). Breadcrumbs are either fresh dried, fine, coarse, or ‘panko.’ Fine and panko bread crumps are used foods of Asian origin (Civitello, 2011).
Originally, to achieve a crispy and textured finish, food is dipped in batter coating before frying. However, battered fried food eventually loses their crispiness after a while which affects the appeal of the food (Vogel, 2017).
There three main types of bread crumbs used in breading fried food: fresh, dry, and panko breadcrumbs. Fresh bread crumbs are mostly coarsely ground bread. These crumbs are best used immediately since they get stale and dry out quickly. Dry breadcrumbs are made from ground toasted bread. These are the most commonly used and are highly preferred for traditional breading. Panko bread crumbs are larger and more flakey than the dry bread crumbs. These are made from dried or toasted white bread with the crust removed. Panko is mostly used for additional crisp in fried foods like fish and chicken (Bowen, 2002). Breadcrumbs are in the same category as cheese. They contain a diverse range of fatty acids with a myriad of microorganisms. Thus, the three types of breadcrumbs may be unhealthy because of the fatty acids.
2.5. Edible coating and its role in fat reduction
An edible coating is defined as a thin layer of food technology which can be consumed. Edible coating plays a vital role in preparation, storage and ensuring the quality of food. Firstly, it used to provide a barrier for microbes, moisture, and solute movement of food Alotaibi & Tahergorabi (2018). Secondly, an effective edible coating does not only make foods tastier but also that extends the shelf life of fresh foods. Besides, edible coatings are used to provide excellent vehicles where different food additives such as antimicrobial and antioxidants agents can be incorporated. The edible coating also ensures that food color is maintained Alotaibi & Tahergorabi (2018). In the deep fry battery system, SPS and crumb bread are used for effective edible coating.
The use of edible coating in the food industry is highly popular especially in reducing the fat uptake during deep frying of food. Many studies have been done to prove this claim. In 2002, Garcıa, Ferrero, Bertola, Martino, and Zaritzky (2002) conducted a study on methylcellulose and hydroxypropyl methylcellulose to test their ability to reduce oil uptake in potato chips and discs of dough when deep-fried. Methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) were utilized in coating formulations to reduce the amount of oil uptake in dough discs and deep-fat fried potato strips. Positive, meaningful results were achieved. The best formulation recorded 1% MC and 0.5% sorbitol for fried potatoes. Also, oil uptake reduction was recorded at 35.2% and 40.6% for dough discs and potatoes, respectively.
Kurek, Scetar, and Galic (2017) conducted a review of various edible coating and their effectiveness on fried food. Edible coatings were found to be successful in reducing excessive uptake of oil by serving as barriers between the food and the oil. The edible coating has shown no negative impact on the taste or quality of the food.
2.5.1. Non-protein-based coatings
Non-protein-based coatings are increasingly growing in popularity as an alternative for protein-based coating in dep-fa frying and studies have been conducted to explore other materials that are not protein-based to widen the choices for food coating. Two major categories that people favor exploring as possible protein alternative for food coating are polysaccharides and lipids (Bourtoom, 2008; Suput, Lazic, Popovic, & Hromis, 2015).
The polysaccharide is good alternatives to protein when it comes to edible coatings and films because of their excellent structural and mechanical properties to reduce oil uptake in deep-frying (Bourtoom, 2008). In 2005, Dogan, Sahin, and Su
and tested the oil uptake reduction property of soy and rice flour by using the two as a coating for chicken nuggets. Both flours were found to provide a higher reduction in oil absorption compared to the control. However, soy flour was found to be more effective in maintaining crispness and color.
Another category of edible coating material that are ideal alternatives to protein is lipids. Lipids are widely used for their property to block the transfer of moisture as well as gases and ethylene. However, because of their hydrophobic nature, they tend to form layers of brittle films. They need to be combined with other film-forming substances, proteins or polysaccharides, to increase their resistance to water (Bourtoom, 2008; Suput et al., 2015).
2.5.2. Protein-based coatings
Protein is the most common material for forming edible food coating because of their good gas and lipid blocking ability. This makes them great films for fat reduction. They have low water resistance and low mechanical strength. However, they still outweigh polysaccharides in these areas as well as in the antimicrobial and antioxidant sphere (Bourtoom, 2008; Wittaya, 2012; Suput, 2015). Cross-linking proteins with different methods are found to improve the water and gas barrier properties of the protein (Bourtoom, 2009).
2.5.2.1. Muscle food proteins
One of the main sources of proteins in fishes is the muscle area. Protein from this portion, particularly myofibrillar and sarcoplasmic proteins are known to produce edible films (Paschoalick et al., 2003; Paulo, dos Santos, and Garcia, 2005). Proteins contained in the muscle give the muscles the power to contract. They include tropomyosin, actin, myosin, and actomyosin. The highlighted proteins make up about 65% of the protein in fish. Apart from proteins that aid in contraction, there are those that constitute the enzymes responsible for metabolism; they are myogenic and globulin. The second type of proteins composes about 30% of fish protein. Lastly, there are the stroma proteins which are the connecting tissue of the muscles.
The utilization of fish-based protein coatings on food may take place in various forms that are not limited to wrapping, coating, or spraying. The aerobic plate counts can be used to determine the level of protein uptake by the muscles. According to Alotaibi & Tahergorabi (2018), the aerobic plate count can be estimated by using a spread-plating of 1 ml of sample solution on sterile Petri-plates containing Plate Count Agar. In their experiment, Alotaibi & Tahergorabi established that seafood provided a good environment for the growth and development of deferent microorganisms. For instance, counts of the bacterial population in coated and uncoated control of shrimps gave different values. The higher the level of microbes, the more the impact on the aerobic count and hence the impact on the muscle food proteins. For instance, essential oils (due to un-coating of shrimps) are known to cause damage to the microbial cells through various mechanisms: disturbing enzyme systems, adverse impact on the membrane’s phospholipid bilayer, distorting the altering genetic material of the patient, and oxidative distortion of unsaturated fatty acids to form lipid hydro-peroxide (Alotaibi & Tahergorabi 2018). All these changes have a damaging impact on the level of muscle proteins.
During the processing of fish, 1%-3% may get removed as skin, and 8%-17% of the fish may get chopped off as trimmings (Valdivia-López et al., 2016). While removing the skin and trimming the fish, a considerable amount of muscle gets left out of the final product as waste. It is from the fish processing by-products that muscle protein emerges. It is logical that muscle protein in the form of trimmings and attached to the skin during removal get used in the preparation of fish protein coatings.
The coating exercise prevents the permeation of oxygen, hence convenient in retardig chemical, physical, and microbiological degradation of food. Use of muscle protein especially one that originates from the processing of fish does make economic sense in making edible films. When compared to other sources of protein films, fish-based sources are viable.
2.5.2.2. Characteristics of fish protein recovered with isoelectric solubilization/precipitation
Fish by-products are essential resources of nutrients such as fish muscle proteins and omega-3 fatty acids (Tahergorabi & Jaczynski, 2014). Instead of discarding these by-products, these essential proteins and lipids can be recovered through isoelectric solubilization/precipitation (Kristinsson & Ingadottir, 2006; Tahergorabi & Jaczynski, 2014).Isoelectric precipitation is the process at which protein can be recovered by solubilizing and precipitating according to their isoelectric point or behavior when subjected to a change in pH. In this process, the pH is selectively changed to induce solubility of the muscle proteins. Once the muscle proteins are dissolved, they separate into lipids and insoluble fractions (skin, bones, etc.). This subsequent change in pH will persist until the functional protein isolate is recovered (Matak, Tahergorabi & Jaczynski, 2015).
There are various aspects that the Independent Seafood Producers (ISP) consider when selecting the trout fish in battery systems. Essential oils from the sea foods (especially from trout fish) can damage microbial cells by several mechanisms: Firstly, it causes damage to the cell membrane’s and the phospholipid bilayer as well as disturbing enzyme systems. Secondly, the altering genetic material, and oxidative degradation of unsaturated fatty acids to form lipid hydro-peroxide (Alotaibi & Tahergorabi 2018, p. 207).
2.5.2.3. Film forming properties of fish-based protein
Proteins from fish muscles are also popular materials for edible films. In fact, Iwata, Ishizaki, Handa, and Tanaka (2000) conducted a study of fish water-soluble proteins and if they can form edible films. The study revealed that fish protein obtained were indeed capable of forming edible films given that it must be denatured to reveal the protein structure.
Similarly, Paulo, dos Santos, and Garcia (2005) explored the film-forming property of sarcoplasmic and myofibrillar proteins obtained from the muscle of Thai Tilapia; the study proved the possibility of the said claim.
Coatings are meant to reduce the fat uptake of food during the deep-frying process. The use of fish films is ideal as the fish protein contains less than 1% of fat and oil; this makes fish protein a perfect choice for film preparation. It is possible to come up with films from fish-based protein when utilizing the pH-shift process. Fish meat may get exposed to either very low pH (2.5-3) or very high pH (10.8-11.2), and to produce an isolate. The isolate gets subjected to the process of centrifugation to remove solids. Then, the soluble protein undergoes precipitation that happens by adjusting the pH of the isolate to the myofibrillary point to make the protein concentrate (Shiku, Yamaguchi & Tanaka, 2003). The fish protein solution acquired from the process can be used as a dipping solution in battering and breading to decrease fat uptake in frying.
From the studies of Shiku, Yamaguchi & Tanaka (2003) an inference can be made that, fish-proteins are good candidates when it comes to the development of protein films and coatings. When Shiku, Yamaguchi & Tanaka (2003) subjected fish-based protein films to different pH, the films exposed to low or high pH retained transparency close to that of synthetic films. Film formation only occurs at pH 2-3, and pH 8-12, at the isoelectric pH the myofibrillar proteins undergo precipitation thus inhibiting film formation.
Rostamzad et al. (2015) prepared protein-based films from Silver carp in the study of the characteristics of biodegradable protein films. Rostamzad et al. (2015) prepared protein-based films from fish myofibrillar protein. The prepared films were capable of delaying oxidation. When compared to polythene films, coatings made from fish inhibited light diffusion hence delayed oxidation. Also, protein-based films are effective at preventing bacterial growth.

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