Role of Natural Additives on Quality and Shelf Life Extension of Fish and Fishery Products

Fish and fishery products have drawn greater attention due to their high nutritional value owing to the presence of cheap superior quality proteins, essential fatty acids, and macro and micronutrients. But higher water content, non- protein nitrogen, and post mortem pH (6–7) in fish favor rapid spoilage by autolysis or putrefaction, and can result in health risk as well as economic loss. Moreover, the quality of fish is affected by species, harvesting season, handling and method of processing. Thus, application of food additives become necessary to maintain the shelf life, nutritional content, texture and flavor of the raw material as well as processed products. Considerable research is being done on applications of natural additives after the emergence of the concept ‘Green consumerism’ which resulted in decreased consumer preference for using synthetic food additives. In this background, this chapter will review the natural additives used for quality maintenance and shelf life extension of fish and fishery products.


Introduction
Fish and fishery products have become increasingly popular due to their high demand and nutritional value. According to Food and Agriculture Organization (FAO), worldwide production of finfish, mollusks (mainly bivalves), and crustaceans are 54.3, 17.7, and 9.4 million tons respectively [1]. Human consumption of fish is around 88% of total production and among them, 44% consist of live, fresh, or chilled products, and 35% consist of frozen products [2]. But, among animalderived products, fish is considered as the most perishable commodity as it contains a high amount of water, high post mortem pH (greater than 6), non-protein-nitrogen content, free amino acids, lower content of connective tissues, and presence of an osmoregulant, trimethylamine oxide (TMAO) [3]. Spoilage or the deterioration process refers to any change in the condition of food in terms of taste, smell, appearance, or texture and becomes undesirable or unacceptable for human consumption. Generally, the process involves 3 stages; rigor mortis, autolysis, and putrefaction. Rigor mortis or the muscle stiffening will last for hours (time may vary with temperature) after their catch. Subsequently softening occurs due to enzymatic or oxidative self-digestion, and completed by microbiological processes (putrefaction) [4].

Quality changes in fish and fishery products
Fish and fishery products deteriorate rapidly as a consequence of various biochemical breakdowns and microbial activities on the chemical composition of meat. The spoilage involves autolysis or self-digestion of these compounds by digestive enzymes or by free radicals [7]. The major spoilage process is lipid degradation, which mainly occurs through oxidation or hydrolysis. The oxidation could be various types such as photo-oxidation, thermal oxidation, enzymatic oxidation, and auto-oxidation. It can also be accelerated by prooxidants within the body such as hemoglobin, myoglobin, cytochrome c, etc. The process involves the reaction of unsaturated fatty acids of triglycerides with atmospheric oxygen to form unstable primary products like free fatty acids (FFAs), dienes, and peroxides and secondary products like aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, trienes, epoxy compounds and carbonyls [8]. The process of lipid hydrolysis or lipolysis is breaking down of triglycerides into FFAs by the action of enzyme lipases. Accumulation of these FFAs stimulates protein denaturation, texture damage, and drip loss by the formation of protein-lipid cross-linkages [9]. Generally, protein denaturation in fish occurs mainly by the action of proteolytic enzymes in the muscle (cathepsins) and the intestinal tract (trypsins), which results in muscle solubilization and leads to undesirable texture damage. End products like amino acids, peptides, amines, H 2 S, ammonia, indole, etc. will be formed and will all act as a medium for microbial growth. Microbial breakdown of amino acids will lead to bitterness, souring, bad odor, sliminess, etc. of the flesh [10].
For fish and fishery products, gram-negative bacteria like Shewanella, Photo bacterium, Pseudomonas, Moraxella, Acinetobacter, Flavobacterium, Aeromonadaceae, and Vibrionaceae and the gram-positive bacteria such as Bacillus, Micrococcus, Lactobacillus, Clostridium, and Corynebacterium are considered as the major spoilers [3,10]. The spoilage resulting in off-flavors is due to the formation of specific alcohols, aldehydes, acids, ketones, and sulfur and nitrogen compounds. One of the other major non-nitrogen compounds formed is trimethylamine (TMA) by the action of several spoilage bacteria on TMAO, an osmoregulant, present in fish (mostly marine and some freshwater fish), and cause a high (positive) redox potential (Eh) in the flesh. Under anoxic conditions, many of the spoilage bacteria utilize TMAO as a terminal hydrogen acceptor, thus allowing them to grow, and resulting in the formation of TMA. TMA reacts with lipids in the muscle to produce the off odor of low-quality fish. This could be a reason for rapid spoilage occurring in seafood than other muscle foods [11]. Thus, microbial spoilage can be determined by TMA level in the product. In the case of shrimps, at above 10°C, indole-positive organisms such as Aeromonas cause subsequent conversion of tryptophan to indole, which is associated with the off-odor of decomposition of shrimp. Thus high levels of indole in the flesh is an indicator of high temperature in the chilled storage process [12]. Clams and oysters undergo fermentative type spoilage also [13]. Generally, the microbial contamination in the fish mainly occurs through microbes associated with the habitat, invasion during processing, handling, and long-term storage. Growth of spoilers differs by habitats like freshwater or marine, temperate or tropical water, and storage or processing conditions. The microbial and chemical stability of food during processing and storage will be determined by the available water for microbial growth, called water activity (a w ). Yeast requires a w of minimum 0.7 for their growth, and except Staphylococcus aureus, most bacteria require at least 0.9 a w to grow [14]. Thus, it can be said that microbiologically stable fish product is with an a w less than 0.6 [15]. Thus, the water content in the product should be minimum to prevent microbial spoilage. Moreover, pathogenic microbes of public health concern are also taken into consideration as they can produce hazardous toxins. Some of these are; toxin produced by Clostridium botulinum (botulinum toxin) in processed food, Scombrotoxin as a result of the microbial conversion of histidine to histamine. Bacteria involved in this process include Morganella morganii, Klebsiella pneumoniae, Hafnia alvei, Pseudomonas putrefaciens, and Clostridium perfringens. Shellfishes can accumulate various algal toxins like brevetoxins, okadaic acids, domoic acids, saxitoxins, etc., and cause serious illness to humans [16].
Another important spoilage mechanism is post-mortem nucleotide catabolism, resulting in ATP depletion and subsequent formation of hypoxanthine (Hx) (Figure 1). The breakdown products do not affect the safety but sensory quality undergoes some changes [17,18]. Based on these compounds formed, the freshness can be expressed. The ratio of inosine (Ino) and Hx to total nucleotides and their Food Additives 4 catabolic derivatives will give the K value, an indicator of loss of freshness [19]. The ratio of Hx to the total of Inosine monophosphate (IMP), Ino, and Hx will give the H value, an indicator of Hx accumulation (bitterness), and its limit for human consumption has been suggested as 60% [20]. Another quality indicator is the F value. It is the ratio of IMP to the total of IMP, Ino, and Hx, and fish with F-value of 10% and higher is considered unacceptable [21]. Thus there is a huge need for the use of additives in the food industry. Application of food additives and low-temperature preservation leads to diminution of most of the spoilage process to a greater extent.

Role of chemical additives and natural alternative solutions
By definition, additives are the substances that are added to maintain or improve the safety, freshness, taste, texture, or appearance of food. Generally additives can occur in fish and fishery products during production, processing, storage, packaging, and transportation. Additives can be of two types; Synthetic or chemical, and natural additives. Some of them are listed in Table 1.

Chemical additives
Among chemical additives, the most common and widely used chemical is sodium chloride (NaCl). Salt drying and brining is the most traditional as well as an effective method of food preservation, and several studies have been made to explore all the preservation properties of NaCl. In Nile tilapia fillets, NaCl improved the weight and minimized drip loss [34], showed weight gain in white shrimp (Litopenaeus vannamei) [35], and had anti-melanotic activity along with the shelf-life extension in shrimp (Xyphopenaeus kroyeri) [36]. Like salt, sugar is also easily available and is a widely used additive for seafood products. Sugar treatment can significantly reduce pH value and decrease volatile bases like total volatile base nitrogen (TVB-N) [37]. It also showed a cryoprotectant action in frozen surimi (wet protein concentrate) and other products [38, 39], protection of myofibrillar protein [40], decrease the accumulation of biogenic amines in sausages and dry-cured grass carp [41,42], and prevention of protein denaturation in minced fish meat [43]. The combination of both sugar and salt could also delay spoilage and improve many sensory qualities [37]. The product 'gravad' traditionally manufactured in Nordic countries is prepared by such a combination of sugar and salt [44]. Additives such as table salt and organic acids like acetic acid or citric acid in the Marination technique not only prevent microbial growth but also improve organoleptic properties of fish and fishery products [45]. In seafood, the addition of organic acids provides great preservative action as an antimicrobial agent. Acetic acid and lactic acid, either single-use or combination had a growth-inhibiting effect against pathogens like Listeria monocytogenes and Escherichia coli [46]. The inhibitory effect of these acids against L. monocytogenes was also reported from mussels [47]. Generally, the addition of citric acid showed a positive impact on TVB-N accumulation, toughness, and pH, but a negative impact on the texture and cooking yield of refrigerated shrimp. In such a case, sodium citrate helps to improve cooking yield and texture by preventing excessive pH drop [48]. Sodium or potassium lactate is also considered a good additive for seafood products. It showed shelf-life extension in minced fish products [49], antibacterial effect in sliced salmon [50], in cold-smoked salmon [51], and in catfish fillets [52].
Many other compounds, including phosphates, carbonates, and sulfites, are used as major seafood additives. Phosphate compounds especially, polyphosphates (PP) have been widely used in fish and fishery products as cryoprotectant [ gel strength, and flavor enhancer [53], for providing higher cooking yield [31], improving weight, and reducing drip loss [34,54], modifying texture, color, and reducing cooking loss [55][56][57], improving quality of fillet [58], minimizing drip loss in shrimp [59,60], drip loss in sea robin (Prionotus punctatus) and pink cuskeel (Genypterus brasiliensis) fillet [31], and weight gain in kutum (Rutilus frisii) fillets [61]. Sodium hexametaphosphate (SHMP) or tripolyphosphate (STPP), or pyrophosphate-tribasic/ tetrabasic (TSPP) are the major phosphate compounds used in processing. Among carbonates, sodium carbonate (Na 2 CO 3 ) sodium bicarbonate (NaHCO 3 ), and magnesium carbonate (MgCO 3 ) have been widely used. Weight gain is observed when white shrimp are treated with Na 2 CO 3 and NaHCO 3 [35]. The addition of NaHCO 3 also provides the highest expansion volume for yellow pike conger crackers [62]. Sulfites have been widely used as additives due to their desirable technical properties like preventing melanosis or discoloration. The most predominant sulfiting agent is sodium sulfite used to prevent melanosis in crustaceans like shrimp, lobster, crab, crayfish, etc. [32]. Nitrite is another chemical commonly used as an antimicrobial agent, and effective against C. botulinum and its toxin production [63]. A combination of nitrite and sorbic acid would also give the best result as it can inhibit most yeasts. A combination of sorbic acid with benzoic acid could preserve brined shrimp [64]. Moreover, additives such as flavor enhancers, sweeteners, colorants, etc. are used to enhance the appeal of the food. Monosodium glutamate (MSG), calcium chloride (CaCl 2 ), and Disodium guanylate/ inosinate are the major flavor enhancers. Commonly used sweetening agents are saccharin, sucralose, glycerol, acesulfame potassium, aspartame, sodium cyclamate, neotam, and neohesperidine. Widely used colorants include carmine, carmosine, caramel, paprika, annatto dye, iron oxides and hydroxides, ponceau, cochineals, titanium dioxide (TiO 2 ), FD&C Yellow, and astaxanthin (Table 1). Butylated hydroxyl toluene (BHT), butylated hydroxyanisole (BHA), tertbutylhydroquinone (TBHQ ), propyl gallate (PG), and sodium acetate are widely used synthetic antioxidants to prevent lipid oxidation through free radicals scavenging, breaking chain reactions, peroxide decomposition, and decreasing oxygen concentrations and thereby increasing the shelf life [50]. But preservatives include sulfites, nitrates, benzoates, sorbates, formaldehyde, and others that may possess carcinogenic side effects. Thus nowadays the use of chemical preservatives in food industries steadily decreases and consumers are turning to the use of natural additives.

Plantderived products
The use of plant-derived natural compounds such as essential oils, plant extracts, hydrocolloids, phenolic compounds, etc. is very popular in seafood preservation. Their strong antimicrobial and antioxidant activities present great potential for use in the food industry [64][65][66].
Plant extracts and essential oils can be derived from plant petals, leaves, fruits, peels, stems, roots, and xylems and their antioxidant effects are due to volatile organic compounds, terpenoid, and phenolic components in the plant. The inhibitory effects of essential oil on gram-negative bacteria are less than that of grampositive bacteria as their lipopolysaccharide cell wall of gram-negative bacteria blocked the invasion of hydrophobic oils into the cell membrane [67]. Using essential oils (EOs) and plant extracts to extend shelf-life and maintain the quality of fish and fishery products has been reported frequently. Some of the recent studies of their application in fish and fishery products are represented in Table 2 Food Additives low bioavailability and stability, and factors affecting chemical compositions like plant genetic variability, extraction techniques, etc. are some limitations for the application of these phytogenic additives [99]. Like other plant-derived products, seaweed and algal extracts are emerging as a rich source of natural antioxidants, along with many nutritional values. The three important widely used hydrocolloids are; agar-agar, align, and Carrageenan. As thickening agent agar-agar is used mainly in fish paste products. Carrageenan is used to enhance the gelling property of fish mince [100][101][102], and organoleptic properties of mussels and squids [103]. The sodium salt of alginic acid is widely used as a stabilizer and thickener in coating films. Sodium alginate coating with rosemary extract reduced the accumulation of biogenic amines and bacterial count in Abalone (Haliotis discus hannai) [104]. Coating with gingerol delayed lipid oxidation, protein degradation, nucleotide breakdown, and inhibited microbial growth in Seabream (Pagrosomus major) [105]. Coating with tea polyphenols had significantly lowered the levels of TVB-N, lipid oxidation, and protein decomposition in Japanese Sea Bass (Lateolabrax japonicas) fillets [106]. The use of alginate-calcium film coating with Citrus wilsonii extract delays the deterioration and results in a higher sensory score for L. vannamei [107]. Significant reduction in the TVB-N, TMA, and thiobarbituric acid reactive substance (TBARS) has been detected during chilled storage with the presence of Gracilaria gracilis extract in shrimp [108], G. verrucosa extract in Indian mackerel [109], and extracts of Hypnea musciformis and A. muscoides in black tiger shrimp [110]. Similarly, seaweeds like Sargassum kjellmanianurn [111], and Grateloupia  filicina [112] exhibits a good antioxidant activity and prevent lipid oxidation in fish oil. Extracts of seaweeds such as Fucus vesiculosus inhibited the hemoglobinmediated lipid oxidation in washed cod muscle and cod protein isolates [113], and extracts of Durvillaea antarctica (cochayuyo/ulte), Pyropia columbina (red luche), and Ulva lactuca (sea lettuce) improved the lipid and sensory qualities in canned salmon [114]. Some phenolic compounds like flavonoids, phenolic acids, hydroxycinnamic acid, and lignans are also used as plant derived natural additives [115].
In surimi-derived products, several hydrocolloids like konjac enhance the gelling property [116]. Other products like starch [101,102], gums such as garrofin, guar, xanthan [117], etc. also provide a gelling effect and assure elasticity of the product. Iota carrageenan and xanthan had a cryoprotective effect too [118]. Other plantderived products such as soybean protein, wheat gluten, and starch are also used as additives for fish-paste products [119].

Animalderived products
Nowadays, animal-derived products like chitosan, gelatin, and whey proteins are widely used as food additives. Chitosan is a natural polymer obtained from chitin, a component of the exoskeleton of shellfish and fungal cell walls. Gelatin is a protein derived from the raw collagen of animal body parts. Whey protein is one of the two proteins, other than casein, found in milk. The bioactive coating of food products with these compounds provides antioxidant and antimicrobial properties and can thereby increase the shelf life of the product. Direct addition of compounds into the packaging materials also provided more potent preservative action [120]. Some of the recent studies on the application of chitosan, gelatin, and whey protein as edible coatings in fish and fish product preservation are represented in Table 3. But in moist environments, edible films and coating showed relatively low stiffness and strength, thus limited their use in specific conditions. Another animal-derived product, bioactive peptide (specific protein fragments) showed antimicrobial [137], and antioxidant activities [138]. In fish paste products, the products like plasma hydrolysate, plasma protein, ovomucoid, egg albumin, egg white, etc. were added as additives for improving strength [119]. The binding effect of egg whites and hydrolyzed beef plasma proteins in surimi gels [139], gel enhancing effect of bovine plasma powder, and egg white powder in arrow tooth surimi [140] were also reported.

Microbialderived products
Bacteriocin, a major bacterial-derived bio preservative (mostly from Lactobacillus) has potent antimicrobial properties. The mode of action is interfering cell wall synthesis of bacteria by pore formation and squeezing out of the inner material thereby restricting their growth [141]. Along with this antimicrobial action, other properties like nontoxicity, active in a wide range of pH and temperature, etc. making them generally recognized as safe (GRAS) additive [142]. The most common bacteriocins produced by Lactobacillus are Nicin, lacticin, pediocin, etc. Many bacteriocins are known to be more effective against endospore-forming bacteria. Bacteriocins were used to reduce the counts of Salmonella and Vibrio spp. in marine fishes and loligo [143], Listeria inaqua, and Pseudomonas spp. in fish homogenates [144], and aerobic and anaerobic bacteria in cold smoked salmon [145]. A novel bacteriocin BCC7293 from Weissella hellenica showed activity against L. monocytogenes, S. aureus, P. aeruginosa, A. hydrophila, E. coli, and S. Typhimurium in Pangasius fillets [146]. Bacteriocin FGC-12 and DY4-2 produced by Lactobacillus plantarum showed some inhibitory effect on Vibrio parahaemolyticus in shrimp [147], and Pseudomonas fluorescens in turbot fillet [148] respectively. Bacteriocin LJR1produced by Pediococcus pentosaceus showed activity against L. monocytogenes in white shrimp [149]. Bacteriocin GP1 produced by Lactobacillus rhamnosus active against Coliforms, Aeromonas, and Vibrio spp. in fish fillets [150]. The combination of bacteriocins with other preservation techniques usually results in better action. Microencapsulated Ziziphora clinopodioides essential oil and Nisin showed the strongest effect on preserving the sensorial quality of fish

Chitosan-based
Grass carp Inhibited cathepsin activities and thereby retarded the proteolysis [121] Olive flounder Coating combined with clove oil improved the quality and shelf life was extended by 6 days [122] White shrimp Coating combined with pomegranate peel extract reduced the melanosis, TVBN and microbial count [123] Mackerel Coating combined with gallic acid decreased microbial growth, protein decomposition, biogenic amine formation, lipid oxidation and nucleotide breakdown and shelf life was extended [124] Fish burgers The chitosan film containing lactoperoxidase system suppress the increase of Pseudomonas spp. and Shewanella spp. and TBARS value [125] Mori Fish Spoilage reduction when coated with rosemary extract on storage [126] Gelatin-based

Rainbow trout fillets
Coating incorporating oregano essential oil minimized the formation of volatile bases, oxidation products, and the growth of total and psychrotrophic bacteria [127] Shrimp Fish gelatin reduced lipid oxidation and extend shelflife [128] Shrimp Coating enriched with orange leaf essential oil extend shelf life about 10 days [73] Tilapia fillets Combined with grape seed extract reduced the formation of undesirable metabolites like TMA and histidine significantly [129] Chitosan-gelatin-based

Golden-pomfret fillets
Inhibits myofibril degradation [130] White shrimp Decreased the total and psychrotrophic bacteria and increased the shelf-life [131] Salmon fillet Incorporated with garlic and lime extracts extended the shelf life by antibacterial and antioxidant activity [132] Minced trout fillet Incorporated with grape seed extract Ziziphora clinopodioides essential oil reduced the spoilage [133] Whey protein-based Pike-Perch Coating with lactoperoxidase system and α-tocopherol extended the shelflife significantly [134] Rainbow trout fillet Reduced microbial growth, and TVB-N and TBA [135] Rainbow trout fillet Inhibited Shewanella and P. fluorescens and shelf life was extended [136] [151]. However the use of bacteriocin is limited due to its high cost. Another microbial-derived product kojic acid, a natural product of many fungi like Aspergillus and Penicillium, has certain anti-enzymatic browning and antibacterial effects, especially against gram-negative bacteria [152]. A combination of kojic acid and tea polyphenols showed an antibacterial effect against spoilage bacteria in refrigerated seabass (Lateolabrax japonicas) [153]. ε-Polylysine is another microbial-derived product with excellent preservative properties. It was isolated originally from bacteria Streptomyces albulus. Treatment with ε-Polylysine lowered the TVB-N, putrescine, cadaverine, and hypoxanthine and extended the shelf-life of shrimp [154]. The addition of ε-polylysine chitosan and carrageenan showed shelf life extension of Chinese shrimp (Fenneropenaeus chinensis) [155], and chitosan-based coatings combined with ε-polylysine and rosmarinic acid contributed to the reduction of TVB-N, TMA, and ATP-related compounds in Half-smooth tongue sole fillets [156]. A combination of plant, animal, and microbial-derived products showed the strongest preservative action than the independent use.

Conclusions
As a perishable food commodity, most of the world's supply of fish and fishery products are lost through chemical and microbial spoilage than other reasons like improper storage, handling and processing damage. Thus, the increasing demand for good quality fish products has intensified the search for applications of additives in preservation strategies. It is well known that none of the additives offer complete protection against spoilage, but can improve the quality of fish as well as shelf life to a greater extent. By considering the potential health hazards associated with chemicals as well as consumer preference, application of natural products from cheap and underutilized resources enabling food safety holds promise.
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. [46] Young KM, Foegeding PM. Acetic, lactic and citric acids and pH inhibition of Listeria monocytogenes Scott A and the effect on intracellular pH. The Journal of applied bacteriology. 1993;74:515-520.