**2. Postharvest technology for fisheries**

Our fisheries resources have not only been a source of food for people but are also economically important because they are a source of livelihood for many. However, the potential for harvesting more products is now very limited because of overexploitation and the demand for food protein is increasing worldwide. Applying effective postharvest technology could reduce gap between production and demand and result in effective utilization of aquatic resources. This includes the different processes and techniques used during the postharvest handling, processing, and marketing of aquatic products.

#### **2.1 Methods for handling and preserving fresh seafood products**

Seafood products are among the world`s most perishable commodities, and their spoilage begins soon after the death of the fish. Improper handling could hasten spoilage, resulting in gradual development of undesirable qualities in seafood products. Thus, effective handling and preservation techniques need to be used to address the problems of postharvest losses.

Many developments have taken place in postharvest technology. Freezing at sea was a major development in the advance nations in the 1950`s along with the bulk chilling in chilled and refrigerated seawater systems on board fishing vessels and no new major technologies have been recently introduced but only a consolidation and anticipated development of current ones (Hermes, 1998). The industry tends to be more perceptive of the necessity of satisfying the requirements and demands of consumers, particularly with regards to the safety and quality of seafood products.

#### **2.1.1 Chilling**

Chilling is most commonly used in the industry to keep seafood fresh after harvest. Chilling is used to reduce the temperature of seafood products to some point below (-2 to -4°C for superchilling) or above (0 to 5°C) the freezing point of water (Hermes, 1998). The methods used for chilling include wet icing and use of chilled seawater, ice slurry, refrigerated air, dry ice, and gel ice mats. Icing is the most common and useful way of chilling the fish catch and is affected by direct contact between the melted ice and the fish. This requires sufficient ice and proper arrangement of ice and the product to allow rapid cooling. The use of chilled seawater or slush ice involves seawater and ice. The amount of ice used depends on the initial temperature of the water and fish, the size of the container and the quality of its insulation, and the length of the trip. Refrigerated air has been used in some big commercial boats, wherein chilled air is circulated by a finned evaporator and a fan situated at the end of the cold room. Cooling of fish through dry ice (solid carbon dioxide) is affected by evaporation of the ice, but dry ice should not be used in direct contact with the product in order to avoid cold burns (Shoemaker, 1991 as cited by Hermes, 1998). This method is normally used for air shipment. However, these chilling methods do not stop spoilage but slow it down considerably; therefore, they are used only to delay spoilage of the fish catch but not for longer storage of the product.

#### **2.1.2 Freezing**

158 Aquaculture

year, accounting for approximately 10% of the total production from capture fisheries and aquaculture. Thus, the postharvest losses in fisheries can be among the highest for all the commodities in the entire food production system. An appropriate preservation method can significantly reduce these losses, particularly those incurred during the handling,

Our fisheries resources have not only been a source of food for people but are also economically important because they are a source of livelihood for many. However, the potential for harvesting more products is now very limited because of overexploitation and the demand for food protein is increasing worldwide. Applying effective postharvest technology could reduce gap between production and demand and result in effective utilization of aquatic resources. This includes the different processes and techniques used

Seafood products are among the world`s most perishable commodities, and their spoilage begins soon after the death of the fish. Improper handling could hasten spoilage, resulting in gradual development of undesirable qualities in seafood products. Thus, effective handling and preservation techniques need to be used to address the problems of postharvest losses. Many developments have taken place in postharvest technology. Freezing at sea was a major development in the advance nations in the 1950`s along with the bulk chilling in chilled and refrigerated seawater systems on board fishing vessels and no new major technologies have been recently introduced but only a consolidation and anticipated development of current ones (Hermes, 1998). The industry tends to be more perceptive of the necessity of satisfying the requirements and demands of consumers, particularly with

Chilling is most commonly used in the industry to keep seafood fresh after harvest. Chilling is used to reduce the temperature of seafood products to some point below (-2 to -4°C for superchilling) or above (0 to 5°C) the freezing point of water (Hermes, 1998). The methods used for chilling include wet icing and use of chilled seawater, ice slurry, refrigerated air, dry ice, and gel ice mats. Icing is the most common and useful way of chilling the fish catch and is affected by direct contact between the melted ice and the fish. This requires sufficient ice and proper arrangement of ice and the product to allow rapid cooling. The use of chilled seawater or slush ice involves seawater and ice. The amount of ice used depends on the initial temperature of the water and fish, the size of the container and the quality of its insulation, and the length of the trip. Refrigerated air has been used in some big commercial boats, wherein chilled air is circulated by a finned evaporator and a fan situated at the end of the cold room. Cooling of fish through dry ice (solid carbon dioxide) is affected by evaporation of the ice, but dry ice should not be used in direct contact with the product in order to avoid cold burns (Shoemaker, 1991 as cited by Hermes, 1998). This method is normally used for air shipment. However, these chilling methods do not stop spoilage but

during the postharvest handling, processing, and marketing of aquatic products.

**2.1 Methods for handling and preserving fresh seafood products** 

regards to the safety and quality of seafood products.

**2.1.1 Chilling** 

processing, distribution, and marketing of fishery products.

**2. Postharvest technology for fisheries** 

Freezing seafood becomes essential when other methods of preserving fish such as chilling are unsuitable for longer storage. Under proper conditions, it can keep the product frozen for several months without considerably changing its quality. Freezing is a method of stopping, either partly or entirely, the deteriorative activities of microorganisms and enzymes.

Microorganisms stop multiplying at approximately around -10°C and below, and the enzymatic activity is generally controlled when the temperature is reduced below the freezing point, to approximately -1°C (Cornell, 1995 as cited by Hermes, 1998). The water in the flesh begins to freeze at temperatures ranging from -1°C to -3 °C, and most of the water is converted into ice during freezing. At -5°C, approximately 75% of the water in fish muscles is frozen.

In the fishing industry, there are 3 basic methods available for freezing seafood products, namely, air-blast freezing, contact or plate freezing, and spray or immersion freezing. Airblast freezing involves the continuous flow of cold air over the product. Uniform freezing is attained only if the temperature and speed of the air over the product is constant. This type of freezing system is very versatile, and is thus very useful in producing individual quick frozen (IQF) products for crustaceans, fish fillets, and value-added products. In contrast, contact or plate freezing allows the product to come into direct contact with hallow freezing metal plates, through which a cold fluid is passed. It generally used for freezing products such as whole fish, fillets, shrimps, and other seafood products into blocks. In the spray- or immersion-freezing method, the product comes into direct contact with the fluid refrigerant, such as liquid nitrogen. The method is normally used for producing very high value and specialized IQF products. The choice regarding freezing systems will depend upon cost, function, and feasibility because this method of preservation can be expensive.

#### **2.1.3 Preservatives**

Various problems are encountered with seafood products even when they are kept in cold storage. Frozen tuna becomes dark brown during cold storage because of oxidation of hemoglobin in the blood and myoglobin (Mb) in the meat. In crustaceans, browning or blackening of frozen shrimps and prawns is also observed. These problems prompted the food industry to look for ways to control quality deterioration in seafood products, and the use of preservatives has been one of the immediate responses.

The addition of antioxidants to products is one of the most widely studied methods for controlling discoloration and lipid oxidation in fish meat and other meat products. Antioxidants have many modes of action which include sequestering catalytic metal ions, decreasing oxygen concentration, quenching singlet oxygen and superoxide anion, decomposing primary oxidation products to non-volatile compounds, preventing first-chain initiation by scavenging initially generated radicals and chain breaking. The chain-breaking mechanism has been studied for several antioxidants (Roginsky & Lissi, 2005). In this mechanism, the antioxidant donates a hydrogen atom to a lipid peroxyl radical and forms an antioxidant radical, the antioxidant radical subsequently either combines with other lipid peroxyl radical or another antioxidant radical to terminate the reaction.

Several categories of antioxidants can be used for food applications. However, selecting antioxidants for foods is a major concern in the industry because of strict regulations. Generally, the antioxidants involved in food additives must be effective at low doses, must not affect sensory flavor, and must not toxic. Therefore, natural antioxidants are generally preferred for food applications.
