Đề cương anh văn chuyên ngành thủy sản (NLU)

Đề cương anh văn chuyên ngành thủy sản (NLU)Đề cương anh văn chuyên ngành thủy sản (NLU)Đề cương anh văn chuyên ngành thủy sản (NLU)Đề cương anh văn chuyên ngành thủy sản (NLU)Đề cương anh văn chuyên ngành thủy sản (NLU)Đề cương anh văn chuyên ngành thủy sản (NLU)Đề cương anh văn chuyên ngành thủy sản (NLU)

Điền vào chỗ trống Đoạn Calcium and magnesium chlorides, even when present in small quantities, tend to slow down the penetration of salt into the flesh; the presence of these salts may also increase the rate of spoilage Magnesium chloride is hygroscopic and tends to absorb water, making the fish more difficult to dry and to keep dry Đoạn If fish are salted before drying, less water needs to be removed to achieve preservation A water content of 35 - 45 per cent, depending on the amount of salt present, will often prevent, or drastically reduce, the action of bacteria Salt: sources, composition and properties Pure common salt is sodium chloride (NaCl) but almost all commercial salts contain varying levels of impurities depending on the source and method of production Đoạn Obviously, it is best to have the fish surrounded by liquid so that the distance through which heat is transferred by conduction is kept to a minimum Most fish canners increase in-can heat transfer rates even further by processing the cans in a rotary retort The movement of the headspace bubble during rotation forces an increase in liquid movement and, therefore, convection heat transfer The fish are more evenly cooked throughout the can and, those nearest the can walls are less likely to be overcooked (See Figure 3) Đoạn Not all fish which are sealed into cans are heat processed Anchovies, for example, are packed in salt and then sealed in cans without any further processing: the very high salt content prevents subsequent growth of micro-organisms However, the product can only be eaten in very small quantities in this form and is generally used as a condiment or flavouring in other dishes If heat sterilisation is to be the method of preservation, it is essential that the effect of severe heat treatment on the fish tissues is known Firstly, it is impossible to produce a high quality canned fish product from fish which are at an advanced stage of spoilage Đoạn Brine evaporated salts - underground salt deposits are brought to the surface in solution (a brine) and this is evaporated, usually by heating (iii) Rock salt - natural deposits of salt are ground to varying degrees of fineness without any purification Đoạn Drying is the removal of water from fish Normally the term 'drying' implies the removal of water by evaporation but water can be removed by other methods: for example, the action of salt and the application of pressure will remove water from fish Since water is essential for the activity of all living organisms its removal will slow down, or stop, microbiological or autolytic activity and can thus be used as a method of preservation Đoạn Drying takes place in two distinct phases In the first phase, whilst the surface of the fish is wet, the rate of drying depends on the condition (velocity, relative humidity etc.) of the air around the fish If the surrounding air conditions remain constant, the rate of drying will remain constant; this phase is called the 'constant rate period' Once all the surface moisture has been carried away, the second phase of drying begins and this depends on the rate at which moisture can be brought to the surface of the fish Đoạn Canned fish is famous for the way it is packed so tightly within the container, leaving very little space for additional liquids Heat transfer through the fish is by conduction and, therefore, very slow; at a processing temperature of 121°C, it would take hours to raise the centre temperature of a 145.5 mm (diameter) by 168 mm (height) can from 10 to 100°C by conduction alone In this time, the fish nearest the walls of the container would be grossly overcooked Đoạn Most fish canners increase in-can heat transfer rates even further by processing the cans in a rotary retort The movement of the headspace bubble during rotation forces an increase in liquid movement and, therefore, convection heat transfer The fish are more evenly cooked throughout the can and, those nearest the can walls are less likely to be overcooked Đoạn 10 The quality of oily fish is much less impaired by the severe heat process than that of non-oily fish, which generally yield a product only suitable for fish paste or pet food manufacture This may merely be a physical effect of the oil in the muscle tissue acting as a barrier to water loss from the protein structures, so enabling canned oily fish to retain their succulence through the heat process Đoạn 11 If fish are salted before drying, less water needs to be removed to achieve preservation A water content of 35 - 45 per cent, depending on the amount of salt present, will often prevent, or drastically reduce, the action of bacteria Đoạn 12 Pure common salt is sodium chloride (NaCl) but almost all commercial salts contain varying levels of impurities depending on the source and method of production Đoạn 13 After the cans are sealed in the retort, steam is admitted and the temperature of the retort allowed to rise to 100°C and maintained at this temperature until all air is flushed out of the retort Air pockets left in the retort can lead to localised under-processing, as air insulates any cans it may surround from the steam Đoạn 14 Secondly, as the temperature rises, the muscle proteins become increasingly denatured and progressively lose the water which is loosely bound in the undenatured protein network The watery exudate is unsightly and may cause a sauce to curdle whilst the partially dehydrated fish muscle, although surrounded by liquid, has a dry 'woolly' feel in the mouth Besides this denaturation, the severe heat treatment may cause some degradation of proteins to amino acids and other simple (but often malodorous) breakdown products which may also react with the metal of the can walls, producing unsightly black deposits Dịch sang tiếng Việt Đoạn Fish and shellfish are perishable and, as a result of a complex series of chemical, physical, bacteriological, and histological changes occurring in muscle, easily spoil after harvesting These interrelated processes are usually accompanied by the gradual loss or development of different compounds that affect fish quality The quality changes are highly influenced by many factors, the most important of which is temperature If fresh fish is not properly stored, exposure to ambient temperature can cause serious deterioration in quality Seafood may harbor viruses, bacteria, or parasites pathogenic to humans It can also be the cause of intoxications due to natural toxins or other toxic agents present in muscle tissues or be responsible for seafood-borne allergies Biotoxins present in seafood are related to harmful algal blooms (HAB) or are of bacterial origin Algal toxins, including ciguatera, paralytic shellfish poisoning (PSP), neurotoxic (brevetoxic) shellfish poisoning (NSP), diarrhetic shellfish poisoning (DSP), and amnesic shellfish poisoning (ASP), are highly regional, species specific and are present in seafood at the time of capture Biotoxins of bacterial origin are either present in seafood at the time of capture (tetrodotoxin— puffer fish poisoning (PFP)) or formed in seafood mishandled during and/or after capture (scombrotoxin) Đoạn Most of us like to eat seafood, especially when it is fresh, although processed products are also favorites of many consumers In addition to sensory attributes, the preference for seafood now includes awareness of its health benefits Thus, when processing seafood, it is important to understand the scientific and technical reasons that are responsible for the sensory and health attributes of seafood, in addition to how the manufacturing process can affect the basic quality of seafood The same knowledge may lead to a reduction in the perishability of seafood, a problem that has existed since the beginning of time, though it has been partially solved by many modern techniques including canning, freezing, and dehydration Seafood processing includes seafood handling (initial processing of raw seafood) and seafood product manufacturing operations Alternatively, the processing is classified as (1) primary processing of seafood, which includes filleting, freezing, chilling, and so on for onward distribution to fresh seafood retail and catering outlets and for export, and (2) secondary processing of seafood, which produces products such as canned, minced, cured, and so on for retail and catering trades Đoạn Fisheries and aquaculture make crucial contributions to the world’s wellbeing and prosperity In the last five decades, world fish food supply has outpaced global population growth, and today fish constitutes an important source of nutritious food and animal protein for much of the world’s population In addition, the sector provides livelihoods and income, both directly and indirectly, for a significant share of the world’s population Fish and fishery products are among the most traded food commodities worldwide, with trade volumes and values reaching new highs in 2011 and expected to carry on rising, with developing countries continuing to account for the bulk of world exports While capture fisheries production remains stable, aquaculture production keeps on expanding Aquaculture is set to remain one of the fastest-growing animal food-producing sectors and, in the next decade, total production from both capture and aquaculture will exceed that of beef, pork or poultry Đoạn As with many animal products, fish and fishery products contain water, proteins and other nitrogenous compounds, lipids, carbohydrates, minerals and vitamins However, the chemical composition of fish varies greatly from one species and one individual fish to another depending on age, sex, environment and season Proteins and lipids are the major components whereas carbohydrates are detected at very limited levels (less than 0.5 percent) Vitamin content is comparable to that of mammals except for vitamins A and D which are found in large amounts in the meat of fatty species, especially in the liver of species such as cod and halibut As for minerals, fish meat is a particularly valuable source of calcium and phosphorus as well as iron, copper and selenium In addition, saltwater fish contain high levels of iodine Depending on their lipid content, which varies greatly from 0.2 percent to 25 percent, fish are classified as lean, semi-fatty or fatty Bottom-dwelling ground fish such as cod, saithe and hake are common lean species Fatty species include pelagics such as herring, mackerel and sprat Some species store lipids in limited parts of their body tissues only or in smaller quantities than typical fatty species, and are consequently termed semi-fatty (e.g barracuda, mullet and shark) Đoạn Among the leading producers, the major groups of species farmed and the farming systems vary greatly India, Bangladesh, Egypt, Myanmar and Brazil rely very heavily on inland aquaculture of finfish while their potential for mariculture production of finfish remains largely untapped Norwegian aquaculture, however, rests almost exclusively on finfish mariculture, particularly marine cage culture of Atlantic salmon, an increasingly popular species in the world market Chilean aquaculture is similar to that of Norway but it also has a significant production of molluscs (mostly mussels) and finfish farmed in freshwater, and all farmed species are targeted at export markets In Japan and the Republic of Korea, well over half of their respective food fish production is marine molluscs, and their farmed finfish production depends more on marine cage culture Half of Thailand’s production is crustaceans, consisting mostly of internationally traded marine shrimp species Indonesia has a relatively large proportion of finfish production from mariculture, which depends primarily on coastal brackish-water ponds It also has the world’s fourth-largest marine shrimp farming subsector In the Philippines, finfish production overshadows that of crustaceans and molluscs The country produces more finfish from mariculture than freshwater aquaculture, and about one-fourth of the mariculture-produced finfish, mostly milkfish, are harvested from cages in marine and brackish water In Viet Nam, more than half of the finfish from inland aquaculture are Pangasius catfish, which are traded overseas