Trends in the Utilization and Production of Seafood Byproducts

Trends in the Utilization and Production of Seafood Byproducts

Advances in Seafood Byproducts 351 Alaska Sea Grant College Program • AK-SG-03-01, 2003 Trends in the Utilization and Production of Seafood Byproducts Hans Nissen Atlas-Stord, Inc., Kansas City, Missouri Abstract Seafood companies in the North Pacific and Alaska generate a significant volume of seafood byproducts and could benefit environmentally and economically by utilizing these byproducts. Today many of the compa- nies have integrated a fish meal plant to process seafood byproduct into valuable high quality fish meal and oil which is sold worldwide in com- petition with other protein meals. In order to justify the investment in a production facility to utilize the byproduct the annual volume must be considered. The trend has been to combine the byproduct from various plants in order to have enough volume to make the operation feasible. In Alaska with many small processors at remote locations this can be a difficult task, and the reason much of the seafood byproduct today is still being dumped or disposed at landfills. We have considered a pro- cess where the byproduct is collected at the different sites and brought to a central location where it is hydrolyzed into silage and dried using a carrier liquid drying process (CLD) producing a stable product that can be marketed worldwide. Introduction As a fish meal equipment manufacturer we are in many cases the first in line to get the call when a fish processor, for various reasons, must con- sider how to utilize the fish byproduct from his process. The reasons can include new environmental regulations regarding disposal of byproduct, or an increase in disposal cost from the local landfill or from the person who hauls the byproduct away. The questions are many, such as “What is included in a modern fish meal line to produce a high quality end product?” and “What about envi- ronmental impact?” 352 Nissen — Trends in Seafood Byproducts Advances in Seafood Byproducts 353 Trends in fish meal production Material Small oily fish like menhaden in the Gulf of Mexico, which is normally not suited for human consumption, is typically used as raw material for the production of fish meal and oil. Another source of raw material is the byproduct or offal from fish processing, such as heads, frames, liver, and viscera. The quality of the raw material is typically measured by its freshness TVN (total volatile nitrogen). A low TVN indicates a fresh, less deterio- rated product that can be used for premium quality fish meal. Process The fish meal and oil process is a separation process in which the content of water, oil, and solids of the fish are separated and the water removed by evaporation and drying. The process has not been altered for a long period of time. Extensive development of the various equipment has been, and currently is, taking place in order to reduce energy consumption, increase product quality, and protect the environment. A modern fish meal line appears in the flow diagram in Fig. 1. Step 1 is the cooking where the fish is heated and the protein coagu- lated in order to release the water and oil. Today the cooker is typically indirectly heated with steam and the flow controlled with respect to time and temperature. Step 2 is mechanically dewatering the heated product using a strainer screw combined with a screw press. The press cake has a water content of approximately 50% and contains about 70% of the solids. Step 3 is a separation of the oil from the press water using high speed decanters, where suspended solids are removed and now are called grax. This is followed by a centrifuge step where the oil is separated. The water is now called stickwater and contains 6-10% soluble protein. Step 4 is the concentration of the stickwater from the centrifuge in an evaporator up to 40-50% solids. The evaporator is typically a “multi-effect” and can use steam, waste heat from the dryers, or electricity in the MVR (mechanical vapor recompression) evaporator. Step 5 is the drying of the press cake mixed with grax from the de- canter, and the soluble material from the evaporator, from approximately 55% to below 10% moisture. The drying process has the largest effect on the protein quality and several types of dryers are today being used. Di- rect fired rotary drum dryers are widely used in large volume plants and produce a fair average quality (FAQ) meal. Steam dryers are used in new installations and can be operated with minimum air intake securing opti- mal conditions for waste heat utilization and protection against pollution of the air. The steam dryer produces what is called steam-dried meal. 352 Nissen — Trends in Seafood Byproducts Advances in Seafood Byproducts 353 Figure 1. Flow diagram for a modern fish meal line. WHE/MVR = waste heat/ mechanical vapor recompression. In order to produce specialty fish meal like LT (low temperature), Prime, etc., from fresh fish, the drying may take place in a vacuum steam dryer, keeping the product temperature below 70ºC (158ºF), or in an indirectly heated hot air dryer where the air is heated to a moderate temperature without getting in contact with the flue gases. Finally, a two-stage drying system using a steam dryer as the first step followed by a hot air dryer is being used to produce high quality fish meal, and at the same time mak- ing it possible to recover the waste heat in the evaporators. Step 6 is the cooling, classification, and milling of the dried product to obtain the final product specification. Classification of the meal consists of a screening where the larger particles such as bones are separated in order to increase the protein level in the meal and produce a high and a low protein product. Environmental protection Normally the authorities, and more often the neighbors, require the fish meal plant to minimize emission of odors and polluted waste water. Newly designed fish meal plants are made air tight and installed with suction and/ or vacuum on all equipment. The non-condensable odors are treated in chemical scrubbers or incinerated in the combustion chamber of the steam boiler or the hot air dryer. 354 Nissen — Trends in Seafood Byproducts Advances in Seafood Byproducts 355 The water contained in the fish byproduct ends up as waste water. It can be discharged with the cooling seawater back to the ocean, or further treated in a waste water treatment plant in cases where zero discharge is required. In this case, the cooling water would be indirect, using a cooling tower, or alternatively using an air cooler for condensing. Economy Prices of fish meal and fish oil fluctuate to a great extent and depend on prices for soy protein and soy oil. Present prices are rather good which helps justify the investment in a fish meal plant. A general trend, however, shows that production plants are getting larger and the production is concentrated in relatively few factories combining raw material from various sources or facilities. This is done in order to secure optimal use of labor, energy, etc., minimizing the production cost. Smaller fish meal plants are being installed onboard factory trawl- ers. Figure 2 shows the feasibility of installing smaller fish meal plants depending on the length of the season. The calculation shows that a sea- son of a minimum of 120 days per year and a capacity of greater than 2 tons per hour are required to make installation of a small fish meal plant feasible onboard factory trawlers. Alternative processes In Alaska many fish processors are located in remote areas where (1) it is not practical or possible to combine the byproducts, (2) there is a rela- tively small volume, and (3) the season is short. These processors will look for alternative processes that are less expensive or with the possibil- ity to produce a special product that could be sold at a much higher level than fish meal and oil. Some of these alternative processes are • Fish silage—liquid fish protein produced by using acid. • Hydrolyzed fish products—liquid fish protein produced by using enzymes. • Fish protein concentrate—liquid fish solubles not added back to the dryer. Common for these processes is a liquid end product, which could be final dehydrated and thereby make it easier to get to the end user market due to lower shipping cost. A dehydrated product will also be of benefit because U.S. feed markets, among others, are based on handling dry products. 354 Nissen — Trends in Seafood Byproducts Advances in Seafood Byproducts 355 Figure 2. Feasibility of a small fish meal plant. Revenue is fish meal $500/t and fish oil $400/t. Cost is steam $20/t, electricity $0.05/kWh, and money 10% p.a. over 5 years. Carrier liquid drying process An alternative to existing drying processes for liquid such as spray dryers and others is the carrier liquid drying (CLD) process. Three applications for CLD are • Separate dewatering of soluble fraction in conventional fish meal process. • Final dewatering in fish silage process. • Final dewatering in enzyme processes. The CLD process appears on the flow diagram shown in Figs. 3 and 4, and the end product characteristics for stickwater during concentration are shown in Fig. 5. The basic processing conditions are • Mixing ratio 1:6 to 1:20 (one part concentrate dry matter to 6 or 20 parts oil). • Dry matter of concentrate not exceeding 35%. • Evaporation temperature 280ºF. • Steam consumption 1.2:1 steam to evaporation. • Electrical consumption 45kWh per ton evaporated. 356 Nissen — Trends in Seafood Byproducts Advances in Seafood Byproducts 357 Figure 3.

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