J.C. Ogunja, K.O. Werimo and E.N. Okemwa
Kenya Marine and Fisheries Research Institute
P.O. Box 81651, Mombasa, Kenya
The importance of Nile perch as a rich source of protein food makes it imperative that the landed catch be efficiently preserved. This paper describes in detail simple handling and preservation processes including storing the fish in ice, filleting, freezing, frying, drying and smoking. The use of fish off-cuts for making cutlets and sausages, and of fish waste for making useful products like leather, isinglass and fish silage is described. Research on the utilization of Nile perch now indicates that it is time to stop regarding this fish as a pest but rather as one offering great nutritive and financial possibilities.
L'importance du capitaine ou perche du Nil comme source riche d'alimentation protéinique impose un besoin de préservation efficace des captures. Le document passe en revue les méthodes simples de sa conservation et de sa transformation, y compris la mise sous glace, le filetage, la congélation, la friture, le séchage et le fumage. II donne des informations sur l'utilisation des parures des filets pour l'élaboration de saucissons, et des déchets pour l'élaboration de produits utiles tels que le cuir, la gélatine et l'ensilage. Les recherches menées sur l'utilisation du capitaine indiquent qu'il faut maintenant le considérer comme une ressource offrant de grandes possibilités alimentaires et financières, plutôt que comme une peste.
1.1 Lake Victoria
Lake Victoria is a large lake, shared between Kenya, Uganda and Tanzania. The surface area is some 68 000 km2 and the shoreline length 3 400 km. The lake empties into the River Nile. The lake is estimated to provide a living for 50 000–70 000 fishermen; Kenyan fishermen alone numbering about 20 000.
1.2 Fish Catches in Lake Victoria
The present total annual catch, taken mainly by small-scale fishermen operating from dugout or planked canoes, is about 350 000 t of which about 130 000 in Kenya. Until the late 1970s the most important fish taken in the lake were Cichlidae, principally Tilapia and Haplochromis, though catfish and lungfish were also important. A small number of Nile perch was introduced to Lake Victoria near Jinja, Uganda in 1959. The fish have spread to both Kenya and Tanzania waters. In Kenya it is estimated that the present monthly Nile perch catch is 8 000 t. The Nile perch is found throughout the Nile system and in certain West African rivers. It thrives well in lakes and in slow-flowing rivers, growing to a large size. Fish of 200 kg are not unknown and fish of 50–100 kg quite common. The majority of the fish taken in the gillnet fisheries are from 5–20 kg though very small fish are also taken.
1.3 Nile Perch
Nile perch has proliferated in Lake Victoria since its introduction some three decades ago. What constituted only 2% of Kenya's total fish landings from the lake a decade ago today represents over 70% of the volume of total catch (see Table 1).
Percentage composition by weight of Nile perch
|Part||average weight as % of whole fish|
|Whole fish (approx 5 kg)||100|
|of which swim bladder||2.3|
|remainder of guts||5.7|
|Fillet (skin on)||50|
|Fillet (without skin)||42|
|Fins + tail||9|
|Skeleton with adhering flesh||10|
The unprecedented growth in the production of Nile Perch has prompted the Kenyan government to study ways of improving its utilization. But the present situation is unlikely to continue in the long term, since the predator-prey equilibrium will probably gradually stabilize, with an attendant reduction in the biomass of Nile perch. The most prudent course of action during such a temporary situation is considered to be the immediate short-term promotion of exploitation of the existing Nile perch stocks using techniques which do not require high permanent investment and to undertake various studies in order to monitor the changing pattern and to ensure the fullest use of this resource in line with longer term overall development strategies.
Due to the difficulty in providing good access roads to many of the artisanal fishing settlements and the lack of adequate fish handling and cold storage facilities, the communities must continue to rely on traditional means of processing, such as smoking, drying and frying, as practical ways of preserving the catch in marketable condition. Despite the initial capital outlay together with large operating costs, industrial filleting is still one of the most attractive Nile perch processing options in the country today. Nile perch filleting plants have mushroomed over the past few years. Not only has the number of plants multiplied, but production capacities have also been expanded.
Currently Nile perch is being utilized to make different products. These include cold smoke, hot smoke, Nile perch fillets, sausages, cutlets, etc. Filleting wastes are now made into useful products such as leather, isinglass, soap, etc. The Kenya Marine and Fisheries Research Institute is currently working on further utilization of Nile perch, including studies on storage life of Nile perch, studies on value-added products, and utilization of by-products.
2. NILE PERCH HANDLING
There are over 200 landing beaches along the Kenya shores of Lake Victoria. In the major landing centres, fish bandas (open-sided buildings with concrete floors, small offices and stores) have been built by the fisheries department to serve as market places for fishermen to dispose of their catch. The operations are administered by the fishermen's cooperative societies, currently some 35.
Inadequate handling facilities and delay between catch and distribution contribute toward fish spoilage. On landing the fish are dumped on the sandy beaches and transferred, often in wheelbarrows, to the bandas where they are weighed, graded and often filleted and sold to buyers. At no stage in this chain is ice used. Even beyond this point, ice is seldom used, except by filleting companies which send insulated trucks and containers in which purchased fish is put on ice. It has, however, been demonstrated that the use of ice for chilling fresh fish enables the fishermen to keep their fish in good condition for long periods. Under ideal (laboratory) conditions fresh Nile perch in ice has a storage life of four weeks, in commercial practice two weeks.
Research has shown that at landing only one third of the Nile perch can be rated as excellent, one third as acceptable and one third as non-acceptable for filleting and export. However, little grading takes place and also in the filleting plants quality control is often no more than trimming discoloured parts off the fillets. Improvement of quality at landing and quality of processed products would increase the overall price of the exported product and further develop the export markets.
Although the present system which relies on transporting fish in baskets is cheap and quite effective, quality problems arise especially for fish transported to distant areas. Outside Kisumu, or the major cities Nairobi and Mombasa, there are no chill or cold storage facilities. The majority of fish is therefore landed and distributed without any form of preservation, except the curing of fish which is on the verge of spoilage.
Under a 20-year development plan to be implemented by Lake Basin Development Authority, five cold stores are to be built in major fishing centres along the Kenyan shore of Lake Victoria. The plan, however, needs to incorporate the establishment of ice-making facilities in these stores to enable fishermen to have easy access to ice. From capture to cold storage, the use of ice could substantially add to the quality of fish especially if the deliveries cover long distances.
3. NILE PERCH PROCESSING
The processing methods for Nile perch are divided into two options:
3.1 Industrial Processing
Although Nile perch today represents over half of the total catch volume in the country, the present situation is unlikely to continue in the long term since the predator-prey equilibrium could gradually stabilize with an attendant reduction in the Nile perch biomass. Thus the most prudent course of action during such a temporary situation is considered to be increased exploitation of existing stocks using techniques which do not require large permanent investment. Among the techniques that do not require substantial investment which we have recommended and examined at KMFRI are:
3.1.1 Industrial filleting
In Kenya there are about 20 filleting plants located in urban centres like Kisumu, Nairobi and Mombasa (Table 3). The fish is purchased and transported using insulated vans which keep the fish fresh in ice during transportation. In the filleting plants the fish is filleted and fillets are blast frozen.
An investor requires in excess of KSh 8 million (US$ 330 000) to establish a filleting plant comprised of a 10 t cold storage facility, a blast freezer with a batch capacity of 6 t, a 2 t ice plant and six 5 t insulated trucks. Estimates from our studies indicate that at present prices such a company, with an annual production capacity of 2 000 t fillets, would break even at producing one third (670 t) of its capacity.
The substantial revenue generated has spurred on this activity. Although filleting yields account for only a third of the fresh fish weight (research at KMFRI has shown that a skilled filleter can obtain a yield of over 40%), frozen fillets sell on the average for KSh 40/kg as against KSh 6/kg for raw whole fish. In addition, filleting companies generate additional income from by-products. With the exception of Nile perch skins which are given away free, the skeletons fetch KSh 2.50/piece on the average, oil costs KSh 200/20 litre container, and swim bladders sell for KSh 70–80/kg locally.
3.1.2 Industrial smoking of fillets
Since the industrial production of frozen fillets is beyond the means of several would-be investors, there has been a need to develop less capital-intensive processing options.
Research on the industrial cold smoking of fillets using AFOS smoking kilns, carried out at KMFRI to determine if this could be a medium cottage industry activity, revealed that such an activity could best be integrated into an existing filleting plants. Cold smoked Nile perch fillets are now produced by one filleting company. They are readily accepted by tourist hotels in Kisumu, Nairobi and Mombasa at a price of KSh 120/kg. The cold smoked fillets are prepared as follows. After filleting, brining, washing and draining, the fillets stay in the kiln for 24 hours drying at temperatures not exceeding 30 °C, and are then cold smoked for another two hours at temperature less than 40 °C.
Work on industrial hot smoking of fillets revealed that at KSh 30/kg for this product would not be feasible. The products were prepared as follows: hot smoked fillets were brined for one hour then subjected to drying for one hour, smoked dried for another hour, followed by two hours of smoking at temperatures not exceeding 70 °C.
3.1.3 Value-added products
The work so far carried out at KMFRI has developed the following value-added products: fish hams, cutlets and sausages.
(a) Fish hams (smoked)
These are chunks of meat approximately 15 cm long, weighing 250 g. The fish is butchered when partially thawed in order to minimize bacterial growth. There appears to be advantage in having the fish slowly deep frozen before processing as ham, since slow freezing allows for formation of long ice crystals within the tissue, rupturing to an extent the muscle fibres and thus producing a more tender product.
The pieces of meat are brined for five days and cool dried for two days. This encourages the formation of a dry skin or pellicle at the surface for smoking. The product is then cold smoked for four hours. Finally, they are refrigerated in plastic bags with holes in order not to retain moisture due to condensation. Fish hams are a new concept in Kenya. They are products which require no subsequent preparation and contain no bone, so may be sliced and served.
(b) Salmon style slices
To prepare this salmon substitute, perch fillets are cut into bricks of meat 10 × 8 cm thick so that the grain runs along the thickness. They are then dry salted with high quality salt, changing the salt periodically as water is drawn off. The chunks are sliced and the slices are hot smoked for three minutes and then cooled. The slices are brushed with vegetable oil, stacked one above the other and placed on small paper trays and tightly covered with plastic wrap. They are stored in a refrigerator. The slices can be used as starters (hors d'oeuvre), in sandwiches or with salads.
(c) Soup (chowder) concentrate
A concentrate base (stock) for making soups and chowders can be prepared and sold as frozen blocks to various hotels and institutions; this will consist mainly of by-products of fish processing - fish heads and trimmings. When boiling is completed it should be poured into suitable containers, cooled and quick frozen.
(d) Fish sausages
Fish sausages were produced from trimmings, dark meat and thick connective tissue which are otherwise discarded. The pieces of meat are minced in a large bore mincing plate, mixed with other ingredients and minced again using a small bore plate. After passing the minced meat plus ingredients into a sausage former they are heat processed for ten minutes. The sausages are then allowed to cool before packaging and refrigeration or freezing. Frozen sausages can be kept for three months or longer and yield a good food when thawed and fried or boiled.
(e) Fish cutlets
These could be termed as basic fish cakes, being prepared in much the same way as sausages. Once again off-cut which has been deboned and cleaned is used. The minced fish, pork fat, ice, polyphosphates, salt and tenderizer are blended together. The mixture is then allowed to set for one hour in a chill room. Baking soda, breadcrumbs and parsley are added. After blending the mixture is formed into cutlets using small dough formers, packed and refrigerated. The cutlets are prepared for consumption by brying in a pan or in boiling oil.
Most of the value added products mentioned above are currently in most of the supermarkets in Kenya. For example sausages are currently selling at KS 21 for a pack of eight pieces. Cutlets are selling at KSh 29.50 for a pack of 400 g. Researchers at KMFRI are continuing with work on value-added products.
3.2 Traditional Processing
Of the 90 000 t of Nile perch landed in Kenya in 1988 half were processed into fillets for the export market. The rest were sun-dried, hot-smoked, fried, for utilization locally. The most widespread method of traditional processing of Nile perch are smoking and frying then sun-drying.
The major constraint to entering into these activities is the working capital. Some processors often have to sell all their cured products before they can accrue enough money to purchase fish for another curing operation. Quite often, this results in curing only once a week.
Traditional smoking of Nile perch is done mostly using mud-walled smoking kilns. These are rectangular ovens of approximately 5 × 9 × 7 ft in size. Before smoking the fish is cut into pieces if it is a large fish. The fish or pieces are then spread out, drip-dried and smoked. A range of smoking materials are used, including firewood, wood shavings, charcoal and grass prepared in tight small bundles. The process takes about two days. The product is cooked, light brown in colour with a reduced fat content.
In traditional smoking fixed costs incurred represent only 5% of the total costs. The major cost in this activity is mainly expenditure on fuel and raw fish. This problem appears to be worsening with filleting companies offering prices as high as KSh 10/kg to obtain the best quality fish in some beaches, and ultimately artisanal processors having to pay KSh 5–6/kg for lower quality fish. At such prices, a significant number of traditional fish smokers have been driven out of work.
Preparation of fish for frying is the same as for smoking, but the pieces are smaller than for smoking. The fish is fried in its own oil made from the visceral fat. The pieces are placed in boiling oil and fried on one side until the colour is light brown and then turned over. The product is cooled, packed in baskets and transported to other parts of the country for sale. Most of the frying is done at the beaches. However, with the recent increase of filleting plants there are many skeletons left after filleting operations which are now being fried and sold locally.
Frying appears to be the most lucrative of all the traditional fish processing options, with a rate of return on investment of 60%. Artisanal smoking, however, still remains the most commonly employed option, perhaps due to consumer preference for smoked products. Fried Nile perch often presents problems since the product breaks easily and becomes less attractive to the consumer.
This is one of the least prevalent of the three popular ways of curing Nile perch. Apart from the low return on investment, another reason is that the fish landed are often too large (with high fat content) and unsuitable for such a processing option. In Kenya small sizes of Nile perch are dried, usually on raised racks or on rocks. Drying of Nile perch is not very popular as it is a difficult process.
3.3 Utilization of Nile Perch By-Products
3.3.1 Swim bladders
The bladders, also known as fish-maws or fish sounds, are the raw material from which isinglass, used as refining agent in the manufacture of beers and wines, is produced. In the Far East swim bladders, fried in cooking oil, are considered a delicacy. The Chinese use them in soups.
To prepare the fish-maws the bladders are removed whole from the freshly dead fish, washed in cold fresh water and carefully scraped to remove the adhering blood and fat and then dried flat or slit with a sharp knife and opened out before being sun-dried. In humid climates the bladders may be dried over a fire but the heat should not be too intense and smoke should be kept at a minimum so that the final product will not be dark in colour.
The price of dried fish-maws is now KSh 160/kg C&F in Hong Kong. The trade in swim bladders is now firmly established, mainly being done by the fish processing plants.
3.3.2 Fish skins
Utilization of Nile perch skins into leather products is still at the experimental stage. Initial work on preservation of the skin prior to utilization has been undertaken by researchers of KMFRI. The Nile perch skins could be easily preserved by a process of dry salting and drying in the shade.
More advanced work on transformation of the skin into leather has been carried out by our sister institute, the Kenya Industrial Research and Development Institute (KIRDI) and the Bata shoe company, both in Nairobi. Finished and semi finished samples of Nile perch leather have been produced. The products are attractive and in strength compare favourably with those produced from land animal skin.
According to the Bata shoe company, it is technically feasible to tan Nile perch skin into leather. However, before an entrepreneur invests in such an activity, market demand as well as regularity of supply of adequate and good quality skins to feed the plant have to be ascertained.
3.3.3 Fish silage for animal feed
Interest in fish silage is related to the desire to make maximum use of waste fish and fish offals in situations where the quantity involved, or the transport costs, prohibit conversion into fishmeal. In small-scale fisheries as here in Kenya this situation is common. Daily and or seasonal gluts of fish occur and, because of transport difficulties and inadequate processing facilities, these surplus fish are often underutilized.
In a country like Kenya where investment capital is not available and fish waste is not concentrated in one area the only way to make use of fish waste is to produce silage. Fish silage can be utilized in animal feed in pig and poultry industries. The technology of fish silage production is simple, essential equipment is cheap and the scale of production may be varied at will.
Silage production relies on the fact that at acidic pH spoilage bacteria are greatly reduced and the enzyme systems in the fish which break down fish protein are able to function more efficiently. Fish silage methods are divided into two major groups: (a) those employing acids, either mineral and or organic, to lower the pH and to produce the conditions necessary for silage production; (b) those employing process of fermentation with the generation of organic acids to conserve the products.
In a pilot-scale test carried out at KMFRI the acid method was used. The raw material was ground with a mincer, then 3.5% (V/W) of 85% formic acid was added. The product liquified after four days to produce a silage with 68.2% moisture, 3.3% oil, 21% protein and 7.5% ash.
3.3.4 Fish body oils
Fish body oils are usually produced during the wet reduction process used for fish meal manufacture, the liquid from the press being passed either to a series of setting tanks or to a series of centrifuges. Fish oils are used in paints, varnishes, in animal feed as carriers for the oil soluble vitamins A and D, in the manufacture of soap, rubber, lubricants, printing inks and cosmetics. Currently, Nile perch oil is made by frying visceral fat obtained manually from the belly cavity, and is used as cooking oil in traditional frying.
4. DOMESTIC MARKETING
Two distinct marketing systems exist. One involves the filleting companies which send insulated trucks to the landing centres to purchase fish. Here ice is used to reserve the quality of the fish during transport to the processing plants.
There is yet another system which involves fishmongers who are almost exclusively engaged in cured fish distribution and trade. Lacking cold storage facilities, the fish is either smoked, sun dried or fried before it enters the distribution chain. The fishmonger generally uses public transportation in sending them to the market.
Kisumu has a well-developed municipal market which handles both fresh and cured fish products. A hall has been specifically constructed for the sale of fresh fish. Concrete slabs, running water, ice and insulated storage facilities have been provided to facilitate this fresh fish trade. Facilities have also been provided for the sale of cured fish.
In addition to the Kisumu municipal market, there is also the Kibuye open market, which operates once a week on Sundays. Here fish processors, wholesalers and retailers converge from nearby towns and fishing villages and transact sales. Elsewhere, e.g., Nairobi and Mombasa, facilities for the sale of fresh fish are not as elaborate, rather the fresh fish trade is concentrated in individual fish shops. For freshwater fish, these shops obtrain their supplies mainly through the filleting companies.
4.1 Fish Prices
While average prices for major species in Lake Victoria have more than doubled since 1975, rises in Nile perch prices have been less dramatic. But as filleting companies begin to compete for top quality fresh Nile perch, prices for this species are bound to increase sharply in the next few years. The average price of Nile perch was KSh 1.50/kg in 1975. This grew to KSh 2.00 in 1986, an increase of only 25% in more than a decade. On the other hand, the price of tilapia has increased by 146% over this period. In real terms, however, fish prices have decreased between 1975 and 1986 as inflation was 237% over this period.
Nile perch continues to be the cheapest fish in the country. At landing beaches it sells for KSh 5–10/kg. Tilapia currently sells for KSh 15–20/kg in most landing beaches. The retail price for whole Nile perch in Kisumu is KSh 15/kg.
Similarly, processors sell their smoked Nile perch to wholesalers at an average price of KSh 10/kg. This is then retailed for KSh 15/kg in Kisumu, KSh 20/kg in Nairobi and KSh 25/kg in Mombasa. The cured product usually passes through a number of middlemen. Transport costs and profit margin are added at each level of the distribution chain.
4.2 Export Markets
Israel has been the major recipient of Kenya's frozen Nile perch fillets taking in more than half of both the volume and value of exports in 1988. Nearly a quarter of the volume and value of this product went to the Spanish market in the same year (Table 4). Other important markets for Kenya's Nile perch products include Australia, Netherlands, France, UK, Japan and Belgium.
In 1988 about 10 000 t of frozen Nile perch fillets (from 30 000 t of raw fish) valued at KSh 400 million were exported. The average f.o.b. price was KSh 38.1/kg. It is reported that consumer prices for frozen Nile perch fillets in importing countries may be as high as KSh 300/kg.
Besides frozen fillets, significant amounts of smoked and dry salted Nile perch are exported to Zaire and Nigeria but the extent and regularity of this trade are not known. The trade in dried swim bladders to the United Kingdom and the Far East is very promising. Currently there are considerable exports of swim bladders to Hong Kong and then to China. Reportedly, dried swim bladders fetch as much as US$11/kg in China for pieces of over 400 g.
While fish such as Protopterus, Haplochromis, Labeo, Bagrus and a few other species continue to gradually disappear from the Kenya waters of Lake Victoria, Nile perch has been proliferating. From a mere 50 t produced in 1975, official landings have shown an unprecedented growth exceeding 90 000 t in 1988.
Fish handling facilities at landing beaches still remain inadequate, although fish bandas have been established in major landing beaches to provide shade, and facilitate handling and marketing operations. It has been demonstrated that use of ice could not only extend the shelflife of fresh fish, but could also generate substantial economic benefits through the sale of top quality fresh fish. However, efforts to stimulate the use of ice have been thwarted as the fishermen have no easy access to ice or find its cost too high. To streamline these operations and encourage the use of ice, it is necessary to locate ice plants in major areas close to the fishing villages. This will cut down drastically on transportation costs and make it more affordable.
Industrial filleting of Nile perch is today the most profitable processing option for this fish in Kenya. This is reflected in the rapid expansion in both the number of filleting companies and the volume of production. Since industrial production of fillets requires high initial capital, an alternative processing option is required. There is need to penetrate the booming tourist market with cold smoked Nile perch fillets which could be used as starters. Cold smoked Nile perch should be developed to meet the tast of this target group by spicing the current ones being produced. It is also necessary for export purposes to develop more value added products so as to increase export revenues. Cold smoked Nile perch in vacuum pack is a good alternative.
Exporters further need to diversify their export markets in order to benefit from price competition. Today a number of Nile perch exporters in Kenya are confined to only one or two markets. This could be achieved through advertisements or attending food fairs to exhibit products.
The prospects of realizing the full economic potential for Nile perch by-products are very bright. This is particularly true for Nile perch swimbladders. The KMFRI is currently serving as a focal point in research efforts on improved utilization of Nile perch, and external funding would be most welcome considering the institute's limited resources.
Average prices to fishermen in Lake Victoria - Kenya waters,
by major species, 1975–1988 (KSh/kg)
Source: Kenya Marine and Fisheries Research Institute, Kisumu
Fish production in Lake Victoria - Kenya waters,
by major species, 1975 – 1988 (t)
|Lates niloticus||51||4 310||50 029||82 019|
|Rastrineobola argentea||4 548||9 443||25 866||50 512|
|Oreochromis spp.||642||5 013||9 442||991|
|Oreochromis niloticus||202||1 184||7 573||2 362|
|Clarias||2 584||1 223||547||856|
|Haplochromis||4 620||3 636||506||399|
|Others||883||1 406||1 821||889|
|Total||16 581||26 914||88 589||138 312|
Source: Kenya Marine and Fisheries Research Institute, Kisumu
Volume of production and export for major Nile Perch filleting companies in Kenya, March 1988
(t raw fish wt)
|Afro Meat Company Ltd.||2 000||Germany, Israel, Australia|
|Tiessens P.T.E.||1 000||Australia, Netherlands, France|
|Kimble Food Dist. Ltd.||120||Israel, Netherlands, Greece, Spain|
|Victoria Nile Perch Ltd.||1 500||Spain, Israel, Australia|
|Kenya Fishnet Industries||NA|
|Victoria Food Ltd.||NA||Japan, Netherlands|
|Kenya Cold Storage Ltd.||1 000||Israel, Spain, Belgium|
|Samaki Industrial Ltd.||900||Israel, Netherlands, UK, Germany, Australia|
|Midas Enterprises||500||Israel, Netherlands, Greece, Spain|
|Trans Africa Fisheries Ltd.||100||France|
|Capital Communications Ltd.||100||Israel, Spain|
|Sosco Fishing Ind. Ltd.||500||Israel|
|Samaki Industries Ltd.||600||Israel, Netherlands, UK, Germany, Australia|
|Kenya Cold Storage Ltd.||700||Israel, Spain, Belgium|
|Redcom Impex Co. Ltd.||100||Israel|
Some companies would not disclose their exact production volume
Exports markets for frozen Nile perch fillets originating from Kenya, March 1988
|Destination||Volume (t)||Percent Volume||Value (KSh 1000)||Price (KSh/kg)|
|Israel||4 483||51.3||1 631 174||36.4|
|Spain||1 858||21.2||70 604||38.0|
|Australia||1 000||11.4||42 300||42.3|
|TOTAL||8 732||100||1 791 137||38.2|
Source: Ministry of Commerce and Industry, Department of External Trade, Nairobi Exchange Rate: US$ 1 = KSh 22
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