VI Minced fish and surimi products

VI Minced fish and surimi products

A significant world trade exists in finfish blocks, minced fish, surimi, and the products made from them. In addition to making finfish blocks from fillets, they can also be prepared from fillet pieces or minced finfish, which are compressed and frozen. Like the blocks from fillets, these are used to prepare fish fingers (sticks) or fish portions, frequently after being breaded and battered. These products are commonly precooked or partially cooked. The prepared products are commonly refrozen, packaged and stored and shipped as frozen foods. Minced finfish blocks are prepared by separating the flesh from skin and skeleton of eviscerated animal using deboning machines and are often prepared from residues of filleting processes. Surimi is also prepared by mechanical deboning, but is reduced essentially to muscle protein fibers by repeated washing. The evisceration of fish for surimi is ususally done manually. The fibers are mixed with cryoprotectants before compression into blocks and freezing. Minced finfish blocks generally have higher bacterial populations than fillet blocks because of both the raw material source and the mixing process during formation of the mince. Surimi varies in bacterial content depending on the pretreatment handling and length of storage of the fish and processing control. In either case, counts

of the order of 10 6 cfu/g are not uncommon. Surimi is the basis of a variety of simulated (imitation) products, which are made by a mechanized procedure. This involves partial thawing to just below freezing, mixing with salt and other additives to yield a smooth paste, which is extruded onto a moving belt as a flat ribbon. The material then passes through various heating steps, which effectively eliminate all but bacterial spores. The material is then texturized to form a rope. This is further treated to form desired shapes. Most commonly, the product simulates crab, shrimp, or scallops. In most processes, but not all, there is a terminal hot-water pasteurization process before the product is frozen.

Surimi is also served as kamaboko which is surimi cooked on a wooden tray and sliced into thin pieces. Surimi products, though made from finfish, are quite different in composition from most seafood.

They contain none of the soluble nitrogen-based compounds, which are the main substrates of spoilage bacteria, but have significant amounts of added sugars and often egg products. Though minced fish that is used to make surimi has a microflora very similar to that of raw fish, surimi products carry only minimal

populations (10 1 –10 2 cfu/g) of mostly spore-forming bacteria (Elliot, 1987; Matches et al., 1987; Yoon et al ., 1988). When thawed and held at refrigeration temperatures the products have a very long shelf life as measured organoleptically. However, it has been shown experimentally that surimi products provide an excellent substrate for the growth of a number of pathogenic bacteria. Thus, there is a potential hazard if such products are subject to temperature abuse and this is compounded by the absence of the usual highly odoros spoilage indicators normally associated with mishandled fish products. Aeromonas hydrophila effectively competed with Pseudomonas fragi on low-salt, but not high-salt surimi (Ingham and Potter, 1988).

215 There is no record of food-borne illness from consumption of products derived from minced fish or

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surimi. The products must, as all foods, be produced observing GHP to avoid cross-contamination for the human–animal resevoir.

VII Cooked crustaceae (frozen or chilled)

A substantial proportion of crustacea in international trade are cooked prior to marketing. This includes products such as shrimp, lobsters, and more recently crayfish. Because the first step in crab processing is

a cooking step, all crab products fall into this category. Once cooked, these products are either distributed in a refrigerated state, or more likely they are frozen. Frozen products are either marketed as such or they are thawed prior to retail display. Breaded frozen shrimp products may be only partially cooked prior to freezing. A substantial portion of crabmeat is pasteurized for extended refrigerated storage (see section on pasteurized products). Examples of process flow diagrams for cooked shrimp and blue crabs are provided in Figures 3.7 and 3.8, respectively.

A Cooking, picking, and packaging Crabs routinely receive a thermal process prior to picking or other processing, and are appropriately

classified as a cooked product. A number of other crustacea (e.g. shrimp, lobster, langostinos, crayfish, etc.) are often marketed as refrigerated or frozen, cooked, ready-to-eat products. The cooking process can be blanching (shrimp, 95–100 ◦ C), boiling, or steaming under pressure (lobsters, crabs, >100 ◦ C). The duration of the cook is generally short to minimize quality loss; typically the equivalent of 20 min in boiling sea-water for crabs. Smaller species are cooked whole but larger crabs (e.g. King crab and snow crab) are split before cooking.

Meat, particularly claw meat, from cooked lobsters and some species of crabs (e.g. blue crab) is picked by hand or with minimal mechanization. Crabmeat is frequently separated from small pieces of shell by flotation in salt brine, then washed in fresh water before packaging and chilling or freezing. Cooked shrimp are marketed both peeled and in-shell. Peeled shrimp are typically but not exclusively cooked prior to removal of the shell. Peeling of shrimp is increasingly done by machine, but hand peeling still accounts for much shrimp in world trade, particularly from non-industrialized countries, and most processing plants will have a manual “fine peeling” step following a mechanical peeler.

The shelf life of crabmeat can be extended by packing the “picked” meat in containers and pasteurizing so that the internal temperature reaches 85 ◦

F) for at least 1 min (FDA, 2001b). The product is then held under refrigeration (≤2 ◦ C). This method allows the crabmeat to be held in bulk storage for up to 6 months. Cooked, peeled shrimp is packaged and frozen without further treatment, or after a batter and breading dip.

C (185 ◦

B Saprophytes and spoilage The cooking step reduces significantly the bacterial counts in crustaceans, destroying vegetative cells

of both spoilage and pathogenic species (Ingham and Moody, 1990). However, care must be exercised to ensure that there are no “cold spots” that would receive less than sufficient thermal processing.

Crab picking and shell separation, which may involve brine flotation, often recontaminates the picked meat with a variety of microorganisms. Refuse containers for picking waste, insects, and cross- contamination from live crab carts have been identified as sources of recontamination after cooking.

Counts of 10 5 cfu/g in picked meat are common, and microorganisms present will include Gram-positive rods and cocci, Gram-negative rods, and yeast. Storage of picked meat under refrigeration normally

MICROORGANISMS IN FOODS 6

Receive

Iced storage

Frozen storage

De-ice / wash

Thaw / wash

Size / grade

Dip (additives) Drain

Individually Quick Forzen

Glaze Package

Weigh Label

Frozen storage Ship

Figure 3.7 Example of a process flow diagram for cooked shrimp (NMFS, 1989).

results in a progressive increase in counts to >10 7 cfu/g in 7 days. The microflora is usually dominated by Gram-negative rods, typically Pseudomonas and Acinetobacter–Moraxella spp. Spoilage typically involves the production of volatile amines.

The arrival of shrimp at the processing plant in a non-living state makes their processing somewhat different from crabs and lobster. Their initial bacterial level at the processing plant will be a function of the quality and extent of shipboard storage, with counts ranging from 10 3 to 10 7 cfu/g. Shrimp taken from tropical waters will tend to have higher counts (Cann, 1977). Shrimp cooked by boiling or steaming for a few minutes either prior to or after peeling show ∼100- and 10 000-fold reductions in mesophilic and psychrotrophic plate counts, respectively (Ridley and Slabyj, 1978). However, there tends to be a rapid return to bacterial levels equivalent to those prior to cooking as the product is held and handled during inspection and grading, though there may be a shift to a more mesophilic microflora.

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Receive Live storage

Cook

Deback

Cool / cool storage

Pick

Pack / Weigh / seal

Frozen storage

Cool

Chilled storage Refrigerated storage

Ship

Figure 3.8 Example of a process flow diagram for hard blue crabs (NMFS, 1990c).

In general, the level of microorganisms post-processing is a reflection of the level on the in-coming raw material (Høegh, 1986). Somewhat smaller recontamination rates are observed with brine-cooked shell-on shrimp (Ridley and Slabyj, 1978). Because of handling, low levels of coliforms, E. coli, and staphylococci may be present in finished products. When cooked shrimp are stored chilled rather than frozen, the spoilage flora is dominated by Pseudomonas or Acinetobacter–Moraxella and sometimes coryneform bacteria (Cann, 1977) or Aeromonas (Palumbo et al., 1985; Palumbo and Buchanan, 1988).

C Pathogens The potential for the presence and growth of pathogenic bacteria in cooked crustacea is a function of the

adequacy of the thermal process, the extent of post-processing contamination, and the maintenance of

MICROORGANISMS IN FOODS 6

proper refrigerated or frozen storage. Temperature abused crabmeat, shrimp, etc., can support the growth of a wide range of species, particularly if competitive microorganisms have been eliminated as a result of the thermal processing. The extent of manual manipulation of product often provides ample opportunity for the introduction of a variety of human pathogens. This is reflected in the reported incidence of food- borne outbreaks associated with cooked crustacea (Bryan, 1980). Vibrio parahaemolyticus, a common member of the microflora associated with raw shrimp and crab, is a cause of food poisoning associated with these products. As an example, boiled crab caused 691 cases of V. parahaemolyticus gastroenteritis in Japan in 1996 (Japanese Ministry of Health, Labour and Welfare, 1999). Cholera cases have been attributed to the consumption of crab from epidemic areas (Finelli et al., 1992). However, a significant percentage of the outbreaks linked to cooked shrimp, lobster, and crabmeat products have been attributed to long-established food-borne pathogens including Staph. aureus, Salmonella, Shigella, and virus. Maintenance of proper storage temperatures is a prime concern, particularly under conditions where growth of pathogens could occur before overt spoilage of the product (Ingham et al., 1990).

As the picking process is by hand, the possibilities for transfer of pathogenic bacteria from humans to crabmeat is high. The extent of human handling with shrimp varies from extensive in operations where product is hand peeled to minimal where peeling, inspection and packaging are mechanized. The ubiquitous association of Staph. aureus with food handlers often results in the introduction of low numbers into raw and cooked products, particularly crabmeat (Ridley and Slabyj, 1978; D’Aoust et al, 1980; Hackney et al., 1980; Swartzentruber et al., 1980; Wentz et al., 1985), though the former should

be eliminated during the cooking step. Reintroduction of the pathogen may be exacerbated by the use of brine flotation as a means of removing shell fragments from the product; the high salt levels select for halotolerant staphylococci over Gram-negative spoilage organisms. Fortunately, staphylococci tend not to compete well with the normal flora of crabmeat, particularly at marginal abuse temperatures, and generally die slowly during refrigerated storage (Slabyj et al., 1965). However, significant growth of staphylococci can occur in temperature-abused product, particularly if the spoilage microflora has been suppressed as a result of the thermal processing (Gerigk, 1985; Buchanan et al., 1992). This has resulted in occasional staphylococcal food poisoning outbreaks, particularly in crabmeat (Bryan, 1980). Hand peeling of cooked shrimp can introduce Staph. aureus on the product and if temperature-abused, it will grow well and can produce enterotoxin. Potentially, the use of processes, such as modified atmosphere packaging, that alter significantly the microflora of the product could impact the potential for significant outgrowth of Staph. aureus before overt spoilage of temperature abused product. A variety of other Staphylococcus spp. has also been isolated from frozen crabmeat (Ellender et al., 1995).

The potential for temperature-abused cooked crustaceans serving as a source for a variety of food- borne pathogens focuses attention on the need to maintain adequate sanitation and temperature control after initial thermal processing. This is reinforced by the linking of cooked crustaceans to occasional outbreaks of enteric pathogens such as Salmonella and Shigella (Bryan, 1980; Mazurkiewicz et al., 1985). The incidence of Salmonella and Shigella in raw and cooked products is typically low; however, this can vary among geographical locations (D’Aoust et al., 1980; Gilbert, 1982; Fraiser and Koburger, 1984; Gerigk, 1985; Sedik et al., 1991). There are indications that modified atmosphere storage slows the growth of salmonellae in marginally temperature abused (11 ◦

C) cooked crab; however, this effect is lost if the product was subjected to higher abuse temperatures (Ingham et al., 1990). The levels of enteric pathogens tend to decline during refrigerated storage; however, this is neither rapid nor sufficient to ensure elimination (Taylor and Nakamura, 1964). Yersinia enterocolitica, a psychrotrophic enteric pathogen, is an exception in that the species will grow in both cooked shrimp and crabmeat at refrigeration temperatures (Peixotto et al., 1979). It can be isolated in low numbers from raw shrimp and crab (Peixotto et al., 1979; Faghri et al., 1984). However, it is readily inactivated by cooking, and declines during frozen storage (Peixotto et al., 1979).

219 Vibrio parahaemolyticus , V. cholerae, and V. vulnificus are routinely part of the microflora of raw

FISH AND FISH PRODUCTS

crustaceans harvested from estuarine waters (Davis and Sizemore, 1982; Faghri et al., 1984; Molitoris et al ., 1985; Varma et al., 1989) and are important bacterial pathogens in cooked crustaceans. The presence of these species in the environment has been correlated with elevated seawater temperatures (Kelly, 1982; Williams and LaRock, 1985; O’Neil et al., 1990); however, they have also been isolated from crabs taken from cold waters (Faghri et al., 1984).

The high incidence of Vibrio in raw crustacea makes adequate thermal inactivation and prevention of cross-contamination important measures for preventing pathogenic Vibrio in cooked product. Prevention of cross-contamination is particularly important (Hackney et al., 1980; Karunasagar et al., 1984), since Vibrio are considered sensitive to thermal inactivation (Delmore and Crisley, 1979; Shultz et al., 1984). However, there have been reports that standard heating procedures for primary treatment of crabs may not be sufficient to destroy V. cholerae in the internal tissues, and more rigorous treatments have been proposed (Blake et al., 1980a). Numbers of Vibrio spp. decline slowly during refrigerated and higher frozen storage temperatures (i.e. 4 ◦

C and −20 ◦ C), but are stable at lower storage temperatures (i.e. −80 ◦

C) (Bradshaw et al., 1974; Oliver, 1981; Boutin et al., 1985; Oliver and Wanucha, 1989).

A cryoprotective agent for V. cholerae has been identified in prawn shells (Shimodori et al., 1989), and chitin has been reported to enhance the pathogen’s acid tolerance (Nalin et al., 1979), but not its thermotolerance (Platt et al., 1995). Non-O1 V. cholerae strains with increased tolerance to refrigerated and frozen storage have been observed (Wong et al., 1995).

Commonly employed microbiological indicator tests, including APC, coliform, fecal coliform, and enterococci assays, are of limited use for indicating the presence of V. parahaemolyticus (Hackney et al ., 1980).

Identification of the role that food-borne transmission plays in the etiology of human listeriosis, along with the ability of L. monocytogenes to grow at refrigeration temperatures, has prompted considerable study of its characteristics in cooked shrimp, crabmeat, and crayfish. For example, the microorganism grew readily on cooked crayfish tail meat at 6 ◦

C, but did not grow if the product was maintained at 0 ◦

C, or after short term abuse at 12 ◦

C (Dorsa et al., 1993a). Pasteurized crabmeat supports the growth of L. monocytogenes at 1 ◦

C increases growth rates substan- tially (Rawles et al., 1995). Listeria monocytogenes is present in a high percentage of fresh and low salinity water samples (Colburn et al., 1990) and can be isolated routinely from raw shrimp and crab (Motes, 1991). The microorganism is isolated at approximately the same rate (10%) from cooked peeled shrimp and cooked crabmeat (Weagant et al., 1988; Hartemink and Georgsson, 1991; Rawles et al., 1995). It is unclear whether this is due to insufficient thermal inactivation, cross-contamination, or post- processing contamination from environmental or food handler sources. The species is often associated with processing environments and Destro et al. (1996) found that several different RAPD/PFGE types were associated with a processing plant producing frozen, un-cooked shrimp. Listeria monocytogenes is considerably more heat resistant than Vibrio or enteric pathogens, particularly at lower thermal pro- cessing temperatures (Harrison and Huang, 1990; McCarthy et al., 1990; Dorsa et al., 1993a). For

C, and increasing storage temperatures to 5 ◦

example, its D 60 ◦ C value in crayfish tail meat homogenate was 4.7 min (Dorsa and Marshall, 1995).

2.4 min by treating the meat with 1% lactic acid. Listeria monocyto- genes is also substantially more tolerant of elevated sodium chloride levels than enterics (Buchanan et al ., 1989), which could favor its presence during brine flotation of crabmeat. Spraying crayfish tails with citric acid or potassium sorbate was not effective as a means of reducing L. monocytogenes on cooked crayfish (Dorsa et al., 1993b). Modified atmosphere packaging can partially retard the growth of L. monocytogenes at refrigeration temperatures, but this effect is lost at abuse temperatures (Oh and Marshall, 1995). Treatment of crayfish tails with ≥1.5% lactic acid increased the effectiveness of modified atmosphere packaging (Pothuri et al., 1996).

This was reduced to D 60 ◦ C =

MICROORGANISMS IN FOODS 6

C, reaching levels in crabmeat in excess of 10 6 cfu/g within 14–21 days in inoculated pack studies (Brackett and Beuchat, 1990; Buchanan and Klawitter, 1992). The microorganism can survive in frozen foods essentially unchanged for extended periods (Harrison et al., 1991; Palumbo and Williams, 1991). While L. monocytogenes has been isolated from both cooked shrimp and crabmeat, and has survival and growth characteristics of concern, it is important to note that there has been no direct link between cooked crustacean products and the etiology of food-borne listeriosis.

Listeria monocytogenes achieved substantial growth at 5 ◦

Strains of Cl. botulinum (usually serotype E) have been isolated from crabs, but so far there is no evidence of a specific botulism problem. Pasteurized crabmeat is stored for several months in cans that can be expected to develop anaerobic conditions. The pasteurization process standard adopted by the U.S. National Blue Crab Industry Association is sufficient to inactivate non-proteolytic, but not proteolytic Cl. botulinum spores. The product should be refrigerated to prevent germination and outgrowth of spores that could impact both microbiological quality and safety. It would be reasonable to assume that temperature-abuse of this product occurs occasionally; however, in the 50 years that the pasteurization process has been used there have been no food-poisoning cases attributable to the practice.