Salting is one of the oldest forms of food preservation. Before the invention of the refrigerator, the majority of households used salt to extend the shelf life of various foods. Today, salting is one of the most prevalent pretreatments for fish products. It reduces the moisture content of fresh fish and acts as a preservative, converting it into shelf-stable items.

Salting does this by preventing the growth of spoilage bacteria and molds while allowing friendly bacteria and local enzymes to populate and break down the relatively flavorless protein molecules and lipids found in fish. This, in turn, reacts to produce even more complex flavors.

Since ancient times, people have been aware of the impact of a food’s water content on its perishability. Between 15,000 and 10,000 BC, our forefathers began to dry foods to preserve them. They used the wind and sun to dry excess fish and meat, and later did the same with excess fruits. The combination of drying and salting contributes to the development of distinctive sensory characteristics of products, which impact their use as food.

Fish that has been salted for a day (with a little salt) often stays fresh for a few days, while fish that has been steeped in salt last for about a year or more. Lean cod and other fish from related families have always been salted before being air dried. In contrast, fish like herrings and their relatives are preserved from rancidity caused by the air through brining and/or smoking.

Let’s discuss further.

WATER ACTIVITY IN FRESH FISH

In food science, the term water activity is a commonly discussed term. It refers to the amount of free or unbound water, water that can be used for various processes, particularly to support microbial growth. Most foods contain a water activity of around 0.95. The water activity of most fresh fish is over 0.85. This is enough for microorganisms to thrive and spoil food. This is why they are highly perishable.

To prevent this, the water activity must be lowered down. Pathogenic bacteria are inhibited by a water activity of 0.85 or lower. While certain yeasts and molds can survive in a 0.75 water activity environment, they can no longer create toxins. In fish salting, the water activity decreases because salt draws the water out in a process called osmosis. The idea is to increase the concentration of salt, a solute. In this manner, water diffuses between cells in the environment. This results in the same concentration of salt on both sides of the cell. According to the Food and Agriculture Organization of the United Nations (FAO), a concentration of between 6 to 10 % salt will prevent the growth of most spoilage bacteria. 

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The procedure results in a saline equilibrium between the muscle and the surrounding salt solutions. Under typical temperature conditions, the maximum concentration obtainable is that of a saturated brine solution. Because of the osmotic pressure between the brine and the fish muscle, sodium chloride or salt diffuses through the fish flesh via a dialysis mechanism, and water diffuses to the outside.

This process does not go on indefinitely. The sodium and chlorine ions create a water-binding complex with protein. This in turn produces an osmotic pressure that attains an equilibrium.

MICROBIAL SPOILAGE OF FISH

Most microorganisms responsible for the spoilage of fish halophobic. Halophiles are microorganisms that can thrive in an environment of high salinity— with a high concentration of salt. And they will not grow until there is 10% salt present. Examples of halophiles include Halobacterium salinaria, H. cutirubum, Pseudomonas spp Sarcina morrhuae and S. litoralis.

These bacteria are aerobic—they require oxygen for growth, and are rarely found in pickled fish, where the brine provides only limited oxygen access. They are also thermophilic, with an optimum growth temperature of approximately 42°C and a minimum growth temperature of approximately 5°C.

These bacteria produce pink spoilage. Pink spoilage are so-called because of the color of their colonies and the resulting appearance of the cured fish. A delicate pink sheen on the surface of the fish in wet stack or during pining is the first indicator of pink spoilage. This can be readily removed without harming the fish.

Maintaining the ambient temperature below 50°F (10°C) is likely to prevent initial germination and growth of halophiles. Treatment with formaldehyde or sulphur dioxide vapors, or dipping the fish in a solution of sodium metabisulphite also work. Although food poisoning cases that were allegedly brought on by eating pink-spoiled fish were likely actually brought on by the spread of Staphylococcus aureus, a bacteria that produces exotoxins.

This bacteria start growing at somewhat greater water activity levels than those required for the growth of pink bacteria. Salt fish has the water activity of a saturated common salt solution of 0.75, regardless of how much it has been dried before and after salting.

Many microorganisms will rupture in very high salt solutions due to the difference in pressure between the exterior and inside of the microorganism.

METHODS OF MAKING SALTED FISH

Depending on the fish composition and size, salting may be dry or wet.

The rate of salt diffusion is proportional to the concentration gradient between the salting medium at the surface and the point in the fish most distant from the salting medium. Hence, the stronger the brine, the faster the salt uptake and to achieve a water activity low enough for preservation.

Fish are salted whole and uneviscerated, eviscerated and split open, or in smaller pieces ranging from fillets to mince, depending on their size. Only small species, such as anchovies and small herring, can be salted whole without gutting. Large fish usually have fish skins that prevents proper salt penetration. Hence, large fish treated in this manner would decay before the salt could have an effect.

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The most frequent approach is a mix of the dry and wet method. The fish are immersed in dry salt before being immersed in the liquid pickle produced by the salt solution in the liquid extracted from the fish. This is also known as ‘blood pickle’.

The dry method involves stacking the fish in salt by directly applying it onto the surface.

And the brine produced is allowed to run away. Anchovies are commonly dry-cured by layering it with sufficient salt to saturate the tissue of the fish.

This is then placed under weight and stored at high temperatures around 86°F (30°C) for 6 to 10 months. This is a very traditional Mediterranean dish that can be eaten as is or combined with oil or butter to make a paste. Muscle, skin, blood cells, and enzymes, along with bacteria and the warm curing temperature, all work together to stimulate the early stages of browning reactions and generate several aromatic molecules.

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Cod can also be dry-cured in 25% salt marinade for at least 15 days. The fish can be stored after for several months as Micrococcus bacteria break down molecules, generating trimethylamine (TMA) and flavor-generating free amino acids. Furthermore, oxygen works on the fat molecules, forming fatty acids that contribute to the aroma of the fish as well. A further 3 days of artificial drying in a controlled cold chamber completes the process.

The wet method involves immersing the fish in a strong brine, or ‘pickle’.

Wet salting is accomplished through brining and pickle curing. The method employed is determined on whether the product will be further processed by drying or smoking, or just preserved by salting. The wet method is ideal for fatty fish such as mackerel and sardine.

Because herrings and comparable species can contain up to 20% fat by weight, traditional dry curing causes rancidity. During the early days of making salted fish, air would be removed from the equation. And the fish would be wet-cured in a mild brine (16%-20% salt solution), allowing the fish to be stored for up to a year.

Then, a method was devised that allowed a portion of the intestine rich in digesting enzymes (the pyloric caecum) to remain inside the fish. In addition to the fish muscle and skin enzymes, the digestive enzymes of the pyloric caecum collaborate to break down proteins. The result is a softer texture and a complex flavor-aroma that was slightly cheesy, fishy, and meaty. This technique is still followed today, and the herrings are eaten as they are, without being salted or cooked.

References:

G.M. Hall (1997). Fish Processing Technology (2nd edition). Blackie Academic and Professional.

M. Gibson (2018). Food Science and the Culinary Arts. Academic Press.

M. Shafiur Rahman (2007). Handbook of Food Preservation (2nd edition). CRC Press.

The post The Science Of Making Salted Fish appeared first on The Food Untold.

When it comes to making a list of expensive foods around the world, foods such as champagne, truffle, fois grais, and Wagyu always make the cut. The seafood version of these is caviar. In fact, a pound of this luxury delicacy could fetch for $2000. What makes it special though? And what does caviar exactly taste like?

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It turns out that the hefty price of caviar was not always the case. Just like oysters, its high value lies behind the rule of supply and behind. Caviar is salt-roe eggs from sturgeon species. There are 27 varieties of sturgeon and 4 types of caviar—Malossol, Beluga, Oscietra, and Sevruga.

Back in the 19th century, caviar was a common food item that establishments would offer caviar for free and farmers would make it as animal feed. But everything changed when water pollution and overfishing of sturgeon during the 20th century diminished their population. As a result, supply could not keep not with the demand, making caviar a rare commodity. Furthermore, it takes several years for a female sturgeon to become sexually mature.

Take Beluga, the largest, the rarest, and the most expensive caviar, for example. This type of caviar is made from beluga sturgeon Huso huso, species that may live for 80 to 100 years but matures only after about 20 years. Its eggs for caviar is the largest, and are very dark gray to light gray on color. A pound of Beluga caviar costs around $4000.

The World Wildlife Fund has listed Beluga sturgeon on the critically endangered list. To combat this, the United States Fish and Wildlife Service banned the importation of the fish in 2005. However, the was ban was partly lifted later to allow sale in the country.

THE TASTE OF CAVIAR

Well, the United States and European countries consume the most caviar. With the high price of caviar, Is it worth it though?

In general, the taste of caviar at first is salty and briny with a hint of fishiness—kind of like raw oysters. And after a few seconds, the taste transitions to produce a creamy, buttery or nutty taste. The taste is heavily influenced by how caviar is prepared, which is usually by mild salting.

The salting process allows part of the salt to enter the egg via osmosis. Osmosis preserves the food by drawing out moisture from bacterial cells. It also activates enzymes that break down proteins. On average, caviar is 75% ovoglobulins, 13% collagen and 11% albumin. The breakdown of these proteins increases the levels of flavor-stimulating free amino acids. Studies have revealed considerably high amount (3 g/100 g) of free glutamic acid in some types of caviar. Glutamic acid is the amino acid responsible for the umami taste in a wide range of foods such as meat, poultry, and other protein-rich foods.

Another function of salting is that triggers the production of the transglutaminase enzyme, an additive that enhances the appearance and texture in foods such as processed meats. In the case of caviar, it aids in the cross-linking of proteins in the egg’s outer membrane. This contributes to the membrane’s strength and plumpness, giving the egg more texture and a firmer mouthfeel overall. And as salt ions affect the proteins inside the egg, the bonded protein becomes a thickening agent where watery egg fluids display greater viscosity in the final product. A high grade caviar is best described as a pleasantly viscous liquid.

CAVIAR LABELLING REQUIREMENTS AND REGULATIONS

The quality and characteristics of caviar vary greatly. And this depends on the type on the type. But we are not talking about fish roe in general. Real caviars are made from eggs of sturgeon. In fact, according to the Food and Drug Administration (FDA), the term “caviar” should be applied only to sturgeon roe. The name of the fish should be listed on the label if the caviar is derived from anything other than sturgeon roe.

Roe made from other fish may be labeled as “_______ Caviar”. The blank needs to be filled in with the common or typical name of the fish that the roe was harvested from. One common alternative to real caviar is salmon roe. It is pale yellowish-orange to dark reddish-orange because of carotenoid pigments. Sturgeon caviar, on the other hand is silver to black because of brown-black melanins.

Caviar is dry salted at concentrations of 3% and 10% for 2 to 4 minutes. Traditionally, sodium borate (borax) has taken the place of some kinds of salt. The alkalinity of borax allows for slight salting of the eggs, improvement of shelf life, while adding sweetness. However, it should be mentioned that, among other nations, the United States has banned the imports containing borax due to concerns over health.

Fresh caviar should be stored at refrigerator temperature, not frozen. The preserved eggs’ integrity is compromised by freezing, especially the membranes. The egg’s quality can remain unopened for four weeks, but once it’s been opened, it is better to eat it right once. Caviar can be pasteurized at 122°F (50°C) to 158°F (70°C) for an hour or 2 to extend its shelf life. However, the mild heat treatment diminishes the flavor of caviar and it becomes chewier.

The post What Does Caviar Exactly Taste Like? appeared first on The Food Untold.

Smoking is one of the earliest forms of food preservation. Evidence suggests that our ancestors first smoked food during the Old Stone Age (Paleolithic Era). Back then, caves or huts were home to primitive cavemen. They would hang meat to dry inside. Once fire was discovered, caves would become smoky since they lacked a chimney. They later on discovered by accident that the smoke changed the flavor of the meat and that it preserved the meat better than simply drying the meat out. This procedure was eventually combined with pre-curing the food in salt or salty brine, creating a very efficient preservation technique.

Fish smoking first appeared incidentally when fishermen had to utilize open flames to dry their excess catch during wet or humid weather conditions rather than the sun and breeze. The microbicidal and antioxidant benefits of smoking were not fully understood until much later. Consumers developed a liking for smoked fish long before they were aware of it as a delicious substitute for eating fresh fish.

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Today, smoking can be used for a wide range of foods. Meats and fish are the most commonly smoked foods. In the cooler northern regions, common smoked fish include haddock and cod in Great Britain, herring in Holland and Germany, skipjack in Japan and smoked sturgeon in Norway, Scotland, and Russia. In the United States, mackerel, salmon, mackerel, trout, and white fish are commonly smoked.

Before we proceed with the discussion, let’s define what smoking is.

WHAT IS SMOKING?

Smoking is the process of exposing food to wood smoke. Smoke is an emulsion of droplets stabilized by electrostatic charges on the droplets in a continuous phase of air and vapors. The vapors in smoking are most significant for flavoring, coloring, and microbistatic functions.

Depending on the technique, various products can be concurrently cooked and smoked, cooked and dried, or smoked but not cooked. The source of smoke can be either by burning wood chips or using an approved liquid smoke preparation. It is also possible to employ liquid smoke preparations by adding them directly to the product during formulation rather than using a smokehouse or another sort of smoking vessel.

Smoking is frequently seen as a pretreatment instead of a drying method. The heat produced during smoking has a drying impact on food, even if it is not typically employed to do so. But the main benefits of the process are that it gives food appealing flavors and colors. Furthermore, some of the compounds created during the process have a preservative function because of the presence of many components. Acids, carbonyls, and phenolic chemicals are all present in smoke. And the phenolic compounds’ volatile nature is largely responsible for the flavor of smoke. More than 400 volatiles have been found in wood smoke, making it exceedingly complex.

It is worth-noting that although smoking helps preserve foods, it may not be sufficient as an antimicrobial treatment, especially for meat and fish products. This is because the smoke does not penetrate the flesh far enough. If this is the case, processors combine smoking with salt-curing or drying.

HOW SMOKING FISH IS DONE

The traditional method of smoking fish entails passing hot smoke from a variety of woods over the fish in order to partially dry the fish and impart the flavor and aroma of the smoke. The drawbacks of this are the lack of control over the process and the final product, as well as potential health risks if the fish’s surface is not adequately dried.

Modern fish smoking techniques include a variety of drying techniques to lower water activity on the surface and liquid smoke compositions to add taste. Before drying, the fish is submerged in smoke solutions. The majority of drying techniques employ heat to alter the air’s relative humidity as it passes over the fish. This wastes energy and also causes numerous aromatic chemicals that contribute to the product’s flavor, color, and aroma to be driven off by heat.

This can be avoided by utilizing a heat pump drier that uses less energy and dries items inside of a sealed chamber. There are two types of smoke solutions: condensed products from the dry distillation of wood and synthesized phenol mixes.

Utilizing smoke condensates has certain benefits. They are simple to use, and you can manage their concentration. They can be examined for antibacterial activity, studied, and purified if necessary. Synthetic smokes are more similar to actual smoke curing and can be made without dangerous ingredients. The nature of the wood has a significant impact on the smell, flavor component composition, and antibacterial activity of the smoke.

Wood for smoking fish

Wood is preferred to sawdust in many regions of the world. The fish is charred rather than smoked as a result of the hotter, less smoke-producing fire. In a sawdust fire, the air cannot easily reach the flames unless there is a forced quick flow, therefore the sawdust smolders rather than burns.

A smoke with more flavoring and preservation agents is produced at lower temperatures and with less oxygen. These compounds are wasted when they are oxidized into carbon dioxide and water at higher temperatures and with more oxygen. However, the majority of smoke used for smoking is still produced by a simple fire globally. Modern smoke producers feed sawdust gently onto an extremely hot surface.

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The flavor of smoked fish depends on the sawdust’s species source. Hardwoods like oak, hickory, cherry, apple, and beech burn with higher phenols, which retain and give the product a distinctive, “medicated” flavor. It is questionable if a product that has been hickory smoked can be distinguished from one that has been similarly beech smoked, especially after the product has been cooled and stored.

There should caution when choosing wood for smoking fish. As per Codex Alimentarius, toxic substances must not be present in wood or other plant material used to generate smoke or smoke-condensates, either naturally or as a result of contamination, treatment with chemicals, paint, or impregnating agents.

Cold smoking vs. hot smoking

There are 2 methods of smoking fish: hot smoking and cold smoking.

In cold smoking, the fish is cured at an air temperature of 68 (20°C) to 86°F (30°C) for 6 and 24 hours to several weeks. Cold smoking produces fish that has a milder flavor than fish that has been hot smoked. Also, cold smoked fish, such smoked salmon, keeps the texture of raw fish while having less moisture content. Fish that is hot smoked is cooked and has a firm but flaky texture. Because microorganisms are not eliminated, salt curing is done before cold smoking.

It is advised to utilize prefrozen fish. This is to ensure that any parasitic worms or bugs that could not be killed during the procedure are truly killed. Industrial smoked products are typically smoked and brined less. Economically speaking, this is better because fish and meat are sold by weight.

One good example of commonly cold-smoked fish is salmon. The fish may be brined with salt (sometimes sugar) for a few hours to several days. This is then rinsed and air-dried prior to cold smoking for 5 to 35 hours.

Hot smoking, on the other hand, involves exposing fish to smoke and heat at 140°F (60°) to 176°F (80°C), usually in a smoker oven or smoker house.  The rich and slightly darkened color of hot-smoked fish is partly caused by condensation of dark resins from the smoke and browning reactions between amino acids in the pellicle and the aldehydes in the smoke.

Hot smoking of fish involves five steps. These are surface drying, smoking, drying, heating/cooking, and cooling. Surface drying is the removal of moisture from the surface and leaving a protein coating (pellicle) on it in order for each piece of fish to absorb an uniform smoke deposit.

METHOD OF PRESERVATION

In most parts of the world, preservation is still the prime objective of smoking. Smoking preserves foods due to a combination of several factors.

Salting

Salting inhibits the growth of many spoilage organisms and pathogens by reducing the water activity of fish. Water activity is one of the factors that controls the rate of deterioration in food. It refers to the amount of unbound or free water available for microbiological reactions. To slow the rate of deterioration, the water activity should ideally be below 0.95.

For a more detailed discussion on water activity regarding food safety, refer to this post: Water Activity (aw) And Food Safety.

Nowadays, fish is “cured” first by salting or brining in salt concentrations of around 3% or so. This is not quite enough to prevent microbial activity, for a few hours to a few days. Instead, it draws proteins found in muscle fibers to the surface, where they dissolve in salt and form a gel-like sticky layer on the surface of the fish after it is dried and hung.

Deposition of phenolic antioxidant substances

Traditional smoking can extend the induction period of autoxidation from 4 days in unsmoked controls to roughly 50 days. Autooxidation is the spontaneous oxidation of a compound in air. This describes the gradual degradation of organic compounds in air. The phenolic antioxidants also delays the development of rancidity generally highly unsaturated fish lipids.

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However, the antioxidant effect of smoking is primarily linked to the particle phase of wood smoke (the vapor phase exhibiting little to no antioxidant activity). And it increases with increasing temperature of the oxidation stage of smoke production while being unaffected by the temperature of pyrolysis (burning process) or air supply.

Deposition of antimicrobial substances

Wood smoke contains a variety of preservatives. Phenol and other phenolic chemicals have antioxidant and antibacterial properties. In fact, vaccine manufacturers use phenol to prevent bacteria from contamination vaccine solutions. Formaldehyde, acetic acid, and other carboxylic acids are examples of other antibacterial substances. Additionally, these substances are removed and used as liquid smoke.

Surface drying

As earlier mentioned, surface drying removes moisture from the surface of the fish, leaving a pellicle on it to absorb an uniform smoke deposit. Another benefit of surface drying is to provide a protective barrier against microbial passage and a hostile environment for any aerobic microbial proliferation.

FLAVOR AND COLOR DEVELOPMENT

Modern smoking techniques should aim to improve product shelf life while preventing the buildup of recognized carcinogens and to impart the required sensory attributes to the product evenly, without unnecessary variation from batch to batch.

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Controlling the quality of the raw materials and process variables such brining treatment, smoking kiln time, temperature, and air speed has a significant impact on the appearance and texture of the smoked product. However, there is evidence to support the notion that some smoke components, such as formaldehyde, toughen the proteins in the muscles.

Flavor

Phenols are usually thought to have a significant part in the desirable characteristic flavor of smoked fish. Eugenol, syringaldehyde, acetosyringone, and acetovanillone appear to be more significant in hot-smoked fish, whereas guaiacol, maltol, phenol, and m-cresol are significant in cold-smoked fish.

Guaiacol is less significant than eugenol in what is thought to be a typical smoked flavor. Furan derivatives have a pleasant, fragrant perfume that is supposed to balance out the potent, smokey aromas of the phenolics in the lower boiling point portion of liquid wood smoke condensate.

Although the appetizing smoked fish flavor notes at low concentrations appear to be primarily caused by the low molecular weight fractions of wood smoke, higher concentrations are perceived as less appealing “burnt” or “phenolic” notes.

Color

The color that the smoking process gives fish is a result of Maillard-type carbonylamino reactions. These reactions have been linked to a quantitative drop in carbonyl groups in the smoke. Additionally, ribose from the breakdown of nucleotides and ribonucleic acids and free amino compounds like anserine and taurine in fish muscle extractives cause the surface of drying fish to brown. The extent of spoilage of fish also contributes to the extent of brown color formation. However, stale fish cannot be used to make good smoked goods. The freshness of the fish before it is smoked determines the quality of the product that is delivered to the customer.

References

V. Vaclavik, E. Christian (2014). Essentials of Food Science (4th edition). Springer.

M. Gibson (2018). Food Science and the Culinary Arts. Academic Press.

M. Shafiur Rahman (2007). Handbook of Food Preservation (2nd edition). CRC Press.

G.M. Hall (1997) Fish Processing Technology. Blackie Academic & Professional.

P. Fellows (2000). Food Processing Technology (2nd edition). CRC Press.

The post Things You Need To Know About Smoking Fish appeared first on The Food Untold.

Meats, fish, and poultry are all perishable foods. Among the three, fish spoil the fastest. Most meats, such as beef and pork, can be stored for 3 to 5 days. Fish, however, have a very short shelf life of just 1 to 2 days. This is one of the reasons why fish contribute to the immense global food waste. In fact, according to the Food and Agriculture Organization of the United (FAO), around 35% of the global harvest is lost or wasted annually.

There are several mechanisms that make fish a highly perishable commodity. Let’s discuss them.

FISH LIVE UNDERWATER

Allow me to say the already obvious: fish live in an environment where the temperature is low—underwater. This is especially true in the deep ocean water where the temperature is just a little bit above freezing. The bad thing about this is that some microorganisms are present in fish that adapt well to low temperatures.

In an earlier post, I mentioned that temperature is one of the factors that affect the growth of microorganisms. Generally, low temperatures slow down the growth of microorganisms. However, certain bacteria called psychrotrophs can survive low temperatures of 44.6°F (7°C) and below, a typical condition underwater. This means if we put a fish in a refrigerator, the bacteria in the fish flesh require lesser time to adapt to the temperature. They would continue to consume and break down the proteins and fats, and produce volatile and undesirable odor molecules. This 1984 study isolated psychrotrophic Pseudomonas fluorescens, Pseudomonas putida and non-fluorescent Pseudomonas sp in raw tuna fish.

Psychrotrophic bacteria is also the reason why cold water (ocean water) fish spoil quicker than warm water (fresh water) fish, as well as other types of meat. Microorganisms and enzymes in living animals for meat such as cattle, pigs, and chickens are used to warmer temperatures. Hence, putting meat in refrigerator temperature at 40°F (4.4°C) would slow things down for the bacteria present.

FISH CONTAIN TRIMETHYLAMINE OXIDE (TMAO)

Fish tissues contain a high concentration of a chemical called trimethylamine oxide (TMAO). TMAO is a piezolytes, whose purpose is to protect the fish from the protein-destabilizing effect of water pressure that may kill the animal. Piezolytes provide the proteins the flexibility they require in order to function properly under great pressure.

TMAO is the most abundant piezolyte in marine animals. This chemical is colorless, odorless, and flavorless. But when the fish dies and its tissues get exposed to air, TMAO is degraded and broken down by bacteria into trimethylamine. Trimethylamine is what gives fish a strong, fishy odor. And considering the soft texture of fish, spoilage microorganisms can easily penetrate and decompose it.

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Majority of ocean water fish contain TMAO. Fresh water fish and land animals do not contain this compound.

FATTY ACIDS IN FISH IS PREDOMINANTLY UNSATURATED

You may have already heard about the term omega-3 fatty acids in many TV commercials. Omega-3 fatty acids are unsaturated fatty acids in fish that help reduce the risk of heart disease. These are fats whose hydrocarbon molecules contain 2 carbons that share several bonds, hence, are not saturated with hydrogen atoms. For this reason, the structures are weak, making them liquid (oil) at oil temperature. Saturated fats, on the other hand, are fats whose hydrocarbon molecules contain hydrogen atom on every carbon. Saturated fats are typically found in meat, and are solid at room temperature.

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While a healthy kind of fat for the human health, unsaturated fats contribute to the short shelf life of fish. This is because unsaturated fats are highly prone to lipid oxidation because of the unstable double bonds, which permit oxygen to react. Oxidation is a complex chemical process where air reacts with food components that results in undesirable quality changes (color, flavor and nutrient content). Oxidation is what happens when a flesh of an apple turn brown after being exposed to oxygen. This is the same reason why sunflower and safflower, and other unsaturated oils have shorter shelf life than saturated oils.

In the case of fish, oxidation results in rancidity that occurs even at refrigeration temperature. Rancidity happens at a faster rate for fish with high oil content. These include herring, salmon, tuna.

Cold water fish contain higher levels of monounsaturated and polyunsaturated fatty acids than freshwater fish.

This review discusses lipid oxidation in fish products in more detail.

FISH HAVE LITTLE GLYCOGEN STORE

Aerobic respiration provides the energy needed for muscular contraction in animals. This causes the breakdown of the glucose to produce 36 molecules of ATP and carbon dioxide. This glucose is kept in the form of glycogen, which is broken down when energy is required.

When an animal dies, its blood flow and aerobic respiration cease, depriving the muscle of oxygen. Glycolysis after death is influenced by a number of variables, including the glycogen reserve before harvest. However, less glycogen is stored in fish than in other animals. They use up their glycogen while they struggle during the catch, which gives them only a little window of time before their ability to metabolize carbohydrates and produce ATP runs out.

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Cells make less ATP from glucose in the absence of oxygen. Glycolysis continues at this point, but glycogen is now transformed into lactic acid. The process continues until the glycogen is depleted or a pH (acidity) of 5.5 is reached. However, higher pH level is typically obtained in fish because of the relatively less glycogen available to produce lactic acid for preservation.

From a microbiological perspective, a low ultimate pH is preferred since it prevents bacteria growth. A high ultimate pH leads to poor microbial growth resistance.

AUTOLYSIS IN FISH IN RAPID

Autolysis (“self-digestion”) or enzymatic spoilage is the destruction of a cell due to the action of its enzymes present. What exactly occurs is the internal breakdown of the structure of the protein and fats because of the complex series of reactions. Phosphorylases, lipases, cathepsins, and gut enzymes are some of the enzymes involved in autolysis. Autolysis of protein starts immediately after rigor and creates a favorable environment for the growth of spoilage microorganisms. All types of meat go through this process, but autolysis occurs at a faster rate in fish.

The action of enzymes affects the flavor and taste of fish. One enzymatic process is the gradual breakdown of ATP into AMP and hypoxanthine. Hypoxanthine is a fish muscle nucleotide that imparts a bitter taste, which is accompanied by the loss of freshness.

Another result of enzymatic actions is belly bursting. This is caused by the weakening of the belly wall as a result of the action of enzymes present in the gut of fish. This may occur several hours after harvest in fish, including sardines and herring. This study found out that dipping fish in 15% sodium chloride (NaCl) solution for 30 minutes prior to freezing is effective in reducing belly bursting.

Now that you know why fish are highly perishable, this post should help you decide if the fish is fresh: These 5 Signs Will Tell You If Fish Is Fresh.

The post 5 Reasons That Make Fish Highly Perishable appeared first on The Food Untold.

Have you ever wondered how the Japanese prepare sashimi to make it safe to eat?

Sashimi (means pierced body) is a very popular dish in Japan. This dish consists of thinly sliced raw fish served on ice with garnishes such as seaweed, daikon radish, red water pepper sprouts, and herbs. Often times, soy sauce is used as dipping sauce. While it is true that fish (usually tuna or salmon) and seafood are more synonymous with sashimi (actually refers to any type of meat), other meat is sometimes used. For that authentic Japanese sashimi experience, people often go to Japan. But because of a large Japanese cuisine following, sashimi restaurants can also be located in other parts of the world such as Canada, United States, South Korea, the Philippines, Hong Kong, and Brazil.

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As with any other food served and eaten raw, sashimi is not risk-free; it may result in foodborne illness, especially if prepared improperly. And this is what most individuals wonder to themselves before trying this Japanese dish. But food poisoning seems like it is not the case. How do the Japanese exactly prepare sashimi ?

Keep reading.

SASHIMI-GRADE

When it comes to sashimi, everything has to be done with utmost care—from harvest to serving. And it is not just any fish, but one that is so-called ‘sashimi-grade’. Sashimi-grade refers to any fish that is the freshest, of the highest quality, and more importantly, safe to eat raw. But do note that the term sashimi-grade is not an official term; purely for marketing purposes only. Hence, no governing body regulates it. But one thing is sure though— sashimi -grade is fish that has been frozen to at least –4ºF (–20ºC) or below before being sold. Hence, it helps indicate that the fish is safe to consume raw.

HOW FISH FOR SASHIMI IS PREPARED

Fish for sashimi are line caught. To slow quality degradation down and preserve them, they are immediately killed by Ikejime (活け締め). Ikejime is a Japanese way of preparing fish in which a spike is inserted quickly into the hindbrain, causing a quick death and minimizing stress. Ikejime ensures the preservation of flavor and texture by minimizing the effects of biochemical reactions, such as the buildup of adrenaline and lactic acid that degrade the quality of the fish. Plus, the aging that takes place makes the umami taste more pronounced.

Afterwards, the fish are placed in ice or frozen to prevent the growth of bacteria. A much bigger problem when it comes sashimi, sushi, and other seafood eaten raw are parasites, particularly round worms, which too, can be eliminated by low temperature. These parasites consume the flesh of fish. They usually are in the belly flaps or the gut. If ingested, they burrow in our intestine. As a result, symptoms such as abdominal pain, diarrhea, vomiting, nausea, and other discomforts may be experienced.

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While sashimi-grade does not actually have any guidelines or standards, the Food and Drug Administration (FDA) has in place some regulations on proper handling and preparation of fish meant for consuming raw. The below guidelines, if religiously followed, ensure the destruction of parasites.

COMMON SASHIMI-GRADE FISH

In Japan, the most common fish for sashimi are tuna, salmon, yellowtail, mollusks like abalone, clams, and scallops, and other seafoods like squid. Ideally, the species of fish must be those that dwell in cold, deep water, or in areas away from fish parasites.

Tuna is considered to be one of the few species of fish that is safe enough to consume raw, even with minimal processing. This is because tuna is highly resistant to parasites. This includes bigeye, bonito, yellowfin tuna, albacore, bluefin, and skipjack.

Sashimi restaurants are very meticulous at all times, from selecting only the highest quality fish to maintaining hygiene. This ensures that the food being served to consumers is extremely safe. If you want to enjoy sashimi at home, you will have to be extra careful.

When selecting fish, ensure that the vendor knows anything sashimi. Do they know the term sashimi -grade? Is the fish kept at low temperature? Do they know how or where the fish was sourced? On your part, check the state of the fish. Look for all signs of freshness. Generally, it should smell fresh like seawater, have red gills, firm flesh, bright and intact scales, and shiny bright eyes. You can refer to this guide: These 5 Signs Will Tell You If Fish Is Fresh.

When opting for salmon, always go for farmed salmon. Wild salmon tends to be infested more by parasites since they live most of the time in fresh water.

Sashimi-grade fish has to stay in a low temperature environment, even on your way home so pack it in ice. Remember that eating raw fish will always have risks.

WHICH FISH ARE NOT SAFE TO EAT RAW?

Not all species of fish are safe to be eaten raw. The main problem with raw fish is bacterial and parasitic contamination.

According to Food and Agriculture Organization (FAO), parasitic round worms that are found in the digestive tract and flesh of fish affect only a portion of species of fish. Cod, herring and mackerel are among those more prone to worm infestation.

The cod worm (Phocanema decipiens) can grow up to 4 cm long. It is often  curled up in the flesh, usually in the belly flaps, of cod and other species of fish.

The herring worm (Anisakis simplex) is usually found in herring, whiting, mackerel and other species. It can grow up to 2 cm long and is usually found tightly coiled in the belly flaps and the gut. The problem with herring worm is that it is colorless, so it may not be easily observed. When the fish is left ungutted after capture, it may migrate from the gut to the flesh.

Generally, larger fish of the same specie are more infested by round worms. The reason for this is that they tend to eat more, and therefore intake more parasites. Furthermore, as the fish grow older, the number of larval worms increases. The case for wild fish is even worst as almost every kind is infested by parasites.

For these reasons, the Centers for Disease Control and Prevention (CDC), advices to refrain from eating raw or undercooked fish and seafood. Parasites such as round worms do not pose any health risk in a thoroughly cooked fish. Anisakis and Phocanema larvae are easily destroyed by cooking at a temperature of at least 140 °F (60°C) for 1 minute.

How is your experience eating sashimi? Leave a comment below. Much appreciate it

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