Prawn Chemistry: What’s Behind the Shell?

Prawns are a delicious and versatile seafood that is enjoyed by people all over the world. They are also a good source of protein, vitamins, and minerals. But what is the chemistry behind the prawn's delicious taste and unique texture? Let's dive into the fascinating world of prawn chemistry, unveiling the secrets behind their succulent taste and vibrant color.

Distinction Between Prawns and Shrimps

Prawns and shrimps are often used interchangeably in cooking, but they are actually different creatures with some important differences. Prawns belong to a group called Dendrobranchiata, while shrimps belong to a group called Pleocyemata.

One of the main differences between prawns and shrimps is how their gills are structured. Prawns have branching gills, while shrimps have plate-like gills. Additionally, prawns have longer legs and claws on three pairs of legs, whereas shrimps have shorter legs and claws on just two pairs. Another distinction is that prawns tend to have a straight body, while shrimps have a more curved body.

These differences may seem small, but they are significant enough to classify prawns and shrimps separately in marine biology. However, when it comes to cooking, their taste and texture are quite similar, which is why they can often be used interchangeably in recipes.

Prawn Composition

The main chemical components of prawns are water, protein, and fat. Water accounts for about 75% of a prawn's weight, while protein makes up about 20%, and fat comprises the remaining 5%. These components are essential for the prawn's structure and overall function.

Carotenoids and Coloration

One of the most interesting aspects of prawn chemistry is their color which is due to compounds called Carotenoids. Carotenoids, especially astaxanthin, are essential for the coloration of prawns. These organic pigments create the bright pink or red colors that prawns display, particularly after being cooked.

In their natural environment, prawns usually look gray or see-through, which helps them blend into their surroundings. This camouflage is crucial for avoiding predators and increasing their chances of survival.

When prawns are cooked, they undergo a transformation in color from gray or green to vibrant red or orange. This change occurs because heat breaks down specific chemical bonds in the prawns, allowing astaxanthin to become more prominent.

Besides making prawns visually appealing, carotenoids also have antioxidant properties that shield them from oxidative stress and promote their overall well-being. This intriguing connection between biochemistry and biology not only affects how prawns look but also has benefits for human nutrition and food science. Here are some key points about the antioxidant benefits of astaxanthin:

Oxidative Stress Prevention: Prawns can experience oxidative stress due to various factors such as environmental conditions or metabolic processes. Astaxanthin helps combat this stress by neutralizing harmful free radicals in the body.
Potential Health Benefits: When consumed as part of a diet, astaxanthin may offer several health benefits including reducing inflammation, supporting cardiovascular health, and enhancing immune function.

Protein and Enzyme Activities

Prawns are an excellent source of high-quality protein, which accounts for about 20-25% of their weight. These proteins are rich in essential amino acids like lysine, methionine, and tryptophan, making prawns a highly nutritious food.

The proteins in prawns are primarily composed of muscle fibers that are categorized into two types:

Myofibrillar proteins: These are responsible for the muscle contraction in prawns and include proteins like actin and myosin.
Sarcoplasmic proteins: These proteins are found in the cytoplasm of muscle cells and include enzymes and other cellular machinery.

During cooking, the denaturation of these proteins occurs. Heat causes the proteins to unfold and form new bonds, resulting in the firm texture that prawns are known for. This process is key to the transformation of prawns from translucent and soft to opaque and firm.

Fats and Lipids

Prawns are relatively low in fat, with around 1-2% of their weight being made up of lipids. The fat found in prawns is largely composed of polyunsaturated fatty acids (PUFAs), including omega-3 fatty acids such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These fatty acids are crucial for heart health and reducing inflammation in the body.

However, the fats in prawns can become rancid during spoilage due to a process called lipid oxidation. This chemical reaction occurs when the unsaturated bonds in the fatty acids react with oxygen, resulting in off-flavors and nutrient degradation. To prevent this from happening and to extend the shelf life of prawns, antioxidants (both natural and artificial) are often used.

Vitamin and Mineral Composition: A Nutrient Rich Shellfish

Prawns are an excellent source of essential minerals, including iodine, selenium, zinc, and phosphorus. Iodine is critical for thyroid function and maintaining metabolic health, while selenium acts as an antioxidant, protecting cells from oxidative damage. Zinc supports immune function, and phosphorus is vital for maintaining healthy bones and teeth.

Interestingly, prawns also contain calcium and chitin in their exoskeleton. Chitin is a polysaccharide that forms the tough, flexible outer shell of prawns. While humans cannot digest chitin, it has applications in food technology and pharmaceuticals as a biodegradable polymer.

Prawns are also a good source of vitamins like vitamin B12, niacin, and vitamin D. These vitamins are crucial for energy metabolism, cell function, and immune system support.

Cooking Prawns

The chemistry of prawns changes significantly during cooking. When exposed to heat, the proteins in prawns denature, or unfold, making them easier to digest. The fat in prawns melts during cooking, contributing to their succulent texture.

The Maillard reaction is essential for developing the flavor of prawns. It happens when amino acids and reducing sugars react under heat, resulting in the creation of complex flavor compounds and a distinct golden-brown color on the surface of grilled or fried prawns. This reaction also adds savory and slightly sweet tastes to cooked prawns. To find out more about Maillard reactions, read our article by clicking here.

Enzymatic reactions can also affect the quality of prawns during cooking and storage. Polyphenol oxidase is an enzyme that causes browning reactions in prawns, which can happen when they are cut or exposed to air. To reduce this effect, prawns are usually kept at low temperatures or treated with antioxidants.

The final chemistry of cooked prawns depends on various factors such as the cooking method, temperature, and time. Each of these factors can alter the taste, texture, and nutritional value of the prawns.

Storing Prawns

Like all seafood, prawns are highly perishable due to their high water and protein content, which provides an ideal environment for microbial growth. Rotting occurs when enzymes and bacteria break down proteins, producing ammonia, hydrogen sulfide, and other volatile compounds that cause off-odors and gross flavors.

To preserve prawns, various chemical and physical methods are used, such as:

Freezing: This slows down the enzymatic activity and microbial growth that cause spoilage.
Salting or brining: The high concentration of salt creates an osmotic environment that inhibits microbial activity.
Vacuum packing: This reduces the oxygen levels, limiting the oxidation of fats and growth of aerobic bacteria.

Conclusion

Prawn chemistry is a complex field that includes different biochemical processes and compounds. It covers topics such as coloration, antioxidant properties, environmental impacts, and nutritional value. Studying prawn chemistry can provide valuable information for scientific research and practical use.

Understanding the chemistry of prawns can enhance our understanding of their intricate flavor, distinct texture, and nutritional benefits. Therefore, the next time you savor a dish of prawns, take a moment to appreciate the captivating chemistry that contributes to this delightful seafood experience. Bon appétit!

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