Shellfish & Their Processing

Shellfish have been consumed all over the world. They are a good source of proteins, and healthy fats, are low in calories, and also provide vitamins like vitamin A, vitamin D, vitamin B12, etc. and minerals like calcium, iron, magnesium, zinc, etc. Shellfish contains polyunsaturated fatty acids (PUFA) as well as omega-3 fatty acids, which help to reduce the risk of heart disease (1). They are highly perishable and require care during handling, processing and storage.

Different Types of Shellfish: There are 2 categories of shellfish- Molluscs & Crustaceans. Crustacean refers to shellfish with hard crusts or shells, whereas molluscs have a soft, segmented body. Molluscs include oysters, clams, mussels, scallops, etc. whereas crustaceans include lobsters, crabs, shrimp, and prawns, etc. (2)

Processing of Shellfish: Before reaching the market, shellfish undergo some processing steps like harvesting, washing, grading, sorting for size, shucking, removing meat, packaging, storage, etc. The processing method of shellfish differs depending on the type and variety. Some shellfish are sold live or pre-cooked. Some are preserved using various preservation methods like freezing, canning, curing, drying, smoking, etc. (3)

After harvesting, the shellfish should be kept cool or chilled, because the temperature rise will allow the bacteria to grow and the shellfish will become unsafe to consume. They are often graded based on quality; this includes external qualities like colour, appearance, odour, etc. Sorting is done based on the size of the shellfish. Shucking is nothing but the removal of shells. The shucking of shellfish is done with the help of a shucking knife; it is one of the oldest and most famous methods of shucking shellfish and is still in use (4).

There are various ways to freeze fresh shellfish that will help retain the flavour and texture of the food. Each type of shellfish has its unique freezing method to achieve the desired results. For example, while freezing crabs live crabs should be first boiled for a specific time, followed by quick cooling (5). Further, the back, legs, and internal organs are removed and then the remaining meat is frozen. Freezing shellfish for a long time can affect the quality and can cause changes in colour, flavour, etc. Some shellfish are frozen whole, while some are shucked and the meat is frozen. The frozen shellfish should be stored at -18°C.

The canning of shellfish has been practised for long. In the case of prawns, they are first peeled, beheaded, cleaned and washed. They are then blanched in boiling brine for a specific time. After blanching they are allowed to cool to avoid further cooking and then filled in a clean can along with the brine. Blanching also brings down the microbial load of the shellfish. The sealed cans are processed at such temperature and for such length of time that results in sterilization of the final product (6). One of the major advantages of canned shellfish is the relatively long shelf-life when stored at ambient temperatures. Different types of shellfish require different canning methods.

Drying is one of the oldest methods of preservation. During the drying process, water is removed from the fish muscle, thereby preventing shellfish from spoilage. Shellfish undergo some pre-treatments before drying, this includes salting. Salting is one of the most common pre-treatment used for fish and shellfish. Salting is done by placing the shellfish in a salting solution (brine) or by covering them in dry salt. Salt helps to extract moisture from the flesh and at the same time penetrates inside the flesh. Salt also prevents microbial growth. The different drying methods include sun drying, solar drying, freeze drying, vacuum drying, tray drying, etc. In the case of dried shellfish, it does not require refrigerated storage and can be stored at room temperature.

Smoking is a process of treating shellfish by exposing it to smoke from smouldering wood or plant materials. Smoking is one of the oldest methods of fish & shellfish preservation. Other than preservation, smoking also plays an important role in imparting desirable flavour and colour to shellfish. There are different types of smoking techniques like hot smoking, cold smoking, liquid smoking, electrostatic smoking, etc.

Packaging is an important step in maintaining the quality and freshness of the product. The shellfish are either packed in vacuum packaging, modified atmosphere packaging, plastic containers, cans, etc. Different types of shellfish require different methods for storage for maintaining the best quality and longest shelf life.

Consumption of raw or undercooked shellfish has been reported to cause health hazards. If shellfish is harvested from water that has been contaminated by harmful bacteria, parasites or viruses, the shellfish might get contaminated. Cooking the food kills harmful organisms and makes the food safer to eat. Thus, it is important to cook them properly before consumption (7). Shellfish is best when it is eaten fresh. However, its quality and freshness can be preserved by various preservation techniques.

Shellfish Products: Shellfish are extremely perishable products. Efforts to preserve them for longer periods have resulted in some very interesting products which have long outlived the necessity for preservation. Some of the shellfish products found in India include:

Dried shellfish such as dried shrimp, dried prawns, dried oysters, etc.
Prawns pickles, squid pickles, etc are available (8).
Ready to fry lobster bites, crab bites& sticks, etc (9).
Ready to cook prawns biryani, prawns curry, prawns momos, etc.
Ready to fry crab & prawn wafers (10).
Dry squid powder, canned prawns, etc.

Shellfish are an important component of human food. Human beings enjoy eating fish and shellfish due to their delightful taste and aroma. Adding shellfish to your diet can be very beneficial as it offers a wide variety of nutrients. The modern-day hectic lifestyle of consumers has contributed to the increased prevalence of several health conditions such as diabetes, cardiovascular diseases, etc. The increasing demand for protein-rich foods to reduce the risk of these health conditions has resulted in the growth of the shellfish market. The global shellfish market is estimated to reach $58.2 billion by 2027. Additionally, it is anticipated to expand at a CAGR of 2.1% from 2022-2027 (11). The emerging shellfish products such as packaged shellfish snacks and ready to eat & cook frozen shellfish products have resulted in market growth.