Value addition to fish in the context of NE India
- Part 1 -

Ranendra K Majumdar *

Annual Fish Fair / Fish Crop Competition at Hapta Kangjeibung on 26th October 2022 :: Pix - Shanker Khangembam

Introduction

Fish plays a major role in human nutrition. Fish contains protein of high biological value, essential minerals, vitamins and fats. Fish and shell-fish contain about 19% protein that is similar in amino aid composition to that found in muscle meats. Tests have shown that 85% to 95% of the protein is assimilable. The protein efficiency ratio (PER), another measure of protein quality, is around 3.5 for fish, which is much higher than beef (2.3) and milk (2.5) and close to that of egg (3.92).

It is now established that fish protein behaves as a hypocholesterolaemia agent, probably because of the characteristic amino acid composition. Another recent finding is that fish protein is a strong cardio-protective agent and can control the symptoms of experimentally induced myocardial infarction in albino rats. It protects the antioxidant system ad thus minimizes the chances of tissue damage caused by oxidative stress. It has also been reported recently that fish protein has a clear protective effect in diabetic renal diseases.

Lipids of fish and other aquatic animals contain high proportion of highly unsaturated long chain fatty acids. Approximately 50% of the fatty acids in lean fish and 25% in fattier fish and polyunsaturated fatty acids (PUFA). Most of the PUFA from fish oil belong to the omega-3 (n-3) groups. EPA (20:5 n-3) and DHA (22:6 n-3) are the most important among n-3 PUFAs as far as human nutrition is concerned.

EPA is believed to play important roles in maintaining the health of heart and circulatory system, whereas DHA is involved in the functioning of brain, nerves etc. Since these acids cannot be synthesized in the human body to the required extent, it is essential that adequate quantities are supplied through food. Fish and other marine products are the best sources for these acids.

Fish is a highly perishable commodity having relatively shorter shelf-life. Spoilage of fish commences immediately after harvesting. A vast array of biochemical and physicochemical changes (reactions) take place from the time that the fish is killed until it is consumed. It is known that fish's loss of freshness and spoilage pattern markedly varies from species to species. One the fish dies several post-mortem changes take place.

These changes are due to the breakdown of the cellular structure and biochemistry as well as to the growth of microorganisms that are either naturally associated with the fish or that become pat of the flora because of the contamination during handling. Within this post-mortem change that directly and strongly affect its quality and shelf-life there are the protein degradation, ATP degradation, drop of pH, lipid oxidation, undesirable compounds production as trimethylamine (TMA-N) and the low molecular weight volatile bases (TVB-N), which are produced by bacterial action.

Likewise, the muscle experiences changes in texture, water holding capacity and colour. Deterioration of fish normally follows four stages: rigor mortis, resolution of rigor, autolysis (loss of freshness) and bacterial spoilage. These stages occur faster or slower depending on the species, the physiological condition of fish, microbial contamination and temperature.

The autolytic processes are carried out through endogenous enzymes present in the muscle whilst deterioration is caused by bacterial growth. It has been observed that capture, handling and processing conditions determine these changes, being temperature the factor with the strongest impact. Therefore, to preserve muscle initial freshness and quality, it is important, after catching the animal, decreased temperature as quick as possible.

Post-harvest losses of fish due to spoilage can be reduced to a great extent through efficient post-harvest management. Fish need immediate care post-harvest to reduce the rate of spoilage in order to retain its good quality life as long as possible. Icing of fish immediately after harvesting remains to be the best solution for short time preservation during transport of fish from harvesting point to distant market.

Value addition is the most talked about word in the food processing in general and fish processing in particular. Value addition means any additional activity such as addition of ingredients or processes (icing, freezing, drying, smoking etc.) that make them more attractive to the buyer and finally change the nature of a product thus adding to its value at the time of sale.

Value can be added to fish and fishery products ranging from live fish and shell fish to ready to use, with enhanced appeal and attraction. Fish being the cheapest animal protein, diversified processing coupled with the promotion of value-added products in marketing is essential to minimize post-harvest losses and to obtain optimum profits.

Usually, the fishes which are less preferred and fetch comparatively low price in fresh condition, viz. silver carp, grass carp, big head carp, pangas etc. are preferentially utilized for preparation of value-added fish products. The people have become more selective in their food choices and such preferences are the result of changes in work cultures and life styles, availability of disposable income and lack of leisure for house hold work.

In the North East sector of India more than 98% of population are fish eater. Fish in any form of either fresh or processed is a common menu of diet irrespective of economic condition. Dried, fermented and smoked fish products are very much popular in the North East. These cheapest means of fish preservation are best suited with the geographical and climatic conditions, socio-economic conditions, food habits and life style of the inhabitants.

People residing in hilly areas comes to market in the plain mostly once in a week and prefer to buy processed fish (dried, fermented or smoked) for consumption until next market day. Therefore, drying, fermenting and smoking are considered as North East specific technologies for value addition to fish.

Value addition to fish through ice preservation

The purpose of chilling is to prolong the shelf-life of fish, which it does by slowing the action of enzymes and bacteria, and the chemical and physical processes that can affect quality. Reducing the temperature at which the fish is kept lowers the rate of deterioration. During chilling the temperature is reduced to that of melting ice, 0-50C. The preservative effect of chilling includes depression of the activity of putrefactive microorganisms and enzymes.

Fish can be chilled stored as long as the changes in them have not yet progressed to the extent that their commercial value is affected. Keeping period of chilled fish depends on quality of the raw material, method of chilling, duration of chilling, storage conditions and cleanliness and hygienic handling during chilling process. The most common means of chilling is by the use of ice.

Icing is relatively a short-term means of preservation when compared to freezing, canning, salting or daring, for instance. When used properly it can keep fish fresh so that it is attractive in the market place. The use of ice for preserving fish and fishery products has proved to be an effective means for the following reasons:

o Ice has a very high cooling capacity
o Latent heat of fusion (melting): 80 kcal/kg
o Ice is harmless, and in general relatively cheap
o Ice can maintain a very definite temperature
o Ice can keep fish moist and as it melts it can wash surface bacteria from the fish
o Ice can be moved from place to place and its refrigeration effect can be taken to wherever it is needed.

Several studies have already determined that the shelf life of IMC can be extended up to 12 to 14 days. Study has been made in the college and found that shelf life of silver carp was 8 days and 12 days when ice preserved as whole fish and as gutted and headed fish respectively. In the prevailing climatic condition of the North East and considering the distance to be transported from fishing areas to market, ice to fish ratio as 1:1 is desirable. However, further enhancement of shelf life could be achieved by storing the ice preserved fish at lower temperature.

Preparation of fish for icing

o Fish should be thoroughly washed with potable water to make it free from dirt, slimes and other extraneous matters before icing.
o In case of large size fish, scales, fins, head and gut is removed and washed again with potable water.
o Ice should be properly crushed before use
o Fish and ice should be equal in quantity
o Fish should be iced in insulated box such as thermocol/polythene lined synthetic/wooden box
o Fish and ice should be arranged alternatively with bottom, top and sides with ice.
o Height of the fish-ice stack should not be more than half meter.
o There should be provision of outlet of ice melt water at the bottom of the container.
o The container should be kept under shade
o If necessary, addition of fresh ice or re-icing with fresh ice can be done.

To be continued....