Microbiology Of Salted Fishery Product
Introduction
Our daily life is adorned inextricably with microorganisms. Microbes are found all of the corner of the earth. Microbes can spread from everywhere because their contamination source are huge such as soil, air, water. It has many applied sector in our daily life, it is not only harmful but also useful sometimes. Among them food microbiology is an important sector. By applying microbiological knowledge many kinds of foods are processed and preserved now-a-days. Fish product also processed and preserve with the help of microbiology. Among them salting is a popular worldwide traditional processing method in most countries in the world. Salting is done with combination of drying and smoking sometimes.
Importance of Salting
- By salting it is possible to control bacterial growth that causing food borne illness.
- At the time of processing the use of heat or smoke at refrigerated temperatures are not always effective in control of microorganisms. Combination of refrigeration with salting bacterial growth can be prohibited sometimes.
- Enzyme activity is delayed by activity of salting. so autolysis can be sopped.
- Pathogen risk of many specific bacteria can be controlled by salt.
- Salting is comparatively a simple process of low cost rather than other techniques of preservation.
- It does not require any costly equipment, and it can be done in everywhere.
- Salt is easily available and salting can be done throughout the year specially during monsoon when sun drying is not possible.
- It keeps fish eatable for long times than other preservation methods.
- It is easily storable, transportable and marketable.
How Does Salt Preserve Food?
Salt work on fish in two ways. They are-
- Water molecules are tied up by salt so bacteria can not get free water for their growth. And indigenous enzyme of fish body also can’t continue their work, so autolytic spoilage can be controlled.
- An osmotic effect can be created in the fish body by salt which dries out the microbes.
Salting Procedure
Common salt sodium chloride is used as a preservative which enters the body tissues which inhibit the growth of bacteria and inactive the enzymes. Small fishes are directly salted without cleaning. Medium and large sized fish at first dressed and then salted. 6-10 % salt is used mainly and it is capable to remove most of the spoilage bacteria. Mainly there are 3 methods of salting.
Dry salting: In this method dressed fish is mixed with crystalline salt in containers, salt and fish are spread in alternative layers, the proportion of salt increasing upwards. The proportion usually 1: 3 to 1: 8 salt in fish. Oily fish needs more salt. Fish is allowed to dried for 2-3 days. Large fish lose about one third and small fish one half of their dressed weight.
Wet salting: In this process cleaned fish are kept in previously prepared salt solution and it should be stirred daily till properly picked. The gut is removed and filled with salt in 1: 3 ratio concentration in seer, Indian black pomfret etc. fishes. At first gut is filled with salt and fish is staked, following day again addition of salt can be done to avoid settle downing of salt at the bottom. This is repeated for proper filling and then kept for 7-10 day. This is used mostly Eastern parts of our country.
Mixed salting: Synchronous use of salt and brine is followed in this process. Until the concentration of salt in surrounding medium and fish body are same salting is continued. Another method are_ Pit curing: It is a process which is generally practiced in South and South East area of our country. Here fish treated with salt which are inserted in pits lined with leaves. After 2-3 days they are marketed directly. Kench salting: A method of dry salting except that the self-brine formed is allowed to drain off.
Microbiological Purity of Salt
Many commercial salts, particularly solar salt contain large number of halophilic bacteria up to 10^5/g recorded till. Halophilic molds can grow on fully dried fish and cause the formation of dark patches, which is called dun. Halophilic molds can occur more frequently in rock salt. At damp condition, even heavily salted fish ‘dun’ spoilage may occur. Molds activity may cause an increase in surface moisture and make fish more susceptible to other forms of spoilage. Storing of salt for long periods of time will reduce the number of microorganisms present.
Bacteria Found In Salted Fish
Halophilic bacteria: Can grow up to saturation of 15% salt. e. g: Halobacterium sp. in commercial processing of wet or partly salted fish, red or pink bacteria such as Halobacterium, Micrococcus etc. cause ‘pink spoilage’ which shows red or pink discoloration. They don’t grow if the fish are fully immersed in brine or fully dried. Halotolerant bacteria: Can resist a wide range of salt concentration and grow up to 10-15% salt such as, Clostridium, Micrococcus etc. Halophobic bacteria: Salt sensitive group of bacteria fail to grow at high concentration although can remain viable for some time. e. g: Pseudomonas, Accromobacter etc.
Factors Affecting Salt Uptake
- Slower salt uptake when higher fat content.
- Salt penetration is slower when fish is thicker.
- Fresh fish results slower salt uptake.
- When temperature high rapid salt uptake is occurred.
Salted Fishery Products
Salted fish: Usually sardines, Mackerels, Seer fishes, Sharks and Prawns are used for salting. Anchovy, Squid fish cork, Mackerel tuna, Flying fish, Stingray etc. fish also processed by salting.
- Red herring: The texture is harder of herring, it is not gutted before processing.
- Bloaters
- Kippers
- Salted Codfish
- Sardines
- Salted Hilsha
- Salted Squid
- Fish sauce
- Canned products
- CaviarIt is a salt cured roe of Acipenseridae family.
Whole herrings are soaked and smoked for less time than Red herring. Milder flavor and soft texture.
Related to herring but they are smaller.
Hilsa is only species in Bangladesh which is commercially processed by salting. Two or three methods of salting are practiced in Bangladesh. In Chadpur, Barishal, Noakhali dry, wet and mixed salting are used. In Chittagong and Cox’s Bazar partial aerobic fermentation is preferred.
It is generally found in coastal Asian countries, Indonesia, Thailand, Malayasia, Vietnum, China, Hongkong, Japan, South Corea.
Usually made up from Shrimp, Mackerel, Tuna, Anchovy and which fishes have strong flavor.
In many canned products also salted. Sometime some product canned in brine.
Spolage Of Salted Fish
Pink spoilage: Halobacterium salinaria, H. cutirubum, Sarcina litoralis, Sarcina morrhuae and are responsible microorganism for pink spoilage. They are obligate aerobic and not found in wet-salted products because oxygen is unavailable in brine solution. They are thermophilic and grow at about 42 degree Celsius. It is recognized by pink colour on the surface of product. Storage in low temperature can prevent germination and growth of such bacteria. Dipping in sodium metabisulphite solution and Sulphur dioxide vapor treatment can prevent this spoilage. These bacteria can not cause food poisoning.
Dun spoilage: It is caused by a mold, Wallemia spp. On the surface of the salted fish causes a brown discoloration, and it is called dun spoilage. This mold is obligate osmophiles can grow at 5-26% salt concentration. It can not grow inside the muscle and decompose the flesh. But discolored appearance reduce consumer demand. It can be can be prevented by using. 1% Sorbic acid solution, brushed of the surface, stored in low temperature. Reddening: During storage redness appears. A bacteria Torula sweetmeri is responsible for reddening.
