Fish products and Byproducts Technology

Unit 5- Hurdle technology in fish preservation

5.2. Marinating
Marinating is a process of dipping the fish in to marinate before cooking to get a desirable flavor and texture. Marinate is a liquid, mixture of salt and acetic acid.
Basic of marinating process
The fish, subjected to one or more pre-processing techniques is rendered eatable by treating with acetic acid and salt. The products obtained this way are among the food items that can be consumed without any subjection to thermal treatment. Marinades are semi preserved foods; acid, usually acetic acid, and salt are added to the fish to retard the action of bacteria and enzymes, resulting in a product with a characteristic flavour and an extended but limited shelf life. Marinating also makes the flesh of the fish firmer in texture; the more salt that is added, the firmer the flesh becomes. The aim is to make a product that has a pleasant taste without being too tough, and one that is safe to eat after a reasonable shelf life. The amounts of acid and salt required can be reduced when the product is kept chilled until eaten.
The measure of acidity or alkalinity of a product is known as the pH, where a pH of 7 is neutral and a pH of 1 is very acid; at a pH of 4•5 or below, that is moderately acid, all food poisoning bacteria, and most spoilage bacteria, are prevented from growing, and marinated products at a pH of 4•5 will keep for several months at a temperature of 4°C.
Some bacteria and enzymes will remain active in marinades throughout storage, even in the presence of acid and salt, and eventually the flesh will break down completely. This residual action is desirable in some semi-preserves, for example those in which salt alone, or a mixture of salt and sugar, is used to preserve the fish; the products of bacterial and enzymic action produce the typical flavour of the product.
The ratio of fish to covering liquid should be between 1:1 and 2:1, and the liquid should contain 1-2 per cent acetic acid and 2-4 per cent salt. The acid taste of a marinade can be reduced by substituting citric or tartaric acid for some or all of the acetic acid, but care must be taken to ensure that the pH of the product does not exceed 4•5. Since not all acids are equally strong, expert advice should be taken where necessary when substituting for acetic acid. Vinegars produced by fermentation are also used instead of acetic acid to give a milder product; the acid
Maturing process
The first phase of marinating is comprised of complex physical and chemical reactions. Marinating process takes place with the effect of neither acetic acid alone nor salt. Salt and acetic acid which although have the same effect on fish meat are in fact, substances with opposite charges cancelling the effect of one another. While salt hardens the material, acetic acid softens it.
In the maturing process, salt and acetic acid transfer into fish tissue continues until the salt and acetic acid levels in the fish tissue liquid are equal with the salt and acetic acid levels in the solution. Although, it has been reported that this transfer is completed fast, generally in two day’s time, it may still vary depending on temperature and meat thickness.
In marinated products, it is aimed to provide the product with a longer shelf life by stopping the activities of present bacterial enzymes in the product with the effect of acetic acid and salt.
Acetic acid and salt along with the enzymes from fish have an effect on the protein and lipid contents of fish although they cause destruction to a certain extent in the protein and lipid contents of fish and as a result, aromatic and delicious products are created