It is used to preserve food for a long time.
Drying aims to reduce the water activity below a certain value and reduce the chemical and prevent microbiological spoilage.
The benefit is used to preserve all the features of fresh foods close to freshness for a long time.
The principle of many preservation methods is based on controlling the water activity in the product. Water activity is the measure of water that microorganisms in the product or food can use for their activities. Foodstuffs whose water ratio is lowered below a certain level are more resistant to chemical, enzymatic and microbiological deterioration under normal atmospheric conditions.
If the food is made unsuitable for microorganisms in terms of water content, microorganisms may not function even if all other factors are appropriate.
Foods with a water activity (aw) below 0.60 are classified as dry foods.
Quality and durability of dried products; Although it is different according to the freshness of the raw material, the microorganism content of the drying air, the hygiene conditions of the enterprise and the working personnel, the water amount of the dried product is the main factor affecting the quality and durability.
During the drying process, many physical, chemical, mechanical, biochemical and microbiological events occur.
It is possible to collect the quality of dried products under three headings.
- Chemical quality
- Microbiological quality
- Sensory quality
The chemical quality of the products that are stored or produced under inappropriate conditions cause them to deteriorate rapidly or to some may contain high levels of harmful substances.
Chemical quality analyses of dried products in terms of human health standards or consumption should be carefully followed in terms of It is necessary not to allow products contrary to the limits to be placed on the market.
As the temperature in the drying process rises, the protein quality of the dried products decreases and the loss of vitamins increases.
Such changes harm the nutritional quality and aroma structure of the product.
The most important chemical problem encountered in dried aquatic products is the oxidation of the product depending on the oil content.
Oxidation is the result of a high concentration of oil in dried fish. It is one of the most common problems due to its effects.
The degradation reactions occurring in oils are limited only by the structure of the oil. is not. These reactions occur in the tissue where the fat is located. Therefore spoiled oil, as well as the consumability and nutritional value of dried products. directly affect its properties.
The changes that occur in the product as a result of the deterioration of oils can be listed as follows; flavour, odour, acidity change, peroxide, aldehyde and ketone formation. This type of change is a general type of change in oils and is called "bitterness".
Bitterness develops with the effect of lipoxidase enzyme or oxygen acting on the fat molecule. As the process progresses, the reaction rate increases. Autoxidation varies depending on different factors.
In general, many bacteria that determine the quality of food and cause deterioration can develop up to 0.90 water activities, and therefore no bacterial deterioration in dried foods.
Microorganisms that can develop at values below 0.90 of water activity are yeast and moulds. However, a water activity value of 0.90 is very close to the minimum water activity value at which normal yeasts can grow. The minimum (aw) value for normal yeasts is around 0.88.
Usually, around 0.65 water activity, microbial degradation is almost Although it can be completely avoided, the water activity of this value and slightly below some osmophilic yeasts and some moulds can grow, albeit very slowly.
Generally, mould and yeast deterioration occurs within 1-2 weeks in dried foods between 0.80-0.85 water activity. A water activity of 0.75 prevents mould and yeast growth and deterioration. delays and microbiological deterioration is not observed for a long time at 0.70 water activity. Generally, an (aw) value of 0.60 is considered the lower limit for microbial growth, but dried foods up to a water activity value of 0.70 can be preserved for a long time without spoiling.
FACTORS DEPENDING ON THE EFFECT OF DRYING ON MICROORGANISMS
- The genus of the microorganism
- The type of microorganism
- Physiological age and number of microorganism
- Drying conditions (drying mode, drying temperature, drying time and dehydration rate) Depending on factors such as the type and composition of the food (pH, inhibitory substances, etc.) as it varies.
PHYSICAL AND SENSORY CHANGES IN DRIED PRODUCTS
- Crack, Scratch, Foam, - cut vs. absence of defects or the products should not have any organ remnants and soft areas in the abdominal cavity parts.
- Again, no aroma change indicating protein denaturation should be observed in these products
- Deterioration due to fat oxidation, rancidity, souring, backbone hunched, sunken, half-moon curved depending on the deformation condition, excessive discolouration of the skin, a musty, bitter odour or external surface Defects such as loss of natural colour due to yellowish colour changes at different points should not be seen.
- The infestation of insects, mesmerization and oxidation of lipids may cause deterioration.
- Changes and losses can occur in the structures of amino acids due to the heat that can be caused by the process when preparing to affect the sensory quality of dried products.
- The salting process was applied to dried fish (drying with dry salting) and if desalination has not been applied, salt crystal formation on their skin is frequently encountered.
- This situation leads to a decrease in the amount of water in the dried fish and, accordingly, to the formation of white spots due to the accumulation of salt on the surface of the skin. The consumer is faced with an emotionally undesirable appearance
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