Preliminary heat treatment of raw materials

Preliminary heat treatment of raw materialsWhat is a preliminary heat treatment of raw materials? Preliminary heat treatment of raw materials is called short-term (5-15 minutes) impact on raw materials of hot water (80-100 ° C), steam or hot vegetable oil. Processing raw materials with hot water or steam is called blanching, and processing in hot vegetable oil is roasting.


In various technological processes, preliminary heat treatment of raw materials pursues the following goals: to change the volume of raw materials, soften it, increase cell permeability, inactivate enzymes, hydrolyze protopectin, remove air from plant tissue, increase caloric content of raw materials and give it specific taste properties.


A change in the volume and mass of the raw material is required, for example, in the manufacture of canned food, in which the recipe includes dry leguminous crops (beans, peas) or rice. In the process of blanching in boiling water, the zea swells due to the absorption of water, and their volume and mass increase by 90–100%.If this is not done before packing into jars, then when sterilizing canned food, these dry cultures swell already in the jar itself, soaking up broth or other filling, and there will not remain a liquid phase in the finished product.


Softening of raw materials is necessary in order that it can then be placed in cans or to facilitate the removal of inedible parts - peel, seeds, seeds - with subsequent wiping on sieves. Fruit softening during heat treatment occurs for two reasons. On the one hand, when heated, protopectin is hydrolyzed, gluing individual cells together and cementing plant tissue. When hydrolyzed, it passes into a soluble form, the cells are peeled off from each other, the fruit tissue becomes loose and soft. On the other hand, when heated, the proteins of the cytoplasmic membrane coagulate, the cytoplasmic membrane is damaged, becomes permeable, the osmotic pressure causing the hardness of the fetus falls, and the raw material softens.


Increase in cell permeability should be made in those cases when it is necessary to extract the contents of cells, for example, in the production of fruit juices, when exactly semipermeable membranes are an obstacle in the extraction of juice by pressing.One of the most effective technological methods for damaging plasma membranes is blanching the fruit with water or steam.


Cytoplasmic membranes are an obstacle and in the opposite case, when you need to soak the cell with something from the outside, such as sugar or salt. So, if you brew fresh fruits or their lobules into sugary syrup, while in the first minutes, when the fruits have not yet warmed up and the cytoplasm is intact, the diffusion penetration of sugar into the fruit cells is delayed by the cytoplasmic membrane and only the osmotic absorption of moisture from the cells occurs, as a result fruits shrivel. If the fruits are blanched before boiling, then their cellular permeability increases and upon subsequent immersion in the syrup, not only the osmotic absorption of moisture occurs immediately, but also the diffusion penetration of sugar into the fruit tissue through the damaged cytoplasm membrane.


Inactivation of the raw material enzymes is necessary in order to prevent undesirable changes that may occur in the fruit or in the products of their processing, if for any reason the enzymes have not been destroyed.In particular, the darkening of sliced ​​fruits (especially pome fruit) in the air is explained by the activity of oxidative enzymes. In this case, the scheme of the oxidative process of enzymatic browning of sliced ​​fruits can be represented as follows. In the first stage, the enzyme (indicated by the letter A) adds molecular oxygen to the air and activates it, forming a compound.


If there are substances in the fruit that can oxidize, for example polyphenolic ganins (indicated by the letter B), then the resulting organic peroxide A02gives up oxygen in the atomic form, thus oxidizing tanning and other substances that are not oxidized by molecular oxygen. Therefore, the second stage of the enzymatic process.


In this case, the enzyme is restored in its original form, and the resulting oxide VO is a dark-colored compound, sometimes called flabaphene.


Polyphenols do not oxidize with oxygen without taking into account the enzymes, in order to prevent the browning process it is necessary to inactivate oxidizing enzymes. For this purpose, kravremennoe (5–10 min) blanching is applied in water at a temperature of 85–100 ° C.Since inactivation is better in an acidic environment, it is recommended that water be blended with citric acid or tartaric acid at a concentration of 0.1-0.2%.


Hydrolysis of protopectin is carried out in the case of obtaining fruit products that have a jelly-like consistency (jam, jams, marmalade, jelly), which is impossible without the presence in the liquid mass of soluble pectin, which is the main component of the gelled mass.


In some fruits there are many pectic substances, but they are represented mainly by the insoluble form, in the form of protopectin. In this case, it is necessary to process the fruits so that propecupin is hydrolyzed and passed into a soluble form, which only then can provide a jelly-like product. In order to hydrolyze protopectin, the fruit is blanched with steam for 10–20 minutes.

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