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refrigerated showcase display cases Explain the characteristics of food ingredients (2)

author: supermarket refrigerated showcase category: commercial refrigeration Views: 761Time: 2016-08-22

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Explain the characteristics of food ingredients (2)

2. The colloidal nature of proteins Protein molecules are very large, and their relative molecular mass is thousands of small, tens of millions of large, forming a colloidal solution in water, most of the protein molecular surface has many hydrophilic groups (such as one SH, CO, etc.) , Attracting water molecules to form a hydration layer around the protein particles, so that the protein particles are not easy to collide with each other, thereby preventing their precipitation, which is a factor that stabilizes the protein (hydrocolloid solution). Another factor that stabilizes the protein solution is that the protein micelles are charged. Therefore, only after these two factors are eliminated, the protein can be precipitated.

3. Protein Denaturation The protein in food is very unstable. As mentioned earlier, it is an amphoteric substance that is both acidic and alkaline. When the temperature of the protein aqueous solution is between 52-54 grams, it has colloidal properties and is a colloidal solution. If the temperature rises or freezes, the protein in the

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will clump and precipitate from the solution and become denatured protein. Protein precipitation can be divided into two types: reversibility and irreversibility:

① Reversible precipitation: alkali metal and alkaline earth metal salts such as Na2S04, NaCl, (NH4) 2S04.MgS04, etc. can make proteins precipitate out of aqueous solutions. The main reason is that these inorganic salts deprive the hydration membrane of the outer layer of protein molecules. The salted out protein retains its original structure and properties, and is redissolved after treatment with water. Under certain conditions, the protein changes caused by cold processing of food are reversible.

② Irreversible precipitation (also known as denaturation): In many cases, due to the influence of various physical and chemical factors, the protein solution solidifies and becomes irreversible Dissolved precipitation, this process is called denaturation. Such proteins are called denatured proteins. Denatured protein cannot be restored to the original protein, so it is irreversible and loses its physiological activity. In short, protein denaturation is reversible at the initial stage, but becomes irreversible after the reversible stageTransgender stage. Enzyme is also a kind of protein and loses activity when it is denatured.

4. Decomposition of protein The decomposition of protein is carried out step by step according to the following steps: protein one vein one peptone one polypeptide one amino acid one amine one NH3+CO2+H2S+CH4+Hzo , The final decomposition product NH3, H2S has a strong pungent odor.

(3) Classification of proteins Proteins are divided into three categories according to their nutritional value, that is, according to the type and quantity of amino acids:

1. Complete protein. Complete protein is a protein of good quality that contains 8 kinds of amino acids that are necessary for the human body but cannot be synthesized in the human body. It contains a complete variety of amino acids, sufficient quantity and appropriate proportions, which can not only maintain human Life and health, and can promote the growth and development of children. Casein, lactalbumin, glutenin, etc. are all complete proteins.

2. Semi-complete protein. This protein contains all kinds of essential amino acids, but due to uneven content, the ratio between each other is not appropriate. When used as the only source of protein in the diet, it can maintain life but cannot promote growth and development. The gliadin in wheat is an incomplete protein.

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refrigerated showcase display cases Explain the characteristics of food ingredients (2)

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