Amino acid score (AAS)Protein Chemistry Score, is a widely used method to evaluate the nutritional value of food proteins, which is not only applicable to the evaluation of single food proteins, but also to the evaluation of mixed food proteins.
Amino acid score (AAS)=[amino acid content in sample protein (mg/g)]/[corresponding in FAO/WHO scoring standard modeessential amino acid Content (mg/g)];
Protein is the basic substance of human body composition, and the evaluation of the nutritional value of food protein is the most basic content of food nutrition.In addition to the content of protein nitrogen, the nutritional value of food protein mainly depends on the composition and proportion of its essential amino acids. If the composition of essential amino acids is close toHuman essential amino acidsMode can effectively improve the absorption and utilization rate of protein and its application value.
Amino acid composition and score
Announce
edit
Amino acid determination
Alanine, arginineAspartate, glutamic acid, glycine, histidineisoleucine, leucine, lysine, methioninePhenylalanine, proline, serine, tyrosine, threonine, valine 16 kinds of amino acids, the results are expressed by the average of the two methods of determination data.
Tryptophan is determined by amino acid automatic analyzer, that is, the sample is hydrolyzed with 4.2molLNaOH and then measured on the computer;The determination of cystine is to oxidize the sample with formic acid first, then convert it into cysteine sulfonic acid, dye it with ninhydrin, and analyze it with amino acid automatic analyzer.In order to compare the difference between hydrolyzed cow hide protein and the protein in dairy products, gelatin (animal source protein), whey powder, casein, skimmed milk powder and milk powder were also selected as the controlAmino acid determination。The determination result is expressed in mg (amino acid)/g (sample).
Amino acid score
In order to compare the amino acid composition of each sample, evaluate the quality of amino acids in the sample, convert the amino acid content of each sample into milligrams of amino acids per gram of protein, and then evaluate the nutritional value according to the FAO/WHO optimal ratio model, amino acid score chemical score andEssential amino acid indexAmino acid ratio coefficient and amino acid ratio coefficient are calculated according to the following formula:
Amino acid score (AAS)=[amino acid content in sample protein (mg/g)]/[corresponding in FAO/WHO scoring standard modeessential amino acid Content (mg/g)];
Chemical score (CS)=[amino acid content in sample protein (mg/g)]/[corresponding essential amino acid content in eggs (mg/g)];
Ratio coefficient of amino acid (RAA)=[content of certain essential amino acid in the sample protein to be tested (mg/g protein)]/[content of corresponding essential amino acid in the FAO/WHO scoring standard mode (mg/g protein)][1]；
Ratio coefficient score of amino acid (RCAA)=[RAA of certain essential amino acid in the sample protein to be tested]/[average value of RAA of various amino acids];
First restricted amino acid
To evaluate the nutritional value of the protein in the sample to be tested, calculate the scores of various essential amino acids. The amino acid with the lowest score of all essential amino acids isFirst restricted amino acid。The first restricted amino acid refers to a class of amino acids lacking the most in restricted amino acids, which will seriously affect the utilization of protein by the body and determine the quality of protein.Main in foodRestricted amino acidIt is lysine and methionine.The former is in cereal protein and some otherVegetable proteinThe content in the quality is very little;The latter is relatively insufficient in soybean, peanut, milk and meat proteins.Generally, lysine is the first limiting amino acid of cereal protein.Methionine（Sulfur-containing amino acid）It is the first limiting amino acid of most non cereal plant proteins.
Identification and Qualitative Experiment of Cow Skin Protein in Milk Powder
As per《Rapid identification of food quality and adulteration》The method introduced in the book was slightly modified: after the solid sample was dissolved in water at a ratio of 1:7, 5% mercuric nitrate was added to mix well, and then it was left to filter. If hydrolyzed cow hide protein was added, the filtrate would be milky white.Take appropriate amount of filtrate and add equal volume of saturated picric acid solution. If there is hydrolyzed cow hide protein, yellow precipitate will be generated.If the content of hydrolyzed protein in cowhide is less than 1%, the solution is suspended due to the slow precipitation. The optical density value (A value) is measured at 450nm. A value is linear with the concentration of hydrolyzed protein in cowhide;If the content of hydrolyzed protein in cowhide is more than 1%, precipitation will occur rapidly.Semi quantitative determination can be carried out according to the rate of precipitation generation.
Amino acid composition and score of hydrolyzed cow hide protein
The amino acid composition of cow hide hydrolysate protein is basically the same as that of gelatin. Compared with whey powder, casein and skimmed milk powder, the glycine content of cow hide hydrolysate protein is high, and the glycine content of ×× milk powder is twice as high as that of other milk powder because it is mixed with cow hide hydrolysate protein;Alanine, arginine, proline, etcNonessential amino acidThe content is also significantly higher, while the content of essential amino acids such as thioamino acid, threonine, glutamic acid, valine and leucine is generally low.Infants recommended by FAO in 1985Amino acid patternThe amino acid score of hydrolyzed cow hide protein was conducted, and it was found thatessential amino acid The total amount is significantly lower than that of casein, whey powder, skimmed milk powderRestricted amino acidbySulfur-containing amino acidThe amino acid score is only 19 (based on 100 amino acid model recommended by FAO), which is far lower than that of casein (55), whey powder (56) and skimmed milk powder (66).It is suggested that the nutritional quality of hydrolyzed protein is low, which is not conducive to absorption and utilization.The amino acid score of ×× milk powder is also low (25), and tryptophan is the first limiting amino acid[2]。
Amino acid score corrected by digestibility
Announce
edit
The method of amino acid scoring is relatively simple, but the digestibility of food protein is not consideredUS Food and Drug Administration(FDA) proposed a new method, namely amino acid score corrected by digestibility.The calculation formula is as follows
