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Structural pattern and digestibility of plant proteins

Plant protein structure

Structure:

From the perspective of a protein molecule, a protein is a peptide chain (primary structure) composed of amino acids. The peptide chain forms a helix or fold (secondary structure), which is further wound to form a group (tertiary structure). Various groups Grouped together according to a certain pattern (four-level structure).

The secondary structure of plant proteins is dominated by β-sheets, while that of animal proteins is dominated by α-helices. Judging from the presence of protein in food, plant protein is often combined with carbohydrates (non-starch polysaccharides and dietary fiber), while animal protein mainly coexists with fat.

These factors will bring about differences in the nutritional value of plant protein and animal protein. For example, the intake of animal protein is often accompanied by the intake of a large amount of saturated fat; the consumption of soybeans includes not only soy protein, but also functional ingredients such as dietary fiber, isoflavones, and soy lecithin.

The human body’s demand for protein, first of all, needs to be sufficient (adults need 1 gram per kilogram of body weight per day), and secondly, it needs to ensure the “quality” of the protein. Protein that can fully meet the nutritional and health needs of the human body is high-quality protein.

We need 20 kinds of amino acids provided by dietary protein; if these amino acids are not enough, some can be “borrowed” (the body uses other nutrients to directly or indirectly synthesize non-essential amino acids), and some must be obtained from food (the 9 essential amino acids are borrowed) less than).

Digestibility:

Digestibility refers to the degree to which protein is broken down by digestive enzymes and the degree to which digested amino acids and peptides are absorbed. The more food is absorbed by the body, the higher its nutritional value. General egg protein is often used as a reference protein, and its digestibility is 100%. The accepted measure of protein quality is the Protein Digestibility Corrected Amino Acid Score (PDCAAS), which is a perfect score of 1.

The four players currently tied for first place are: whey protein, casein, egg protein, and soy protein isolate. A PDCAAS of 1 means that the protein contains all 9 essential amino acids required by the human body, and each reaches the required amount (there should be a wooden barrel in the mind immediately, with 9 boards, any one is short. Not full of water). In other words, if you are willful and want to be healthy even if you only eat one kind of protein, then you can only choose a protein with a PDCAAS of 1.

Plant proteins often coexist with anti-nutritional factors such as phytic acid, protease inhibitors, phytohemagglutinins and tannins that affect protein digestion. Coupled with structural differences, plant proteins tend to be less digestible than animal proteins. Therefore, food processing is particularly important to improve the digestion and utilization of plant proteins. Simply cooking food can increase protein digestibility by 18%. The protein digestibility of soy flour is only 80%, while soy protein isolate can reach 98%.

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