Effects Of The Composition Of The Textured Plant Proteins On The Digestion And Absorption Of Protein

In recent years,plant-based meat has attracted wide attention all over the world and is expected to become an important meat substitute.Textured plant protein is the main composition of plant-based meat.It is of great significance to study the digestion and absorption characteristics of protein in the textured plant proteins.However,there are few related studies available yet.Our research group has previously found that the protein digestion characteristics of textured plant proteins mainly depends on their composition and structure.In order to further clarify the influence and mechanism of the composition of textured plant proteins on the digestion and absorption of protein,a series of textured plant proteins were prepared in this study by changing the composition(including protein type and proportion,and starch content).The influence of the composition of the textured plant proteins on their fibrous structure and the protein digestion and absorption characteristics was explored,and the influence mechanism from the perspective of the fibrous structure of textured plant proteins was proposed.The main conclusions are as follows:1.Effects of type and proportion of proteins in the textured plant proteins on the digestion and absorption characteristics of protein(1)Proteins are the most important component of textured plant proteins.Four textured plant proteins(TVP-S5,TVP-S10,TVP-S20,and TVP-S30)were prepared with soy protein isolate(SPI)and gluten(WG)in the ratio of 5:95,10:90,20:80,and 30:70,and 10% wheat starch using a twin screw extruder to explore the effects of the types and proportions of proteins on the digestion and absorption characteristics of textured plant proteins.Firstly,the effects of the types and proportions of proteins on the structural characteristics of textured plant proteins were analyzed by using millet replacement method,texture analyzer and microscope.The results showed that with the increase of SPI ratio,the hardness,springiness and chewiness of the textured plant proteins increased first and then decreased,and the bulk density and degree of texturization decreased,the internal fiber structure became gradually sparse.The results of protein solubility showed that the content of native protein and hydrogen bond,disulfide bond,and hydrophobic bond were significantly reduced after extrusion,while the interaction between hydrogen bond and disulfide bond was enhanced after extrusion.With the increase of SPI ratio,the disulfide bond and hydrophobic interaction in the textured plant proteins were significantly enhanced.The results of secondary structure of protein showed that the β-sheet content firstly decreased and then increased with the increase of SPI ratio.(2)Then,the protein digestion characteristics of the textured plant proteins were studied using an in vitro digestion model.The results of SDS-PAGE and total free amino acid content showed that the rate and degree of digestion of plant proteins were decreased after extrusion,indicating that the formation of fiber structure was not conducive to the digestion of protein.When the SPI:WG ratio increased from 5:95 to 30:70,the rate and degree of protein digestion first increased and then decreased,with the highest protein digestibility in TVP-S10(with a total free amino acid content of 322.8±2.5 μmol/m L digesta after digestion).The increase in the gaps between fibers,and the exposure of hydrophobic groups,and the decrease in β-sheet promoted protein digestion,while the increase in disulfide bonds inhibited protein digestion.The type and proportion of proteins in the textured plant proteins affect their digestion characteristics mainly by affecting the fibrous structure,the interactions between protein molecules,and the secondary structure of proteins.(3)Finally,samples(TVP-S10 raw powder,TVP-S10,and TVP-S30)with big differences in the protein digestion were selected,and an in vivo protein absorption evaluation model was adopted to analyze the absorption characteristics of protein in the textured plant proteins and verify the results of in vitro digestion studies.The results showed that the utilization rate of plant protein in rats was lower than that of casein.There were no significant differences in the apparent and true digestibility of protein,total protein and urea nitrogen contents in blood among different test groups,however,the formation of fibrous structure increased the intake of plant protein and the contents of amino acids(including essential and non-essential amino acids)in blood and improved the utilization of protein.The type and proportion of proteins in the textured plant proteins had significant effects on the growth performance of rats.The daily weight gain of rats,the relative protein efficacy ratio,the serum essential amino acid content,and the duodenal villus length increased with the increase of SPI:WG ratio.2.Effects of starch content of the textured plant proteins on the digestion and absorption characteristics of protein(1)Starch is the most commonly used excipient in textured plant proteins.In this study,five textured plant proteins with different starch contents(0%,5%,10%,15%,20%)and an SPI: WG ratio of 10:90 were prepared to explore the relationship between starch content and protein digestion and absorption characteristics in textured plant protein.The structural results showed that with the increase of starch content,the hardness,springiness and chewiness of the textured plant proteins increased first and then decreased,the cohesiveness decreased,the internal fiber structure became gradually sparse.The results of protein solubility showed that hydrogen bond and hydrophobic interaction were enhanced with the increase of starch content.The results of secondary structure analysis of protein showed that with the increase of starch content,the β-sheet content in the textured plant proteins increased first and then decreased,and the α-helix content decreased first and then increased,and both reached the maximum or minimum value when the starch content was 10%.(2)In vitro simulated digestion results showed that with the increase of starch content from0 to 20%,the protein digestibility of textured plant proteins increased gradually,the size of chyme after digestion decreased,and the total free amino acid content released after digestion increased from 314.5±2.2 to 337.8±2.4 μmol/m L digesta.This may be because the increase of starch content reduced the cohesiveness of textured plant proteins,increased the space between fibers,and promoted the exposure of hydrophobic groups,thus promoting protein digestion.(3)The animal test showed that the starch content of textured plant proteins had no significant effects on the daily feed intake,daily weight gain,feed conversion ratio,relative protein efficacy ratio,and total protein and urea nitrogen in the serum of rats.However,the content of amino acids in blood showed that the starch content of textured plant proteins had a significant effect on the absorption and utilization of protein.When the starch content was 10%,the contents of total amino acids,essential amino acids and non-essential amino acids in the serum of rats were the highest,and the value of villus length/crypt depth in duodenum was the largest.In conclusion,the composition(protein type and proportion,and starch content)of textured plant proteins can affect the efficiency of digestibility,absorption and utilization of proteins by influencing the fibrous structure,the interaction between protein molecules and the secondary structure of proteins.This study can provide theoretical reference for the development of plant-based meat with high protein nutritional value.