Effects Of Pulse Cellular Macrostructure On The Starch Structure And Digestion Properties

Whole food has an intact cellular structure that limits the access of digestive enzymes to starch and protein substrates and reduces digestion,thereby preventing type 2 diabetes,obesity,and cardiovascular disease;therefore,a whole food diet is considered a healthy and nutritious diet.Pulse is a general term used for small beans excepting soybeans,contain high protein and carbohydrates.Pulse intracellular starch is a natural slow-digestible starch with a lower glycemic index compared with other starches.In this thesis,pulse intact cells were isolated as an example of a whole food model to investigate the impact of pulse macrostructures（cell walls and cellular protein matrix）on controlling cell morphology（cell wall macrostructures）,starch structure（crystallinity,thermal stability,and molecular order）,and in vitro digestion properties（rate and extent of starch digestion）.The research results have an important theoretical basis and guiding significance for the development of pulse functional and low glycemic index（GI）foods.The main research contents and results are as follows:1.The in vitro digestion properties of starch were studied in different pulse varieties,intact cells were isolated hydrothermally from smooth peas,red kidney beans,chickpeas,white hyacinth beans,runner beans,adzuki beans,broad beans,large white kidney beans,and mung beans.Pearson’s correlation analysis of isolated pulse cell varieties showed a negative correlation between pulse cell properties（fiber content,protein content,and particle size）,and the digestion rate and extent of starch.In the comparison of pulse cell varieties,broad bean cells showed the lowest digestion rate and extent(0.0098 min^-1 and 23.1%)of starch in the presence of the highest amounts of fiber content（24.3%）,protein content（22.1%）,and particle size（131μm）.Our results indicated that the rate and extent of starch digestion are regulated by the structural variations in the pulse varieties.2.To explore the effects of cell wall integrity on the in vitro starch and protein digestion properties,intact pea cells were first isolated as a whole food model,and a series of cotyledon cells with different cell wall integrity were prepared by cell wall degrading enzymes.Thermal properties showed that cell samples with different cell wall integrity exhibited higher starch gelatinization temperatures before and after gelatinization compared to the native starch.The intact cells limited the in vitro digestion of starch（16.2%）and protein（6.7%）compared with damaged cell wall samples.Most of the cells with intact cell walls maintained their cell wall integrity throughout gastrointestinal digestion,with only a few cells showing signs of damage,and presented the higher protein molecular weight（70 k Da）in the SDS-PAGE profiles.These results suggested that the in vitro starch and protein digestion properties are modulated by the cell wall integrity.3.To investigate the effects of cellular protein matrix modulating the in vitro digestion properties of intracellular starch,intact pea cells were isolated as whole food model to prepare a series of cell samples with different cellular protein matrix contents by protease enzyme.The intact cells with the highest protein matrix exhibited the lowest starch digestion rate and extent(0.013 min^–1 and 11.9%)compared to cells with the lowest protein matrix.The intact cell walls of cells with the lowest protein matrix still reduced the starch digestion rate and extent(0.0298 min^–1 and 39.7%)compared with the digestion rate and extent of native starch(0.0371 min^–1 and 56.8%).Results indicated that the cellular protein matrix and cell walls work as a dual encapsulation system to slow down the starch hydrolysis process.4.To investigate the effects of salt ions and p H on the intact pea cellular starch structure and regulation of in vitro starch digestion properties,whole peas were soaked in 0.1M alkaline salt（Na₂CO₃）,slightly acidic salt（Ca Cl₂,Mg Cl₂,KCl,and Na Cl）,and highly acidic salt（Al Cl₃,Fe Cl₂,and Fe Cl₃）solutions to isolate cotyledon cells.Intact cells of entrapped cellular starch isolated with a slightly acidic salt soaking treatment have stronger birefringence,more ordered crystalline structure,and higher gelatinization temperatures compared with alkaline and highly acidic salt soaking treatments.Intact cells treated with slightly acidic salts reduced cell wall permeability and in vitro starch digestion rate and extent(0.0073–0.0151 min^-1 and 2.5%–5.0%)compared with corresponding cotyledon cells.Results suggested that intact cells obtained by soaking in Ca Cl₂,Mg Cl₂,KCl,and Na Cl salt solutions can effectively limit cell wall permeability and reduce the in vitro digestion properties of intracellular starch.