Effect Of Lactic Acid Bacteria Fermentation On Multilevel Structure And Digestibility Of Chickpea Protein And Its Application

Plant protein is an indispensable part of human healthy diet,and its main component legume protein comes from a wide range of sources.However,the stiffness,tight spatial structure of protein,and anti-nutritional factors in legume limit protein absorption in the human body.Lactic acid bacteria fermentation not only gives food a distinct flavor but also increases the digestibility and nutritional value of legume protein.Therefore,chickpea milk was fermented with Lactobacillus plantarum HLJ29 L in this study to produce fermented chickpea flour to investigate the changes in digestibility of chickpea protein and its link with its multilevel structures during fermentation.And the effects of fermentation on the particle state and protein structure of chickpea digestive products was discussed during in vitro digestion.Finally,fermented chickpea flour was used to create fermented crackers.The purpose of this study was to provide theoretical basis and technical support for improving the nutritional value of chickpea protein and its application in baked products.The main conclusions are as follows:First of all,chickpea milk was fermented with Lactobacillus plantarum HLJ29 L.During fermentation,we evaluated the biochemical properties and in vitro protein digestibility of chickpea milk,as well as changes in the multilevel structures of chickpea protein.The detection of biochemical properties of chickpea milk showed that microbial metabolic acid production decreased its pH from 6.37 to 3.65,while the quantity of organic acid rose.The solubility of protein chickpea climbed from 11.37% to 17.35%,while gastric and intestinal protein digestibility(IVPD)enhanced by 29.61% and 11.85%,respectively.Fermentation significantly decreased the content of phytic acid and trypsin inhibitor activity(TIA)in chickpea(p<0.05).In addition,chickpea milk acidification increased the activity of endogenous protease by three times,hydrolyzed part of chickpea protein and increased the release of free amino acids(FAA)of chickpea protein by 61.24%.Sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE)revealed that part of indigestible subunits in chickpea globulin were gradually degraded,the intensity of some bands diminished,and a few low molecular weight bands appeared.Raman and UV spectra indicated that the specific gravity of α-helix in fermented chickpea protein increased by 69.00% while its β-sheet fell by 29.45%.Fermentation also made the aromatic acid side chain groups of chickpea protein more exposed to the polar environment,and the stable gauche-gauche-gauche configuration of disulfide bonds was converted into the unstable gauche-gauche-trans and trans-gauche-trans forms.As a result,fermentation not only reduced the anti-nutritional factors of chickpea,but also activated the endogenous protease of chickpea to hydrolyze its own protein and loosened the dense structure of chickpea protein.Then,the effects of fermentation on the molecular aggregation and multilevel structure of chickpea protein digestive products during in vitro digestion were studied.The release,particle size and microstructure of FAA from digested products of chickpea showed that fermentation significantly increased the release of FAA from chickpea protein during digestion(p<0.05).During gastric digestion,fermentation not only made chickpea more easily hydrolyzed at the initial stage of digestion,but also promoted digestive enzymes to further hydrolyze protein into small molecules.In the early stage of intestinal digestion,the particle size of unfermented chickpea significantly increased and obvious protein-lipid aggregation structure appeared,while the aggregate size of fermented chickpea digested products was smaller and disappeared more quickly.The activity of lipoxygenase(LOX)peaked at pH 7.0(11065.32 U),which indicated that LOX activity rose dramatically in intestinal digestion.During the intestinal stage,fermentation reduced chickpea LOX activity significantly compared to unfermented samples,which diminished the oxidation efficiency of unsaturated lipids and weakened protein-lipid aggregation,which was positive for protein digestion.SDS-PAGE,sulfhydryl content,circular dichroism,and fluorescence scanning spectra revealed that the indigestible 7S β-subunits in fermented chickpea protein were hydrolyzed during digestion,and it also showed rapid alterations from ordered to disorganized and expanded structure.The increase in the β-sheet fraction at the start of intestinal digestion and amino acid residues were buried proved that macromolecules in unfermented and fermented chickpea digestive products were aggregated.Finally,unfermented and fermented chickpea flour was utilized to partially replace wheat flour to make fermented crackers,and the effects of adding chickpea on cracker dough and cracker properties were analyzed.The water distribution,dynamic rheology and texture properties of the dough showed that the addition of fermented chickpea reduced the water fluidity,increased the hardness,made the structure more compact,and its viscosity was lower than that of the dough with unfermented chickpea.Therefore,the dough with fermented chickpea was easier to be processed than the dough with unfermented samples.Fermented crackers were prepared by baking three kinds of cracker dough,and the nutritional value,texture and sensory properties of protein were evaluated.It was found that the addition of two kinds of chickpea could make up for the deficiency of protein content and the lack of restricted amino acids in wheat cracker.Compared with unfermented chickpea cracker,the gastrointestinal protein digestibility of fermented chickpea cracker increased by 28.01% and11.76% respectively,and its amino acid composition was optimized,which was more beneficial to human absorption.In addition,fermented chickpea crackers have higher density and hardness.Compared with wheat cracker,although the overall acceptance of crackers decreased slightly by adding two kinds of chickpea flour,the acceptance of crackers with fermented chickpea flour was higher than that of wheat cracker.This showed that fermentation made the application of chickpea in crackers better and more popular by consumers.This study provided a theoretical basis for the application of fermented chickpea in fermented crackers and other baked products.